Source file src/cmd/go/internal/modload/load.go

Documentation: cmd/go/internal/modload

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package modload
     6  
     7  // This file contains the module-mode package loader, as well as some accessory
     8  // functions pertaining to the package import graph.
     9  //
    10  // There are two exported entry points into package loading — LoadPackages and
    11  // ImportFromFiles — both implemented in terms of loadFromRoots, which itself
    12  // manipulates an instance of the loader struct.
    13  //
    14  // Although most of the loading state is maintained in the loader struct,
    15  // one key piece - the build list - is a global, so that it can be modified
    16  // separate from the loading operation, such as during "go get"
    17  // upgrades/downgrades or in "go mod" operations.
    18  // TODO(#40775): It might be nice to make the loader take and return
    19  // a buildList rather than hard-coding use of the global.
    20  //
    21  // Loading is an iterative process. On each iteration, we try to load the
    22  // requested packages and their transitive imports, then try to resolve modules
    23  // for any imported packages that are still missing.
    24  //
    25  // The first step of each iteration identifies a set of “root” packages.
    26  // Normally the root packages are exactly those matching the named pattern
    27  // arguments. However, for the "all" meta-pattern, the final set of packages is
    28  // computed from the package import graph, and therefore cannot be an initial
    29  // input to loading that graph. Instead, the root packages for the "all" pattern
    30  // are those contained in the main module, and allPatternIsRoot parameter to the
    31  // loader instructs it to dynamically expand those roots to the full "all"
    32  // pattern as loading progresses.
    33  //
    34  // The pkgInAll flag on each loadPkg instance tracks whether that
    35  // package is known to match the "all" meta-pattern.
    36  // A package matches the "all" pattern if:
    37  // 	- it is in the main module, or
    38  // 	- it is imported by any test in the main module, or
    39  // 	- it is imported by another package in "all", or
    40  // 	- the main module specifies a go version ≤ 1.15, and the package is imported
    41  // 	  by a *test of* another package in "all".
    42  //
    43  // When graph pruning is in effect, we want to spot-check the graph-pruning
    44  // invariants — which depend on which packages are known to be in "all" — even
    45  // when we are only loading individual packages, so we set the pkgInAll flag
    46  // regardless of the whether the "all" pattern is a root.
    47  // (This is necessary to maintain the “import invariant” described in
    48  // https://golang.org/design/36460-lazy-module-loading.)
    49  //
    50  // Because "go mod vendor" prunes out the tests of vendored packages, the
    51  // behavior of the "all" pattern with -mod=vendor in Go 1.11–1.15 is the same
    52  // as the "all" pattern (regardless of the -mod flag) in 1.16+.
    53  // The loader uses the GoVersion parameter to determine whether the "all"
    54  // pattern should close over tests (as in Go 1.11–1.15) or stop at only those
    55  // packages transitively imported by the packages and tests in the main module
    56  // ("all" in Go 1.16+ and "go mod vendor" in Go 1.11+).
    57  //
    58  // Note that it is possible for a loaded package NOT to be in "all" even when we
    59  // are loading the "all" pattern. For example, packages that are transitive
    60  // dependencies of other roots named on the command line must be loaded, but are
    61  // not in "all". (The mod_notall test illustrates this behavior.)
    62  // Similarly, if the LoadTests flag is set but the "all" pattern does not close
    63  // over test dependencies, then when we load the test of a package that is in
    64  // "all" but outside the main module, the dependencies of that test will not
    65  // necessarily themselves be in "all". (That configuration does not arise in Go
    66  // 1.11–1.15, but it will be possible in Go 1.16+.)
    67  //
    68  // Loading proceeds from the roots, using a parallel work-queue with a limit on
    69  // the amount of active work (to avoid saturating disks, CPU cores, and/or
    70  // network connections). Each package is added to the queue the first time it is
    71  // imported by another package. When we have finished identifying the imports of
    72  // a package, we add the test for that package if it is needed. A test may be
    73  // needed if:
    74  // 	- the package matches a root pattern and tests of the roots were requested, or
    75  // 	- the package is in the main module and the "all" pattern is requested
    76  // 	  (because the "all" pattern includes the dependencies of tests in the main
    77  // 	  module), or
    78  // 	- the package is in "all" and the definition of "all" we are using includes
    79  // 	  dependencies of tests (as is the case in Go ≤1.15).
    80  //
    81  // After all available packages have been loaded, we examine the results to
    82  // identify any requested or imported packages that are still missing, and if
    83  // so, which modules we could add to the module graph in order to make the
    84  // missing packages available. We add those to the module graph and iterate,
    85  // until either all packages resolve successfully or we cannot identify any
    86  // module that would resolve any remaining missing package.
    87  //
    88  // If the main module is “tidy” (that is, if "go mod tidy" is a no-op for it)
    89  // and all requested packages are in "all", then loading completes in a single
    90  // iteration.
    91  // TODO(bcmills): We should also be able to load in a single iteration if the
    92  // requested packages all come from modules that are themselves tidy, regardless
    93  // of whether those packages are in "all". Today, that requires two iterations
    94  // if those packages are not found in existing dependencies of the main module.
    95  
    96  import (
    97  	"context"
    98  	"errors"
    99  	"fmt"
   100  	"go/build"
   101  	"internal/diff"
   102  	"io/fs"
   103  	"maps"
   104  	"os"
   105  	"path"
   106  	pathpkg "path"
   107  	"path/filepath"
   108  	"runtime"
   109  	"slices"
   110  	"sort"
   111  	"strings"
   112  	"sync"
   113  	"sync/atomic"
   114  
   115  	"cmd/go/internal/base"
   116  	"cmd/go/internal/cfg"
   117  	"cmd/go/internal/fsys"
   118  	"cmd/go/internal/gover"
   119  	"cmd/go/internal/imports"
   120  	"cmd/go/internal/modfetch"
   121  	"cmd/go/internal/modindex"
   122  	"cmd/go/internal/mvs"
   123  	"cmd/go/internal/par"
   124  	"cmd/go/internal/search"
   125  	"cmd/go/internal/str"
   126  
   127  	"golang.org/x/mod/module"
   128  )
   129  
   130  // loaded is the most recently-used package loader.
   131  // It holds details about individual packages.
   132  //
   133  // This variable should only be accessed directly in top-level exported
   134  // functions. All other functions that require or produce a *loader should pass
   135  // or return it as an explicit parameter.
   136  var loaded *loader
   137  
   138  // PackageOpts control the behavior of the LoadPackages function.
   139  type PackageOpts struct {
   140  	// TidyGoVersion is the Go version to which the go.mod file should be updated
   141  	// after packages have been loaded.
   142  	//
   143  	// An empty TidyGoVersion means to use the Go version already specified in the
   144  	// main module's go.mod file, or the latest Go version if there is no main
   145  	// module.
   146  	TidyGoVersion string
   147  
   148  	// Tags are the build tags in effect (as interpreted by the
   149  	// cmd/go/internal/imports package).
   150  	// If nil, treated as equivalent to imports.Tags().
   151  	Tags map[string]bool
   152  
   153  	// Tidy, if true, requests that the build list and go.sum file be reduced to
   154  	// the minimal dependencies needed to reproducibly reload the requested
   155  	// packages.
   156  	Tidy bool
   157  
   158  	// TidyDiff, if true, causes tidy not to modify go.mod or go.sum but
   159  	// instead print the necessary changes as a unified diff. It exits
   160  	// with a non-zero code if the diff is not empty.
   161  	TidyDiff bool
   162  
   163  	// TidyCompatibleVersion is the oldest Go version that must be able to
   164  	// reproducibly reload the requested packages.
   165  	//
   166  	// If empty, the compatible version is the Go version immediately prior to the
   167  	// 'go' version listed in the go.mod file.
   168  	TidyCompatibleVersion string
   169  
   170  	// VendorModulesInGOROOTSrc indicates that if we are within a module in
   171  	// GOROOT/src, packages in the module's vendor directory should be resolved as
   172  	// actual module dependencies (instead of standard-library packages).
   173  	VendorModulesInGOROOTSrc bool
   174  
   175  	// ResolveMissingImports indicates that we should attempt to add module
   176  	// dependencies as needed to resolve imports of packages that are not found.
   177  	//
   178  	// For commands that support the -mod flag, resolving imports may still fail
   179  	// if the flag is set to "readonly" (the default) or "vendor".
   180  	ResolveMissingImports bool
   181  
   182  	// AssumeRootsImported indicates that the transitive dependencies of the root
   183  	// packages should be treated as if those roots will be imported by the main
   184  	// module.
   185  	AssumeRootsImported bool
   186  
   187  	// AllowPackage, if non-nil, is called after identifying the module providing
   188  	// each package. If AllowPackage returns a non-nil error, that error is set
   189  	// for the package, and the imports and test of that package will not be
   190  	// loaded.
   191  	//
   192  	// AllowPackage may be invoked concurrently by multiple goroutines,
   193  	// and may be invoked multiple times for a given package path.
   194  	AllowPackage func(ctx context.Context, path string, mod module.Version) error
   195  
   196  	// LoadTests loads the test dependencies of each package matching a requested
   197  	// pattern. If ResolveMissingImports is also true, test dependencies will be
   198  	// resolved if missing.
   199  	LoadTests bool
   200  
   201  	// UseVendorAll causes the "all" package pattern to be interpreted as if
   202  	// running "go mod vendor" (or building with "-mod=vendor").
   203  	//
   204  	// This is a no-op for modules that declare 'go 1.16' or higher, for which this
   205  	// is the default (and only) interpretation of the "all" pattern in module mode.
   206  	UseVendorAll bool
   207  
   208  	// AllowErrors indicates that LoadPackages should not terminate the process if
   209  	// an error occurs.
   210  	AllowErrors bool
   211  
   212  	// SilencePackageErrors indicates that LoadPackages should not print errors
   213  	// that occur while matching or loading packages, and should not terminate the
   214  	// process if such an error occurs.
   215  	//
   216  	// Errors encountered in the module graph will still be reported.
   217  	//
   218  	// The caller may retrieve the silenced package errors using the Lookup
   219  	// function, and matching errors are still populated in the Errs field of the
   220  	// associated search.Match.)
   221  	SilencePackageErrors bool
   222  
   223  	// SilenceMissingStdImports indicates that LoadPackages should not print
   224  	// errors or terminate the process if an imported package is missing, and the
   225  	// import path looks like it might be in the standard library (perhaps in a
   226  	// future version).
   227  	SilenceMissingStdImports bool
   228  
   229  	// SilenceNoGoErrors indicates that LoadPackages should not print
   230  	// imports.ErrNoGo errors.
   231  	// This allows the caller to invoke LoadPackages (and report other errors)
   232  	// without knowing whether the requested packages exist for the given tags.
   233  	//
   234  	// Note that if a requested package does not exist *at all*, it will fail
   235  	// during module resolution and the error will not be suppressed.
   236  	SilenceNoGoErrors bool
   237  
   238  	// SilenceUnmatchedWarnings suppresses the warnings normally emitted for
   239  	// patterns that did not match any packages.
   240  	SilenceUnmatchedWarnings bool
   241  
   242  	// Resolve the query against this module.
   243  	MainModule module.Version
   244  
   245  	// If Switcher is non-nil, then LoadPackages passes all encountered errors
   246  	// to Switcher.Error and tries Switcher.Switch before base.ExitIfErrors.
   247  	Switcher gover.Switcher
   248  }
   249  
   250  // LoadPackages identifies the set of packages matching the given patterns and
   251  // loads the packages in the import graph rooted at that set.
   252  func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (matches []*search.Match, loadedPackages []string) {
   253  	if opts.Tags == nil {
   254  		opts.Tags = imports.Tags()
   255  	}
   256  
   257  	patterns = search.CleanPatterns(patterns)
   258  	matches = make([]*search.Match, 0, len(patterns))
   259  	allPatternIsRoot := false
   260  	for _, pattern := range patterns {
   261  		matches = append(matches, search.NewMatch(pattern))
   262  		if pattern == "all" {
   263  			allPatternIsRoot = true
   264  		}
   265  	}
   266  
   267  	updateMatches := func(rs *Requirements, ld *loader) {
   268  		for _, m := range matches {
   269  			switch {
   270  			case m.IsLocal():
   271  				// Evaluate list of file system directories on first iteration.
   272  				if m.Dirs == nil {
   273  					matchModRoots := modRoots
   274  					if opts.MainModule != (module.Version{}) {
   275  						matchModRoots = []string{MainModules.ModRoot(opts.MainModule)}
   276  					}
   277  					matchLocalDirs(ctx, matchModRoots, m, rs)
   278  				}
   279  
   280  				// Make a copy of the directory list and translate to import paths.
   281  				// Note that whether a directory corresponds to an import path
   282  				// changes as the build list is updated, and a directory can change
   283  				// from not being in the build list to being in it and back as
   284  				// the exact version of a particular module increases during
   285  				// the loader iterations.
   286  				m.Pkgs = m.Pkgs[:0]
   287  				for _, dir := range m.Dirs {
   288  					pkg, err := resolveLocalPackage(ctx, dir, rs)
   289  					if err != nil {
   290  						if !m.IsLiteral() && (err == errPkgIsBuiltin || err == errPkgIsGorootSrc) {
   291  							continue // Don't include "builtin" or GOROOT/src in wildcard patterns.
   292  						}
   293  
   294  						// If we're outside of a module, ensure that the failure mode
   295  						// indicates that.
   296  						if !HasModRoot() {
   297  							die()
   298  						}
   299  
   300  						if ld != nil {
   301  							m.AddError(err)
   302  						}
   303  						continue
   304  					}
   305  					m.Pkgs = append(m.Pkgs, pkg)
   306  				}
   307  
   308  			case m.IsLiteral():
   309  				m.Pkgs = []string{m.Pattern()}
   310  
   311  			case strings.Contains(m.Pattern(), "..."):
   312  				m.Errs = m.Errs[:0]
   313  				mg, err := rs.Graph(ctx)
   314  				if err != nil {
   315  					// The module graph is (or may be) incomplete — perhaps we failed to
   316  					// load the requirements of some module. This is an error in matching
   317  					// the patterns to packages, because we may be missing some packages
   318  					// or we may erroneously match packages in the wrong versions of
   319  					// modules. However, for cases like 'go list -e', the error should not
   320  					// necessarily prevent us from loading the packages we could find.
   321  					m.Errs = append(m.Errs, err)
   322  				}
   323  				matchPackages(ctx, m, opts.Tags, includeStd, mg.BuildList())
   324  
   325  			case m.Pattern() == "all":
   326  				if ld == nil {
   327  					// The initial roots are the packages in the main module.
   328  					// loadFromRoots will expand that to "all".
   329  					m.Errs = m.Errs[:0]
   330  					matchModules := MainModules.Versions()
   331  					if opts.MainModule != (module.Version{}) {
   332  						matchModules = []module.Version{opts.MainModule}
   333  					}
   334  					matchPackages(ctx, m, opts.Tags, omitStd, matchModules)
   335  				} else {
   336  					// Starting with the packages in the main module,
   337  					// enumerate the full list of "all".
   338  					m.Pkgs = ld.computePatternAll()
   339  				}
   340  
   341  			case m.Pattern() == "std" || m.Pattern() == "cmd":
   342  				if m.Pkgs == nil {
   343  					m.MatchPackages() // Locate the packages within GOROOT/src.
   344  				}
   345  
   346  			default:
   347  				panic(fmt.Sprintf("internal error: modload missing case for pattern %s", m.Pattern()))
   348  			}
   349  		}
   350  	}
   351  
   352  	initialRS, err := loadModFile(ctx, &opts)
   353  	if err != nil {
   354  		base.Fatal(err)
   355  	}
   356  
   357  	ld := loadFromRoots(ctx, loaderParams{
   358  		PackageOpts:  opts,
   359  		requirements: initialRS,
   360  
   361  		allPatternIsRoot: allPatternIsRoot,
   362  
   363  		listRoots: func(rs *Requirements) (roots []string) {
   364  			updateMatches(rs, nil)
   365  			for _, m := range matches {
   366  				roots = append(roots, m.Pkgs...)
   367  			}
   368  			return roots
   369  		},
   370  	})
   371  
   372  	// One last pass to finalize wildcards.
   373  	updateMatches(ld.requirements, ld)
   374  
   375  	// List errors in matching patterns (such as directory permission
   376  	// errors for wildcard patterns).
   377  	if !ld.SilencePackageErrors {
   378  		for _, match := range matches {
   379  			for _, err := range match.Errs {
   380  				ld.error(err)
   381  			}
   382  		}
   383  	}
   384  	ld.exitIfErrors(ctx)
   385  
   386  	if !opts.SilenceUnmatchedWarnings {
   387  		search.WarnUnmatched(matches)
   388  	}
   389  
   390  	if opts.Tidy {
   391  		if cfg.BuildV {
   392  			mg, _ := ld.requirements.Graph(ctx)
   393  			for _, m := range initialRS.rootModules {
   394  				var unused bool
   395  				if ld.requirements.pruning == unpruned {
   396  					// m is unused if it was dropped from the module graph entirely. If it
   397  					// was only demoted from direct to indirect, it may still be in use via
   398  					// a transitive import.
   399  					unused = mg.Selected(m.Path) == "none"
   400  				} else {
   401  					// m is unused if it was dropped from the roots. If it is still present
   402  					// as a transitive dependency, that transitive dependency is not needed
   403  					// by any package or test in the main module.
   404  					_, ok := ld.requirements.rootSelected(m.Path)
   405  					unused = !ok
   406  				}
   407  				if unused {
   408  					fmt.Fprintf(os.Stderr, "unused %s\n", m.Path)
   409  				}
   410  			}
   411  		}
   412  
   413  		keep := keepSums(ctx, ld, ld.requirements, loadedZipSumsOnly)
   414  		compatVersion := ld.TidyCompatibleVersion
   415  		goVersion := ld.requirements.GoVersion()
   416  		if compatVersion == "" {
   417  			if gover.Compare(goVersion, gover.GoStrictVersion) < 0 {
   418  				compatVersion = gover.Prev(goVersion)
   419  			} else {
   420  				// Starting at GoStrictVersion, we no longer maintain compatibility with
   421  				// versions older than what is listed in the go.mod file.
   422  				compatVersion = goVersion
   423  			}
   424  		}
   425  		if gover.Compare(compatVersion, goVersion) > 0 {
   426  			// Each version of the Go toolchain knows how to interpret go.mod and
   427  			// go.sum files produced by all previous versions, so a compatibility
   428  			// version higher than the go.mod version adds nothing.
   429  			compatVersion = goVersion
   430  		}
   431  		if compatPruning := pruningForGoVersion(compatVersion); compatPruning != ld.requirements.pruning {
   432  			compatRS := newRequirements(compatPruning, ld.requirements.rootModules, ld.requirements.direct)
   433  			ld.checkTidyCompatibility(ctx, compatRS, compatVersion)
   434  
   435  			for m := range keepSums(ctx, ld, compatRS, loadedZipSumsOnly) {
   436  				keep[m] = true
   437  			}
   438  		}
   439  
   440  		if opts.TidyDiff {
   441  			cfg.BuildMod = "readonly"
   442  			loaded = ld
   443  			requirements = loaded.requirements
   444  			currentGoMod, updatedGoMod, _, err := UpdateGoModFromReqs(ctx, WriteOpts{})
   445  			if err != nil {
   446  				base.Fatal(err)
   447  			}
   448  			goModDiff := diff.Diff("current/go.mod", currentGoMod, "tidy/go.mod", updatedGoMod)
   449  
   450  			modfetch.TrimGoSum(keep)
   451  			// Dropping compatibility for 1.16 may result in a strictly smaller go.sum.
   452  			// Update the keep map with only the loaded.requirements.
   453  			if gover.Compare(compatVersion, "1.16") > 0 {
   454  				keep = keepSums(ctx, loaded, requirements, addBuildListZipSums)
   455  			}
   456  			currentGoSum, tidyGoSum := modfetch.TidyGoSum(keep)
   457  			goSumDiff := diff.Diff("current/go.sum", currentGoSum, "tidy/go.sum", tidyGoSum)
   458  
   459  			if len(goModDiff) > 0 {
   460  				fmt.Println(string(goModDiff))
   461  				base.SetExitStatus(1)
   462  			}
   463  			if len(goSumDiff) > 0 {
   464  				fmt.Println(string(goSumDiff))
   465  				base.SetExitStatus(1)
   466  			}
   467  			base.Exit()
   468  		}
   469  
   470  		if !ExplicitWriteGoMod {
   471  			modfetch.TrimGoSum(keep)
   472  
   473  			// commitRequirements below will also call WriteGoSum, but the "keep" map
   474  			// we have here could be strictly larger: commitRequirements only commits
   475  			// loaded.requirements, but here we may have also loaded (and want to
   476  			// preserve checksums for) additional entities from compatRS, which are
   477  			// only needed for compatibility with ld.TidyCompatibleVersion.
   478  			if err := modfetch.WriteGoSum(ctx, keep, mustHaveCompleteRequirements()); err != nil {
   479  				base.Fatal(err)
   480  			}
   481  		}
   482  	}
   483  
   484  	if opts.TidyDiff && !opts.Tidy {
   485  		panic("TidyDiff is set but Tidy is not.")
   486  	}
   487  
   488  	// Success! Update go.mod and go.sum (if needed) and return the results.
   489  	// We'll skip updating if ExplicitWriteGoMod is true (the caller has opted
   490  	// to call WriteGoMod itself) or if ResolveMissingImports is false (the
   491  	// command wants to examine the package graph as-is).
   492  	loaded = ld
   493  	requirements = loaded.requirements
   494  
   495  	for _, pkg := range ld.pkgs {
   496  		if !pkg.isTest() {
   497  			loadedPackages = append(loadedPackages, pkg.path)
   498  		}
   499  	}
   500  	sort.Strings(loadedPackages)
   501  
   502  	if !ExplicitWriteGoMod && opts.ResolveMissingImports {
   503  		if err := commitRequirements(ctx, WriteOpts{}); err != nil {
   504  			base.Fatal(err)
   505  		}
   506  	}
   507  
   508  	return matches, loadedPackages
   509  }
   510  
   511  // matchLocalDirs is like m.MatchDirs, but tries to avoid scanning directories
   512  // outside of the standard library and active modules.
   513  func matchLocalDirs(ctx context.Context, modRoots []string, m *search.Match, rs *Requirements) {
   514  	if !m.IsLocal() {
   515  		panic(fmt.Sprintf("internal error: resolveLocalDirs on non-local pattern %s", m.Pattern()))
   516  	}
   517  
   518  	if i := strings.Index(m.Pattern(), "..."); i >= 0 {
   519  		// The pattern is local, but it is a wildcard. Its packages will
   520  		// only resolve to paths if they are inside of the standard
   521  		// library, the main module, or some dependency of the main
   522  		// module. Verify that before we walk the filesystem: a filesystem
   523  		// walk in a directory like /var or /etc can be very expensive!
   524  		dir := filepath.Dir(filepath.Clean(m.Pattern()[:i+3]))
   525  		absDir := dir
   526  		if !filepath.IsAbs(dir) {
   527  			absDir = filepath.Join(base.Cwd(), dir)
   528  		}
   529  
   530  		modRoot := findModuleRoot(absDir)
   531  		found := false
   532  		for _, mainModuleRoot := range modRoots {
   533  			if mainModuleRoot == modRoot {
   534  				found = true
   535  				break
   536  			}
   537  		}
   538  		if !found && search.InDir(absDir, cfg.GOROOTsrc) == "" && pathInModuleCache(ctx, absDir, rs) == "" {
   539  			m.Dirs = []string{}
   540  			scope := "main module or its selected dependencies"
   541  			if inWorkspaceMode() {
   542  				scope = "modules listed in go.work or their selected dependencies"
   543  			}
   544  			m.AddError(fmt.Errorf("directory prefix %s does not contain %s", base.ShortPath(absDir), scope))
   545  			return
   546  		}
   547  	}
   548  
   549  	m.MatchDirs(modRoots)
   550  }
   551  
   552  // resolveLocalPackage resolves a filesystem path to a package path.
   553  func resolveLocalPackage(ctx context.Context, dir string, rs *Requirements) (string, error) {
   554  	var absDir string
   555  	if filepath.IsAbs(dir) {
   556  		absDir = filepath.Clean(dir)
   557  	} else {
   558  		absDir = filepath.Join(base.Cwd(), dir)
   559  	}
   560  
   561  	bp, err := cfg.BuildContext.ImportDir(absDir, 0)
   562  	if err != nil && (bp == nil || len(bp.IgnoredGoFiles) == 0) {
   563  		// golang.org/issue/32917: We should resolve a relative path to a
   564  		// package path only if the relative path actually contains the code
   565  		// for that package.
   566  		//
   567  		// If the named directory does not exist or contains no Go files,
   568  		// the package does not exist.
   569  		// Other errors may affect package loading, but not resolution.
   570  		if _, err := fsys.Stat(absDir); err != nil {
   571  			if os.IsNotExist(err) {
   572  				// Canonicalize OS-specific errors to errDirectoryNotFound so that error
   573  				// messages will be easier for users to search for.
   574  				return "", &fs.PathError{Op: "stat", Path: absDir, Err: errDirectoryNotFound}
   575  			}
   576  			return "", err
   577  		}
   578  		if _, noGo := err.(*build.NoGoError); noGo {
   579  			// A directory that does not contain any Go source files — even ignored
   580  			// ones! — is not a Go package, and we can't resolve it to a package
   581  			// path because that path could plausibly be provided by some other
   582  			// module.
   583  			//
   584  			// Any other error indicates that the package “exists” (at least in the
   585  			// sense that it cannot exist in any other module), but has some other
   586  			// problem (such as a syntax error).
   587  			return "", err
   588  		}
   589  	}
   590  
   591  	for _, mod := range MainModules.Versions() {
   592  		modRoot := MainModules.ModRoot(mod)
   593  		if modRoot != "" && absDir == modRoot {
   594  			if absDir == cfg.GOROOTsrc {
   595  				return "", errPkgIsGorootSrc
   596  			}
   597  			return MainModules.PathPrefix(mod), nil
   598  		}
   599  	}
   600  
   601  	// Note: The checks for @ here are just to avoid misinterpreting
   602  	// the module cache directories (formerly GOPATH/src/mod/foo@v1.5.2/bar).
   603  	// It's not strictly necessary but helpful to keep the checks.
   604  	var pkgNotFoundErr error
   605  	pkgNotFoundLongestPrefix := ""
   606  	for _, mainModule := range MainModules.Versions() {
   607  		modRoot := MainModules.ModRoot(mainModule)
   608  		if modRoot != "" && str.HasFilePathPrefix(absDir, modRoot) && !strings.Contains(absDir[len(modRoot):], "@") {
   609  			suffix := filepath.ToSlash(str.TrimFilePathPrefix(absDir, modRoot))
   610  			if pkg, found := strings.CutPrefix(suffix, "vendor/"); found {
   611  				if cfg.BuildMod != "vendor" {
   612  					return "", fmt.Errorf("without -mod=vendor, directory %s has no package path", absDir)
   613  				}
   614  
   615  				readVendorList(VendorDir())
   616  				if _, ok := vendorPkgModule[pkg]; !ok {
   617  					return "", fmt.Errorf("directory %s is not a package listed in vendor/modules.txt", absDir)
   618  				}
   619  				return pkg, nil
   620  			}
   621  
   622  			mainModulePrefix := MainModules.PathPrefix(mainModule)
   623  			if mainModulePrefix == "" {
   624  				pkg := suffix
   625  				if pkg == "builtin" {
   626  					// "builtin" is a pseudo-package with a real source file.
   627  					// It's not included in "std", so it shouldn't resolve from "."
   628  					// within module "std" either.
   629  					return "", errPkgIsBuiltin
   630  				}
   631  				return pkg, nil
   632  			}
   633  
   634  			pkg := pathpkg.Join(mainModulePrefix, suffix)
   635  			if _, ok, err := dirInModule(pkg, mainModulePrefix, modRoot, true); err != nil {
   636  				return "", err
   637  			} else if !ok {
   638  				// This main module could contain the directory but doesn't. Other main
   639  				// modules might contain the directory, so wait till we finish the loop
   640  				// to see if another main module contains directory. But if not,
   641  				// return an error.
   642  				if len(mainModulePrefix) > len(pkgNotFoundLongestPrefix) {
   643  					pkgNotFoundLongestPrefix = mainModulePrefix
   644  					pkgNotFoundErr = &PackageNotInModuleError{MainModules: []module.Version{mainModule}, Pattern: pkg}
   645  				}
   646  				continue
   647  			}
   648  			return pkg, nil
   649  		}
   650  	}
   651  	if pkgNotFoundErr != nil {
   652  		return "", pkgNotFoundErr
   653  	}
   654  
   655  	if sub := search.InDir(absDir, cfg.GOROOTsrc); sub != "" && sub != "." && !strings.Contains(sub, "@") {
   656  		pkg := filepath.ToSlash(sub)
   657  		if pkg == "builtin" {
   658  			return "", errPkgIsBuiltin
   659  		}
   660  		return pkg, nil
   661  	}
   662  
   663  	pkg := pathInModuleCache(ctx, absDir, rs)
   664  	if pkg == "" {
   665  		dirstr := fmt.Sprintf("directory %s", base.ShortPath(absDir))
   666  		if dirstr == "directory ." {
   667  			dirstr = "current directory"
   668  		}
   669  		if inWorkspaceMode() {
   670  			if mr := findModuleRoot(absDir); mr != "" {
   671  				return "", fmt.Errorf("%s is contained in a module that is not one of the workspace modules listed in go.work. You can add the module to the workspace using:\n\tgo work use %s", dirstr, base.ShortPath(mr))
   672  			}
   673  			return "", fmt.Errorf("%s outside modules listed in go.work or their selected dependencies", dirstr)
   674  		}
   675  		return "", fmt.Errorf("%s outside main module or its selected dependencies", dirstr)
   676  	}
   677  	return pkg, nil
   678  }
   679  
   680  var (
   681  	errDirectoryNotFound = errors.New("directory not found")
   682  	errPkgIsGorootSrc    = errors.New("GOROOT/src is not an importable package")
   683  	errPkgIsBuiltin      = errors.New(`"builtin" is a pseudo-package, not an importable package`)
   684  )
   685  
   686  // pathInModuleCache returns the import path of the directory dir,
   687  // if dir is in the module cache copy of a module in our build list.
   688  func pathInModuleCache(ctx context.Context, dir string, rs *Requirements) string {
   689  	tryMod := func(m module.Version) (string, bool) {
   690  		if gover.IsToolchain(m.Path) {
   691  			return "", false
   692  		}
   693  		var root string
   694  		var err error
   695  		if repl := Replacement(m); repl.Path != "" && repl.Version == "" {
   696  			root = repl.Path
   697  			if !filepath.IsAbs(root) {
   698  				root = filepath.Join(replaceRelativeTo(), root)
   699  			}
   700  		} else if repl.Path != "" {
   701  			root, err = modfetch.DownloadDir(ctx, repl)
   702  		} else {
   703  			root, err = modfetch.DownloadDir(ctx, m)
   704  		}
   705  		if err != nil {
   706  			return "", false
   707  		}
   708  
   709  		sub := search.InDir(dir, root)
   710  		if sub == "" {
   711  			return "", false
   712  		}
   713  		sub = filepath.ToSlash(sub)
   714  		if strings.Contains(sub, "/vendor/") || strings.HasPrefix(sub, "vendor/") || strings.Contains(sub, "@") {
   715  			return "", false
   716  		}
   717  
   718  		return path.Join(m.Path, filepath.ToSlash(sub)), true
   719  	}
   720  
   721  	if rs.pruning == pruned {
   722  		for _, m := range rs.rootModules {
   723  			if v, _ := rs.rootSelected(m.Path); v != m.Version {
   724  				continue // m is a root, but we have a higher root for the same path.
   725  			}
   726  			if importPath, ok := tryMod(m); ok {
   727  				// checkMultiplePaths ensures that a module can be used for at most one
   728  				// requirement, so this must be it.
   729  				return importPath
   730  			}
   731  		}
   732  	}
   733  
   734  	// None of the roots contained dir, or the graph is unpruned (so we don't want
   735  	// to distinguish between roots and transitive dependencies). Either way,
   736  	// check the full graph to see if the directory is a non-root dependency.
   737  	//
   738  	// If the roots are not consistent with the full module graph, the selected
   739  	// versions of root modules may differ from what we already checked above.
   740  	// Re-check those paths too.
   741  
   742  	mg, _ := rs.Graph(ctx)
   743  	var importPath string
   744  	for _, m := range mg.BuildList() {
   745  		var found bool
   746  		importPath, found = tryMod(m)
   747  		if found {
   748  			break
   749  		}
   750  	}
   751  	return importPath
   752  }
   753  
   754  // ImportFromFiles adds modules to the build list as needed
   755  // to satisfy the imports in the named Go source files.
   756  //
   757  // Errors in missing dependencies are silenced.
   758  //
   759  // TODO(bcmills): Silencing errors seems off. Take a closer look at this and
   760  // figure out what the error-reporting actually ought to be.
   761  func ImportFromFiles(ctx context.Context, gofiles []string) {
   762  	rs := LoadModFile(ctx)
   763  
   764  	tags := imports.Tags()
   765  	imports, testImports, err := imports.ScanFiles(gofiles, tags)
   766  	if err != nil {
   767  		base.Fatal(err)
   768  	}
   769  
   770  	loaded = loadFromRoots(ctx, loaderParams{
   771  		PackageOpts: PackageOpts{
   772  			Tags:                  tags,
   773  			ResolveMissingImports: true,
   774  			SilencePackageErrors:  true,
   775  		},
   776  		requirements: rs,
   777  		listRoots: func(*Requirements) (roots []string) {
   778  			roots = append(roots, imports...)
   779  			roots = append(roots, testImports...)
   780  			return roots
   781  		},
   782  	})
   783  	requirements = loaded.requirements
   784  
   785  	if !ExplicitWriteGoMod {
   786  		if err := commitRequirements(ctx, WriteOpts{}); err != nil {
   787  			base.Fatal(err)
   788  		}
   789  	}
   790  }
   791  
   792  // DirImportPath returns the effective import path for dir,
   793  // provided it is within a main module, or else returns ".".
   794  func (mms *MainModuleSet) DirImportPath(ctx context.Context, dir string) (path string, m module.Version) {
   795  	if !HasModRoot() {
   796  		return ".", module.Version{}
   797  	}
   798  	LoadModFile(ctx) // Sets targetPrefix.
   799  
   800  	if !filepath.IsAbs(dir) {
   801  		dir = filepath.Join(base.Cwd(), dir)
   802  	} else {
   803  		dir = filepath.Clean(dir)
   804  	}
   805  
   806  	var longestPrefix string
   807  	var longestPrefixPath string
   808  	var longestPrefixVersion module.Version
   809  	for _, v := range mms.Versions() {
   810  		modRoot := mms.ModRoot(v)
   811  		if dir == modRoot {
   812  			return mms.PathPrefix(v), v
   813  		}
   814  		if str.HasFilePathPrefix(dir, modRoot) {
   815  			pathPrefix := MainModules.PathPrefix(v)
   816  			if pathPrefix > longestPrefix {
   817  				longestPrefix = pathPrefix
   818  				longestPrefixVersion = v
   819  				suffix := filepath.ToSlash(str.TrimFilePathPrefix(dir, modRoot))
   820  				if strings.HasPrefix(suffix, "vendor/") {
   821  					longestPrefixPath = suffix[len("vendor/"):]
   822  					continue
   823  				}
   824  				longestPrefixPath = pathpkg.Join(mms.PathPrefix(v), suffix)
   825  			}
   826  		}
   827  	}
   828  	if len(longestPrefix) > 0 {
   829  		return longestPrefixPath, longestPrefixVersion
   830  	}
   831  
   832  	return ".", module.Version{}
   833  }
   834  
   835  // PackageModule returns the module providing the package named by the import path.
   836  func PackageModule(path string) module.Version {
   837  	pkg, ok := loaded.pkgCache.Get(path)
   838  	if !ok {
   839  		return module.Version{}
   840  	}
   841  	return pkg.mod
   842  }
   843  
   844  // Lookup returns the source directory, import path, and any loading error for
   845  // the package at path as imported from the package in parentDir.
   846  // Lookup requires that one of the Load functions in this package has already
   847  // been called.
   848  func Lookup(parentPath string, parentIsStd bool, path string) (dir, realPath string, err error) {
   849  	if path == "" {
   850  		panic("Lookup called with empty package path")
   851  	}
   852  
   853  	if parentIsStd {
   854  		path = loaded.stdVendor(parentPath, path)
   855  	}
   856  	pkg, ok := loaded.pkgCache.Get(path)
   857  	if !ok {
   858  		// The loader should have found all the relevant paths.
   859  		// There are a few exceptions, though:
   860  		//	- during go list without -test, the p.Resolve calls to process p.TestImports and p.XTestImports
   861  		//	  end up here to canonicalize the import paths.
   862  		//	- during any load, non-loaded packages like "unsafe" end up here.
   863  		//	- during any load, build-injected dependencies like "runtime/cgo" end up here.
   864  		//	- because we ignore appengine/* in the module loader,
   865  		//	  the dependencies of any actual appengine/* library end up here.
   866  		dir := findStandardImportPath(path)
   867  		if dir != "" {
   868  			return dir, path, nil
   869  		}
   870  		return "", "", errMissing
   871  	}
   872  	return pkg.dir, pkg.path, pkg.err
   873  }
   874  
   875  // A loader manages the process of loading information about
   876  // the required packages for a particular build,
   877  // checking that the packages are available in the module set,
   878  // and updating the module set if needed.
   879  type loader struct {
   880  	loaderParams
   881  
   882  	// allClosesOverTests indicates whether the "all" pattern includes
   883  	// dependencies of tests outside the main module (as in Go 1.11–1.15).
   884  	// (Otherwise — as in Go 1.16+ — the "all" pattern includes only the packages
   885  	// transitively *imported by* the packages and tests in the main module.)
   886  	allClosesOverTests bool
   887  
   888  	// skipImportModFiles indicates whether we may skip loading go.mod files
   889  	// for imported packages (as in 'go mod tidy' in Go 1.17–1.20).
   890  	skipImportModFiles bool
   891  
   892  	work *par.Queue
   893  
   894  	// reset on each iteration
   895  	roots    []*loadPkg
   896  	pkgCache *par.Cache[string, *loadPkg]
   897  	pkgs     []*loadPkg // transitive closure of loaded packages and tests; populated in buildStacks
   898  }
   899  
   900  // loaderParams configure the packages loaded by, and the properties reported
   901  // by, a loader instance.
   902  type loaderParams struct {
   903  	PackageOpts
   904  	requirements *Requirements
   905  
   906  	allPatternIsRoot bool // Is the "all" pattern an additional root?
   907  
   908  	listRoots func(rs *Requirements) []string
   909  }
   910  
   911  func (ld *loader) reset() {
   912  	select {
   913  	case <-ld.work.Idle():
   914  	default:
   915  		panic("loader.reset when not idle")
   916  	}
   917  
   918  	ld.roots = nil
   919  	ld.pkgCache = new(par.Cache[string, *loadPkg])
   920  	ld.pkgs = nil
   921  }
   922  
   923  // error reports an error via either os.Stderr or base.Error,
   924  // according to whether ld.AllowErrors is set.
   925  func (ld *loader) error(err error) {
   926  	if ld.AllowErrors {
   927  		fmt.Fprintf(os.Stderr, "go: %v\n", err)
   928  	} else if ld.Switcher != nil {
   929  		ld.Switcher.Error(err)
   930  	} else {
   931  		base.Error(err)
   932  	}
   933  }
   934  
   935  // switchIfErrors switches toolchains if a switch is needed.
   936  func (ld *loader) switchIfErrors(ctx context.Context) {
   937  	if ld.Switcher != nil {
   938  		ld.Switcher.Switch(ctx)
   939  	}
   940  }
   941  
   942  // exitIfErrors switches toolchains if a switch is needed
   943  // or else exits if any errors have been reported.
   944  func (ld *loader) exitIfErrors(ctx context.Context) {
   945  	ld.switchIfErrors(ctx)
   946  	base.ExitIfErrors()
   947  }
   948  
   949  // goVersion reports the Go version that should be used for the loader's
   950  // requirements: ld.TidyGoVersion if set, or ld.requirements.GoVersion()
   951  // otherwise.
   952  func (ld *loader) goVersion() string {
   953  	if ld.TidyGoVersion != "" {
   954  		return ld.TidyGoVersion
   955  	}
   956  	return ld.requirements.GoVersion()
   957  }
   958  
   959  // A loadPkg records information about a single loaded package.
   960  type loadPkg struct {
   961  	// Populated at construction time:
   962  	path   string // import path
   963  	testOf *loadPkg
   964  
   965  	// Populated at construction time and updated by (*loader).applyPkgFlags:
   966  	flags atomicLoadPkgFlags
   967  
   968  	// Populated by (*loader).load:
   969  	mod         module.Version // module providing package
   970  	dir         string         // directory containing source code
   971  	err         error          // error loading package
   972  	imports     []*loadPkg     // packages imported by this one
   973  	testImports []string       // test-only imports, saved for use by pkg.test.
   974  	inStd       bool
   975  	altMods     []module.Version // modules that could have contained the package but did not
   976  
   977  	// Populated by (*loader).pkgTest:
   978  	testOnce sync.Once
   979  	test     *loadPkg
   980  
   981  	// Populated by postprocessing in (*loader).buildStacks:
   982  	stack *loadPkg // package importing this one in minimal import stack for this pkg
   983  }
   984  
   985  // loadPkgFlags is a set of flags tracking metadata about a package.
   986  type loadPkgFlags int8
   987  
   988  const (
   989  	// pkgInAll indicates that the package is in the "all" package pattern,
   990  	// regardless of whether we are loading the "all" package pattern.
   991  	//
   992  	// When the pkgInAll flag and pkgImportsLoaded flags are both set, the caller
   993  	// who set the last of those flags must propagate the pkgInAll marking to all
   994  	// of the imports of the marked package.
   995  	//
   996  	// A test is marked with pkgInAll if that test would promote the packages it
   997  	// imports to be in "all" (such as when the test is itself within the main
   998  	// module, or when ld.allClosesOverTests is true).
   999  	pkgInAll loadPkgFlags = 1 << iota
  1000  
  1001  	// pkgIsRoot indicates that the package matches one of the root package
  1002  	// patterns requested by the caller.
  1003  	//
  1004  	// If LoadTests is set, then when pkgIsRoot and pkgImportsLoaded are both set,
  1005  	// the caller who set the last of those flags must populate a test for the
  1006  	// package (in the pkg.test field).
  1007  	//
  1008  	// If the "all" pattern is included as a root, then non-test packages in "all"
  1009  	// are also roots (and must be marked pkgIsRoot).
  1010  	pkgIsRoot
  1011  
  1012  	// pkgFromRoot indicates that the package is in the transitive closure of
  1013  	// imports starting at the roots. (Note that every package marked as pkgIsRoot
  1014  	// is also trivially marked pkgFromRoot.)
  1015  	pkgFromRoot
  1016  
  1017  	// pkgImportsLoaded indicates that the imports and testImports fields of a
  1018  	// loadPkg have been populated.
  1019  	pkgImportsLoaded
  1020  )
  1021  
  1022  // has reports whether all of the flags in cond are set in f.
  1023  func (f loadPkgFlags) has(cond loadPkgFlags) bool {
  1024  	return f&cond == cond
  1025  }
  1026  
  1027  // An atomicLoadPkgFlags stores a loadPkgFlags for which individual flags can be
  1028  // added atomically.
  1029  type atomicLoadPkgFlags struct {
  1030  	bits atomic.Int32
  1031  }
  1032  
  1033  // update sets the given flags in af (in addition to any flags already set).
  1034  //
  1035  // update returns the previous flag state so that the caller may determine which
  1036  // flags were newly-set.
  1037  func (af *atomicLoadPkgFlags) update(flags loadPkgFlags) (old loadPkgFlags) {
  1038  	for {
  1039  		old := af.bits.Load()
  1040  		new := old | int32(flags)
  1041  		if new == old || af.bits.CompareAndSwap(old, new) {
  1042  			return loadPkgFlags(old)
  1043  		}
  1044  	}
  1045  }
  1046  
  1047  // has reports whether all of the flags in cond are set in af.
  1048  func (af *atomicLoadPkgFlags) has(cond loadPkgFlags) bool {
  1049  	return loadPkgFlags(af.bits.Load())&cond == cond
  1050  }
  1051  
  1052  // isTest reports whether pkg is a test of another package.
  1053  func (pkg *loadPkg) isTest() bool {
  1054  	return pkg.testOf != nil
  1055  }
  1056  
  1057  // fromExternalModule reports whether pkg was loaded from a module other than
  1058  // the main module.
  1059  func (pkg *loadPkg) fromExternalModule() bool {
  1060  	if pkg.mod.Path == "" {
  1061  		return false // loaded from the standard library, not a module
  1062  	}
  1063  	return !MainModules.Contains(pkg.mod.Path)
  1064  }
  1065  
  1066  var errMissing = errors.New("cannot find package")
  1067  
  1068  // loadFromRoots attempts to load the build graph needed to process a set of
  1069  // root packages and their dependencies.
  1070  //
  1071  // The set of root packages is returned by the params.listRoots function, and
  1072  // expanded to the full set of packages by tracing imports (and possibly tests)
  1073  // as needed.
  1074  func loadFromRoots(ctx context.Context, params loaderParams) *loader {
  1075  	ld := &loader{
  1076  		loaderParams: params,
  1077  		work:         par.NewQueue(runtime.GOMAXPROCS(0)),
  1078  	}
  1079  
  1080  	if ld.requirements.pruning == unpruned {
  1081  		// If the module graph does not support pruning, we assume that we will need
  1082  		// the full module graph in order to load package dependencies.
  1083  		//
  1084  		// This might not be strictly necessary, but it matches the historical
  1085  		// behavior of the 'go' command and keeps the go.mod file more consistent in
  1086  		// case of erroneous hand-edits — which are less likely to be detected by
  1087  		// spot-checks in modules that do not maintain the expanded go.mod
  1088  		// requirements needed for graph pruning.
  1089  		var err error
  1090  		ld.requirements, _, err = expandGraph(ctx, ld.requirements)
  1091  		if err != nil {
  1092  			ld.error(err)
  1093  		}
  1094  	}
  1095  	ld.exitIfErrors(ctx)
  1096  
  1097  	updateGoVersion := func() {
  1098  		goVersion := ld.goVersion()
  1099  
  1100  		if ld.requirements.pruning != workspace {
  1101  			var err error
  1102  			ld.requirements, err = convertPruning(ctx, ld.requirements, pruningForGoVersion(goVersion))
  1103  			if err != nil {
  1104  				ld.error(err)
  1105  				ld.exitIfErrors(ctx)
  1106  			}
  1107  		}
  1108  
  1109  		// If the module's Go version omits go.sum entries for go.mod files for test
  1110  		// dependencies of external packages, avoid loading those files in the first
  1111  		// place.
  1112  		ld.skipImportModFiles = ld.Tidy && gover.Compare(goVersion, gover.TidyGoModSumVersion) < 0
  1113  
  1114  		// If the module's go version explicitly predates the change in "all" for
  1115  		// graph pruning, continue to use the older interpretation.
  1116  		ld.allClosesOverTests = gover.Compare(goVersion, gover.NarrowAllVersion) < 0 && !ld.UseVendorAll
  1117  	}
  1118  
  1119  	for {
  1120  		ld.reset()
  1121  		updateGoVersion()
  1122  
  1123  		// Load the root packages and their imports.
  1124  		// Note: the returned roots can change on each iteration,
  1125  		// since the expansion of package patterns depends on the
  1126  		// build list we're using.
  1127  		rootPkgs := ld.listRoots(ld.requirements)
  1128  
  1129  		if ld.requirements.pruning == pruned && cfg.BuildMod == "mod" {
  1130  			// Before we start loading transitive imports of packages, locate all of
  1131  			// the root packages and promote their containing modules to root modules
  1132  			// dependencies. If their go.mod files are tidy (the common case) and the
  1133  			// set of root packages does not change then we can select the correct
  1134  			// versions of all transitive imports on the first try and complete
  1135  			// loading in a single iteration.
  1136  			changedBuildList := ld.preloadRootModules(ctx, rootPkgs)
  1137  			if changedBuildList {
  1138  				// The build list has changed, so the set of root packages may have also
  1139  				// changed. Start over to pick up the changes. (Preloading roots is much
  1140  				// cheaper than loading the full import graph, so we would rather pay
  1141  				// for an extra iteration of preloading than potentially end up
  1142  				// discarding the result of a full iteration of loading.)
  1143  				continue
  1144  			}
  1145  		}
  1146  
  1147  		inRoots := map[*loadPkg]bool{}
  1148  		for _, path := range rootPkgs {
  1149  			root := ld.pkg(ctx, path, pkgIsRoot)
  1150  			if !inRoots[root] {
  1151  				ld.roots = append(ld.roots, root)
  1152  				inRoots[root] = true
  1153  			}
  1154  		}
  1155  
  1156  		// ld.pkg adds imported packages to the work queue and calls applyPkgFlags,
  1157  		// which adds tests (and test dependencies) as needed.
  1158  		//
  1159  		// When all of the work in the queue has completed, we'll know that the
  1160  		// transitive closure of dependencies has been loaded.
  1161  		<-ld.work.Idle()
  1162  
  1163  		ld.buildStacks()
  1164  
  1165  		changed, err := ld.updateRequirements(ctx)
  1166  		if err != nil {
  1167  			ld.error(err)
  1168  			break
  1169  		}
  1170  		if changed {
  1171  			// Don't resolve missing imports until the module graph has stabilized.
  1172  			// If the roots are still changing, they may turn out to specify a
  1173  			// requirement on the missing package(s), and we would rather use a
  1174  			// version specified by a new root than add a new dependency on an
  1175  			// unrelated version.
  1176  			continue
  1177  		}
  1178  
  1179  		if !ld.ResolveMissingImports || (!HasModRoot() && !allowMissingModuleImports) {
  1180  			// We've loaded as much as we can without resolving missing imports.
  1181  			break
  1182  		}
  1183  
  1184  		modAddedBy, err := ld.resolveMissingImports(ctx)
  1185  		if err != nil {
  1186  			ld.error(err)
  1187  			break
  1188  		}
  1189  		if len(modAddedBy) == 0 {
  1190  			// The roots are stable, and we've resolved all of the missing packages
  1191  			// that we can.
  1192  			break
  1193  		}
  1194  
  1195  		toAdd := make([]module.Version, 0, len(modAddedBy))
  1196  		for m := range modAddedBy {
  1197  			toAdd = append(toAdd, m)
  1198  		}
  1199  		gover.ModSort(toAdd) // to make errors deterministic
  1200  
  1201  		// We ran updateRequirements before resolving missing imports and it didn't
  1202  		// make any changes, so we know that the requirement graph is already
  1203  		// consistent with ld.pkgs: we don't need to pass ld.pkgs to updateRoots
  1204  		// again. (That would waste time looking for changes that we have already
  1205  		// applied.)
  1206  		var noPkgs []*loadPkg
  1207  		// We also know that we're going to call updateRequirements again next
  1208  		// iteration so we don't need to also update it here. (That would waste time
  1209  		// computing a "direct" map that we'll have to recompute later anyway.)
  1210  		direct := ld.requirements.direct
  1211  		rs, err := updateRoots(ctx, direct, ld.requirements, noPkgs, toAdd, ld.AssumeRootsImported)
  1212  		if err != nil {
  1213  			// If an error was found in a newly added module, report the package
  1214  			// import stack instead of the module requirement stack. Packages
  1215  			// are more descriptive.
  1216  			if err, ok := err.(*mvs.BuildListError); ok {
  1217  				if pkg := modAddedBy[err.Module()]; pkg != nil {
  1218  					ld.error(fmt.Errorf("%s: %w", pkg.stackText(), err.Err))
  1219  					break
  1220  				}
  1221  			}
  1222  			ld.error(err)
  1223  			break
  1224  		}
  1225  		if slices.Equal(rs.rootModules, ld.requirements.rootModules) {
  1226  			// Something is deeply wrong. resolveMissingImports gave us a non-empty
  1227  			// set of modules to add to the graph, but adding those modules had no
  1228  			// effect — either they were already in the graph, or updateRoots did not
  1229  			// add them as requested.
  1230  			panic(fmt.Sprintf("internal error: adding %v to module graph had no effect on root requirements (%v)", toAdd, rs.rootModules))
  1231  		}
  1232  		ld.requirements = rs
  1233  	}
  1234  	ld.exitIfErrors(ctx)
  1235  
  1236  	// Tidy the build list, if applicable, before we report errors.
  1237  	// (The process of tidying may remove errors from irrelevant dependencies.)
  1238  	if ld.Tidy {
  1239  		rs, err := tidyRoots(ctx, ld.requirements, ld.pkgs)
  1240  		if err != nil {
  1241  			ld.error(err)
  1242  		} else {
  1243  			if ld.TidyGoVersion != "" {
  1244  				// Attempt to switch to the requested Go version. We have been using its
  1245  				// pruning and semantics all along, but there may have been — and may
  1246  				// still be — requirements on higher versions in the graph.
  1247  				tidy := overrideRoots(ctx, rs, []module.Version{{Path: "go", Version: ld.TidyGoVersion}})
  1248  				mg, err := tidy.Graph(ctx)
  1249  				if err != nil {
  1250  					ld.error(err)
  1251  				}
  1252  				if v := mg.Selected("go"); v == ld.TidyGoVersion {
  1253  					rs = tidy
  1254  				} else {
  1255  					conflict := Conflict{
  1256  						Path: mg.g.FindPath(func(m module.Version) bool {
  1257  							return m.Path == "go" && m.Version == v
  1258  						})[1:],
  1259  						Constraint: module.Version{Path: "go", Version: ld.TidyGoVersion},
  1260  					}
  1261  					msg := conflict.Summary()
  1262  					if cfg.BuildV {
  1263  						msg = conflict.String()
  1264  					}
  1265  					ld.error(errors.New(msg))
  1266  				}
  1267  			}
  1268  
  1269  			if ld.requirements.pruning == pruned {
  1270  				// We continuously add tidy roots to ld.requirements during loading, so
  1271  				// at this point the tidy roots (other than possibly the "go" version
  1272  				// edited above) should be a subset of the roots of ld.requirements,
  1273  				// ensuring that no new dependencies are brought inside the
  1274  				// graph-pruning horizon.
  1275  				// If that is not the case, there is a bug in the loading loop above.
  1276  				for _, m := range rs.rootModules {
  1277  					if m.Path == "go" && ld.TidyGoVersion != "" {
  1278  						continue
  1279  					}
  1280  					if v, ok := ld.requirements.rootSelected(m.Path); !ok || v != m.Version {
  1281  						ld.error(fmt.Errorf("internal error: a requirement on %v is needed but was not added during package loading (selected %s)", m, v))
  1282  					}
  1283  				}
  1284  			}
  1285  
  1286  			ld.requirements = rs
  1287  		}
  1288  
  1289  		ld.exitIfErrors(ctx)
  1290  	}
  1291  
  1292  	// Report errors, if any.
  1293  	for _, pkg := range ld.pkgs {
  1294  		if pkg.err == nil {
  1295  			continue
  1296  		}
  1297  
  1298  		// Add importer information to checksum errors.
  1299  		if sumErr := (*ImportMissingSumError)(nil); errors.As(pkg.err, &sumErr) {
  1300  			if importer := pkg.stack; importer != nil {
  1301  				sumErr.importer = importer.path
  1302  				sumErr.importerVersion = importer.mod.Version
  1303  				sumErr.importerIsTest = importer.testOf != nil
  1304  			}
  1305  		}
  1306  
  1307  		if stdErr := (*ImportMissingError)(nil); errors.As(pkg.err, &stdErr) && stdErr.isStd {
  1308  			// Add importer go version information to import errors of standard
  1309  			// library packages arising from newer releases.
  1310  			if importer := pkg.stack; importer != nil {
  1311  				if v, ok := rawGoVersion.Load(importer.mod); ok && gover.Compare(gover.Local(), v.(string)) < 0 {
  1312  					stdErr.importerGoVersion = v.(string)
  1313  				}
  1314  			}
  1315  			if ld.SilenceMissingStdImports {
  1316  				continue
  1317  			}
  1318  		}
  1319  		if ld.SilencePackageErrors {
  1320  			continue
  1321  		}
  1322  		if ld.SilenceNoGoErrors && errors.Is(pkg.err, imports.ErrNoGo) {
  1323  			continue
  1324  		}
  1325  
  1326  		ld.error(fmt.Errorf("%s: %w", pkg.stackText(), pkg.err))
  1327  	}
  1328  
  1329  	ld.checkMultiplePaths()
  1330  	return ld
  1331  }
  1332  
  1333  // updateRequirements ensures that ld.requirements is consistent with the
  1334  // information gained from ld.pkgs.
  1335  //
  1336  // In particular:
  1337  //
  1338  //   - Modules that provide packages directly imported from the main module are
  1339  //     marked as direct, and are promoted to explicit roots. If a needed root
  1340  //     cannot be promoted due to -mod=readonly or -mod=vendor, the importing
  1341  //     package is marked with an error.
  1342  //
  1343  //   - If ld scanned the "all" pattern independent of build constraints, it is
  1344  //     guaranteed to have seen every direct import. Module dependencies that did
  1345  //     not provide any directly-imported package are then marked as indirect.
  1346  //
  1347  //   - Root dependencies are updated to their selected versions.
  1348  //
  1349  // The "changed" return value reports whether the update changed the selected
  1350  // version of any module that either provided a loaded package or may now
  1351  // provide a package that was previously unresolved.
  1352  func (ld *loader) updateRequirements(ctx context.Context) (changed bool, err error) {
  1353  	rs := ld.requirements
  1354  
  1355  	// direct contains the set of modules believed to provide packages directly
  1356  	// imported by the main module.
  1357  	var direct map[string]bool
  1358  
  1359  	// If we didn't scan all of the imports from the main module, or didn't use
  1360  	// imports.AnyTags, then we didn't necessarily load every package that
  1361  	// contributes “direct” imports — so we can't safely mark existing direct
  1362  	// dependencies in ld.requirements as indirect-only. Propagate them as direct.
  1363  	loadedDirect := ld.allPatternIsRoot && maps.Equal(ld.Tags, imports.AnyTags())
  1364  	if loadedDirect {
  1365  		direct = make(map[string]bool)
  1366  	} else {
  1367  		// TODO(bcmills): It seems like a shame to allocate and copy a map here when
  1368  		// it will only rarely actually vary from rs.direct. Measure this cost and
  1369  		// maybe avoid the copy.
  1370  		direct = make(map[string]bool, len(rs.direct))
  1371  		for mPath := range rs.direct {
  1372  			direct[mPath] = true
  1373  		}
  1374  	}
  1375  
  1376  	var maxTooNew *gover.TooNewError
  1377  	for _, pkg := range ld.pkgs {
  1378  		if pkg.err != nil {
  1379  			if tooNew := (*gover.TooNewError)(nil); errors.As(pkg.err, &tooNew) {
  1380  				if maxTooNew == nil || gover.Compare(tooNew.GoVersion, maxTooNew.GoVersion) > 0 {
  1381  					maxTooNew = tooNew
  1382  				}
  1383  			}
  1384  		}
  1385  		if pkg.mod.Version != "" || !MainModules.Contains(pkg.mod.Path) {
  1386  			continue
  1387  		}
  1388  
  1389  		for _, dep := range pkg.imports {
  1390  			if !dep.fromExternalModule() {
  1391  				continue
  1392  			}
  1393  
  1394  			if inWorkspaceMode() {
  1395  				// In workspace mode / workspace pruning mode, the roots are the main modules
  1396  				// rather than the main module's direct dependencies. The check below on the selected
  1397  				// roots does not apply.
  1398  				if cfg.BuildMod == "vendor" {
  1399  					// In workspace vendor mode, we don't need to load the requirements of the workspace
  1400  					// modules' dependencies so the check below doesn't work. But that's okay, because
  1401  					// checking whether modules are required directly for the purposes of pruning is
  1402  					// less important in vendor mode: if we were able to load the package, we have
  1403  					// everything we need  to build the package, and dependencies' tests are pruned out
  1404  					// of the vendor directory anyway.
  1405  					continue
  1406  				}
  1407  				if mg, err := rs.Graph(ctx); err != nil {
  1408  					return false, err
  1409  				} else if _, ok := mg.RequiredBy(dep.mod); !ok {
  1410  					// dep.mod is not an explicit dependency, but needs to be.
  1411  					// See comment on error returned below.
  1412  					pkg.err = &DirectImportFromImplicitDependencyError{
  1413  						ImporterPath: pkg.path,
  1414  						ImportedPath: dep.path,
  1415  						Module:       dep.mod,
  1416  					}
  1417  				}
  1418  			} else if pkg.err == nil && cfg.BuildMod != "mod" {
  1419  				if v, ok := rs.rootSelected(dep.mod.Path); !ok || v != dep.mod.Version {
  1420  					// dep.mod is not an explicit dependency, but needs to be.
  1421  					// Because we are not in "mod" mode, we will not be able to update it.
  1422  					// Instead, mark the importing package with an error.
  1423  					//
  1424  					// TODO(#41688): The resulting error message fails to include the file
  1425  					// position of the import statement (because that information is not
  1426  					// tracked by the module loader). Figure out how to plumb the import
  1427  					// position through.
  1428  					pkg.err = &DirectImportFromImplicitDependencyError{
  1429  						ImporterPath: pkg.path,
  1430  						ImportedPath: dep.path,
  1431  						Module:       dep.mod,
  1432  					}
  1433  					// cfg.BuildMod does not allow us to change dep.mod to be a direct
  1434  					// dependency, so don't mark it as such.
  1435  					continue
  1436  				}
  1437  			}
  1438  
  1439  			// dep is a package directly imported by a package or test in the main
  1440  			// module and loaded from some other module (not the standard library).
  1441  			// Mark its module as a direct dependency.
  1442  			direct[dep.mod.Path] = true
  1443  		}
  1444  	}
  1445  	if maxTooNew != nil {
  1446  		return false, maxTooNew
  1447  	}
  1448  
  1449  	var addRoots []module.Version
  1450  	if ld.Tidy {
  1451  		// When we are tidying a module with a pruned dependency graph, we may need
  1452  		// to add roots to preserve the versions of indirect, test-only dependencies
  1453  		// that are upgraded above or otherwise missing from the go.mod files of
  1454  		// direct dependencies. (For example, the direct dependency might be a very
  1455  		// stable codebase that predates modules and thus lacks a go.mod file, or
  1456  		// the author of the direct dependency may have forgotten to commit a change
  1457  		// to the go.mod file, or may have made an erroneous hand-edit that causes
  1458  		// it to be untidy.)
  1459  		//
  1460  		// Promoting an indirect dependency to a root adds the next layer of its
  1461  		// dependencies to the module graph, which may increase the selected
  1462  		// versions of other modules from which we have already loaded packages.
  1463  		// So after we promote an indirect dependency to a root, we need to reload
  1464  		// packages, which means another iteration of loading.
  1465  		//
  1466  		// As an extra wrinkle, the upgrades due to promoting a root can cause
  1467  		// previously-resolved packages to become unresolved. For example, the
  1468  		// module providing an unstable package might be upgraded to a version
  1469  		// that no longer contains that package. If we then resolve the missing
  1470  		// package, we might add yet another root that upgrades away some other
  1471  		// dependency. (The tests in mod_tidy_convergence*.txt illustrate some
  1472  		// particularly worrisome cases.)
  1473  		//
  1474  		// To ensure that this process of promoting, adding, and upgrading roots
  1475  		// eventually terminates, during iteration we only ever add modules to the
  1476  		// root set — we only remove irrelevant roots at the very end of
  1477  		// iteration, after we have already added every root that we plan to need
  1478  		// in the (eventual) tidy root set.
  1479  		//
  1480  		// Since we do not remove any roots during iteration, even if they no
  1481  		// longer provide any imported packages, the selected versions of the
  1482  		// roots can only increase and the set of roots can only expand. The set
  1483  		// of extant root paths is finite and the set of versions of each path is
  1484  		// finite, so the iteration *must* reach a stable fixed-point.
  1485  		tidy, err := tidyRoots(ctx, rs, ld.pkgs)
  1486  		if err != nil {
  1487  			return false, err
  1488  		}
  1489  		addRoots = tidy.rootModules
  1490  	}
  1491  
  1492  	rs, err = updateRoots(ctx, direct, rs, ld.pkgs, addRoots, ld.AssumeRootsImported)
  1493  	if err != nil {
  1494  		// We don't actually know what even the root requirements are supposed to be,
  1495  		// so we can't proceed with loading. Return the error to the caller
  1496  		return false, err
  1497  	}
  1498  
  1499  	if rs.GoVersion() != ld.requirements.GoVersion() {
  1500  		// A change in the selected Go version may or may not affect the set of
  1501  		// loaded packages, but in some cases it can change the meaning of the "all"
  1502  		// pattern, the level of pruning in the module graph, and even the set of
  1503  		// packages present in the standard library. If it has changed, it's best to
  1504  		// reload packages once more to be sure everything is stable.
  1505  		changed = true
  1506  	} else if rs != ld.requirements && !slices.Equal(rs.rootModules, ld.requirements.rootModules) {
  1507  		// The roots of the module graph have changed in some way (not just the
  1508  		// "direct" markings). Check whether the changes affected any of the loaded
  1509  		// packages.
  1510  		mg, err := rs.Graph(ctx)
  1511  		if err != nil {
  1512  			return false, err
  1513  		}
  1514  		for _, pkg := range ld.pkgs {
  1515  			if pkg.fromExternalModule() && mg.Selected(pkg.mod.Path) != pkg.mod.Version {
  1516  				changed = true
  1517  				break
  1518  			}
  1519  			if pkg.err != nil {
  1520  				// Promoting a module to a root may resolve an import that was
  1521  				// previously missing (by pulling in a previously-prune dependency that
  1522  				// provides it) or ambiguous (by promoting exactly one of the
  1523  				// alternatives to a root and ignoring the second-level alternatives) or
  1524  				// otherwise errored out (by upgrading from a version that cannot be
  1525  				// fetched to one that can be).
  1526  				//
  1527  				// Instead of enumerating all of the possible errors, we'll just check
  1528  				// whether importFromModules returns nil for the package.
  1529  				// False-positives are ok: if we have a false-positive here, we'll do an
  1530  				// extra iteration of package loading this time, but we'll still
  1531  				// converge when the root set stops changing.
  1532  				//
  1533  				// In some sense, we can think of this as ‘upgraded the module providing
  1534  				// pkg.path from "none" to a version higher than "none"’.
  1535  				if _, _, _, _, err = importFromModules(ctx, pkg.path, rs, nil, ld.skipImportModFiles); err == nil {
  1536  					changed = true
  1537  					break
  1538  				}
  1539  			}
  1540  		}
  1541  	}
  1542  
  1543  	ld.requirements = rs
  1544  	return changed, nil
  1545  }
  1546  
  1547  // resolveMissingImports returns a set of modules that could be added as
  1548  // dependencies in order to resolve missing packages from pkgs.
  1549  //
  1550  // The newly-resolved packages are added to the addedModuleFor map, and
  1551  // resolveMissingImports returns a map from each new module version to
  1552  // the first missing package that module would resolve.
  1553  func (ld *loader) resolveMissingImports(ctx context.Context) (modAddedBy map[module.Version]*loadPkg, err error) {
  1554  	type pkgMod struct {
  1555  		pkg *loadPkg
  1556  		mod *module.Version
  1557  	}
  1558  	var pkgMods []pkgMod
  1559  	for _, pkg := range ld.pkgs {
  1560  		if pkg.err == nil {
  1561  			continue
  1562  		}
  1563  		if pkg.isTest() {
  1564  			// If we are missing a test, we are also missing its non-test version, and
  1565  			// we should only add the missing import once.
  1566  			continue
  1567  		}
  1568  		if !errors.As(pkg.err, new(*ImportMissingError)) {
  1569  			// Leave other errors for Import or load.Packages to report.
  1570  			continue
  1571  		}
  1572  
  1573  		pkg := pkg
  1574  		var mod module.Version
  1575  		ld.work.Add(func() {
  1576  			var err error
  1577  			mod, err = queryImport(ctx, pkg.path, ld.requirements)
  1578  			if err != nil {
  1579  				var ime *ImportMissingError
  1580  				if errors.As(err, &ime) {
  1581  					for curstack := pkg.stack; curstack != nil; curstack = curstack.stack {
  1582  						if MainModules.Contains(curstack.mod.Path) {
  1583  							ime.ImportingMainModule = curstack.mod
  1584  							break
  1585  						}
  1586  					}
  1587  				}
  1588  				// pkg.err was already non-nil, so we can reasonably attribute the error
  1589  				// for pkg to either the original error or the one returned by
  1590  				// queryImport. The existing error indicates only that we couldn't find
  1591  				// the package, whereas the query error also explains why we didn't fix
  1592  				// the problem — so we prefer the latter.
  1593  				pkg.err = err
  1594  			}
  1595  
  1596  			// err is nil, but we intentionally leave pkg.err non-nil and pkg.mod
  1597  			// unset: we still haven't satisfied other invariants of a
  1598  			// successfully-loaded package, such as scanning and loading the imports
  1599  			// of that package. If we succeed in resolving the new dependency graph,
  1600  			// the caller can reload pkg and update the error at that point.
  1601  			//
  1602  			// Even then, the package might not be loaded from the version we've
  1603  			// identified here. The module may be upgraded by some other dependency,
  1604  			// or by a transitive dependency of mod itself, or — less likely — the
  1605  			// package may be rejected by an AllowPackage hook or rendered ambiguous
  1606  			// by some other newly-added or newly-upgraded dependency.
  1607  		})
  1608  
  1609  		pkgMods = append(pkgMods, pkgMod{pkg: pkg, mod: &mod})
  1610  	}
  1611  	<-ld.work.Idle()
  1612  
  1613  	modAddedBy = map[module.Version]*loadPkg{}
  1614  
  1615  	var (
  1616  		maxTooNew    *gover.TooNewError
  1617  		maxTooNewPkg *loadPkg
  1618  	)
  1619  	for _, pm := range pkgMods {
  1620  		if tooNew := (*gover.TooNewError)(nil); errors.As(pm.pkg.err, &tooNew) {
  1621  			if maxTooNew == nil || gover.Compare(tooNew.GoVersion, maxTooNew.GoVersion) > 0 {
  1622  				maxTooNew = tooNew
  1623  				maxTooNewPkg = pm.pkg
  1624  			}
  1625  		}
  1626  	}
  1627  	if maxTooNew != nil {
  1628  		fmt.Fprintf(os.Stderr, "go: toolchain upgrade needed to resolve %s\n", maxTooNewPkg.path)
  1629  		return nil, maxTooNew
  1630  	}
  1631  
  1632  	for _, pm := range pkgMods {
  1633  		pkg, mod := pm.pkg, *pm.mod
  1634  		if mod.Path == "" {
  1635  			continue
  1636  		}
  1637  
  1638  		fmt.Fprintf(os.Stderr, "go: found %s in %s %s\n", pkg.path, mod.Path, mod.Version)
  1639  		if modAddedBy[mod] == nil {
  1640  			modAddedBy[mod] = pkg
  1641  		}
  1642  	}
  1643  
  1644  	return modAddedBy, nil
  1645  }
  1646  
  1647  // pkg locates the *loadPkg for path, creating and queuing it for loading if
  1648  // needed, and updates its state to reflect the given flags.
  1649  //
  1650  // The imports of the returned *loadPkg will be loaded asynchronously in the
  1651  // ld.work queue, and its test (if requested) will also be populated once
  1652  // imports have been resolved. When ld.work goes idle, all transitive imports of
  1653  // the requested package (and its test, if requested) will have been loaded.
  1654  func (ld *loader) pkg(ctx context.Context, path string, flags loadPkgFlags) *loadPkg {
  1655  	if flags.has(pkgImportsLoaded) {
  1656  		panic("internal error: (*loader).pkg called with pkgImportsLoaded flag set")
  1657  	}
  1658  
  1659  	pkg := ld.pkgCache.Do(path, func() *loadPkg {
  1660  		pkg := &loadPkg{
  1661  			path: path,
  1662  		}
  1663  		ld.applyPkgFlags(ctx, pkg, flags)
  1664  
  1665  		ld.work.Add(func() { ld.load(ctx, pkg) })
  1666  		return pkg
  1667  	})
  1668  
  1669  	ld.applyPkgFlags(ctx, pkg, flags)
  1670  	return pkg
  1671  }
  1672  
  1673  // applyPkgFlags updates pkg.flags to set the given flags and propagate the
  1674  // (transitive) effects of those flags, possibly loading or enqueueing further
  1675  // packages as a result.
  1676  func (ld *loader) applyPkgFlags(ctx context.Context, pkg *loadPkg, flags loadPkgFlags) {
  1677  	if flags == 0 {
  1678  		return
  1679  	}
  1680  
  1681  	if flags.has(pkgInAll) && ld.allPatternIsRoot && !pkg.isTest() {
  1682  		// This package matches a root pattern by virtue of being in "all".
  1683  		flags |= pkgIsRoot
  1684  	}
  1685  	if flags.has(pkgIsRoot) {
  1686  		flags |= pkgFromRoot
  1687  	}
  1688  
  1689  	old := pkg.flags.update(flags)
  1690  	new := old | flags
  1691  	if new == old || !new.has(pkgImportsLoaded) {
  1692  		// We either didn't change the state of pkg, or we don't know anything about
  1693  		// its dependencies yet. Either way, we can't usefully load its test or
  1694  		// update its dependencies.
  1695  		return
  1696  	}
  1697  
  1698  	if !pkg.isTest() {
  1699  		// Check whether we should add (or update the flags for) a test for pkg.
  1700  		// ld.pkgTest is idempotent and extra invocations are inexpensive,
  1701  		// so it's ok if we call it more than is strictly necessary.
  1702  		wantTest := false
  1703  		switch {
  1704  		case ld.allPatternIsRoot && MainModules.Contains(pkg.mod.Path):
  1705  			// We are loading the "all" pattern, which includes packages imported by
  1706  			// tests in the main module. This package is in the main module, so we
  1707  			// need to identify the imports of its test even if LoadTests is not set.
  1708  			//
  1709  			// (We will filter out the extra tests explicitly in computePatternAll.)
  1710  			wantTest = true
  1711  
  1712  		case ld.allPatternIsRoot && ld.allClosesOverTests && new.has(pkgInAll):
  1713  			// This variant of the "all" pattern includes imports of tests of every
  1714  			// package that is itself in "all", and pkg is in "all", so its test is
  1715  			// also in "all" (as above).
  1716  			wantTest = true
  1717  
  1718  		case ld.LoadTests && new.has(pkgIsRoot):
  1719  			// LoadTest explicitly requests tests of “the root packages”.
  1720  			wantTest = true
  1721  		}
  1722  
  1723  		if wantTest {
  1724  			var testFlags loadPkgFlags
  1725  			if MainModules.Contains(pkg.mod.Path) || (ld.allClosesOverTests && new.has(pkgInAll)) {
  1726  				// Tests of packages in the main module are in "all", in the sense that
  1727  				// they cause the packages they import to also be in "all". So are tests
  1728  				// of packages in "all" if "all" closes over test dependencies.
  1729  				testFlags |= pkgInAll
  1730  			}
  1731  			ld.pkgTest(ctx, pkg, testFlags)
  1732  		}
  1733  	}
  1734  
  1735  	if new.has(pkgInAll) && !old.has(pkgInAll|pkgImportsLoaded) {
  1736  		// We have just marked pkg with pkgInAll, or we have just loaded its
  1737  		// imports, or both. Now is the time to propagate pkgInAll to the imports.
  1738  		for _, dep := range pkg.imports {
  1739  			ld.applyPkgFlags(ctx, dep, pkgInAll)
  1740  		}
  1741  	}
  1742  
  1743  	if new.has(pkgFromRoot) && !old.has(pkgFromRoot|pkgImportsLoaded) {
  1744  		for _, dep := range pkg.imports {
  1745  			ld.applyPkgFlags(ctx, dep, pkgFromRoot)
  1746  		}
  1747  	}
  1748  }
  1749  
  1750  // preloadRootModules loads the module requirements needed to identify the
  1751  // selected version of each module providing a package in rootPkgs,
  1752  // adding new root modules to the module graph if needed.
  1753  func (ld *loader) preloadRootModules(ctx context.Context, rootPkgs []string) (changedBuildList bool) {
  1754  	needc := make(chan map[module.Version]bool, 1)
  1755  	needc <- map[module.Version]bool{}
  1756  	for _, path := range rootPkgs {
  1757  		path := path
  1758  		ld.work.Add(func() {
  1759  			// First, try to identify the module containing the package using only roots.
  1760  			//
  1761  			// If the main module is tidy and the package is in "all" — or if we're
  1762  			// lucky — we can identify all of its imports without actually loading the
  1763  			// full module graph.
  1764  			m, _, _, _, err := importFromModules(ctx, path, ld.requirements, nil, ld.skipImportModFiles)
  1765  			if err != nil {
  1766  				var missing *ImportMissingError
  1767  				if errors.As(err, &missing) && ld.ResolveMissingImports {
  1768  					// This package isn't provided by any selected module.
  1769  					// If we can find it, it will be a new root dependency.
  1770  					m, err = queryImport(ctx, path, ld.requirements)
  1771  				}
  1772  				if err != nil {
  1773  					// We couldn't identify the root module containing this package.
  1774  					// Leave it unresolved; we will report it during loading.
  1775  					return
  1776  				}
  1777  			}
  1778  			if m.Path == "" {
  1779  				// The package is in std or cmd. We don't need to change the root set.
  1780  				return
  1781  			}
  1782  
  1783  			v, ok := ld.requirements.rootSelected(m.Path)
  1784  			if !ok || v != m.Version {
  1785  				// We found the requested package in m, but m is not a root, so
  1786  				// loadModGraph will not load its requirements. We need to promote the
  1787  				// module to a root to ensure that any other packages this package
  1788  				// imports are resolved from correct dependency versions.
  1789  				//
  1790  				// (This is the “argument invariant” from
  1791  				// https://golang.org/design/36460-lazy-module-loading.)
  1792  				need := <-needc
  1793  				need[m] = true
  1794  				needc <- need
  1795  			}
  1796  		})
  1797  	}
  1798  	<-ld.work.Idle()
  1799  
  1800  	need := <-needc
  1801  	if len(need) == 0 {
  1802  		return false // No roots to add.
  1803  	}
  1804  
  1805  	toAdd := make([]module.Version, 0, len(need))
  1806  	for m := range need {
  1807  		toAdd = append(toAdd, m)
  1808  	}
  1809  	gover.ModSort(toAdd)
  1810  
  1811  	rs, err := updateRoots(ctx, ld.requirements.direct, ld.requirements, nil, toAdd, ld.AssumeRootsImported)
  1812  	if err != nil {
  1813  		// We are missing some root dependency, and for some reason we can't load
  1814  		// enough of the module dependency graph to add the missing root. Package
  1815  		// loading is doomed to fail, so fail quickly.
  1816  		ld.error(err)
  1817  		ld.exitIfErrors(ctx)
  1818  		return false
  1819  	}
  1820  	if slices.Equal(rs.rootModules, ld.requirements.rootModules) {
  1821  		// Something is deeply wrong. resolveMissingImports gave us a non-empty
  1822  		// set of modules to add to the graph, but adding those modules had no
  1823  		// effect — either they were already in the graph, or updateRoots did not
  1824  		// add them as requested.
  1825  		panic(fmt.Sprintf("internal error: adding %v to module graph had no effect on root requirements (%v)", toAdd, rs.rootModules))
  1826  	}
  1827  
  1828  	ld.requirements = rs
  1829  	return true
  1830  }
  1831  
  1832  // load loads an individual package.
  1833  func (ld *loader) load(ctx context.Context, pkg *loadPkg) {
  1834  	var mg *ModuleGraph
  1835  	if ld.requirements.pruning == unpruned {
  1836  		var err error
  1837  		mg, err = ld.requirements.Graph(ctx)
  1838  		if err != nil {
  1839  			// We already checked the error from Graph in loadFromRoots and/or
  1840  			// updateRequirements, so we ignored the error on purpose and we should
  1841  			// keep trying to push past it.
  1842  			//
  1843  			// However, because mg may be incomplete (and thus may select inaccurate
  1844  			// versions), we shouldn't use it to load packages. Instead, we pass a nil
  1845  			// *ModuleGraph, which will cause mg to first try loading from only the
  1846  			// main module and root dependencies.
  1847  			mg = nil
  1848  		}
  1849  	}
  1850  
  1851  	var modroot string
  1852  	pkg.mod, modroot, pkg.dir, pkg.altMods, pkg.err = importFromModules(ctx, pkg.path, ld.requirements, mg, ld.skipImportModFiles)
  1853  	if pkg.dir == "" {
  1854  		return
  1855  	}
  1856  	if MainModules.Contains(pkg.mod.Path) {
  1857  		// Go ahead and mark pkg as in "all". This provides the invariant that a
  1858  		// package that is *only* imported by other packages in "all" is always
  1859  		// marked as such before loading its imports.
  1860  		//
  1861  		// We don't actually rely on that invariant at the moment, but it may
  1862  		// improve efficiency somewhat and makes the behavior a bit easier to reason
  1863  		// about (by reducing churn on the flag bits of dependencies), and costs
  1864  		// essentially nothing (these atomic flag ops are essentially free compared
  1865  		// to scanning source code for imports).
  1866  		ld.applyPkgFlags(ctx, pkg, pkgInAll)
  1867  	}
  1868  	if ld.AllowPackage != nil {
  1869  		if err := ld.AllowPackage(ctx, pkg.path, pkg.mod); err != nil {
  1870  			pkg.err = err
  1871  		}
  1872  	}
  1873  
  1874  	pkg.inStd = (search.IsStandardImportPath(pkg.path) && search.InDir(pkg.dir, cfg.GOROOTsrc) != "")
  1875  
  1876  	var imports, testImports []string
  1877  
  1878  	if cfg.BuildContext.Compiler == "gccgo" && pkg.inStd {
  1879  		// We can't scan standard packages for gccgo.
  1880  	} else {
  1881  		var err error
  1882  		imports, testImports, err = scanDir(modroot, pkg.dir, ld.Tags)
  1883  		if err != nil {
  1884  			pkg.err = err
  1885  			return
  1886  		}
  1887  	}
  1888  
  1889  	pkg.imports = make([]*loadPkg, 0, len(imports))
  1890  	var importFlags loadPkgFlags
  1891  	if pkg.flags.has(pkgInAll) {
  1892  		importFlags = pkgInAll
  1893  	}
  1894  	for _, path := range imports {
  1895  		if pkg.inStd {
  1896  			// Imports from packages in "std" and "cmd" should resolve using
  1897  			// GOROOT/src/vendor even when "std" is not the main module.
  1898  			path = ld.stdVendor(pkg.path, path)
  1899  		}
  1900  		pkg.imports = append(pkg.imports, ld.pkg(ctx, path, importFlags))
  1901  	}
  1902  	pkg.testImports = testImports
  1903  
  1904  	ld.applyPkgFlags(ctx, pkg, pkgImportsLoaded)
  1905  }
  1906  
  1907  // pkgTest locates the test of pkg, creating it if needed, and updates its state
  1908  // to reflect the given flags.
  1909  //
  1910  // pkgTest requires that the imports of pkg have already been loaded (flagged
  1911  // with pkgImportsLoaded).
  1912  func (ld *loader) pkgTest(ctx context.Context, pkg *loadPkg, testFlags loadPkgFlags) *loadPkg {
  1913  	if pkg.isTest() {
  1914  		panic("pkgTest called on a test package")
  1915  	}
  1916  
  1917  	createdTest := false
  1918  	pkg.testOnce.Do(func() {
  1919  		pkg.test = &loadPkg{
  1920  			path:   pkg.path,
  1921  			testOf: pkg,
  1922  			mod:    pkg.mod,
  1923  			dir:    pkg.dir,
  1924  			err:    pkg.err,
  1925  			inStd:  pkg.inStd,
  1926  		}
  1927  		ld.applyPkgFlags(ctx, pkg.test, testFlags)
  1928  		createdTest = true
  1929  	})
  1930  
  1931  	test := pkg.test
  1932  	if createdTest {
  1933  		test.imports = make([]*loadPkg, 0, len(pkg.testImports))
  1934  		var importFlags loadPkgFlags
  1935  		if test.flags.has(pkgInAll) {
  1936  			importFlags = pkgInAll
  1937  		}
  1938  		for _, path := range pkg.testImports {
  1939  			if pkg.inStd {
  1940  				path = ld.stdVendor(test.path, path)
  1941  			}
  1942  			test.imports = append(test.imports, ld.pkg(ctx, path, importFlags))
  1943  		}
  1944  		pkg.testImports = nil
  1945  		ld.applyPkgFlags(ctx, test, pkgImportsLoaded)
  1946  	} else {
  1947  		ld.applyPkgFlags(ctx, test, testFlags)
  1948  	}
  1949  
  1950  	return test
  1951  }
  1952  
  1953  // stdVendor returns the canonical import path for the package with the given
  1954  // path when imported from the standard-library package at parentPath.
  1955  func (ld *loader) stdVendor(parentPath, path string) string {
  1956  	if search.IsStandardImportPath(path) {
  1957  		return path
  1958  	}
  1959  
  1960  	if str.HasPathPrefix(parentPath, "cmd") {
  1961  		if !ld.VendorModulesInGOROOTSrc || !MainModules.Contains("cmd") {
  1962  			vendorPath := pathpkg.Join("cmd", "vendor", path)
  1963  
  1964  			if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
  1965  				return vendorPath
  1966  			}
  1967  		}
  1968  	} else if !ld.VendorModulesInGOROOTSrc || !MainModules.Contains("std") || str.HasPathPrefix(parentPath, "vendor") {
  1969  		// If we are outside of the 'std' module, resolve imports from within 'std'
  1970  		// to the vendor directory.
  1971  		//
  1972  		// Do the same for importers beginning with the prefix 'vendor/' even if we
  1973  		// are *inside* of the 'std' module: the 'vendor/' packages that resolve
  1974  		// globally from GOROOT/src/vendor (and are listed as part of 'go list std')
  1975  		// are distinct from the real module dependencies, and cannot import
  1976  		// internal packages from the real module.
  1977  		//
  1978  		// (Note that although the 'vendor/' packages match the 'std' *package*
  1979  		// pattern, they are not part of the std *module*, and do not affect
  1980  		// 'go mod tidy' and similar module commands when working within std.)
  1981  		vendorPath := pathpkg.Join("vendor", path)
  1982  		if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
  1983  			return vendorPath
  1984  		}
  1985  	}
  1986  
  1987  	// Not vendored: resolve from modules.
  1988  	return path
  1989  }
  1990  
  1991  // computePatternAll returns the list of packages matching pattern "all",
  1992  // starting with a list of the import paths for the packages in the main module.
  1993  func (ld *loader) computePatternAll() (all []string) {
  1994  	for _, pkg := range ld.pkgs {
  1995  		if pkg.flags.has(pkgInAll) && !pkg.isTest() {
  1996  			all = append(all, pkg.path)
  1997  		}
  1998  	}
  1999  	sort.Strings(all)
  2000  	return all
  2001  }
  2002  
  2003  // checkMultiplePaths verifies that a given module path is used as itself
  2004  // or as a replacement for another module, but not both at the same time.
  2005  //
  2006  // (See https://golang.org/issue/26607 and https://golang.org/issue/34650.)
  2007  func (ld *loader) checkMultiplePaths() {
  2008  	mods := ld.requirements.rootModules
  2009  	if cached := ld.requirements.graph.Load(); cached != nil {
  2010  		if mg := cached.mg; mg != nil {
  2011  			mods = mg.BuildList()
  2012  		}
  2013  	}
  2014  
  2015  	firstPath := map[module.Version]string{}
  2016  	for _, mod := range mods {
  2017  		src := resolveReplacement(mod)
  2018  		if prev, ok := firstPath[src]; !ok {
  2019  			firstPath[src] = mod.Path
  2020  		} else if prev != mod.Path {
  2021  			ld.error(fmt.Errorf("%s@%s used for two different module paths (%s and %s)", src.Path, src.Version, prev, mod.Path))
  2022  		}
  2023  	}
  2024  }
  2025  
  2026  // checkTidyCompatibility emits an error if any package would be loaded from a
  2027  // different module under rs than under ld.requirements.
  2028  func (ld *loader) checkTidyCompatibility(ctx context.Context, rs *Requirements, compatVersion string) {
  2029  	goVersion := rs.GoVersion()
  2030  	suggestUpgrade := false
  2031  	suggestEFlag := false
  2032  	suggestFixes := func() {
  2033  		if ld.AllowErrors {
  2034  			// The user is explicitly ignoring these errors, so don't bother them with
  2035  			// other options.
  2036  			return
  2037  		}
  2038  
  2039  		// We print directly to os.Stderr because this information is advice about
  2040  		// how to fix errors, not actually an error itself.
  2041  		// (The actual errors should have been logged already.)
  2042  
  2043  		fmt.Fprintln(os.Stderr)
  2044  
  2045  		goFlag := ""
  2046  		if goVersion != MainModules.GoVersion() {
  2047  			goFlag = " -go=" + goVersion
  2048  		}
  2049  
  2050  		compatFlag := ""
  2051  		if compatVersion != gover.Prev(goVersion) {
  2052  			compatFlag = " -compat=" + compatVersion
  2053  		}
  2054  		if suggestUpgrade {
  2055  			eDesc := ""
  2056  			eFlag := ""
  2057  			if suggestEFlag {
  2058  				eDesc = ", leaving some packages unresolved"
  2059  				eFlag = " -e"
  2060  			}
  2061  			fmt.Fprintf(os.Stderr, "To upgrade to the versions selected by go %s%s:\n\tgo mod tidy%s -go=%s && go mod tidy%s -go=%s%s\n", compatVersion, eDesc, eFlag, compatVersion, eFlag, goVersion, compatFlag)
  2062  		} else if suggestEFlag {
  2063  			// If some packages are missing but no package is upgraded, then we
  2064  			// shouldn't suggest upgrading to the Go 1.16 versions explicitly — that
  2065  			// wouldn't actually fix anything for Go 1.16 users, and *would* break
  2066  			// something for Go 1.17 users.
  2067  			fmt.Fprintf(os.Stderr, "To proceed despite packages unresolved in go %s:\n\tgo mod tidy -e%s%s\n", compatVersion, goFlag, compatFlag)
  2068  		}
  2069  
  2070  		fmt.Fprintf(os.Stderr, "If reproducibility with go %s is not needed:\n\tgo mod tidy%s -compat=%s\n", compatVersion, goFlag, goVersion)
  2071  
  2072  		// TODO(#46141): Populate the linked wiki page.
  2073  		fmt.Fprintf(os.Stderr, "For other options, see:\n\thttps://golang.org/doc/modules/pruning\n")
  2074  	}
  2075  
  2076  	mg, err := rs.Graph(ctx)
  2077  	if err != nil {
  2078  		ld.error(fmt.Errorf("error loading go %s module graph: %w", compatVersion, err))
  2079  		ld.switchIfErrors(ctx)
  2080  		suggestFixes()
  2081  		ld.exitIfErrors(ctx)
  2082  		return
  2083  	}
  2084  
  2085  	// Re-resolve packages in parallel.
  2086  	//
  2087  	// We re-resolve each package — rather than just checking versions — to ensure
  2088  	// that we have fetched module source code (and, importantly, checksums for
  2089  	// that source code) for all modules that are necessary to ensure that imports
  2090  	// are unambiguous. That also produces clearer diagnostics, since we can say
  2091  	// exactly what happened to the package if it became ambiguous or disappeared
  2092  	// entirely.
  2093  	//
  2094  	// We re-resolve the packages in parallel because this process involves disk
  2095  	// I/O to check for package sources, and because the process of checking for
  2096  	// ambiguous imports may require us to download additional modules that are
  2097  	// otherwise pruned out in Go 1.17 — we don't want to block progress on other
  2098  	// packages while we wait for a single new download.
  2099  	type mismatch struct {
  2100  		mod module.Version
  2101  		err error
  2102  	}
  2103  	mismatchMu := make(chan map[*loadPkg]mismatch, 1)
  2104  	mismatchMu <- map[*loadPkg]mismatch{}
  2105  	for _, pkg := range ld.pkgs {
  2106  		if pkg.mod.Path == "" && pkg.err == nil {
  2107  			// This package is from the standard library (which does not vary based on
  2108  			// the module graph).
  2109  			continue
  2110  		}
  2111  
  2112  		pkg := pkg
  2113  		ld.work.Add(func() {
  2114  			mod, _, _, _, err := importFromModules(ctx, pkg.path, rs, mg, ld.skipImportModFiles)
  2115  			if mod != pkg.mod {
  2116  				mismatches := <-mismatchMu
  2117  				mismatches[pkg] = mismatch{mod: mod, err: err}
  2118  				mismatchMu <- mismatches
  2119  			}
  2120  		})
  2121  	}
  2122  	<-ld.work.Idle()
  2123  
  2124  	mismatches := <-mismatchMu
  2125  	if len(mismatches) == 0 {
  2126  		// Since we're running as part of 'go mod tidy', the roots of the module
  2127  		// graph should contain only modules that are relevant to some package in
  2128  		// the package graph. We checked every package in the package graph and
  2129  		// didn't find any mismatches, so that must mean that all of the roots of
  2130  		// the module graph are also consistent.
  2131  		//
  2132  		// If we're wrong, Go 1.16 in -mod=readonly mode will error out with
  2133  		// "updates to go.mod needed", which would be very confusing. So instead,
  2134  		// we'll double-check that our reasoning above actually holds — if it
  2135  		// doesn't, we'll emit an internal error and hopefully the user will report
  2136  		// it as a bug.
  2137  		for _, m := range ld.requirements.rootModules {
  2138  			if v := mg.Selected(m.Path); v != m.Version {
  2139  				fmt.Fprintln(os.Stderr)
  2140  				base.Fatalf("go: internal error: failed to diagnose selected-version mismatch for module %s: go %s selects %s, but go %s selects %s\n\tPlease report this at https://golang.org/issue.", m.Path, goVersion, m.Version, compatVersion, v)
  2141  			}
  2142  		}
  2143  		return
  2144  	}
  2145  
  2146  	// Iterate over the packages (instead of the mismatches map) to emit errors in
  2147  	// deterministic order.
  2148  	for _, pkg := range ld.pkgs {
  2149  		mismatch, ok := mismatches[pkg]
  2150  		if !ok {
  2151  			continue
  2152  		}
  2153  
  2154  		if pkg.isTest() {
  2155  			// We already did (or will) report an error for the package itself,
  2156  			// so don't report a duplicate (and more verbose) error for its test.
  2157  			if _, ok := mismatches[pkg.testOf]; !ok {
  2158  				base.Fatalf("go: internal error: mismatch recorded for test %s, but not its non-test package", pkg.path)
  2159  			}
  2160  			continue
  2161  		}
  2162  
  2163  		switch {
  2164  		case mismatch.err != nil:
  2165  			// pkg resolved successfully, but errors out using the requirements in rs.
  2166  			//
  2167  			// This could occur because the import is provided by a single root (and
  2168  			// is thus unambiguous in a main module with a pruned module graph) and
  2169  			// also one or more transitive dependencies (and is ambiguous with an
  2170  			// unpruned graph).
  2171  			//
  2172  			// It could also occur because some transitive dependency upgrades the
  2173  			// module that previously provided the package to a version that no
  2174  			// longer does, or to a version for which the module source code (but
  2175  			// not the go.mod file in isolation) has a checksum error.
  2176  			if missing := (*ImportMissingError)(nil); errors.As(mismatch.err, &missing) {
  2177  				selected := module.Version{
  2178  					Path:    pkg.mod.Path,
  2179  					Version: mg.Selected(pkg.mod.Path),
  2180  				}
  2181  				ld.error(fmt.Errorf("%s loaded from %v,\n\tbut go %s would fail to locate it in %s", pkg.stackText(), pkg.mod, compatVersion, selected))
  2182  			} else {
  2183  				if ambiguous := (*AmbiguousImportError)(nil); errors.As(mismatch.err, &ambiguous) {
  2184  					// TODO: Is this check needed?
  2185  				}
  2186  				ld.error(fmt.Errorf("%s loaded from %v,\n\tbut go %s would fail to locate it:\n\t%v", pkg.stackText(), pkg.mod, compatVersion, mismatch.err))
  2187  			}
  2188  
  2189  			suggestEFlag = true
  2190  
  2191  			// Even if we press ahead with the '-e' flag, the older version will
  2192  			// error out in readonly mode if it thinks the go.mod file contains
  2193  			// any *explicit* dependency that is not at its selected version,
  2194  			// even if that dependency is not relevant to any package being loaded.
  2195  			//
  2196  			// We check for that condition here. If all of the roots are consistent
  2197  			// the '-e' flag suffices, but otherwise we need to suggest an upgrade.
  2198  			if !suggestUpgrade {
  2199  				for _, m := range ld.requirements.rootModules {
  2200  					if v := mg.Selected(m.Path); v != m.Version {
  2201  						suggestUpgrade = true
  2202  						break
  2203  					}
  2204  				}
  2205  			}
  2206  
  2207  		case pkg.err != nil:
  2208  			// pkg had an error in with a pruned module graph (presumably suppressed
  2209  			// with the -e flag), but the error went away using an unpruned graph.
  2210  			//
  2211  			// This is possible, if, say, the import is unresolved in the pruned graph
  2212  			// (because the "latest" version of each candidate module either is
  2213  			// unavailable or does not contain the package), but is resolved in the
  2214  			// unpruned graph due to a newer-than-latest dependency that is normally
  2215  			// pruned out.
  2216  			//
  2217  			// This could also occur if the source code for the module providing the
  2218  			// package in the pruned graph has a checksum error, but the unpruned
  2219  			// graph upgrades that module to a version with a correct checksum.
  2220  			//
  2221  			// pkg.err should have already been logged elsewhere — along with a
  2222  			// stack trace — so log only the import path and non-error info here.
  2223  			suggestUpgrade = true
  2224  			ld.error(fmt.Errorf("%s failed to load from any module,\n\tbut go %s would load it from %v", pkg.path, compatVersion, mismatch.mod))
  2225  
  2226  		case pkg.mod != mismatch.mod:
  2227  			// The package is loaded successfully by both Go versions, but from a
  2228  			// different module in each. This could lead to subtle (and perhaps even
  2229  			// unnoticed!) variations in behavior between builds with different
  2230  			// toolchains.
  2231  			suggestUpgrade = true
  2232  			ld.error(fmt.Errorf("%s loaded from %v,\n\tbut go %s would select %v\n", pkg.stackText(), pkg.mod, compatVersion, mismatch.mod.Version))
  2233  
  2234  		default:
  2235  			base.Fatalf("go: internal error: mismatch recorded for package %s, but no differences found", pkg.path)
  2236  		}
  2237  	}
  2238  
  2239  	ld.switchIfErrors(ctx)
  2240  	suggestFixes()
  2241  	ld.exitIfErrors(ctx)
  2242  }
  2243  
  2244  // scanDir is like imports.ScanDir but elides known magic imports from the list,
  2245  // so that we do not go looking for packages that don't really exist.
  2246  //
  2247  // The standard magic import is "C", for cgo.
  2248  //
  2249  // The only other known magic imports are appengine and appengine/*.
  2250  // These are so old that they predate "go get" and did not use URL-like paths.
  2251  // Most code today now uses google.golang.org/appengine instead,
  2252  // but not all code has been so updated. When we mostly ignore build tags
  2253  // during "go vendor", we look into "// +build appengine" files and
  2254  // may see these legacy imports. We drop them so that the module
  2255  // search does not look for modules to try to satisfy them.
  2256  func scanDir(modroot string, dir string, tags map[string]bool) (imports_, testImports []string, err error) {
  2257  	if ip, mierr := modindex.GetPackage(modroot, dir); mierr == nil {
  2258  		imports_, testImports, err = ip.ScanDir(tags)
  2259  		goto Happy
  2260  	} else if !errors.Is(mierr, modindex.ErrNotIndexed) {
  2261  		return nil, nil, mierr
  2262  	}
  2263  
  2264  	imports_, testImports, err = imports.ScanDir(dir, tags)
  2265  Happy:
  2266  
  2267  	filter := func(x []string) []string {
  2268  		w := 0
  2269  		for _, pkg := range x {
  2270  			if pkg != "C" && pkg != "appengine" && !strings.HasPrefix(pkg, "appengine/") &&
  2271  				pkg != "appengine_internal" && !strings.HasPrefix(pkg, "appengine_internal/") {
  2272  				x[w] = pkg
  2273  				w++
  2274  			}
  2275  		}
  2276  		return x[:w]
  2277  	}
  2278  
  2279  	return filter(imports_), filter(testImports), err
  2280  }
  2281  
  2282  // buildStacks computes minimal import stacks for each package,
  2283  // for use in error messages. When it completes, packages that
  2284  // are part of the original root set have pkg.stack == nil,
  2285  // and other packages have pkg.stack pointing at the next
  2286  // package up the import stack in their minimal chain.
  2287  // As a side effect, buildStacks also constructs ld.pkgs,
  2288  // the list of all packages loaded.
  2289  func (ld *loader) buildStacks() {
  2290  	if len(ld.pkgs) > 0 {
  2291  		panic("buildStacks")
  2292  	}
  2293  	for _, pkg := range ld.roots {
  2294  		pkg.stack = pkg // sentinel to avoid processing in next loop
  2295  		ld.pkgs = append(ld.pkgs, pkg)
  2296  	}
  2297  	for i := 0; i < len(ld.pkgs); i++ { // not range: appending to ld.pkgs in loop
  2298  		pkg := ld.pkgs[i]
  2299  		for _, next := range pkg.imports {
  2300  			if next.stack == nil {
  2301  				next.stack = pkg
  2302  				ld.pkgs = append(ld.pkgs, next)
  2303  			}
  2304  		}
  2305  		if next := pkg.test; next != nil && next.stack == nil {
  2306  			next.stack = pkg
  2307  			ld.pkgs = append(ld.pkgs, next)
  2308  		}
  2309  	}
  2310  	for _, pkg := range ld.roots {
  2311  		pkg.stack = nil
  2312  	}
  2313  }
  2314  
  2315  // stackText builds the import stack text to use when
  2316  // reporting an error in pkg. It has the general form
  2317  //
  2318  //	root imports
  2319  //		other imports
  2320  //		other2 tested by
  2321  //		other2.test imports
  2322  //		pkg
  2323  func (pkg *loadPkg) stackText() string {
  2324  	var stack []*loadPkg
  2325  	for p := pkg; p != nil; p = p.stack {
  2326  		stack = append(stack, p)
  2327  	}
  2328  
  2329  	var buf strings.Builder
  2330  	for i := len(stack) - 1; i >= 0; i-- {
  2331  		p := stack[i]
  2332  		fmt.Fprint(&buf, p.path)
  2333  		if p.testOf != nil {
  2334  			fmt.Fprint(&buf, ".test")
  2335  		}
  2336  		if i > 0 {
  2337  			if stack[i-1].testOf == p {
  2338  				fmt.Fprint(&buf, " tested by\n\t")
  2339  			} else {
  2340  				fmt.Fprint(&buf, " imports\n\t")
  2341  			}
  2342  		}
  2343  	}
  2344  	return buf.String()
  2345  }
  2346  
  2347  // why returns the text to use in "go mod why" output about the given package.
  2348  // It is less ornate than the stackText but contains the same information.
  2349  func (pkg *loadPkg) why() string {
  2350  	var buf strings.Builder
  2351  	var stack []*loadPkg
  2352  	for p := pkg; p != nil; p = p.stack {
  2353  		stack = append(stack, p)
  2354  	}
  2355  
  2356  	for i := len(stack) - 1; i >= 0; i-- {
  2357  		p := stack[i]
  2358  		if p.testOf != nil {
  2359  			fmt.Fprintf(&buf, "%s.test\n", p.testOf.path)
  2360  		} else {
  2361  			fmt.Fprintf(&buf, "%s\n", p.path)
  2362  		}
  2363  	}
  2364  	return buf.String()
  2365  }
  2366  
  2367  // Why returns the "go mod why" output stanza for the given package,
  2368  // without the leading # comment.
  2369  // The package graph must have been loaded already, usually by LoadPackages.
  2370  // If there is no reason for the package to be in the current build,
  2371  // Why returns an empty string.
  2372  func Why(path string) string {
  2373  	pkg, ok := loaded.pkgCache.Get(path)
  2374  	if !ok {
  2375  		return ""
  2376  	}
  2377  	return pkg.why()
  2378  }
  2379  
  2380  // WhyDepth returns the number of steps in the Why listing.
  2381  // If there is no reason for the package to be in the current build,
  2382  // WhyDepth returns 0.
  2383  func WhyDepth(path string) int {
  2384  	n := 0
  2385  	pkg, _ := loaded.pkgCache.Get(path)
  2386  	for p := pkg; p != nil; p = p.stack {
  2387  		n++
  2388  	}
  2389  	return n
  2390  }
  2391  

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