download.go

Documentation: cmd/go/internal/modcmd

     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 modcmd
     6  
     7  import (
     8  	"context"
     9  	"encoding/json"
    10  	"errors"
    11  	"os"
    12  	"runtime"
    13  	"sync"
    14  
    15  	"cmd/go/internal/base"
    16  	"cmd/go/internal/cfg"
    17  	"cmd/go/internal/gover"
    18  	"cmd/go/internal/modfetch"
    19  	"cmd/go/internal/modfetch/codehost"
    20  	"cmd/go/internal/modload"
    21  	"cmd/go/internal/toolchain"
    22  
    23  	"golang.org/x/mod/module"
    24  )
    25  
    26  var cmdDownload = &base.Command{
    27  	UsageLine: "go mod download [-x] [-json] [-reuse=old.json] [modules]",
    28  	Short:     "download modules to local cache",
    29  	Long: `
    30  Download downloads the named modules, which can be module patterns selecting
    31  dependencies of the main module or module queries of the form path@version.
    32  
    33  With no arguments, download applies to the modules needed to build and test
    34  the packages in the main module: the modules explicitly required by the main
    35  module if it is at 'go 1.17' or higher, or all transitively-required modules
    36  if at 'go 1.16' or lower.
    37  
    38  The go command will automatically download modules as needed during ordinary
    39  execution. The "go mod download" command is useful mainly for pre-filling
    40  the local cache or to compute the answers for a Go module proxy.
    41  
    42  By default, download writes nothing to standard output. It may print progress
    43  messages and errors to standard error.
    44  
    45  The -json flag causes download to print a sequence of JSON objects
    46  to standard output, describing each downloaded module (or failure),
    47  corresponding to this Go struct:
    48  
    49      type Module struct {
    50          Path     string // module path
    51          Query    string // version query corresponding to this version
    52          Version  string // module version
    53          Error    string // error loading module
    54          Info     string // absolute path to cached .info file
    55          GoMod    string // absolute path to cached .mod file
    56          Zip      string // absolute path to cached .zip file
    57          Dir      string // absolute path to cached source root directory
    58          Sum      string // checksum for path, version (as in go.sum)
    59          GoModSum string // checksum for go.mod (as in go.sum)
    60          Origin   any    // provenance of module
    61          Reuse    bool   // reuse of old module info is safe
    62      }
    63  
    64  The -reuse flag accepts the name of file containing the JSON output of a
    65  previous 'go mod download -json' invocation. The go command may use this
    66  file to determine that a module is unchanged since the previous invocation
    67  and avoid redownloading it. Modules that are not redownloaded will be marked
    68  in the new output by setting the Reuse field to true. Normally the module
    69  cache provides this kind of reuse automatically; the -reuse flag can be
    70  useful on systems that do not preserve the module cache.
    71  
    72  The -x flag causes download to print the commands download executes.
    73  
    74  See https://golang.org/ref/mod#go-mod-download for more about 'go mod download'.
    75  
    76  See https://golang.org/ref/mod#version-queries for more about version queries.
    77  	`,
    78  }
    79  
    80  var (
    81  	downloadJSON  = cmdDownload.Flag.Bool("json", false, "")
    82  	downloadReuse = cmdDownload.Flag.String("reuse", "", "")
    83  )
    84  
    85  func init() {
    86  	cmdDownload.Run = runDownload // break init cycle
    87  
    88  	// TODO(jayconrod): https://golang.org/issue/35849 Apply -x to other 'go mod' commands.
    89  	cmdDownload.Flag.BoolVar(&cfg.BuildX, "x", false, "")
    90  	base.AddChdirFlag(&cmdDownload.Flag)
    91  	base.AddModCommonFlags(&cmdDownload.Flag)
    92  }
    93  
    94  // A ModuleJSON describes the result of go mod download.
    95  type ModuleJSON struct {
    96  	Path     string `json:",omitempty"`
    97  	Version  string `json:",omitempty"`
    98  	Query    string `json:",omitempty"`
    99  	Error    string `json:",omitempty"`
   100  	Info     string `json:",omitempty"`
   101  	GoMod    string `json:",omitempty"`
   102  	Zip      string `json:",omitempty"`
   103  	Dir      string `json:",omitempty"`
   104  	Sum      string `json:",omitempty"`
   105  	GoModSum string `json:",omitempty"`
   106  
   107  	Origin *codehost.Origin `json:",omitempty"`
   108  	Reuse  bool             `json:",omitempty"`
   109  }
   110  
   111  func runDownload(ctx context.Context, cmd *base.Command, args []string) {
   112  	modload.InitWorkfile()
   113  
   114  	// Check whether modules are enabled and whether we're in a module.
   115  	modload.ForceUseModules = true
   116  	modload.ExplicitWriteGoMod = true
   117  	haveExplicitArgs := len(args) > 0
   118  
   119  	if modload.HasModRoot() || modload.WorkFilePath() != "" {
   120  		modload.LoadModFile(ctx) // to fill MainModules
   121  
   122  		if haveExplicitArgs {
   123  			for _, mainModule := range modload.MainModules.Versions() {
   124  				targetAtUpgrade := mainModule.Path + "@upgrade"
   125  				targetAtPatch := mainModule.Path + "@patch"
   126  				for _, arg := range args {
   127  					switch arg {
   128  					case mainModule.Path, targetAtUpgrade, targetAtPatch:
   129  						os.Stderr.WriteString("go: skipping download of " + arg + " that resolves to the main module\n")
   130  					}
   131  				}
   132  			}
   133  		} else if modload.WorkFilePath() != "" {
   134  			// TODO(#44435): Think about what the correct query is to download the
   135  			// right set of modules. Also see code review comment at
   136  			// https://go-review.googlesource.com/c/go/+/359794/comments/ce946a80_6cf53992.
   137  			args = []string{"all"}
   138  		} else {
   139  			mainModule := modload.MainModules.Versions()[0]
   140  			modFile := modload.MainModules.ModFile(mainModule)
   141  			if modFile.Go == nil || gover.Compare(modFile.Go.Version, gover.ExplicitIndirectVersion) < 0 {
   142  				if len(modFile.Require) > 0 {
   143  					args = []string{"all"}
   144  				}
   145  			} else {
   146  				// As of Go 1.17, the go.mod file explicitly requires every module
   147  				// that provides any package imported by the main module.
   148  				// 'go mod download' is typically run before testing packages in the
   149  				// main module, so by default we shouldn't download the others
   150  				// (which are presumed irrelevant to the packages in the main module).
   151  				// See https://golang.org/issue/44435.
   152  				//
   153  				// However, we also need to load the full module graph, to ensure that
   154  				// we have downloaded enough of the module graph to run 'go list all',
   155  				// 'go mod graph', and similar commands.
   156  				_, err := modload.LoadModGraph(ctx, "")
   157  				if err != nil {
   158  					// TODO(#64008): call base.Fatalf instead of toolchain.SwitchOrFatal
   159  					// here, since we can only reach this point with an outdated toolchain
   160  					// if the go.mod file is inconsistent.
   161  					toolchain.SwitchOrFatal(ctx, err)
   162  				}
   163  
   164  				for _, m := range modFile.Require {
   165  					args = append(args, m.Mod.Path)
   166  				}
   167  			}
   168  		}
   169  	}
   170  
   171  	if len(args) == 0 {
   172  		if modload.HasModRoot() {
   173  			os.Stderr.WriteString("go: no module dependencies to download\n")
   174  		} else {
   175  			base.Errorf("go: no modules specified (see 'go help mod download')")
   176  		}
   177  		base.Exit()
   178  	}
   179  
   180  	if *downloadReuse != "" && modload.HasModRoot() {
   181  		base.Fatalf("go mod download -reuse cannot be used inside a module")
   182  	}
   183  
   184  	var mods []*ModuleJSON
   185  	type token struct{}
   186  	sem := make(chan token, runtime.GOMAXPROCS(0))
   187  	infos, infosErr := modload.ListModules(ctx, args, 0, *downloadReuse)
   188  
   189  	// There is a bit of a chicken-and-egg problem here: ideally we need to know
   190  	// which Go version to switch to to download the requested modules, but if we
   191  	// haven't downloaded the module's go.mod file yet the GoVersion field of its
   192  	// info struct is not yet populated.
   193  	//
   194  	// We also need to be careful to only print the info for each module once
   195  	// if the -json flag is set.
   196  	//
   197  	// In theory we could go through each module in the list, attempt to download
   198  	// its go.mod file, and record the maximum version (either from the file or
   199  	// from the resulting TooNewError), all before we try the actual full download
   200  	// of each module.
   201  	//
   202  	// For now, we go ahead and try all the downloads and collect the errors, and
   203  	// if any download failed due to a TooNewError, we switch toolchains and try
   204  	// again. Any downloads that already succeeded will still be in cache.
   205  	// That won't give optimal concurrency (we'll do two batches of concurrent
   206  	// downloads instead of all in one batch), and it might add a little overhead
   207  	// to look up the downloads from the first batch in the module cache when
   208  	// we see them again in the second batch. On the other hand, it's way simpler
   209  	// to implement, and not really any more expensive if the user is requesting
   210  	// no explicit arguments (their go.mod file should already list an appropriate
   211  	// toolchain version) or only one module (as is used by the Go Module Proxy).
   212  
   213  	if infosErr != nil {
   214  		var sw toolchain.Switcher
   215  		sw.Error(infosErr)
   216  		if sw.NeedSwitch() {
   217  			sw.Switch(ctx)
   218  		}
   219  		// Otherwise, wait to report infosErr after we have downloaded
   220  		// when we can.
   221  	}
   222  
   223  	if !haveExplicitArgs && modload.WorkFilePath() == "" {
   224  		// 'go mod download' is sometimes run without arguments to pre-populate the
   225  		// module cache. In modules that aren't at go 1.17 or higher, it may fetch
   226  		// modules that aren't needed to build packages in the main module. This is
   227  		// usually not intended, so don't save sums for downloaded modules
   228  		// (golang.org/issue/45332). We do still fix inconsistencies in go.mod
   229  		// though.
   230  		//
   231  		// TODO(#64008): In the future, report an error if go.mod or go.sum need to
   232  		// be updated after loading the build list. This may require setting
   233  		// the mode to "mod" or "readonly" depending on haveExplicitArgs.
   234  		if err := modload.WriteGoMod(ctx, modload.WriteOpts{}); err != nil {
   235  			base.Fatal(err)
   236  		}
   237  	}
   238  
   239  	var downloadErrs sync.Map
   240  	for _, info := range infos {
   241  		if info.Replace != nil {
   242  			info = info.Replace
   243  		}
   244  		if info.Version == "" && info.Error == nil {
   245  			// main module or module replaced with file path.
   246  			// Nothing to download.
   247  			continue
   248  		}
   249  		m := &ModuleJSON{
   250  			Path:    info.Path,
   251  			Version: info.Version,
   252  			Query:   info.Query,
   253  			Reuse:   info.Reuse,
   254  			Origin:  info.Origin,
   255  		}
   256  		mods = append(mods, m)
   257  		if info.Error != nil {
   258  			m.Error = info.Error.Err
   259  			continue
   260  		}
   261  		if m.Reuse {
   262  			continue
   263  		}
   264  		sem <- token{}
   265  		go func() {
   266  			err := DownloadModule(ctx, m)
   267  			if err != nil {
   268  				downloadErrs.Store(m, err)
   269  				m.Error = err.Error()
   270  			}
   271  			<-sem
   272  		}()
   273  	}
   274  
   275  	// Fill semaphore channel to wait for goroutines to finish.
   276  	for n := cap(sem); n > 0; n-- {
   277  		sem <- token{}
   278  	}
   279  
   280  	// If there were explicit arguments
   281  	// (like 'go mod download golang.org/x/tools@latest'),
   282  	// check whether we need to upgrade the toolchain in order to download them.
   283  	//
   284  	// (If invoked without arguments, we expect the module graph to already
   285  	// be tidy and the go.mod file to declare a 'go' version that satisfies
   286  	// transitive requirements. If that invariant holds, then we should have
   287  	// already upgraded when we loaded the module graph, and should not need
   288  	// an additional check here. See https://go.dev/issue/45551.)
   289  	//
   290  	// We also allow upgrades if in a workspace because in workspace mode
   291  	// with no arguments we download the module pattern "all",
   292  	// which may include dependencies that are normally pruned out
   293  	// of the individual modules in the workspace.
   294  	if haveExplicitArgs || modload.WorkFilePath() != "" {
   295  		var sw toolchain.Switcher
   296  		// Add errors to the Switcher in deterministic order so that they will be
   297  		// logged deterministically.
   298  		for _, m := range mods {
   299  			if erri, ok := downloadErrs.Load(m); ok {
   300  				sw.Error(erri.(error))
   301  			}
   302  		}
   303  		// Only call sw.Switch if it will actually switch.
   304  		// Otherwise, we may want to write the errors as JSON
   305  		// (instead of using base.Error as sw.Switch would),
   306  		// and we may also have other errors to report from the
   307  		// initial infos returned by ListModules.
   308  		if sw.NeedSwitch() {
   309  			sw.Switch(ctx)
   310  		}
   311  	}
   312  
   313  	if *downloadJSON {
   314  		for _, m := range mods {
   315  			b, err := json.MarshalIndent(m, "", "\t")
   316  			if err != nil {
   317  				base.Fatal(err)
   318  			}
   319  			os.Stdout.Write(append(b, '\n'))
   320  			if m.Error != "" {
   321  				base.SetExitStatus(1)
   322  			}
   323  		}
   324  	} else {
   325  		for _, m := range mods {
   326  			if m.Error != "" {
   327  				base.Error(errors.New(m.Error))
   328  			}
   329  		}
   330  		base.ExitIfErrors()
   331  	}
   332  
   333  	// If there were explicit arguments, update go.mod and especially go.sum.
   334  	// 'go mod download mod@version' is a useful way to add a sum without using
   335  	// 'go get mod@version', which may have other side effects. We print this in
   336  	// some error message hints.
   337  	//
   338  	// If we're in workspace mode, update go.work.sum with checksums for all of
   339  	// the modules we downloaded that aren't already recorded. Since a requirement
   340  	// in one module may upgrade a dependency of another, we can't be sure that
   341  	// the import graph matches the import graph of any given module in isolation,
   342  	// so we may end up needing to load packages from modules that wouldn't
   343  	// otherwise be relevant.
   344  	//
   345  	// TODO(#44435): If we adjust the set of modules downloaded in workspace mode,
   346  	// we may also need to adjust the logic for saving checksums here.
   347  	//
   348  	// Don't save sums for 'go mod download' without arguments unless we're in
   349  	// workspace mode; see comment above.
   350  	if haveExplicitArgs || modload.WorkFilePath() != "" {
   351  		if err := modload.WriteGoMod(ctx, modload.WriteOpts{}); err != nil {
   352  			base.Error(err)
   353  		}
   354  	}
   355  
   356  	// If there was an error matching some of the requested packages, emit it now
   357  	// (after we've written the checksums for the modules that were downloaded
   358  	// successfully).
   359  	if infosErr != nil {
   360  		base.Error(infosErr)
   361  	}
   362  }
   363  
   364  // DownloadModule runs 'go mod download' for m.Path@m.Version,
   365  // leaving the results (including any error) in m itself.
   366  func DownloadModule(ctx context.Context, m *ModuleJSON) error {
   367  	var err error
   368  	_, file, err := modfetch.InfoFile(ctx, m.Path, m.Version)
   369  	if err != nil {
   370  		return err
   371  	}
   372  	m.Info = file
   373  	m.GoMod, err = modfetch.GoModFile(ctx, m.Path, m.Version)
   374  	if err != nil {
   375  		return err
   376  	}
   377  	m.GoModSum, err = modfetch.GoModSum(ctx, m.Path, m.Version)
   378  	if err != nil {
   379  		return err
   380  	}
   381  	mod := module.Version{Path: m.Path, Version: m.Version}
   382  	m.Zip, err = modfetch.DownloadZip(ctx, mod)
   383  	if err != nil {
   384  		return err
   385  	}
   386  	m.Sum = modfetch.Sum(ctx, mod)
   387  	m.Dir, err = modfetch.Download(ctx, mod)
   388  	return err
   389  }
   390
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