resolver.go

Documentation: go/types

     1  // Copyright 2013 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 types
     6  
     7  import (
     8  	"fmt"
     9  	"go/ast"
    10  	"go/constant"
    11  	"go/internal/typeparams"
    12  	"go/token"
    13  	. "internal/types/errors"
    14  	"sort"
    15  	"strconv"
    16  	"strings"
    17  	"unicode"
    18  )
    19  
    20  // A declInfo describes a package-level const, type, var, or func declaration.
    21  type declInfo struct {
    22  	file      *Scope        // scope of file containing this declaration
    23  	lhs       []*Var        // lhs of n:1 variable declarations, or nil
    24  	vtyp      ast.Expr      // type, or nil (for const and var declarations only)
    25  	init      ast.Expr      // init/orig expression, or nil (for const and var declarations only)
    26  	inherited bool          // if set, the init expression is inherited from a previous constant declaration
    27  	tdecl     *ast.TypeSpec // type declaration, or nil
    28  	fdecl     *ast.FuncDecl // func declaration, or nil
    29  
    30  	// The deps field tracks initialization expression dependencies.
    31  	deps map[Object]bool // lazily initialized
    32  }
    33  
    34  // hasInitializer reports whether the declared object has an initialization
    35  // expression or function body.
    36  func (d *declInfo) hasInitializer() bool {
    37  	return d.init != nil || d.fdecl != nil && d.fdecl.Body != nil
    38  }
    39  
    40  // addDep adds obj to the set of objects d's init expression depends on.
    41  func (d *declInfo) addDep(obj Object) {
    42  	m := d.deps
    43  	if m == nil {
    44  		m = make(map[Object]bool)
    45  		d.deps = m
    46  	}
    47  	m[obj] = true
    48  }
    49  
    50  // arityMatch checks that the lhs and rhs of a const or var decl
    51  // have the appropriate number of names and init exprs. For const
    52  // decls, init is the value spec providing the init exprs; for
    53  // var decls, init is nil (the init exprs are in s in this case).
    54  func (check *Checker) arityMatch(s, init *ast.ValueSpec) {
    55  	l := len(s.Names)
    56  	r := len(s.Values)
    57  	if init != nil {
    58  		r = len(init.Values)
    59  	}
    60  
    61  	const code = WrongAssignCount
    62  	switch {
    63  	case init == nil && r == 0:
    64  		// var decl w/o init expr
    65  		if s.Type == nil {
    66  			check.error(s, code, "missing type or init expr")
    67  		}
    68  	case l < r:
    69  		if l < len(s.Values) {
    70  			// init exprs from s
    71  			n := s.Values[l]
    72  			check.errorf(n, code, "extra init expr %s", n)
    73  			// TODO(gri) avoid declared and not used error here
    74  		} else {
    75  			// init exprs "inherited"
    76  			check.errorf(s, code, "extra init expr at %s", check.fset.Position(init.Pos()))
    77  			// TODO(gri) avoid declared and not used error here
    78  		}
    79  	case l > r && (init != nil || r != 1):
    80  		n := s.Names[r]
    81  		check.errorf(n, code, "missing init expr for %s", n)
    82  	}
    83  }
    84  
    85  func validatedImportPath(path string) (string, error) {
    86  	s, err := strconv.Unquote(path)
    87  	if err != nil {
    88  		return "", err
    89  	}
    90  	if s == "" {
    91  		return "", fmt.Errorf("empty string")
    92  	}
    93  	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
    94  	for _, r := range s {
    95  		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
    96  			return s, fmt.Errorf("invalid character %#U", r)
    97  		}
    98  	}
    99  	return s, nil
   100  }
   101  
   102  // declarePkgObj declares obj in the package scope, records its ident -> obj mapping,
   103  // and updates check.objMap. The object must not be a function or method.
   104  func (check *Checker) declarePkgObj(ident *ast.Ident, obj Object, d *declInfo) {
   105  	assert(ident.Name == obj.Name())
   106  
   107  	// spec: "A package-scope or file-scope identifier with name init
   108  	// may only be declared to be a function with this (func()) signature."
   109  	if ident.Name == "init" {
   110  		check.error(ident, InvalidInitDecl, "cannot declare init - must be func")
   111  		return
   112  	}
   113  
   114  	// spec: "The main package must have package name main and declare
   115  	// a function main that takes no arguments and returns no value."
   116  	if ident.Name == "main" && check.pkg.name == "main" {
   117  		check.error(ident, InvalidMainDecl, "cannot declare main - must be func")
   118  		return
   119  	}
   120  
   121  	check.declare(check.pkg.scope, ident, obj, nopos)
   122  	check.objMap[obj] = d
   123  	obj.setOrder(uint32(len(check.objMap)))
   124  }
   125  
   126  // filename returns a filename suitable for debugging output.
   127  func (check *Checker) filename(fileNo int) string {
   128  	file := check.files[fileNo]
   129  	if pos := file.Pos(); pos.IsValid() {
   130  		return check.fset.File(pos).Name()
   131  	}
   132  	return fmt.Sprintf("file[%d]", fileNo)
   133  }
   134  
   135  func (check *Checker) importPackage(at positioner, path, dir string) *Package {
   136  	// If we already have a package for the given (path, dir)
   137  	// pair, use it instead of doing a full import.
   138  	// Checker.impMap only caches packages that are marked Complete
   139  	// or fake (dummy packages for failed imports). Incomplete but
   140  	// non-fake packages do require an import to complete them.
   141  	key := importKey{path, dir}
   142  	imp := check.impMap[key]
   143  	if imp != nil {
   144  		return imp
   145  	}
   146  
   147  	// no package yet => import it
   148  	if path == "C" && (check.conf.FakeImportC || check.conf.go115UsesCgo) {
   149  		imp = NewPackage("C", "C")
   150  		imp.fake = true // package scope is not populated
   151  		imp.cgo = check.conf.go115UsesCgo
   152  	} else {
   153  		// ordinary import
   154  		var err error
   155  		if importer := check.conf.Importer; importer == nil {
   156  			err = fmt.Errorf("Config.Importer not installed")
   157  		} else if importerFrom, ok := importer.(ImporterFrom); ok {
   158  			imp, err = importerFrom.ImportFrom(path, dir, 0)
   159  			if imp == nil && err == nil {
   160  				err = fmt.Errorf("Config.Importer.ImportFrom(%s, %s, 0) returned nil but no error", path, dir)
   161  			}
   162  		} else {
   163  			imp, err = importer.Import(path)
   164  			if imp == nil && err == nil {
   165  				err = fmt.Errorf("Config.Importer.Import(%s) returned nil but no error", path)
   166  			}
   167  		}
   168  		// make sure we have a valid package name
   169  		// (errors here can only happen through manipulation of packages after creation)
   170  		if err == nil && imp != nil && (imp.name == "_" || imp.name == "") {
   171  			err = fmt.Errorf("invalid package name: %q", imp.name)
   172  			imp = nil // create fake package below
   173  		}
   174  		if err != nil {
   175  			check.errorf(at, BrokenImport, "could not import %s (%s)", path, err)
   176  			if imp == nil {
   177  				// create a new fake package
   178  				// come up with a sensible package name (heuristic)
   179  				name := path
   180  				if i := len(name); i > 0 && name[i-1] == '/' {
   181  					name = name[:i-1]
   182  				}
   183  				if i := strings.LastIndex(name, "/"); i >= 0 {
   184  					name = name[i+1:]
   185  				}
   186  				imp = NewPackage(path, name)
   187  			}
   188  			// continue to use the package as best as we can
   189  			imp.fake = true // avoid follow-up lookup failures
   190  		}
   191  	}
   192  
   193  	// package should be complete or marked fake, but be cautious
   194  	if imp.complete || imp.fake {
   195  		check.impMap[key] = imp
   196  		// Once we've formatted an error message, keep the pkgPathMap
   197  		// up-to-date on subsequent imports. It is used for package
   198  		// qualification in error messages.
   199  		if check.pkgPathMap != nil {
   200  			check.markImports(imp)
   201  		}
   202  		return imp
   203  	}
   204  
   205  	// something went wrong (importer may have returned incomplete package without error)
   206  	return nil
   207  }
   208  
   209  // collectObjects collects all file and package objects and inserts them
   210  // into their respective scopes. It also performs imports and associates
   211  // methods with receiver base type names.
   212  func (check *Checker) collectObjects() {
   213  	pkg := check.pkg
   214  
   215  	// pkgImports is the set of packages already imported by any package file seen
   216  	// so far. Used to avoid duplicate entries in pkg.imports. Allocate and populate
   217  	// it (pkg.imports may not be empty if we are checking test files incrementally).
   218  	// Note that pkgImports is keyed by package (and thus package path), not by an
   219  	// importKey value. Two different importKey values may map to the same package
   220  	// which is why we cannot use the check.impMap here.
   221  	var pkgImports = make(map[*Package]bool)
   222  	for _, imp := range pkg.imports {
   223  		pkgImports[imp] = true
   224  	}
   225  
   226  	type methodInfo struct {
   227  		obj  *Func      // method
   228  		ptr  bool       // true if pointer receiver
   229  		recv *ast.Ident // receiver type name
   230  	}
   231  	var methods []methodInfo // collected methods with valid receivers and non-blank _ names
   232  	var fileScopes []*Scope
   233  	for fileNo, file := range check.files {
   234  		// The package identifier denotes the current package,
   235  		// but there is no corresponding package object.
   236  		check.recordDef(file.Name, nil)
   237  
   238  		// Use the actual source file extent rather than *ast.File extent since the
   239  		// latter doesn't include comments which appear at the start or end of the file.
   240  		// Be conservative and use the *ast.File extent if we don't have a *token.File.
   241  		pos, end := file.Pos(), file.End()
   242  		if f := check.fset.File(file.Pos()); f != nil {
   243  			pos, end = token.Pos(f.Base()), token.Pos(f.Base()+f.Size())
   244  		}
   245  		fileScope := NewScope(pkg.scope, pos, end, check.filename(fileNo))
   246  		fileScopes = append(fileScopes, fileScope)
   247  		check.recordScope(file, fileScope)
   248  
   249  		// determine file directory, necessary to resolve imports
   250  		// FileName may be "" (typically for tests) in which case
   251  		// we get "." as the directory which is what we would want.
   252  		fileDir := dir(check.fset.Position(file.Name.Pos()).Filename)
   253  
   254  		check.walkDecls(file.Decls, func(d decl) {
   255  			switch d := d.(type) {
   256  			case importDecl:
   257  				// import package
   258  				if d.spec.Path.Value == "" {
   259  					return // error reported by parser
   260  				}
   261  				path, err := validatedImportPath(d.spec.Path.Value)
   262  				if err != nil {
   263  					check.errorf(d.spec.Path, BadImportPath, "invalid import path (%s)", err)
   264  					return
   265  				}
   266  
   267  				imp := check.importPackage(d.spec.Path, path, fileDir)
   268  				if imp == nil {
   269  					return
   270  				}
   271  
   272  				// local name overrides imported package name
   273  				name := imp.name
   274  				if d.spec.Name != nil {
   275  					name = d.spec.Name.Name
   276  					if path == "C" {
   277  						// match 1.17 cmd/compile (not prescribed by spec)
   278  						check.error(d.spec.Name, ImportCRenamed, `cannot rename import "C"`)
   279  						return
   280  					}
   281  				}
   282  
   283  				if name == "init" {
   284  					check.error(d.spec, InvalidInitDecl, "cannot import package as init - init must be a func")
   285  					return
   286  				}
   287  
   288  				// add package to list of explicit imports
   289  				// (this functionality is provided as a convenience
   290  				// for clients; it is not needed for type-checking)
   291  				if !pkgImports[imp] {
   292  					pkgImports[imp] = true
   293  					pkg.imports = append(pkg.imports, imp)
   294  				}
   295  
   296  				pkgName := NewPkgName(d.spec.Pos(), pkg, name, imp)
   297  				if d.spec.Name != nil {
   298  					// in a dot-import, the dot represents the package
   299  					check.recordDef(d.spec.Name, pkgName)
   300  				} else {
   301  					check.recordImplicit(d.spec, pkgName)
   302  				}
   303  
   304  				if imp.fake {
   305  					// match 1.17 cmd/compile (not prescribed by spec)
   306  					pkgName.used = true
   307  				}
   308  
   309  				// add import to file scope
   310  				check.imports = append(check.imports, pkgName)
   311  				if name == "." {
   312  					// dot-import
   313  					if check.dotImportMap == nil {
   314  						check.dotImportMap = make(map[dotImportKey]*PkgName)
   315  					}
   316  					// merge imported scope with file scope
   317  					for name, obj := range imp.scope.elems {
   318  						// Note: Avoid eager resolve(name, obj) here, so we only
   319  						// resolve dot-imported objects as needed.
   320  
   321  						// A package scope may contain non-exported objects,
   322  						// do not import them!
   323  						if token.IsExported(name) {
   324  							// declare dot-imported object
   325  							// (Do not use check.declare because it modifies the object
   326  							// via Object.setScopePos, which leads to a race condition;
   327  							// the object may be imported into more than one file scope
   328  							// concurrently. See go.dev/issue/32154.)
   329  							if alt := fileScope.Lookup(name); alt != nil {
   330  								check.errorf(d.spec.Name, DuplicateDecl, "%s redeclared in this block", alt.Name())
   331  								check.reportAltDecl(alt)
   332  							} else {
   333  								fileScope.insert(name, obj)
   334  								check.dotImportMap[dotImportKey{fileScope, name}] = pkgName
   335  							}
   336  						}
   337  					}
   338  				} else {
   339  					// declare imported package object in file scope
   340  					// (no need to provide s.Name since we called check.recordDef earlier)
   341  					check.declare(fileScope, nil, pkgName, nopos)
   342  				}
   343  			case constDecl:
   344  				// declare all constants
   345  				for i, name := range d.spec.Names {
   346  					obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(d.iota)))
   347  
   348  					var init ast.Expr
   349  					if i < len(d.init) {
   350  						init = d.init[i]
   351  					}
   352  
   353  					d := &declInfo{file: fileScope, vtyp: d.typ, init: init, inherited: d.inherited}
   354  					check.declarePkgObj(name, obj, d)
   355  				}
   356  
   357  			case varDecl:
   358  				lhs := make([]*Var, len(d.spec.Names))
   359  				// If there's exactly one rhs initializer, use
   360  				// the same declInfo d1 for all lhs variables
   361  				// so that each lhs variable depends on the same
   362  				// rhs initializer (n:1 var declaration).
   363  				var d1 *declInfo
   364  				if len(d.spec.Values) == 1 {
   365  					// The lhs elements are only set up after the for loop below,
   366  					// but that's ok because declareVar only collects the declInfo
   367  					// for a later phase.
   368  					d1 = &declInfo{file: fileScope, lhs: lhs, vtyp: d.spec.Type, init: d.spec.Values[0]}
   369  				}
   370  
   371  				// declare all variables
   372  				for i, name := range d.spec.Names {
   373  					obj := NewVar(name.Pos(), pkg, name.Name, nil)
   374  					lhs[i] = obj
   375  
   376  					di := d1
   377  					if di == nil {
   378  						// individual assignments
   379  						var init ast.Expr
   380  						if i < len(d.spec.Values) {
   381  							init = d.spec.Values[i]
   382  						}
   383  						di = &declInfo{file: fileScope, vtyp: d.spec.Type, init: init}
   384  					}
   385  
   386  					check.declarePkgObj(name, obj, di)
   387  				}
   388  			case typeDecl:
   389  				_ = d.spec.TypeParams.NumFields() != 0 && check.verifyVersionf(d.spec.TypeParams.List[0], go1_18, "type parameter")
   390  				obj := NewTypeName(d.spec.Name.Pos(), pkg, d.spec.Name.Name, nil)
   391  				check.declarePkgObj(d.spec.Name, obj, &declInfo{file: fileScope, tdecl: d.spec})
   392  			case funcDecl:
   393  				name := d.decl.Name.Name
   394  				obj := NewFunc(d.decl.Name.Pos(), pkg, name, nil)
   395  				hasTParamError := false // avoid duplicate type parameter errors
   396  				if d.decl.Recv.NumFields() == 0 {
   397  					// regular function
   398  					if d.decl.Recv != nil {
   399  						check.error(d.decl.Recv, BadRecv, "method has no receiver")
   400  						// treat as function
   401  					}
   402  					if name == "init" || (name == "main" && check.pkg.name == "main") {
   403  						code := InvalidInitDecl
   404  						if name == "main" {
   405  							code = InvalidMainDecl
   406  						}
   407  						if d.decl.Type.TypeParams.NumFields() != 0 {
   408  							check.softErrorf(d.decl.Type.TypeParams.List[0], code, "func %s must have no type parameters", name)
   409  							hasTParamError = true
   410  						}
   411  						if t := d.decl.Type; t.Params.NumFields() != 0 || t.Results != nil {
   412  							// TODO(rFindley) Should this be a hard error?
   413  							check.softErrorf(d.decl.Name, code, "func %s must have no arguments and no return values", name)
   414  						}
   415  					}
   416  					if name == "init" {
   417  						// don't declare init functions in the package scope - they are invisible
   418  						obj.parent = pkg.scope
   419  						check.recordDef(d.decl.Name, obj)
   420  						// init functions must have a body
   421  						if d.decl.Body == nil {
   422  							// TODO(gri) make this error message consistent with the others above
   423  							check.softErrorf(obj, MissingInitBody, "missing function body")
   424  						}
   425  					} else {
   426  						check.declare(pkg.scope, d.decl.Name, obj, nopos)
   427  					}
   428  				} else {
   429  					// method
   430  
   431  					// TODO(rFindley) earlier versions of this code checked that methods
   432  					//                have no type parameters, but this is checked later
   433  					//                when type checking the function type. Confirm that
   434  					//                we don't need to check tparams here.
   435  
   436  					ptr, recv, _ := check.unpackRecv(d.decl.Recv.List[0].Type, false)
   437  					// (Methods with invalid receiver cannot be associated to a type, and
   438  					// methods with blank _ names are never found; no need to collect any
   439  					// of them. They will still be type-checked with all the other functions.)
   440  					if recv != nil && name != "_" {
   441  						methods = append(methods, methodInfo{obj, ptr, recv})
   442  					}
   443  					check.recordDef(d.decl.Name, obj)
   444  				}
   445  				_ = d.decl.Type.TypeParams.NumFields() != 0 && !hasTParamError && check.verifyVersionf(d.decl.Type.TypeParams.List[0], go1_18, "type parameter")
   446  				info := &declInfo{file: fileScope, fdecl: d.decl}
   447  				// Methods are not package-level objects but we still track them in the
   448  				// object map so that we can handle them like regular functions (if the
   449  				// receiver is invalid); also we need their fdecl info when associating
   450  				// them with their receiver base type, below.
   451  				check.objMap[obj] = info
   452  				obj.setOrder(uint32(len(check.objMap)))
   453  			}
   454  		})
   455  	}
   456  
   457  	// verify that objects in package and file scopes have different names
   458  	for _, scope := range fileScopes {
   459  		for name, obj := range scope.elems {
   460  			if alt := pkg.scope.Lookup(name); alt != nil {
   461  				obj = resolve(name, obj)
   462  				if pkg, ok := obj.(*PkgName); ok {
   463  					check.errorf(alt, DuplicateDecl, "%s already declared through import of %s", alt.Name(), pkg.Imported())
   464  					check.reportAltDecl(pkg)
   465  				} else {
   466  					check.errorf(alt, DuplicateDecl, "%s already declared through dot-import of %s", alt.Name(), obj.Pkg())
   467  					// TODO(gri) dot-imported objects don't have a position; reportAltDecl won't print anything
   468  					check.reportAltDecl(obj)
   469  				}
   470  			}
   471  		}
   472  	}
   473  
   474  	// Now that we have all package scope objects and all methods,
   475  	// associate methods with receiver base type name where possible.
   476  	// Ignore methods that have an invalid receiver. They will be
   477  	// type-checked later, with regular functions.
   478  	if methods == nil {
   479  		return // nothing to do
   480  	}
   481  	check.methods = make(map[*TypeName][]*Func)
   482  	for i := range methods {
   483  		m := &methods[i]
   484  		// Determine the receiver base type and associate m with it.
   485  		ptr, base := check.resolveBaseTypeName(m.ptr, m.recv, fileScopes)
   486  		if base != nil {
   487  			m.obj.hasPtrRecv_ = ptr
   488  			check.methods[base] = append(check.methods[base], m.obj)
   489  		}
   490  	}
   491  }
   492  
   493  // unpackRecv unpacks a receiver type and returns its components: ptr indicates whether
   494  // rtyp is a pointer receiver, rname is the receiver type name, and tparams are its
   495  // type parameters, if any. The type parameters are only unpacked if unpackParams is
   496  // set. If rname is nil, the receiver is unusable (i.e., the source has a bug which we
   497  // cannot easily work around).
   498  func (check *Checker) unpackRecv(rtyp ast.Expr, unpackParams bool) (ptr bool, rname *ast.Ident, tparams []*ast.Ident) {
   499  L: // unpack receiver type
   500  	// This accepts invalid receivers such as ***T and does not
   501  	// work for other invalid receivers, but we don't care. The
   502  	// validity of receiver expressions is checked elsewhere.
   503  	for {
   504  		switch t := rtyp.(type) {
   505  		case *ast.ParenExpr:
   506  			rtyp = t.X
   507  		case *ast.StarExpr:
   508  			ptr = true
   509  			rtyp = t.X
   510  		default:
   511  			break L
   512  		}
   513  	}
   514  
   515  	// unpack type parameters, if any
   516  	switch rtyp.(type) {
   517  	case *ast.IndexExpr, *ast.IndexListExpr:
   518  		ix := typeparams.UnpackIndexExpr(rtyp)
   519  		rtyp = ix.X
   520  		if unpackParams {
   521  			for _, arg := range ix.Indices {
   522  				var par *ast.Ident
   523  				switch arg := arg.(type) {
   524  				case *ast.Ident:
   525  					par = arg
   526  				case *ast.BadExpr:
   527  					// ignore - error already reported by parser
   528  				case nil:
   529  					check.error(ix.Orig, InvalidSyntaxTree, "parameterized receiver contains nil parameters")
   530  				default:
   531  					check.errorf(arg, BadDecl, "receiver type parameter %s must be an identifier", arg)
   532  				}
   533  				if par == nil {
   534  					par = &ast.Ident{NamePos: arg.Pos(), Name: "_"}
   535  				}
   536  				tparams = append(tparams, par)
   537  			}
   538  		}
   539  	}
   540  
   541  	// unpack receiver name
   542  	if name, _ := rtyp.(*ast.Ident); name != nil {
   543  		rname = name
   544  	}
   545  
   546  	return
   547  }
   548  
   549  // resolveBaseTypeName returns the non-alias base type name for typ, and whether
   550  // there was a pointer indirection to get to it. The base type name must be declared
   551  // in package scope, and there can be at most one pointer indirection. If no such type
   552  // name exists, the returned base is nil.
   553  func (check *Checker) resolveBaseTypeName(seenPtr bool, typ ast.Expr, fileScopes []*Scope) (ptr bool, base *TypeName) {
   554  	// Algorithm: Starting from a type expression, which may be a name,
   555  	// we follow that type through alias declarations until we reach a
   556  	// non-alias type name. If we encounter anything but pointer types or
   557  	// parentheses we're done. If we encounter more than one pointer type
   558  	// we're done.
   559  	ptr = seenPtr
   560  	var seen map[*TypeName]bool
   561  	for {
   562  		// Note: this differs from types2, but is necessary. The syntax parser
   563  		// strips unnecessary parens.
   564  		typ = unparen(typ)
   565  
   566  		// check if we have a pointer type
   567  		if pexpr, _ := typ.(*ast.StarExpr); pexpr != nil {
   568  			// if we've already seen a pointer, we're done
   569  			if ptr {
   570  				return false, nil
   571  			}
   572  			ptr = true
   573  			typ = unparen(pexpr.X) // continue with pointer base type
   574  		}
   575  
   576  		// typ must be a name, or a C.name cgo selector.
   577  		var name string
   578  		switch typ := typ.(type) {
   579  		case *ast.Ident:
   580  			name = typ.Name
   581  		case *ast.SelectorExpr:
   582  			// C.struct_foo is a valid type name for packages using cgo.
   583  			//
   584  			// Detect this case, and adjust name so that the correct TypeName is
   585  			// resolved below.
   586  			if ident, _ := typ.X.(*ast.Ident); ident != nil && ident.Name == "C" {
   587  				// Check whether "C" actually resolves to an import of "C", by looking
   588  				// in the appropriate file scope.
   589  				var obj Object
   590  				for _, scope := range fileScopes {
   591  					if scope.Contains(ident.Pos()) {
   592  						obj = scope.Lookup(ident.Name)
   593  					}
   594  				}
   595  				// If Config.go115UsesCgo is set, the typechecker will resolve Cgo
   596  				// selectors to their cgo name. We must do the same here.
   597  				if pname, _ := obj.(*PkgName); pname != nil {
   598  					if pname.imported.cgo { // only set if Config.go115UsesCgo is set
   599  						name = "_Ctype_" + typ.Sel.Name
   600  					}
   601  				}
   602  			}
   603  			if name == "" {
   604  				return false, nil
   605  			}
   606  		default:
   607  			return false, nil
   608  		}
   609  
   610  		// name must denote an object found in the current package scope
   611  		// (note that dot-imported objects are not in the package scope!)
   612  		obj := check.pkg.scope.Lookup(name)
   613  		if obj == nil {
   614  			return false, nil
   615  		}
   616  
   617  		// the object must be a type name...
   618  		tname, _ := obj.(*TypeName)
   619  		if tname == nil {
   620  			return false, nil
   621  		}
   622  
   623  		// ... which we have not seen before
   624  		if seen[tname] {
   625  			return false, nil
   626  		}
   627  
   628  		// we're done if tdecl defined tname as a new type
   629  		// (rather than an alias)
   630  		tdecl := check.objMap[tname].tdecl // must exist for objects in package scope
   631  		if !tdecl.Assign.IsValid() {
   632  			return ptr, tname
   633  		}
   634  
   635  		// otherwise, continue resolving
   636  		typ = tdecl.Type
   637  		if seen == nil {
   638  			seen = make(map[*TypeName]bool)
   639  		}
   640  		seen[tname] = true
   641  	}
   642  }
   643  
   644  // packageObjects typechecks all package objects, but not function bodies.
   645  func (check *Checker) packageObjects() {
   646  	// process package objects in source order for reproducible results
   647  	objList := make([]Object, len(check.objMap))
   648  	i := 0
   649  	for obj := range check.objMap {
   650  		objList[i] = obj
   651  		i++
   652  	}
   653  	sort.Sort(inSourceOrder(objList))
   654  
   655  	// add new methods to already type-checked types (from a prior Checker.Files call)
   656  	for _, obj := range objList {
   657  		if obj, _ := obj.(*TypeName); obj != nil && obj.typ != nil {
   658  			check.collectMethods(obj)
   659  		}
   660  	}
   661  
   662  	if check.enableAlias {
   663  		// With Alias nodes we can process declarations in any order.
   664  		for _, obj := range objList {
   665  			check.objDecl(obj, nil)
   666  		}
   667  	} else {
   668  		// Without Alias nodes, we process non-alias type declarations first, followed by
   669  		// alias declarations, and then everything else. This appears to avoid most situations
   670  		// where the type of an alias is needed before it is available.
   671  		// There may still be cases where this is not good enough (see also go.dev/issue/25838).
   672  		// In those cases Checker.ident will report an error ("invalid use of type alias").
   673  		var aliasList []*TypeName
   674  		var othersList []Object // everything that's not a type
   675  		// phase 1: non-alias type declarations
   676  		for _, obj := range objList {
   677  			if tname, _ := obj.(*TypeName); tname != nil {
   678  				if check.objMap[tname].tdecl.Assign.IsValid() {
   679  					aliasList = append(aliasList, tname)
   680  				} else {
   681  					check.objDecl(obj, nil)
   682  				}
   683  			} else {
   684  				othersList = append(othersList, obj)
   685  			}
   686  		}
   687  		// phase 2: alias type declarations
   688  		for _, obj := range aliasList {
   689  			check.objDecl(obj, nil)
   690  		}
   691  		// phase 3: all other declarations
   692  		for _, obj := range othersList {
   693  			check.objDecl(obj, nil)
   694  		}
   695  	}
   696  
   697  	// At this point we may have a non-empty check.methods map; this means that not all
   698  	// entries were deleted at the end of typeDecl because the respective receiver base
   699  	// types were not found. In that case, an error was reported when declaring those
   700  	// methods. We can now safely discard this map.
   701  	check.methods = nil
   702  }
   703  
   704  // inSourceOrder implements the sort.Sort interface.
   705  type inSourceOrder []Object
   706  
   707  func (a inSourceOrder) Len() int           { return len(a) }
   708  func (a inSourceOrder) Less(i, j int) bool { return a[i].order() < a[j].order() }
   709  func (a inSourceOrder) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
   710  
   711  // unusedImports checks for unused imports.
   712  func (check *Checker) unusedImports() {
   713  	// If function bodies are not checked, packages' uses are likely missing - don't check.
   714  	if check.conf.IgnoreFuncBodies {
   715  		return
   716  	}
   717  
   718  	// spec: "It is illegal (...) to directly import a package without referring to
   719  	// any of its exported identifiers. To import a package solely for its side-effects
   720  	// (initialization), use the blank identifier as explicit package name."
   721  
   722  	for _, obj := range check.imports {
   723  		if !obj.used && obj.name != "_" {
   724  			check.errorUnusedPkg(obj)
   725  		}
   726  	}
   727  }
   728  
   729  func (check *Checker) errorUnusedPkg(obj *PkgName) {
   730  	// If the package was imported with a name other than the final
   731  	// import path element, show it explicitly in the error message.
   732  	// Note that this handles both renamed imports and imports of
   733  	// packages containing unconventional package declarations.
   734  	// Note that this uses / always, even on Windows, because Go import
   735  	// paths always use forward slashes.
   736  	path := obj.imported.path
   737  	elem := path
   738  	if i := strings.LastIndex(elem, "/"); i >= 0 {
   739  		elem = elem[i+1:]
   740  	}
   741  	if obj.name == "" || obj.name == "." || obj.name == elem {
   742  		check.softErrorf(obj, UnusedImport, "%q imported and not used", path)
   743  	} else {
   744  		check.softErrorf(obj, UnusedImport, "%q imported as %s and not used", path, obj.name)
   745  	}
   746  }
   747  
   748  // dir makes a good-faith attempt to return the directory
   749  // portion of path. If path is empty, the result is ".".
   750  // (Per the go/build package dependency tests, we cannot import
   751  // path/filepath and simply use filepath.Dir.)
   752  func dir(path string) string {
   753  	if i := strings.LastIndexAny(path, `/\`); i > 0 {
   754  		return path[:i]
   755  	}
   756  	// i <= 0
   757  	return "."
   758  }
   759
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