resolver.go

     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 types2
     6  
     7  import (
     8  	"cmd/compile/internal/syntax"
     9  	"fmt"
    10  	"go/constant"
    11  	"sort"
    12  	"strconv"
    13  	"strings"
    14  	"unicode"
    15  )
    16  
    17  // A declInfo describes a package-level const, type, var, or func declaration.
    18  type declInfo struct {
    19  	file      *Scope           // scope of file containing this declaration
    20  	lhs       []*Var           // lhs of n:1 variable declarations, or nil
    21  	vtyp      syntax.Expr      // type, or nil (for const and var declarations only)
    22  	init      syntax.Expr      // init/orig expression, or nil (for const and var declarations only)
    23  	inherited bool             // if set, the init expression is inherited from a previous constant declaration
    24  	tdecl     *syntax.TypeDecl // type declaration, or nil
    25  	fdecl     *syntax.FuncDecl // func declaration, or nil
    26  
    27  	// The deps field tracks initialization expression dependencies.
    28  	deps map[Object]bool // lazily initialized
    29  }
    30  
    31  // hasInitializer reports whether the declared object has an initialization
    32  // expression or function body.
    33  func (d *declInfo) hasInitializer() bool {
    34  	return d.init != nil || d.fdecl != nil && d.fdecl.Body != nil
    35  }
    36  
    37  // addDep adds obj to the set of objects d's init expression depends on.
    38  func (d *declInfo) addDep(obj Object) {
    39  	m := d.deps
    40  	if m == nil {
    41  		m = make(map[Object]bool)
    42  		d.deps = m
    43  	}
    44  	m[obj] = true
    45  }
    46  
    47  // arity checks that the lhs and rhs of a const or var decl
    48  // have a matching number of names and initialization values.
    49  // If inherited is set, the initialization values are from
    50  // another (constant) declaration.
    51  func (check *Checker) arity(pos syntax.Pos, names []*syntax.Name, inits []syntax.Expr, constDecl, inherited bool) {
    52  	l := len(names)
    53  	r := len(inits)
    54  
    55  	switch {
    56  	case l < r:
    57  		n := inits[l]
    58  		if inherited {
    59  			check.errorf(pos, "extra init expr at %s", n.Pos())
    60  		} else {
    61  			check.errorf(n, "extra init expr %s", n)
    62  		}
    63  	case l > r && (constDecl || r != 1): // if r == 1 it may be a multi-valued function and we can't say anything yet
    64  		n := names[r]
    65  		check.errorf(n, "missing init expr for %s", n.Value)
    66  	}
    67  }
    68  
    69  func validatedImportPath(path string) (string, error) {
    70  	s, err := strconv.Unquote(path)
    71  	if err != nil {
    72  		return "", err
    73  	}
    74  	if s == "" {
    75  		return "", fmt.Errorf("empty string")
    76  	}
    77  	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
    78  	for _, r := range s {
    79  		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
    80  			return s, fmt.Errorf("invalid character %#U", r)
    81  		}
    82  	}
    83  	return s, nil
    84  }
    85  
    86  // declarePkgObj declares obj in the package scope, records its ident -> obj mapping,
    87  // and updates check.objMap. The object must not be a function or method.
    88  func (check *Checker) declarePkgObj(ident *syntax.Name, obj Object, d *declInfo) {
    89  	assert(ident.Value == obj.Name())
    90  
    91  	// spec: "A package-scope or file-scope identifier with name init
    92  	// may only be declared to be a function with this (func()) signature."
    93  	if ident.Value == "init" {
    94  		check.error(ident, "cannot declare init - must be func")
    95  		return
    96  	}
    97  
    98  	// spec: "The main package must have package name main and declare
    99  	// a function main that takes no arguments and returns no value."
   100  	if ident.Value == "main" && check.pkg.name == "main" {
   101  		check.error(ident, "cannot declare main - must be func")
   102  		return
   103  	}
   104  
   105  	check.declare(check.pkg.scope, ident, obj, nopos)
   106  	check.objMap[obj] = d
   107  	obj.setOrder(uint32(len(check.objMap)))
   108  }
   109  
   110  // filename returns a filename suitable for debugging output.
   111  func (check *Checker) filename(fileNo int) string {
   112  	file := check.files[fileNo]
   113  	if pos := file.Pos(); pos.IsKnown() {
   114  		// return check.fset.File(pos).Name()
   115  		// TODO(gri) do we need the actual file name here?
   116  		return pos.RelFilename()
   117  	}
   118  	return fmt.Sprintf("file[%d]", fileNo)
   119  }
   120  
   121  func (check *Checker) importPackage(pos syntax.Pos, path, dir string) *Package {
   122  	// If we already have a package for the given (path, dir)
   123  	// pair, use it instead of doing a full import.
   124  	// Checker.impMap only caches packages that are marked Complete
   125  	// or fake (dummy packages for failed imports). Incomplete but
   126  	// non-fake packages do require an import to complete them.
   127  	key := importKey{path, dir}
   128  	imp := check.impMap[key]
   129  	if imp != nil {
   130  		return imp
   131  	}
   132  
   133  	// no package yet => import it
   134  	if path == "C" && (check.conf.FakeImportC || check.conf.go115UsesCgo) {
   135  		imp = NewPackage("C", "C")
   136  		imp.fake = true // package scope is not populated
   137  		imp.cgo = check.conf.go115UsesCgo
   138  	} else {
   139  		// ordinary import
   140  		var err error
   141  		if importer := check.conf.Importer; importer == nil {
   142  			err = fmt.Errorf("Config.Importer not installed")
   143  		} else if importerFrom, ok := importer.(ImporterFrom); ok {
   144  			imp, err = importerFrom.ImportFrom(path, dir, 0)
   145  			if imp == nil && err == nil {
   146  				err = fmt.Errorf("Config.Importer.ImportFrom(%s, %s, 0) returned nil but no error", path, dir)
   147  			}
   148  		} else {
   149  			imp, err = importer.Import(path)
   150  			if imp == nil && err == nil {
   151  				err = fmt.Errorf("Config.Importer.Import(%s) returned nil but no error", path)
   152  			}
   153  		}
   154  		// make sure we have a valid package name
   155  		// (errors here can only happen through manipulation of packages after creation)
   156  		if err == nil && imp != nil && (imp.name == "_" || imp.name == "") {
   157  			err = fmt.Errorf("invalid package name: %q", imp.name)
   158  			imp = nil // create fake package below
   159  		}
   160  		if err != nil {
   161  			check.errorf(pos, "could not import %s (%s)", path, err)
   162  			if imp == nil {
   163  				// create a new fake package
   164  				// come up with a sensible package name (heuristic)
   165  				name := path
   166  				if i := len(name); i > 0 && name[i-1] == '/' {
   167  					name = name[:i-1]
   168  				}
   169  				if i := strings.LastIndex(name, "/"); i >= 0 {
   170  					name = name[i+1:]
   171  				}
   172  				imp = NewPackage(path, name)
   173  			}
   174  			// continue to use the package as best as we can
   175  			imp.fake = true // avoid follow-up lookup failures
   176  		}
   177  	}
   178  
   179  	// package should be complete or marked fake, but be cautious
   180  	if imp.complete || imp.fake {
   181  		check.impMap[key] = imp
   182  		// Once we've formatted an error message once, keep the pkgPathMap
   183  		// up-to-date on subsequent imports.
   184  		if check.pkgPathMap != nil {
   185  			check.markImports(imp)
   186  		}
   187  		return imp
   188  	}
   189  
   190  	// something went wrong (importer may have returned incomplete package without error)
   191  	return nil
   192  }
   193  
   194  // collectObjects collects all file and package objects and inserts them
   195  // into their respective scopes. It also performs imports and associates
   196  // methods with receiver base type names.
   197  func (check *Checker) collectObjects() {
   198  	pkg := check.pkg
   199  	pkg.height = 0
   200  
   201  	// pkgImports is the set of packages already imported by any package file seen
   202  	// so far. Used to avoid duplicate entries in pkg.imports. Allocate and populate
   203  	// it (pkg.imports may not be empty if we are checking test files incrementally).
   204  	// Note that pkgImports is keyed by package (and thus package path), not by an
   205  	// importKey value. Two different importKey values may map to the same package
   206  	// which is why we cannot use the check.impMap here.
   207  	var pkgImports = make(map[*Package]bool)
   208  	for _, imp := range pkg.imports {
   209  		pkgImports[imp] = true
   210  	}
   211  
   212  	type methodInfo struct {
   213  		obj  *Func        // method
   214  		ptr  bool         // true if pointer receiver
   215  		recv *syntax.Name // receiver type name
   216  	}
   217  	var methods []methodInfo // collected methods with valid receivers and non-blank _ names
   218  	var fileScopes []*Scope
   219  	for fileNo, file := range check.files {
   220  		// The package identifier denotes the current package,
   221  		// but there is no corresponding package object.
   222  		check.recordDef(file.PkgName, nil)
   223  
   224  		fileScope := NewScope(check.pkg.scope, syntax.StartPos(file), syntax.EndPos(file), check.filename(fileNo))
   225  		fileScopes = append(fileScopes, fileScope)
   226  		check.recordScope(file, fileScope)
   227  
   228  		// determine file directory, necessary to resolve imports
   229  		// FileName may be "" (typically for tests) in which case
   230  		// we get "." as the directory which is what we would want.
   231  		fileDir := dir(file.PkgName.Pos().RelFilename()) // TODO(gri) should this be filename?
   232  
   233  		first := -1                // index of first ConstDecl in the current group, or -1
   234  		var last *syntax.ConstDecl // last ConstDecl with init expressions, or nil
   235  		for index, decl := range file.DeclList {
   236  			if _, ok := decl.(*syntax.ConstDecl); !ok {
   237  				first = -1 // we're not in a constant declaration
   238  			}
   239  
   240  			switch s := decl.(type) {
   241  			case *syntax.ImportDecl:
   242  				// import package
   243  				if s.Path == nil || s.Path.Bad {
   244  					continue // error reported during parsing
   245  				}
   246  				path, err := validatedImportPath(s.Path.Value)
   247  				if err != nil {
   248  					check.errorf(s.Path, "invalid import path (%s)", err)
   249  					continue
   250  				}
   251  
   252  				imp := check.importPackage(s.Path.Pos(), path, fileDir)
   253  				if imp == nil {
   254  					continue
   255  				}
   256  
   257  				if imp == Unsafe {
   258  					// typecheck ignores imports of package unsafe for
   259  					// calculating height.
   260  					// TODO(mdempsky): Revisit this. This seems fine, but I
   261  					// don't remember explicitly considering this case.
   262  				} else if h := imp.height + 1; h > pkg.height {
   263  					pkg.height = h
   264  				}
   265  
   266  				// local name overrides imported package name
   267  				name := imp.name
   268  				if s.LocalPkgName != nil {
   269  					name = s.LocalPkgName.Value
   270  					if path == "C" {
   271  						// match cmd/compile (not prescribed by spec)
   272  						check.error(s.LocalPkgName, `cannot rename import "C"`)
   273  						continue
   274  					}
   275  				}
   276  
   277  				if name == "init" {
   278  					check.error(s, "cannot import package as init - init must be a func")
   279  					continue
   280  				}
   281  
   282  				// add package to list of explicit imports
   283  				// (this functionality is provided as a convenience
   284  				// for clients; it is not needed for type-checking)
   285  				if !pkgImports[imp] {
   286  					pkgImports[imp] = true
   287  					pkg.imports = append(pkg.imports, imp)
   288  				}
   289  
   290  				pkgName := NewPkgName(s.Pos(), pkg, name, imp)
   291  				if s.LocalPkgName != nil {
   292  					// in a dot-import, the dot represents the package
   293  					check.recordDef(s.LocalPkgName, pkgName)
   294  				} else {
   295  					check.recordImplicit(s, pkgName)
   296  				}
   297  
   298  				if path == "C" {
   299  					// match cmd/compile (not prescribed by spec)
   300  					pkgName.used = true
   301  				}
   302  
   303  				// add import to file scope
   304  				check.imports = append(check.imports, pkgName)
   305  				if name == "." {
   306  					// dot-import
   307  					if check.dotImportMap == nil {
   308  						check.dotImportMap = make(map[dotImportKey]*PkgName)
   309  					}
   310  					// merge imported scope with file scope
   311  					for name, obj := range imp.scope.elems {
   312  						// Note: Avoid eager resolve(name, obj) here, so we only
   313  						// resolve dot-imported objects as needed.
   314  
   315  						// A package scope may contain non-exported objects,
   316  						// do not import them!
   317  						if isExported(name) {
   318  							// declare dot-imported object
   319  							// (Do not use check.declare because it modifies the object
   320  							// via Object.setScopePos, which leads to a race condition;
   321  							// the object may be imported into more than one file scope
   322  							// concurrently. See issue #32154.)
   323  							if alt := fileScope.Lookup(name); alt != nil {
   324  								var err error_
   325  								err.errorf(s.LocalPkgName, "%s redeclared in this block", alt.Name())
   326  								err.recordAltDecl(alt)
   327  								check.report(&err)
   328  							} else {
   329  								fileScope.insert(name, obj)
   330  								check.dotImportMap[dotImportKey{fileScope, name}] = pkgName
   331  							}
   332  						}
   333  					}
   334  				} else {
   335  					// declare imported package object in file scope
   336  					// (no need to provide s.LocalPkgName since we called check.recordDef earlier)
   337  					check.declare(fileScope, nil, pkgName, nopos)
   338  				}
   339  
   340  			case *syntax.ConstDecl:
   341  				// iota is the index of the current constDecl within the group
   342  				if first < 0 || s.Group == nil || file.DeclList[index-1].(*syntax.ConstDecl).Group != s.Group {
   343  					first = index
   344  					last = nil
   345  				}
   346  				iota := constant.MakeInt64(int64(index - first))
   347  
   348  				// determine which initialization expressions to use
   349  				inherited := true
   350  				switch {
   351  				case s.Type != nil || s.Values != nil:
   352  					last = s
   353  					inherited = false
   354  				case last == nil:
   355  					last = new(syntax.ConstDecl) // make sure last exists
   356  					inherited = false
   357  				}
   358  
   359  				// declare all constants
   360  				values := unpackExpr(last.Values)
   361  				for i, name := range s.NameList {
   362  					obj := NewConst(name.Pos(), pkg, name.Value, nil, iota)
   363  
   364  					var init syntax.Expr
   365  					if i < len(values) {
   366  						init = values[i]
   367  					}
   368  
   369  					d := &declInfo{file: fileScope, vtyp: last.Type, init: init, inherited: inherited}
   370  					check.declarePkgObj(name, obj, d)
   371  				}
   372  
   373  				// Constants must always have init values.
   374  				check.arity(s.Pos(), s.NameList, values, true, inherited)
   375  
   376  			case *syntax.VarDecl:
   377  				lhs := make([]*Var, len(s.NameList))
   378  				// If there's exactly one rhs initializer, use
   379  				// the same declInfo d1 for all lhs variables
   380  				// so that each lhs variable depends on the same
   381  				// rhs initializer (n:1 var declaration).
   382  				var d1 *declInfo
   383  				if _, ok := s.Values.(*syntax.ListExpr); !ok {
   384  					// The lhs elements are only set up after the for loop below,
   385  					// but that's ok because declarePkgObj only collects the declInfo
   386  					// for a later phase.
   387  					d1 = &declInfo{file: fileScope, lhs: lhs, vtyp: s.Type, init: s.Values}
   388  				}
   389  
   390  				// declare all variables
   391  				values := unpackExpr(s.Values)
   392  				for i, name := range s.NameList {
   393  					obj := NewVar(name.Pos(), pkg, name.Value, nil)
   394  					lhs[i] = obj
   395  
   396  					d := d1
   397  					if d == nil {
   398  						// individual assignments
   399  						var init syntax.Expr
   400  						if i < len(values) {
   401  							init = values[i]
   402  						}
   403  						d = &declInfo{file: fileScope, vtyp: s.Type, init: init}
   404  					}
   405  
   406  					check.declarePkgObj(name, obj, d)
   407  				}
   408  
   409  				// If we have no type, we must have values.
   410  				if s.Type == nil || values != nil {
   411  					check.arity(s.Pos(), s.NameList, values, false, false)
   412  				}
   413  
   414  			case *syntax.TypeDecl:
   415  				if len(s.TParamList) != 0 && !check.allowVersion(pkg, 1, 18) {
   416  					check.versionErrorf(s.TParamList[0], "go1.18", "type parameter")
   417  				}
   418  				obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Value, nil)
   419  				check.declarePkgObj(s.Name, obj, &declInfo{file: fileScope, tdecl: s})
   420  
   421  			case *syntax.FuncDecl:
   422  				name := s.Name.Value
   423  				obj := NewFunc(s.Name.Pos(), pkg, name, nil)
   424  				hasTParamError := false // avoid duplicate type parameter errors
   425  				if s.Recv == nil {
   426  					// regular function
   427  					if name == "init" || name == "main" && pkg.name == "main" {
   428  						if len(s.TParamList) != 0 {
   429  							check.softErrorf(s.TParamList[0], "func %s must have no type parameters", name)
   430  							hasTParamError = true
   431  						}
   432  						if t := s.Type; len(t.ParamList) != 0 || len(t.ResultList) != 0 {
   433  							check.softErrorf(s, "func %s must have no arguments and no return values", name)
   434  						}
   435  					}
   436  					// don't declare init functions in the package scope - they are invisible
   437  					if name == "init" {
   438  						obj.parent = pkg.scope
   439  						check.recordDef(s.Name, obj)
   440  						// init functions must have a body
   441  						if s.Body == nil {
   442  							// TODO(gri) make this error message consistent with the others above
   443  							check.softErrorf(obj.pos, "missing function body")
   444  						}
   445  					} else {
   446  						check.declare(pkg.scope, s.Name, obj, nopos)
   447  					}
   448  				} else {
   449  					// method
   450  					// d.Recv != nil
   451  					ptr, recv, _ := check.unpackRecv(s.Recv.Type, false)
   452  					// Methods with invalid receiver cannot be associated to a type, and
   453  					// methods with blank _ names are never found; no need to collect any
   454  					// of them. They will still be type-checked with all the other functions.
   455  					if recv != nil && name != "_" {
   456  						methods = append(methods, methodInfo{obj, ptr, recv})
   457  					}
   458  					check.recordDef(s.Name, obj)
   459  				}
   460  				if len(s.TParamList) != 0 && !check.allowVersion(pkg, 1, 18) && !hasTParamError {
   461  					check.versionErrorf(s.TParamList[0], "go1.18", "type parameter")
   462  				}
   463  				info := &declInfo{file: fileScope, fdecl: s}
   464  				// Methods are not package-level objects but we still track them in the
   465  				// object map so that we can handle them like regular functions (if the
   466  				// receiver is invalid); also we need their fdecl info when associating
   467  				// them with their receiver base type, below.
   468  				check.objMap[obj] = info
   469  				obj.setOrder(uint32(len(check.objMap)))
   470  
   471  			default:
   472  				check.errorf(s, invalidAST+"unknown syntax.Decl node %T", s)
   473  			}
   474  		}
   475  	}
   476  
   477  	// verify that objects in package and file scopes have different names
   478  	for _, scope := range fileScopes {
   479  		for name, obj := range scope.elems {
   480  			if alt := pkg.scope.Lookup(name); alt != nil {
   481  				obj = resolve(name, obj)
   482  				var err error_
   483  				if pkg, ok := obj.(*PkgName); ok {
   484  					err.errorf(alt, "%s already declared through import of %s", alt.Name(), pkg.Imported())
   485  					err.recordAltDecl(pkg)
   486  				} else {
   487  					err.errorf(alt, "%s already declared through dot-import of %s", alt.Name(), obj.Pkg())
   488  					// TODO(gri) dot-imported objects don't have a position; recordAltDecl won't print anything
   489  					err.recordAltDecl(obj)
   490  				}
   491  				check.report(&err)
   492  			}
   493  		}
   494  	}
   495  
   496  	// Now that we have all package scope objects and all methods,
   497  	// associate methods with receiver base type name where possible.
   498  	// Ignore methods that have an invalid receiver. They will be
   499  	// type-checked later, with regular functions.
   500  	if methods != nil {
   501  		check.methods = make(map[*TypeName][]*Func)
   502  		for i := range methods {
   503  			m := &methods[i]
   504  			// Determine the receiver base type and associate m with it.
   505  			ptr, base := check.resolveBaseTypeName(m.ptr, m.recv)
   506  			if base != nil {
   507  				m.obj.hasPtrRecv_ = ptr
   508  				check.methods[base] = append(check.methods[base], m.obj)
   509  			}
   510  		}
   511  	}
   512  }
   513  
   514  // unpackRecv unpacks a receiver type and returns its components: ptr indicates whether
   515  // rtyp is a pointer receiver, rname is the receiver type name, and tparams are its
   516  // type parameters, if any. The type parameters are only unpacked if unpackParams is
   517  // set. If rname is nil, the receiver is unusable (i.e., the source has a bug which we
   518  // cannot easily work around).
   519  func (check *Checker) unpackRecv(rtyp syntax.Expr, unpackParams bool) (ptr bool, rname *syntax.Name, tparams []*syntax.Name) {
   520  L: // unpack receiver type
   521  	// This accepts invalid receivers such as ***T and does not
   522  	// work for other invalid receivers, but we don't care. The
   523  	// validity of receiver expressions is checked elsewhere.
   524  	for {
   525  		switch t := rtyp.(type) {
   526  		case *syntax.ParenExpr:
   527  			rtyp = t.X
   528  		// case *ast.StarExpr:
   529  		//      ptr = true
   530  		// 	rtyp = t.X
   531  		case *syntax.Operation:
   532  			if t.Op != syntax.Mul || t.Y != nil {
   533  				break
   534  			}
   535  			ptr = true
   536  			rtyp = t.X
   537  		default:
   538  			break L
   539  		}
   540  	}
   541  
   542  	// unpack type parameters, if any
   543  	if ptyp, _ := rtyp.(*syntax.IndexExpr); ptyp != nil {
   544  		rtyp = ptyp.X
   545  		if unpackParams {
   546  			for _, arg := range unpackExpr(ptyp.Index) {
   547  				var par *syntax.Name
   548  				switch arg := arg.(type) {
   549  				case *syntax.Name:
   550  					par = arg
   551  				case *syntax.BadExpr:
   552  					// ignore - error already reported by parser
   553  				case nil:
   554  					check.error(ptyp, invalidAST+"parameterized receiver contains nil parameters")
   555  				default:
   556  					check.errorf(arg, "receiver type parameter %s must be an identifier", arg)
   557  				}
   558  				if par == nil {
   559  					par = syntax.NewName(arg.Pos(), "_")
   560  				}
   561  				tparams = append(tparams, par)
   562  			}
   563  
   564  		}
   565  	}
   566  
   567  	// unpack receiver name
   568  	if name, _ := rtyp.(*syntax.Name); name != nil {
   569  		rname = name
   570  	}
   571  
   572  	return
   573  }
   574  
   575  // resolveBaseTypeName returns the non-alias base type name for typ, and whether
   576  // there was a pointer indirection to get to it. The base type name must be declared
   577  // in package scope, and there can be at most one pointer indirection. If no such type
   578  // name exists, the returned base is nil.
   579  func (check *Checker) resolveBaseTypeName(seenPtr bool, typ syntax.Expr) (ptr bool, base *TypeName) {
   580  	// Algorithm: Starting from a type expression, which may be a name,
   581  	// we follow that type through alias declarations until we reach a
   582  	// non-alias type name. If we encounter anything but pointer types or
   583  	// parentheses we're done. If we encounter more than one pointer type
   584  	// we're done.
   585  	ptr = seenPtr
   586  	var seen map[*TypeName]bool
   587  	for {
   588  		typ = unparen(typ)
   589  
   590  		// check if we have a pointer type
   591  		// if pexpr, _ := typ.(*ast.StarExpr); pexpr != nil {
   592  		if pexpr, _ := typ.(*syntax.Operation); pexpr != nil && pexpr.Op == syntax.Mul && pexpr.Y == nil {
   593  			// if we've already seen a pointer, we're done
   594  			if ptr {
   595  				return false, nil
   596  			}
   597  			ptr = true
   598  			typ = unparen(pexpr.X) // continue with pointer base type
   599  		}
   600  
   601  		// typ must be a name
   602  		name, _ := typ.(*syntax.Name)
   603  		if name == nil {
   604  			return false, nil
   605  		}
   606  
   607  		// name must denote an object found in the current package scope
   608  		// (note that dot-imported objects are not in the package scope!)
   609  		obj := check.pkg.scope.Lookup(name.Value)
   610  		if obj == nil {
   611  			return false, nil
   612  		}
   613  
   614  		// the object must be a type name...
   615  		tname, _ := obj.(*TypeName)
   616  		if tname == nil {
   617  			return false, nil
   618  		}
   619  
   620  		// ... which we have not seen before
   621  		if seen[tname] {
   622  			return false, nil
   623  		}
   624  
   625  		// we're done if tdecl defined tname as a new type
   626  		// (rather than an alias)
   627  		tdecl := check.objMap[tname].tdecl // must exist for objects in package scope
   628  		if !tdecl.Alias {
   629  			return ptr, tname
   630  		}
   631  
   632  		// otherwise, continue resolving
   633  		typ = tdecl.Type
   634  		if seen == nil {
   635  			seen = make(map[*TypeName]bool)
   636  		}
   637  		seen[tname] = true
   638  	}
   639  }
   640  
   641  // packageObjects typechecks all package objects, but not function bodies.
   642  func (check *Checker) packageObjects() {
   643  	// process package objects in source order for reproducible results
   644  	objList := make([]Object, len(check.objMap))
   645  	i := 0
   646  	for obj := range check.objMap {
   647  		objList[i] = obj
   648  		i++
   649  	}
   650  	sort.Sort(inSourceOrder(objList))
   651  
   652  	// add new methods to already type-checked types (from a prior Checker.Files call)
   653  	for _, obj := range objList {
   654  		if obj, _ := obj.(*TypeName); obj != nil && obj.typ != nil {
   655  			check.collectMethods(obj)
   656  		}
   657  	}
   658  
   659  	// We process non-alias type declarations first, followed by alias declarations,
   660  	// and then everything else. This appears to avoid most situations where the type
   661  	// of an alias is needed before it is available.
   662  	// There may still be cases where this is not good enough (see also issue #25838).
   663  	// In those cases Checker.ident will report an error ("invalid use of type alias").
   664  	var aliasList []*TypeName
   665  	var othersList []Object // everything that's not a type
   666  	// phase 1: non-alias type declarations
   667  	for _, obj := range objList {
   668  		if tname, _ := obj.(*TypeName); tname != nil {
   669  			if check.objMap[tname].tdecl.Alias {
   670  				aliasList = append(aliasList, tname)
   671  			} else {
   672  				check.objDecl(obj, nil)
   673  			}
   674  		} else {
   675  			othersList = append(othersList, obj)
   676  		}
   677  	}
   678  	// phase 2: alias type declarations
   679  	for _, obj := range aliasList {
   680  		check.objDecl(obj, nil)
   681  	}
   682  	// phase 3: all other declarations
   683  	for _, obj := range othersList {
   684  		check.objDecl(obj, nil)
   685  	}
   686  
   687  	// At this point we may have a non-empty check.methods map; this means that not all
   688  	// entries were deleted at the end of typeDecl because the respective receiver base
   689  	// types were not found. In that case, an error was reported when declaring those
   690  	// methods. We can now safely discard this map.
   691  	check.methods = nil
   692  }
   693  
   694  // inSourceOrder implements the sort.Sort interface.
   695  type inSourceOrder []Object
   696  
   697  func (a inSourceOrder) Len() int           { return len(a) }
   698  func (a inSourceOrder) Less(i, j int) bool { return a[i].order() < a[j].order() }
   699  func (a inSourceOrder) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
   700  
   701  // unusedImports checks for unused imports.
   702  func (check *Checker) unusedImports() {
   703  	// if function bodies are not checked, packages' uses are likely missing - don't check
   704  	if check.conf.IgnoreFuncBodies {
   705  		return
   706  	}
   707  
   708  	// spec: "It is illegal (...) to directly import a package without referring to
   709  	// any of its exported identifiers. To import a package solely for its side-effects
   710  	// (initialization), use the blank identifier as explicit package name."
   711  
   712  	for _, obj := range check.imports {
   713  		if !obj.used && obj.name != "_" {
   714  			check.errorUnusedPkg(obj)
   715  		}
   716  	}
   717  }
   718  
   719  func (check *Checker) errorUnusedPkg(obj *PkgName) {
   720  	// If the package was imported with a name other than the final
   721  	// import path element, show it explicitly in the error message.
   722  	// Note that this handles both renamed imports and imports of
   723  	// packages containing unconventional package declarations.
   724  	// Note that this uses / always, even on Windows, because Go import
   725  	// paths always use forward slashes.
   726  	path := obj.imported.path
   727  	elem := path
   728  	if i := strings.LastIndex(elem, "/"); i >= 0 {
   729  		elem = elem[i+1:]
   730  	}
   731  	if obj.name == "" || obj.name == "." || obj.name == elem {
   732  		if check.conf.CompilerErrorMessages {
   733  			check.softErrorf(obj, "imported and not used: %q", path)
   734  		} else {
   735  			check.softErrorf(obj, "%q imported but not used", path)
   736  		}
   737  	} else {
   738  		if check.conf.CompilerErrorMessages {
   739  			check.softErrorf(obj, "imported and not used: %q as %s", path, obj.name)
   740  		} else {
   741  			check.softErrorf(obj, "%q imported but not used as %s", path, obj.name)
   742  		}
   743  	}
   744  }
   745  
   746  // dir makes a good-faith attempt to return the directory
   747  // portion of path. If path is empty, the result is ".".
   748  // (Per the go/build package dependency tests, we cannot import
   749  // path/filepath and simply use filepath.Dir.)
   750  func dir(path string) string {
   751  	if i := strings.LastIndexAny(path, `/\`); i > 0 {
   752  		return path[:i]
   753  	}
   754  	// i <= 0
   755  	return "."
   756  }
   757
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