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Source file src/go/types/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/token"
    12  	"sort"
    13  	"strconv"
    14  	"strings"
    15  	"unicode"
    16  )
    17  
    18  // A declInfo describes a package-level const, type, var, or func declaration.
    19  type declInfo struct {
    20  	file      *Scope        // scope of file containing this declaration
    21  	lhs       []*Var        // lhs of n:1 variable declarations, or nil
    22  	typ       ast.Expr      // type, or nil
    23  	init      ast.Expr      // init/orig expression, or nil
    24  	inherited bool          // if set, the init expression is inherited from a previous constant declaration
    25  	fdecl     *ast.FuncDecl // func declaration, or nil
    26  	alias     bool          // type alias declaration
    27  
    28  	// The deps field tracks initialization expression dependencies.
    29  	deps map[Object]bool // lazily initialized
    30  }
    31  
    32  // hasInitializer reports whether the declared object has an initialization
    33  // expression or function body.
    34  func (d *declInfo) hasInitializer() bool {
    35  	return d.init != nil || d.fdecl != nil && d.fdecl.Body != nil
    36  }
    37  
    38  // addDep adds obj to the set of objects d's init expression depends on.
    39  func (d *declInfo) addDep(obj Object) {
    40  	m := d.deps
    41  	if m == nil {
    42  		m = make(map[Object]bool)
    43  		d.deps = m
    44  	}
    45  	m[obj] = true
    46  }
    47  
    48  // arityMatch checks that the lhs and rhs of a const or var decl
    49  // have the appropriate number of names and init exprs. For const
    50  // decls, init is the value spec providing the init exprs; for
    51  // var decls, init is nil (the init exprs are in s in this case).
    52  func (check *Checker) arityMatch(s, init *ast.ValueSpec) {
    53  	l := len(s.Names)
    54  	r := len(s.Values)
    55  	if init != nil {
    56  		r = len(init.Values)
    57  	}
    58  
    59  	const code = _WrongAssignCount
    60  	switch {
    61  	case init == nil && r == 0:
    62  		// var decl w/o init expr
    63  		if s.Type == nil {
    64  			check.errorf(s, code, "missing type or init expr")
    65  		}
    66  	case l < r:
    67  		if l < len(s.Values) {
    68  			// init exprs from s
    69  			n := s.Values[l]
    70  			check.errorf(n, code, "extra init expr %s", n)
    71  			// TODO(gri) avoid declared but not used error here
    72  		} else {
    73  			// init exprs "inherited"
    74  			check.errorf(s, code, "extra init expr at %s", check.fset.Position(init.Pos()))
    75  			// TODO(gri) avoid declared but not used error here
    76  		}
    77  	case l > r && (init != nil || r != 1):
    78  		n := s.Names[r]
    79  		check.errorf(n, code, "missing init expr for %s", n)
    80  	}
    81  }
    82  
    83  func validatedImportPath(path string) (string, error) {
    84  	s, err := strconv.Unquote(path)
    85  	if err != nil {
    86  		return "", err
    87  	}
    88  	if s == "" {
    89  		return "", fmt.Errorf("empty string")
    90  	}
    91  	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
    92  	for _, r := range s {
    93  		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
    94  			return s, fmt.Errorf("invalid character %#U", r)
    95  		}
    96  	}
    97  	return s, nil
    98  }
    99  
   100  // declarePkgObj declares obj in the package scope, records its ident -> obj mapping,
   101  // and updates check.objMap. The object must not be a function or method.
   102  func (check *Checker) declarePkgObj(ident *ast.Ident, obj Object, d *declInfo) {
   103  	assert(ident.Name == obj.Name())
   104  
   105  	// spec: "A package-scope or file-scope identifier with name init
   106  	// may only be declared to be a function with this (func()) signature."
   107  	if ident.Name == "init" {
   108  		check.errorf(ident, _InvalidInitDecl, "cannot declare init - must be func")
   109  		return
   110  	}
   111  
   112  	// spec: "The main package must have package name main and declare
   113  	// a function main that takes no arguments and returns no value."
   114  	if ident.Name == "main" && check.pkg.name == "main" {
   115  		check.errorf(ident, _InvalidMainDecl, "cannot declare main - must be func")
   116  		return
   117  	}
   118  
   119  	check.declare(check.pkg.scope, ident, obj, token.NoPos)
   120  	check.objMap[obj] = d
   121  	obj.setOrder(uint32(len(check.objMap)))
   122  }
   123  
   124  // filename returns a filename suitable for debugging output.
   125  func (check *Checker) filename(fileNo int) string {
   126  	file := check.files[fileNo]
   127  	if pos := file.Pos(); pos.IsValid() {
   128  		return check.fset.File(pos).Name()
   129  	}
   130  	return fmt.Sprintf("file[%d]", fileNo)
   131  }
   132  
   133  func (check *Checker) importPackage(pos token.Pos, path, dir string) *Package {
   134  	// If we already have a package for the given (path, dir)
   135  	// pair, use it instead of doing a full import.
   136  	// Checker.impMap only caches packages that are marked Complete
   137  	// or fake (dummy packages for failed imports). Incomplete but
   138  	// non-fake packages do require an import to complete them.
   139  	key := importKey{path, dir}
   140  	imp := check.impMap[key]
   141  	if imp != nil {
   142  		return imp
   143  	}
   144  
   145  	// no package yet => import it
   146  	if path == "C" && (check.conf.FakeImportC || check.conf.go115UsesCgo) {
   147  		imp = NewPackage("C", "C")
   148  		imp.fake = true // package scope is not populated
   149  		imp.cgo = check.conf.go115UsesCgo
   150  	} else {
   151  		// ordinary import
   152  		var err error
   153  		if importer := check.conf.Importer; importer == nil {
   154  			err = fmt.Errorf("Config.Importer not installed")
   155  		} else if importerFrom, ok := importer.(ImporterFrom); ok {
   156  			imp, err = importerFrom.ImportFrom(path, dir, 0)
   157  			if imp == nil && err == nil {
   158  				err = fmt.Errorf("Config.Importer.ImportFrom(%s, %s, 0) returned nil but no error", path, dir)
   159  			}
   160  		} else {
   161  			imp, err = importer.Import(path)
   162  			if imp == nil && err == nil {
   163  				err = fmt.Errorf("Config.Importer.Import(%s) returned nil but no error", path)
   164  			}
   165  		}
   166  		// make sure we have a valid package name
   167  		// (errors here can only happen through manipulation of packages after creation)
   168  		if err == nil && imp != nil && (imp.name == "_" || imp.name == "") {
   169  			err = fmt.Errorf("invalid package name: %q", imp.name)
   170  			imp = nil // create fake package below
   171  		}
   172  		if err != nil {
   173  			check.errorf(atPos(pos), _BrokenImport, "could not import %s (%s)", path, err)
   174  			if imp == nil {
   175  				// create a new fake package
   176  				// come up with a sensible package name (heuristic)
   177  				name := path
   178  				if i := len(name); i > 0 && name[i-1] == '/' {
   179  					name = name[:i-1]
   180  				}
   181  				if i := strings.LastIndex(name, "/"); i >= 0 {
   182  					name = name[i+1:]
   183  				}
   184  				imp = NewPackage(path, name)
   185  			}
   186  			// continue to use the package as best as we can
   187  			imp.fake = true // avoid follow-up lookup failures
   188  		}
   189  	}
   190  
   191  	// package should be complete or marked fake, but be cautious
   192  	if imp.complete || imp.fake {
   193  		check.impMap[key] = imp
   194  		check.pkgCnt[imp.name]++
   195  		return imp
   196  	}
   197  
   198  	// something went wrong (importer may have returned incomplete package without error)
   199  	return nil
   200  }
   201  
   202  // collectObjects collects all file and package objects and inserts them
   203  // into their respective scopes. It also performs imports and associates
   204  // methods with receiver base type names.
   205  func (check *Checker) collectObjects() {
   206  	pkg := check.pkg
   207  
   208  	// pkgImports is the set of packages already imported by any package file seen
   209  	// so far. Used to avoid duplicate entries in pkg.imports. Allocate and populate
   210  	// it (pkg.imports may not be empty if we are checking test files incrementally).
   211  	// Note that pkgImports is keyed by package (and thus package path), not by an
   212  	// importKey value. Two different importKey values may map to the same package
   213  	// which is why we cannot use the check.impMap here.
   214  	var pkgImports = make(map[*Package]bool)
   215  	for _, imp := range pkg.imports {
   216  		pkgImports[imp] = true
   217  	}
   218  
   219  	var methods []*Func // list of methods with non-blank _ names
   220  	for fileNo, file := range check.files {
   221  		// The package identifier denotes the current package,
   222  		// but there is no corresponding package object.
   223  		check.recordDef(file.Name, nil)
   224  
   225  		// Use the actual source file extent rather than *ast.File extent since the
   226  		// latter doesn't include comments which appear at the start or end of the file.
   227  		// Be conservative and use the *ast.File extent if we don't have a *token.File.
   228  		pos, end := file.Pos(), file.End()
   229  		if f := check.fset.File(file.Pos()); f != nil {
   230  			pos, end = token.Pos(f.Base()), token.Pos(f.Base()+f.Size())
   231  		}
   232  		fileScope := NewScope(check.pkg.scope, pos, end, check.filename(fileNo))
   233  		check.recordScope(file, fileScope)
   234  
   235  		// determine file directory, necessary to resolve imports
   236  		// FileName may be "" (typically for tests) in which case
   237  		// we get "." as the directory which is what we would want.
   238  		fileDir := dir(check.fset.Position(file.Name.Pos()).Filename)
   239  
   240  		check.walkDecls(file.Decls, func(d decl) {
   241  			switch d := d.(type) {
   242  			case importDecl:
   243  				// import package
   244  				path, err := validatedImportPath(d.spec.Path.Value)
   245  				if err != nil {
   246  					check.errorf(d.spec.Path, _BadImportPath, "invalid import path (%s)", err)
   247  					return
   248  				}
   249  
   250  				imp := check.importPackage(d.spec.Path.Pos(), path, fileDir)
   251  				if imp == nil {
   252  					return
   253  				}
   254  
   255  				// add package to list of explicit imports
   256  				// (this functionality is provided as a convenience
   257  				// for clients; it is not needed for type-checking)
   258  				if !pkgImports[imp] {
   259  					pkgImports[imp] = true
   260  					pkg.imports = append(pkg.imports, imp)
   261  				}
   262  
   263  				// local name overrides imported package name
   264  				name := imp.name
   265  				if d.spec.Name != nil {
   266  					name = d.spec.Name.Name
   267  					if path == "C" {
   268  						// match cmd/compile (not prescribed by spec)
   269  						check.errorf(d.spec.Name, _ImportCRenamed, `cannot rename import "C"`)
   270  						return
   271  					}
   272  					if name == "init" {
   273  						check.errorf(d.spec.Name, _InvalidInitDecl, "cannot declare init - must be func")
   274  						return
   275  					}
   276  				}
   277  
   278  				obj := NewPkgName(d.spec.Pos(), pkg, name, imp)
   279  				if d.spec.Name != nil {
   280  					// in a dot-import, the dot represents the package
   281  					check.recordDef(d.spec.Name, obj)
   282  				} else {
   283  					check.recordImplicit(d.spec, obj)
   284  				}
   285  
   286  				if path == "C" {
   287  					// match cmd/compile (not prescribed by spec)
   288  					obj.used = true
   289  				}
   290  
   291  				// add import to file scope
   292  				if name == "." {
   293  					// merge imported scope with file scope
   294  					for _, obj := range imp.scope.elems {
   295  						// A package scope may contain non-exported objects,
   296  						// do not import them!
   297  						if obj.Exported() {
   298  							// declare dot-imported object
   299  							// (Do not use check.declare because it modifies the object
   300  							// via Object.setScopePos, which leads to a race condition;
   301  							// the object may be imported into more than one file scope
   302  							// concurrently. See issue #32154.)
   303  							if alt := fileScope.Insert(obj); alt != nil {
   304  								check.errorf(d.spec.Name, _DuplicateDecl, "%s redeclared in this block", obj.Name())
   305  								check.reportAltDecl(alt)
   306  							}
   307  						}
   308  					}
   309  					// add position to set of dot-import positions for this file
   310  					// (this is only needed for "imported but not used" errors)
   311  					check.addUnusedDotImport(fileScope, imp, d.spec)
   312  				} else {
   313  					// declare imported package object in file scope
   314  					// (no need to provide s.Name since we called check.recordDef earlier)
   315  					check.declare(fileScope, nil, obj, token.NoPos)
   316  				}
   317  			case constDecl:
   318  				// declare all constants
   319  				for i, name := range d.spec.Names {
   320  					obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(d.iota)))
   321  
   322  					var init ast.Expr
   323  					if i < len(d.init) {
   324  						init = d.init[i]
   325  					}
   326  
   327  					d := &declInfo{file: fileScope, typ: d.typ, init: init, inherited: d.inherited}
   328  					check.declarePkgObj(name, obj, d)
   329  				}
   330  
   331  			case varDecl:
   332  				lhs := make([]*Var, len(d.spec.Names))
   333  				// If there's exactly one rhs initializer, use
   334  				// the same declInfo d1 for all lhs variables
   335  				// so that each lhs variable depends on the same
   336  				// rhs initializer (n:1 var declaration).
   337  				var d1 *declInfo
   338  				if len(d.spec.Values) == 1 {
   339  					// The lhs elements are only set up after the for loop below,
   340  					// but that's ok because declareVar only collects the declInfo
   341  					// for a later phase.
   342  					d1 = &declInfo{file: fileScope, lhs: lhs, typ: d.spec.Type, init: d.spec.Values[0]}
   343  				}
   344  
   345  				// declare all variables
   346  				for i, name := range d.spec.Names {
   347  					obj := NewVar(name.Pos(), pkg, name.Name, nil)
   348  					lhs[i] = obj
   349  
   350  					di := d1
   351  					if di == nil {
   352  						// individual assignments
   353  						var init ast.Expr
   354  						if i < len(d.spec.Values) {
   355  							init = d.spec.Values[i]
   356  						}
   357  						di = &declInfo{file: fileScope, typ: d.spec.Type, init: init}
   358  					}
   359  
   360  					check.declarePkgObj(name, obj, di)
   361  				}
   362  			case typeDecl:
   363  				obj := NewTypeName(d.spec.Name.Pos(), pkg, d.spec.Name.Name, nil)
   364  				check.declarePkgObj(d.spec.Name, obj, &declInfo{file: fileScope, typ: d.spec.Type, alias: d.spec.Assign.IsValid()})
   365  			case funcDecl:
   366  				info := &declInfo{file: fileScope, fdecl: d.decl}
   367  				name := d.decl.Name.Name
   368  				obj := NewFunc(d.decl.Name.Pos(), pkg, name, nil)
   369  				if d.decl.Recv == nil {
   370  					// regular function
   371  					if name == "init" {
   372  						// don't declare init functions in the package scope - they are invisible
   373  						obj.parent = pkg.scope
   374  						check.recordDef(d.decl.Name, obj)
   375  						// init functions must have a body
   376  						if d.decl.Body == nil {
   377  							check.softErrorf(obj, _MissingInitBody, "missing function body")
   378  						}
   379  					} else {
   380  						check.declare(pkg.scope, d.decl.Name, obj, token.NoPos)
   381  					}
   382  				} else {
   383  					// method
   384  					// (Methods with blank _ names are never found; no need to collect
   385  					// them for later type association. They will still be type-checked
   386  					// with all the other functions.)
   387  					if name != "_" {
   388  						methods = append(methods, obj)
   389  					}
   390  					check.recordDef(d.decl.Name, obj)
   391  				}
   392  				// Methods are not package-level objects but we still track them in the
   393  				// object map so that we can handle them like regular functions (if the
   394  				// receiver is invalid); also we need their fdecl info when associating
   395  				// them with their receiver base type, below.
   396  				check.objMap[obj] = info
   397  				obj.setOrder(uint32(len(check.objMap)))
   398  			}
   399  		})
   400  	}
   401  
   402  	// verify that objects in package and file scopes have different names
   403  	for _, scope := range check.pkg.scope.children /* file scopes */ {
   404  		for _, obj := range scope.elems {
   405  			if alt := pkg.scope.Lookup(obj.Name()); alt != nil {
   406  				if pkg, ok := obj.(*PkgName); ok {
   407  					check.errorf(alt, _DuplicateDecl, "%s already declared through import of %s", alt.Name(), pkg.Imported())
   408  					check.reportAltDecl(pkg)
   409  				} else {
   410  					check.errorf(alt, _DuplicateDecl, "%s already declared through dot-import of %s", alt.Name(), obj.Pkg())
   411  					// TODO(gri) dot-imported objects don't have a position; reportAltDecl won't print anything
   412  					check.reportAltDecl(obj)
   413  				}
   414  			}
   415  		}
   416  	}
   417  
   418  	// Now that we have all package scope objects and all methods,
   419  	// associate methods with receiver base type name where possible.
   420  	// Ignore methods that have an invalid receiver. They will be
   421  	// type-checked later, with regular functions.
   422  	if methods == nil {
   423  		return // nothing to do
   424  	}
   425  	check.methods = make(map[*TypeName][]*Func)
   426  	for _, f := range methods {
   427  		fdecl := check.objMap[f].fdecl
   428  		if list := fdecl.Recv.List; len(list) > 0 {
   429  			// f is a method.
   430  			// Determine the receiver base type and associate f with it.
   431  			ptr, base := check.resolveBaseTypeName(list[0].Type)
   432  			if base != nil {
   433  				f.hasPtrRecv = ptr
   434  				check.methods[base] = append(check.methods[base], f)
   435  			}
   436  		}
   437  	}
   438  }
   439  
   440  // resolveBaseTypeName returns the non-alias base type name for typ, and whether
   441  // there was a pointer indirection to get to it. The base type name must be declared
   442  // in package scope, and there can be at most one pointer indirection. If no such type
   443  // name exists, the returned base is nil.
   444  func (check *Checker) resolveBaseTypeName(typ ast.Expr) (ptr bool, base *TypeName) {
   445  	// Algorithm: Starting from a type expression, which may be a name,
   446  	// we follow that type through alias declarations until we reach a
   447  	// non-alias type name. If we encounter anything but pointer types or
   448  	// parentheses we're done. If we encounter more than one pointer type
   449  	// we're done.
   450  	var seen map[*TypeName]bool
   451  	for {
   452  		typ = unparen(typ)
   453  
   454  		// check if we have a pointer type
   455  		if pexpr, _ := typ.(*ast.StarExpr); pexpr != nil {
   456  			// if we've already seen a pointer, we're done
   457  			if ptr {
   458  				return false, nil
   459  			}
   460  			ptr = true
   461  			typ = unparen(pexpr.X) // continue with pointer base type
   462  		}
   463  
   464  		// typ must be a name
   465  		name, _ := typ.(*ast.Ident)
   466  		if name == nil {
   467  			return false, nil
   468  		}
   469  
   470  		// name must denote an object found in the current package scope
   471  		// (note that dot-imported objects are not in the package scope!)
   472  		obj := check.pkg.scope.Lookup(name.Name)
   473  		if obj == nil {
   474  			return false, nil
   475  		}
   476  
   477  		// the object must be a type name...
   478  		tname, _ := obj.(*TypeName)
   479  		if tname == nil {
   480  			return false, nil
   481  		}
   482  
   483  		// ... which we have not seen before
   484  		if seen[tname] {
   485  			return false, nil
   486  		}
   487  
   488  		// we're done if tdecl defined tname as a new type
   489  		// (rather than an alias)
   490  		tdecl := check.objMap[tname] // must exist for objects in package scope
   491  		if !tdecl.alias {
   492  			return ptr, tname
   493  		}
   494  
   495  		// otherwise, continue resolving
   496  		typ = tdecl.typ
   497  		if seen == nil {
   498  			seen = make(map[*TypeName]bool)
   499  		}
   500  		seen[tname] = true
   501  	}
   502  }
   503  
   504  // packageObjects typechecks all package objects, but not function bodies.
   505  func (check *Checker) packageObjects() {
   506  	// process package objects in source order for reproducible results
   507  	objList := make([]Object, len(check.objMap))
   508  	i := 0
   509  	for obj := range check.objMap {
   510  		objList[i] = obj
   511  		i++
   512  	}
   513  	sort.Sort(inSourceOrder(objList))
   514  
   515  	// add new methods to already type-checked types (from a prior Checker.Files call)
   516  	for _, obj := range objList {
   517  		if obj, _ := obj.(*TypeName); obj != nil && obj.typ != nil {
   518  			check.addMethodDecls(obj)
   519  		}
   520  	}
   521  
   522  	// We process non-alias declarations first, in order to avoid situations where
   523  	// the type of an alias declaration is needed before it is available. In general
   524  	// this is still not enough, as it is possible to create sufficiently convoluted
   525  	// recursive type definitions that will cause a type alias to be needed before it
   526  	// is available (see issue #25838 for examples).
   527  	// As an aside, the cmd/compiler suffers from the same problem (#25838).
   528  	var aliasList []*TypeName
   529  	// phase 1
   530  	for _, obj := range objList {
   531  		// If we have a type alias, collect it for the 2nd phase.
   532  		if tname, _ := obj.(*TypeName); tname != nil && check.objMap[tname].alias {
   533  			aliasList = append(aliasList, tname)
   534  			continue
   535  		}
   536  
   537  		check.objDecl(obj, nil)
   538  	}
   539  	// phase 2
   540  	for _, obj := range aliasList {
   541  		check.objDecl(obj, nil)
   542  	}
   543  
   544  	// At this point we may have a non-empty check.methods map; this means that not all
   545  	// entries were deleted at the end of typeDecl because the respective receiver base
   546  	// types were not found. In that case, an error was reported when declaring those
   547  	// methods. We can now safely discard this map.
   548  	check.methods = nil
   549  }
   550  
   551  // inSourceOrder implements the sort.Sort interface.
   552  type inSourceOrder []Object
   553  
   554  func (a inSourceOrder) Len() int           { return len(a) }
   555  func (a inSourceOrder) Less(i, j int) bool { return a[i].order() < a[j].order() }
   556  func (a inSourceOrder) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
   557  
   558  // unusedImports checks for unused imports.
   559  func (check *Checker) unusedImports() {
   560  	// if function bodies are not checked, packages' uses are likely missing - don't check
   561  	if check.conf.IgnoreFuncBodies {
   562  		return
   563  	}
   564  
   565  	// spec: "It is illegal (...) to directly import a package without referring to
   566  	// any of its exported identifiers. To import a package solely for its side-effects
   567  	// (initialization), use the blank identifier as explicit package name."
   568  
   569  	// check use of regular imported packages
   570  	for _, scope := range check.pkg.scope.children /* file scopes */ {
   571  		for _, obj := range scope.elems {
   572  			if obj, ok := obj.(*PkgName); ok {
   573  				// Unused "blank imports" are automatically ignored
   574  				// since _ identifiers are not entered into scopes.
   575  				if !obj.used {
   576  					path := obj.imported.path
   577  					base := pkgName(path)
   578  					if obj.name == base {
   579  						check.softErrorf(obj, _UnusedImport, "%q imported but not used", path)
   580  					} else {
   581  						check.softErrorf(obj, _UnusedImport, "%q imported but not used as %s", path, obj.name)
   582  					}
   583  				}
   584  			}
   585  		}
   586  	}
   587  
   588  	// check use of dot-imported packages
   589  	for _, unusedDotImports := range check.unusedDotImports {
   590  		for pkg, pos := range unusedDotImports {
   591  			check.softErrorf(pos, _UnusedImport, "%q imported but not used", pkg.path)
   592  		}
   593  	}
   594  }
   595  
   596  // pkgName returns the package name (last element) of an import path.
   597  func pkgName(path string) string {
   598  	if i := strings.LastIndex(path, "/"); i >= 0 {
   599  		path = path[i+1:]
   600  	}
   601  	return path
   602  }
   603  
   604  // dir makes a good-faith attempt to return the directory
   605  // portion of path. If path is empty, the result is ".".
   606  // (Per the go/build package dependency tests, we cannot import
   607  // path/filepath and simply use filepath.Dir.)
   608  func dir(path string) string {
   609  	if i := strings.LastIndexAny(path, `/\`); i > 0 {
   610  		return path[:i]
   611  	}
   612  	// i <= 0
   613  	return "."
   614  }
   615  

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