check.go

Documentation: golang.org/x/tools/refactor/rename

     1  // Copyright 2014 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 rename
     6  
     7  // This file defines the safety checks for each kind of renaming.
     8  
     9  import (
    10  	"fmt"
    11  	"go/ast"
    12  	"go/token"
    13  	"go/types"
    14  
    15  	"golang.org/x/tools/go/loader"
    16  	"golang.org/x/tools/refactor/satisfy"
    17  )
    18  
    19  // errorf reports an error (e.g. conflict) and prevents file modification.
    20  func (r *renamer) errorf(pos token.Pos, format string, args ...interface{}) {
    21  	r.hadConflicts = true
    22  	reportError(r.iprog.Fset.Position(pos), fmt.Sprintf(format, args...))
    23  }
    24  
    25  // check performs safety checks of the renaming of the 'from' object to r.to.
    26  func (r *renamer) check(from types.Object) {
    27  	if r.objsToUpdate[from] {
    28  		return
    29  	}
    30  	r.objsToUpdate[from] = true
    31  
    32  	// NB: order of conditions is important.
    33  	if from_, ok := from.(*types.PkgName); ok {
    34  		r.checkInFileBlock(from_)
    35  	} else if from_, ok := from.(*types.Label); ok {
    36  		r.checkLabel(from_)
    37  	} else if isPackageLevel(from) {
    38  		r.checkInPackageBlock(from)
    39  	} else if v, ok := from.(*types.Var); ok && v.IsField() {
    40  		r.checkStructField(v)
    41  	} else if f, ok := from.(*types.Func); ok && recv(f) != nil {
    42  		r.checkMethod(f)
    43  	} else if isLocal(from) {
    44  		r.checkInLocalScope(from)
    45  	} else {
    46  		r.errorf(from.Pos(), "unexpected %s object %q (please report a bug)\n",
    47  			objectKind(from), from)
    48  	}
    49  }
    50  
    51  // checkInFileBlock performs safety checks for renames of objects in the file block,
    52  // i.e. imported package names.
    53  func (r *renamer) checkInFileBlock(from *types.PkgName) {
    54  	// Check import name is not "init".
    55  	if r.to == "init" {
    56  		r.errorf(from.Pos(), "%q is not a valid imported package name", r.to)
    57  	}
    58  
    59  	// Check for conflicts between file and package block.
    60  	if prev := from.Pkg().Scope().Lookup(r.to); prev != nil {
    61  		r.errorf(from.Pos(), "renaming this %s %q to %q would conflict",
    62  			objectKind(from), from.Name(), r.to)
    63  		r.errorf(prev.Pos(), "\twith this package member %s",
    64  			objectKind(prev))
    65  		return // since checkInPackageBlock would report redundant errors
    66  	}
    67  
    68  	// Check for conflicts in lexical scope.
    69  	r.checkInLexicalScope(from, r.packages[from.Pkg()])
    70  
    71  	// Finally, modify ImportSpec syntax to add or remove the Name as needed.
    72  	info, path, _ := r.iprog.PathEnclosingInterval(from.Pos(), from.Pos())
    73  	if from.Imported().Name() == r.to {
    74  		// ImportSpec.Name not needed
    75  		path[1].(*ast.ImportSpec).Name = nil
    76  	} else {
    77  		// ImportSpec.Name needed
    78  		if spec := path[1].(*ast.ImportSpec); spec.Name == nil {
    79  			spec.Name = &ast.Ident{NamePos: spec.Path.Pos(), Name: r.to}
    80  			info.Defs[spec.Name] = from
    81  		}
    82  	}
    83  }
    84  
    85  // checkInPackageBlock performs safety checks for renames of
    86  // func/var/const/type objects in the package block.
    87  func (r *renamer) checkInPackageBlock(from types.Object) {
    88  	// Check that there are no references to the name from another
    89  	// package if the renaming would make it unexported.
    90  	if ast.IsExported(from.Name()) && !ast.IsExported(r.to) {
    91  		for pkg, info := range r.packages {
    92  			if pkg == from.Pkg() {
    93  				continue
    94  			}
    95  			if id := someUse(info, from); id != nil &&
    96  				!r.checkExport(id, pkg, from) {
    97  				break
    98  			}
    99  		}
   100  	}
   101  
   102  	info := r.packages[from.Pkg()]
   103  
   104  	// Check that in the package block, "init" is a function, and never referenced.
   105  	if r.to == "init" {
   106  		kind := objectKind(from)
   107  		if kind == "func" {
   108  			// Reject if intra-package references to it exist.
   109  			for id, obj := range info.Uses {
   110  				if obj == from {
   111  					r.errorf(from.Pos(),
   112  						"renaming this func %q to %q would make it a package initializer",
   113  						from.Name(), r.to)
   114  					r.errorf(id.Pos(), "\tbut references to it exist")
   115  					break
   116  				}
   117  			}
   118  		} else {
   119  			r.errorf(from.Pos(), "you cannot have a %s at package level named %q",
   120  				kind, r.to)
   121  		}
   122  	}
   123  
   124  	// Check for conflicts between package block and all file blocks.
   125  	for _, f := range info.Files {
   126  		fileScope := info.Info.Scopes[f]
   127  		b, prev := fileScope.LookupParent(r.to, token.NoPos)
   128  		if b == fileScope {
   129  			r.errorf(from.Pos(), "renaming this %s %q to %q would conflict",
   130  				objectKind(from), from.Name(), r.to)
   131  			r.errorf(prev.Pos(), "\twith this %s",
   132  				objectKind(prev))
   133  			return // since checkInPackageBlock would report redundant errors
   134  		}
   135  	}
   136  
   137  	// Check for conflicts in lexical scope.
   138  	if from.Exported() {
   139  		for _, info := range r.packages {
   140  			r.checkInLexicalScope(from, info)
   141  		}
   142  	} else {
   143  		r.checkInLexicalScope(from, info)
   144  	}
   145  }
   146  
   147  func (r *renamer) checkInLocalScope(from types.Object) {
   148  	info := r.packages[from.Pkg()]
   149  
   150  	// Is this object an implicit local var for a type switch?
   151  	// Each case has its own var, whose position is the decl of y,
   152  	// but Ident in that decl does not appear in the Uses map.
   153  	//
   154  	//   switch y := x.(type) {	 // Defs[Ident(y)] is undefined
   155  	//   case int:    print(y)       // Implicits[CaseClause(int)]    = Var(y_int)
   156  	//   case string: print(y)       // Implicits[CaseClause(string)] = Var(y_string)
   157  	//   }
   158  	//
   159  	var isCaseVar bool
   160  	for syntax, obj := range info.Implicits {
   161  		if _, ok := syntax.(*ast.CaseClause); ok && obj.Pos() == from.Pos() {
   162  			isCaseVar = true
   163  			r.check(obj)
   164  		}
   165  	}
   166  
   167  	r.checkInLexicalScope(from, info)
   168  
   169  	// Finally, if this was a type switch, change the variable y.
   170  	if isCaseVar {
   171  		_, path, _ := r.iprog.PathEnclosingInterval(from.Pos(), from.Pos())
   172  		path[0].(*ast.Ident).Name = r.to // path is [Ident AssignStmt TypeSwitchStmt...]
   173  	}
   174  }
   175  
   176  // checkInLexicalScope performs safety checks that a renaming does not
   177  // change the lexical reference structure of the specified package.
   178  //
   179  // For objects in lexical scope, there are three kinds of conflicts:
   180  // same-, sub-, and super-block conflicts.  We will illustrate all three
   181  // using this example:
   182  //
   183  //	var x int
   184  //	var z int
   185  //
   186  //	func f(y int) {
   187  //		print(x)
   188  //		print(y)
   189  //	}
   190  //
   191  // Renaming x to z encounters a SAME-BLOCK CONFLICT, because an object
   192  // with the new name already exists, defined in the same lexical block
   193  // as the old object.
   194  //
   195  // Renaming x to y encounters a SUB-BLOCK CONFLICT, because there exists
   196  // a reference to x from within (what would become) a hole in its scope.
   197  // The definition of y in an (inner) sub-block would cast a shadow in
   198  // the scope of the renamed variable.
   199  //
   200  // Renaming y to x encounters a SUPER-BLOCK CONFLICT.  This is the
   201  // converse situation: there is an existing definition of the new name
   202  // (x) in an (enclosing) super-block, and the renaming would create a
   203  // hole in its scope, within which there exist references to it.  The
   204  // new name casts a shadow in scope of the existing definition of x in
   205  // the super-block.
   206  //
   207  // Removing the old name (and all references to it) is always safe, and
   208  // requires no checks.
   209  func (r *renamer) checkInLexicalScope(from types.Object, info *loader.PackageInfo) {
   210  	b := from.Parent() // the block defining the 'from' object
   211  	if b != nil {
   212  		toBlock, to := b.LookupParent(r.to, from.Parent().End())
   213  		if toBlock == b {
   214  			// same-block conflict
   215  			r.errorf(from.Pos(), "renaming this %s %q to %q",
   216  				objectKind(from), from.Name(), r.to)
   217  			r.errorf(to.Pos(), "\tconflicts with %s in same block",
   218  				objectKind(to))
   219  			return
   220  		} else if toBlock != nil {
   221  			// Check for super-block conflict.
   222  			// The name r.to is defined in a superblock.
   223  			// Is that name referenced from within this block?
   224  			forEachLexicalRef(info, to, func(id *ast.Ident, block *types.Scope) bool {
   225  				_, obj := lexicalLookup(block, from.Name(), id.Pos())
   226  				if obj == from {
   227  					// super-block conflict
   228  					r.errorf(from.Pos(), "renaming this %s %q to %q",
   229  						objectKind(from), from.Name(), r.to)
   230  					r.errorf(id.Pos(), "\twould shadow this reference")
   231  					r.errorf(to.Pos(), "\tto the %s declared here",
   232  						objectKind(to))
   233  					return false // stop
   234  				}
   235  				return true
   236  			})
   237  		}
   238  	}
   239  
   240  	// Check for sub-block conflict.
   241  	// Is there an intervening definition of r.to between
   242  	// the block defining 'from' and some reference to it?
   243  	forEachLexicalRef(info, from, func(id *ast.Ident, block *types.Scope) bool {
   244  		// Find the block that defines the found reference.
   245  		// It may be an ancestor.
   246  		fromBlock, _ := lexicalLookup(block, from.Name(), id.Pos())
   247  
   248  		// See what r.to would resolve to in the same scope.
   249  		toBlock, to := lexicalLookup(block, r.to, id.Pos())
   250  		if to != nil {
   251  			// sub-block conflict
   252  			if deeper(toBlock, fromBlock) {
   253  				r.errorf(from.Pos(), "renaming this %s %q to %q",
   254  					objectKind(from), from.Name(), r.to)
   255  				r.errorf(id.Pos(), "\twould cause this reference to become shadowed")
   256  				r.errorf(to.Pos(), "\tby this intervening %s definition",
   257  					objectKind(to))
   258  				return false // stop
   259  			}
   260  		}
   261  		return true
   262  	})
   263  
   264  	// Renaming a type that is used as an embedded field
   265  	// requires renaming the field too. e.g.
   266  	// 	type T int // if we rename this to U..
   267  	// 	var s struct {T}
   268  	// 	print(s.T) // ...this must change too
   269  	if _, ok := from.(*types.TypeName); ok {
   270  		for id, obj := range info.Uses {
   271  			if obj == from {
   272  				if field := info.Defs[id]; field != nil {
   273  					r.check(field)
   274  				}
   275  			}
   276  		}
   277  	}
   278  }
   279  
   280  // lexicalLookup is like (*types.Scope).LookupParent but respects the
   281  // environment visible at pos.  It assumes the relative position
   282  // information is correct with each file.
   283  func lexicalLookup(block *types.Scope, name string, pos token.Pos) (*types.Scope, types.Object) {
   284  	for b := block; b != nil; b = b.Parent() {
   285  		obj := b.Lookup(name)
   286  		// The scope of a package-level object is the entire package,
   287  		// so ignore pos in that case.
   288  		// No analogous clause is needed for file-level objects
   289  		// since no reference can appear before an import decl.
   290  		if obj != nil && (b == obj.Pkg().Scope() || obj.Pos() < pos) {
   291  			return b, obj
   292  		}
   293  	}
   294  	return nil, nil
   295  }
   296  
   297  // deeper reports whether block x is lexically deeper than y.
   298  func deeper(x, y *types.Scope) bool {
   299  	if x == y || x == nil {
   300  		return false
   301  	} else if y == nil {
   302  		return true
   303  	} else {
   304  		return deeper(x.Parent(), y.Parent())
   305  	}
   306  }
   307  
   308  // forEachLexicalRef calls fn(id, block) for each identifier id in package
   309  // info that is a reference to obj in lexical scope.  block is the
   310  // lexical block enclosing the reference.  If fn returns false the
   311  // iteration is terminated and findLexicalRefs returns false.
   312  func forEachLexicalRef(info *loader.PackageInfo, obj types.Object, fn func(id *ast.Ident, block *types.Scope) bool) bool {
   313  	ok := true
   314  	var stack []ast.Node
   315  
   316  	var visit func(n ast.Node) bool
   317  	visit = func(n ast.Node) bool {
   318  		if n == nil {
   319  			stack = stack[:len(stack)-1] // pop
   320  			return false
   321  		}
   322  		if !ok {
   323  			return false // bail out
   324  		}
   325  
   326  		stack = append(stack, n) // push
   327  		switch n := n.(type) {
   328  		case *ast.Ident:
   329  			if info.Uses[n] == obj {
   330  				block := enclosingBlock(&info.Info, stack)
   331  				if !fn(n, block) {
   332  					ok = false
   333  				}
   334  			}
   335  			return visit(nil) // pop stack
   336  
   337  		case *ast.SelectorExpr:
   338  			// don't visit n.Sel
   339  			ast.Inspect(n.X, visit)
   340  			return visit(nil) // pop stack, don't descend
   341  
   342  		case *ast.CompositeLit:
   343  			// Handle recursion ourselves for struct literals
   344  			// so we don't visit field identifiers.
   345  			tv := info.Types[n]
   346  			if _, ok := deref(tv.Type).Underlying().(*types.Struct); ok {
   347  				if n.Type != nil {
   348  					ast.Inspect(n.Type, visit)
   349  				}
   350  				for _, elt := range n.Elts {
   351  					if kv, ok := elt.(*ast.KeyValueExpr); ok {
   352  						ast.Inspect(kv.Value, visit)
   353  					} else {
   354  						ast.Inspect(elt, visit)
   355  					}
   356  				}
   357  				return visit(nil) // pop stack, don't descend
   358  			}
   359  		}
   360  		return true
   361  	}
   362  
   363  	for _, f := range info.Files {
   364  		ast.Inspect(f, visit)
   365  		if len(stack) != 0 {
   366  			panic(stack)
   367  		}
   368  		if !ok {
   369  			break
   370  		}
   371  	}
   372  	return ok
   373  }
   374  
   375  // enclosingBlock returns the innermost block enclosing the specified
   376  // AST node, specified in the form of a path from the root of the file,
   377  // [file...n].
   378  func enclosingBlock(info *types.Info, stack []ast.Node) *types.Scope {
   379  	for i := range stack {
   380  		n := stack[len(stack)-1-i]
   381  		// For some reason, go/types always associates a
   382  		// function's scope with its FuncType.
   383  		// TODO(adonovan): feature or a bug?
   384  		switch f := n.(type) {
   385  		case *ast.FuncDecl:
   386  			n = f.Type
   387  		case *ast.FuncLit:
   388  			n = f.Type
   389  		}
   390  		if b := info.Scopes[n]; b != nil {
   391  			return b
   392  		}
   393  	}
   394  	panic("no Scope for *ast.File")
   395  }
   396  
   397  func (r *renamer) checkLabel(label *types.Label) {
   398  	// Check there are no identical labels in the function's label block.
   399  	// (Label blocks don't nest, so this is easy.)
   400  	if prev := label.Parent().Lookup(r.to); prev != nil {
   401  		r.errorf(label.Pos(), "renaming this label %q to %q", label.Name(), prev.Name())
   402  		r.errorf(prev.Pos(), "\twould conflict with this one")
   403  	}
   404  }
   405  
   406  // checkStructField checks that the field renaming will not cause
   407  // conflicts at its declaration, or ambiguity or changes to any selection.
   408  func (r *renamer) checkStructField(from *types.Var) {
   409  	// Check that the struct declaration is free of field conflicts,
   410  	// and field/method conflicts.
   411  
   412  	// go/types offers no easy way to get from a field (or interface
   413  	// method) to its declaring struct (or interface), so we must
   414  	// ascend the AST.
   415  	info, path, _ := r.iprog.PathEnclosingInterval(from.Pos(), from.Pos())
   416  	// path matches this pattern:
   417  	// [Ident SelectorExpr? StarExpr? Field FieldList StructType ParenExpr* ... File]
   418  
   419  	// Ascend to FieldList.
   420  	var i int
   421  	for {
   422  		if _, ok := path[i].(*ast.FieldList); ok {
   423  			break
   424  		}
   425  		i++
   426  	}
   427  	i++
   428  	tStruct := path[i].(*ast.StructType)
   429  	i++
   430  	// Ascend past parens (unlikely).
   431  	for {
   432  		_, ok := path[i].(*ast.ParenExpr)
   433  		if !ok {
   434  			break
   435  		}
   436  		i++
   437  	}
   438  	if spec, ok := path[i].(*ast.TypeSpec); ok {
   439  		// This struct is also a named type.
   440  		// We must check for direct (non-promoted) field/field
   441  		// and method/field conflicts.
   442  		named := info.Defs[spec.Name].Type()
   443  		prev, indices, _ := types.LookupFieldOrMethod(named, true, info.Pkg, r.to)
   444  		if len(indices) == 1 {
   445  			r.errorf(from.Pos(), "renaming this field %q to %q",
   446  				from.Name(), r.to)
   447  			r.errorf(prev.Pos(), "\twould conflict with this %s",
   448  				objectKind(prev))
   449  			return // skip checkSelections to avoid redundant errors
   450  		}
   451  	} else {
   452  		// This struct is not a named type.
   453  		// We need only check for direct (non-promoted) field/field conflicts.
   454  		T := info.Types[tStruct].Type.Underlying().(*types.Struct)
   455  		for i := 0; i < T.NumFields(); i++ {
   456  			if prev := T.Field(i); prev.Name() == r.to {
   457  				r.errorf(from.Pos(), "renaming this field %q to %q",
   458  					from.Name(), r.to)
   459  				r.errorf(prev.Pos(), "\twould conflict with this field")
   460  				return // skip checkSelections to avoid redundant errors
   461  			}
   462  		}
   463  	}
   464  
   465  	// Renaming an anonymous field requires renaming the type too. e.g.
   466  	// 	print(s.T)       // if we rename T to U,
   467  	// 	type T int       // this and
   468  	// 	var s struct {T} // this must change too.
   469  	if from.Anonymous() {
   470  		if named, ok := from.Type().(*types.Named); ok {
   471  			r.check(named.Obj())
   472  		} else if named, ok := deref(from.Type()).(*types.Named); ok {
   473  			r.check(named.Obj())
   474  		}
   475  	}
   476  
   477  	// Check integrity of existing (field and method) selections.
   478  	r.checkSelections(from)
   479  }
   480  
   481  // checkSelection checks that all uses and selections that resolve to
   482  // the specified object would continue to do so after the renaming.
   483  func (r *renamer) checkSelections(from types.Object) {
   484  	for pkg, info := range r.packages {
   485  		if id := someUse(info, from); id != nil {
   486  			if !r.checkExport(id, pkg, from) {
   487  				return
   488  			}
   489  		}
   490  
   491  		for syntax, sel := range info.Selections {
   492  			// There may be extant selections of only the old
   493  			// name or only the new name, so we must check both.
   494  			// (If neither, the renaming is sound.)
   495  			//
   496  			// In both cases, we wish to compare the lengths
   497  			// of the implicit field path (Selection.Index)
   498  			// to see if the renaming would change it.
   499  			//
   500  			// If a selection that resolves to 'from', when renamed,
   501  			// would yield a path of the same or shorter length,
   502  			// this indicates ambiguity or a changed referent,
   503  			// analogous to same- or sub-block lexical conflict.
   504  			//
   505  			// If a selection using the name 'to' would
   506  			// yield a path of the same or shorter length,
   507  			// this indicates ambiguity or shadowing,
   508  			// analogous to same- or super-block lexical conflict.
   509  
   510  			// TODO(adonovan): fix: derive from Types[syntax.X].Mode
   511  			// TODO(adonovan): test with pointer, value, addressable value.
   512  			isAddressable := true
   513  
   514  			if sel.Obj() == from {
   515  				if obj, indices, _ := types.LookupFieldOrMethod(sel.Recv(), isAddressable, from.Pkg(), r.to); obj != nil {
   516  					// Renaming this existing selection of
   517  					// 'from' may block access to an existing
   518  					// type member named 'to'.
   519  					delta := len(indices) - len(sel.Index())
   520  					if delta > 0 {
   521  						continue // no ambiguity
   522  					}
   523  					r.selectionConflict(from, delta, syntax, obj)
   524  					return
   525  				}
   526  
   527  			} else if sel.Obj().Name() == r.to {
   528  				if obj, indices, _ := types.LookupFieldOrMethod(sel.Recv(), isAddressable, from.Pkg(), from.Name()); obj == from {
   529  					// Renaming 'from' may cause this existing
   530  					// selection of the name 'to' to change
   531  					// its meaning.
   532  					delta := len(indices) - len(sel.Index())
   533  					if delta > 0 {
   534  						continue //  no ambiguity
   535  					}
   536  					r.selectionConflict(from, -delta, syntax, sel.Obj())
   537  					return
   538  				}
   539  			}
   540  		}
   541  	}
   542  }
   543  
   544  func (r *renamer) selectionConflict(from types.Object, delta int, syntax *ast.SelectorExpr, obj types.Object) {
   545  	r.errorf(from.Pos(), "renaming this %s %q to %q",
   546  		objectKind(from), from.Name(), r.to)
   547  
   548  	switch {
   549  	case delta < 0:
   550  		// analogous to sub-block conflict
   551  		r.errorf(syntax.Sel.Pos(),
   552  			"\twould change the referent of this selection")
   553  		r.errorf(obj.Pos(), "\tof this %s", objectKind(obj))
   554  	case delta == 0:
   555  		// analogous to same-block conflict
   556  		r.errorf(syntax.Sel.Pos(),
   557  			"\twould make this reference ambiguous")
   558  		r.errorf(obj.Pos(), "\twith this %s", objectKind(obj))
   559  	case delta > 0:
   560  		// analogous to super-block conflict
   561  		r.errorf(syntax.Sel.Pos(),
   562  			"\twould shadow this selection")
   563  		r.errorf(obj.Pos(), "\tof the %s declared here",
   564  			objectKind(obj))
   565  	}
   566  }
   567  
   568  // checkMethod performs safety checks for renaming a method.
   569  // There are three hazards:
   570  //   - declaration conflicts
   571  //   - selection ambiguity/changes
   572  //   - entailed renamings of assignable concrete/interface types.
   573  //
   574  // We reject renamings initiated at concrete methods if it would
   575  // change the assignability relation.  For renamings of abstract
   576  // methods, we rename all methods transitively coupled to it via
   577  // assignability.
   578  func (r *renamer) checkMethod(from *types.Func) {
   579  	// e.g. error.Error
   580  	if from.Pkg() == nil {
   581  		r.errorf(from.Pos(), "you cannot rename built-in method %s", from)
   582  		return
   583  	}
   584  
   585  	// ASSIGNABILITY: We reject renamings of concrete methods that
   586  	// would break a 'satisfy' constraint; but renamings of abstract
   587  	// methods are allowed to proceed, and we rename affected
   588  	// concrete and abstract methods as necessary.  It is the
   589  	// initial method that determines the policy.
   590  
   591  	// Check for conflict at point of declaration.
   592  	// Check to ensure preservation of assignability requirements.
   593  	R := recv(from).Type()
   594  	if isInterface(R) {
   595  		// Abstract method
   596  
   597  		// declaration
   598  		prev, _, _ := types.LookupFieldOrMethod(R, false, from.Pkg(), r.to)
   599  		if prev != nil {
   600  			r.errorf(from.Pos(), "renaming this interface method %q to %q",
   601  				from.Name(), r.to)
   602  			r.errorf(prev.Pos(), "\twould conflict with this method")
   603  			return
   604  		}
   605  
   606  		// Check all interfaces that embed this one for
   607  		// declaration conflicts too.
   608  		for _, info := range r.packages {
   609  			// Start with named interface types (better errors)
   610  			for _, obj := range info.Defs {
   611  				if obj, ok := obj.(*types.TypeName); ok && isInterface(obj.Type()) {
   612  					f, _, _ := types.LookupFieldOrMethod(
   613  						obj.Type(), false, from.Pkg(), from.Name())
   614  					if f == nil {
   615  						continue
   616  					}
   617  					t, _, _ := types.LookupFieldOrMethod(
   618  						obj.Type(), false, from.Pkg(), r.to)
   619  					if t == nil {
   620  						continue
   621  					}
   622  					r.errorf(from.Pos(), "renaming this interface method %q to %q",
   623  						from.Name(), r.to)
   624  					r.errorf(t.Pos(), "\twould conflict with this method")
   625  					r.errorf(obj.Pos(), "\tin named interface type %q", obj.Name())
   626  				}
   627  			}
   628  
   629  			// Now look at all literal interface types (includes named ones again).
   630  			for e, tv := range info.Types {
   631  				if e, ok := e.(*ast.InterfaceType); ok {
   632  					_ = e
   633  					_ = tv.Type.(*types.Interface)
   634  					// TODO(adonovan): implement same check as above.
   635  				}
   636  			}
   637  		}
   638  
   639  		// assignability
   640  		//
   641  		// Find the set of concrete or abstract methods directly
   642  		// coupled to abstract method 'from' by some
   643  		// satisfy.Constraint, and rename them too.
   644  		for key := range r.satisfy() {
   645  			// key = (lhs, rhs) where lhs is always an interface.
   646  
   647  			lsel := r.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
   648  			if lsel == nil {
   649  				continue
   650  			}
   651  			rmethods := r.msets.MethodSet(key.RHS)
   652  			rsel := rmethods.Lookup(from.Pkg(), from.Name())
   653  			if rsel == nil {
   654  				continue
   655  			}
   656  
   657  			// If both sides have a method of this name,
   658  			// and one of them is m, the other must be coupled.
   659  			var coupled *types.Func
   660  			switch from {
   661  			case lsel.Obj():
   662  				coupled = rsel.Obj().(*types.Func)
   663  			case rsel.Obj():
   664  				coupled = lsel.Obj().(*types.Func)
   665  			default:
   666  				continue
   667  			}
   668  
   669  			// We must treat concrete-to-interface
   670  			// constraints like an implicit selection C.f of
   671  			// each interface method I.f, and check that the
   672  			// renaming leaves the selection unchanged and
   673  			// unambiguous.
   674  			//
   675  			// Fun fact: the implicit selection of C.f
   676  			// 	type I interface{f()}
   677  			// 	type C struct{I}
   678  			// 	func (C) g()
   679  			//      var _ I = C{} // here
   680  			// yields abstract method I.f.  This can make error
   681  			// messages less than obvious.
   682  			//
   683  			if !isInterface(key.RHS) {
   684  				// The logic below was derived from checkSelections.
   685  
   686  				rtosel := rmethods.Lookup(from.Pkg(), r.to)
   687  				if rtosel != nil {
   688  					rto := rtosel.Obj().(*types.Func)
   689  					delta := len(rsel.Index()) - len(rtosel.Index())
   690  					if delta < 0 {
   691  						continue // no ambiguity
   692  					}
   693  
   694  					// TODO(adonovan): record the constraint's position.
   695  					keyPos := token.NoPos
   696  
   697  					r.errorf(from.Pos(), "renaming this method %q to %q",
   698  						from.Name(), r.to)
   699  					if delta == 0 {
   700  						// analogous to same-block conflict
   701  						r.errorf(keyPos, "\twould make the %s method of %s invoked via interface %s ambiguous",
   702  							r.to, key.RHS, key.LHS)
   703  						r.errorf(rto.Pos(), "\twith (%s).%s",
   704  							recv(rto).Type(), r.to)
   705  					} else {
   706  						// analogous to super-block conflict
   707  						r.errorf(keyPos, "\twould change the %s method of %s invoked via interface %s",
   708  							r.to, key.RHS, key.LHS)
   709  						r.errorf(coupled.Pos(), "\tfrom (%s).%s",
   710  							recv(coupled).Type(), r.to)
   711  						r.errorf(rto.Pos(), "\tto (%s).%s",
   712  							recv(rto).Type(), r.to)
   713  					}
   714  					return // one error is enough
   715  				}
   716  			}
   717  
   718  			if !r.changeMethods {
   719  				// This should be unreachable.
   720  				r.errorf(from.Pos(), "internal error: during renaming of abstract method %s", from)
   721  				r.errorf(coupled.Pos(), "\tchangedMethods=false, coupled method=%s", coupled)
   722  				r.errorf(from.Pos(), "\tPlease file a bug report")
   723  				return
   724  			}
   725  
   726  			// Rename the coupled method to preserve assignability.
   727  			r.check(coupled)
   728  		}
   729  	} else {
   730  		// Concrete method
   731  
   732  		// declaration
   733  		prev, indices, _ := types.LookupFieldOrMethod(R, true, from.Pkg(), r.to)
   734  		if prev != nil && len(indices) == 1 {
   735  			r.errorf(from.Pos(), "renaming this method %q to %q",
   736  				from.Name(), r.to)
   737  			r.errorf(prev.Pos(), "\twould conflict with this %s",
   738  				objectKind(prev))
   739  			return
   740  		}
   741  
   742  		// assignability
   743  		//
   744  		// Find the set of abstract methods coupled to concrete
   745  		// method 'from' by some satisfy.Constraint, and rename
   746  		// them too.
   747  		//
   748  		// Coupling may be indirect, e.g. I.f <-> C.f via type D.
   749  		//
   750  		// 	type I interface {f()}
   751  		//	type C int
   752  		//	type (C) f()
   753  		//	type D struct{C}
   754  		//	var _ I = D{}
   755  		//
   756  		for key := range r.satisfy() {
   757  			// key = (lhs, rhs) where lhs is always an interface.
   758  			if isInterface(key.RHS) {
   759  				continue
   760  			}
   761  			rsel := r.msets.MethodSet(key.RHS).Lookup(from.Pkg(), from.Name())
   762  			if rsel == nil || rsel.Obj() != from {
   763  				continue // rhs does not have the method
   764  			}
   765  			lsel := r.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
   766  			if lsel == nil {
   767  				continue
   768  			}
   769  			imeth := lsel.Obj().(*types.Func)
   770  
   771  			// imeth is the abstract method (e.g. I.f)
   772  			// and key.RHS is the concrete coupling type (e.g. D).
   773  			if !r.changeMethods {
   774  				r.errorf(from.Pos(), "renaming this method %q to %q",
   775  					from.Name(), r.to)
   776  				var pos token.Pos
   777  				var iface string
   778  
   779  				I := recv(imeth).Type()
   780  				if named, ok := I.(*types.Named); ok {
   781  					pos = named.Obj().Pos()
   782  					iface = "interface " + named.Obj().Name()
   783  				} else {
   784  					pos = from.Pos()
   785  					iface = I.String()
   786  				}
   787  				r.errorf(pos, "\twould make %s no longer assignable to %s",
   788  					key.RHS, iface)
   789  				r.errorf(imeth.Pos(), "\t(rename %s.%s if you intend to change both types)",
   790  					I, from.Name())
   791  				return // one error is enough
   792  			}
   793  
   794  			// Rename the coupled interface method to preserve assignability.
   795  			r.check(imeth)
   796  		}
   797  	}
   798  
   799  	// Check integrity of existing (field and method) selections.
   800  	// We skip this if there were errors above, to avoid redundant errors.
   801  	r.checkSelections(from)
   802  }
   803  
   804  func (r *renamer) checkExport(id *ast.Ident, pkg *types.Package, from types.Object) bool {
   805  	// Reject cross-package references if r.to is unexported.
   806  	// (Such references may be qualified identifiers or field/method
   807  	// selections.)
   808  	if !ast.IsExported(r.to) && pkg != from.Pkg() {
   809  		r.errorf(from.Pos(),
   810  			"renaming this %s %q to %q would make it unexported",
   811  			objectKind(from), from.Name(), r.to)
   812  		r.errorf(id.Pos(), "\tbreaking references from packages such as %q",
   813  			pkg.Path())
   814  		return false
   815  	}
   816  	return true
   817  }
   818  
   819  // satisfy returns the set of interface satisfaction constraints.
   820  func (r *renamer) satisfy() map[satisfy.Constraint]bool {
   821  	if r.satisfyConstraints == nil {
   822  		// Compute on demand: it's expensive.
   823  		var f satisfy.Finder
   824  		for _, info := range r.packages {
   825  			f.Find(&info.Info, info.Files)
   826  		}
   827  		r.satisfyConstraints = f.Result
   828  	}
   829  	return r.satisfyConstraints
   830  }
   831  
   832  // -- helpers ----------------------------------------------------------
   833  
   834  // recv returns the method's receiver.
   835  func recv(meth *types.Func) *types.Var {
   836  	return meth.Type().(*types.Signature).Recv()
   837  }
   838  
   839  // someUse returns an arbitrary use of obj within info.
   840  func someUse(info *loader.PackageInfo, obj types.Object) *ast.Ident {
   841  	for id, o := range info.Uses {
   842  		if o == obj {
   843  			return id
   844  		}
   845  	}
   846  	return nil
   847  }
   848  
   849  // -- Plundered from golang.org/x/tools/go/ssa -----------------
   850  
   851  func isInterface(T types.Type) bool { return types.IsInterface(T) }
   852  
   853  func deref(typ types.Type) types.Type {
   854  	if p, _ := typ.(*types.Pointer); p != nil {
   855  		return p.Elem()
   856  	}
   857  	return typ
   858  }
   859
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