Source file src/go/types/generate_test.go

     1  // Copyright 2023 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  // This file implements a custom generator to create various go/types
     6  // source files from the corresponding types2 files.
     7  
     8  package types_test
     9  
    10  import (
    11  	"bytes"
    12  	"flag"
    13  	"fmt"
    14  	"go/ast"
    15  	"go/format"
    16  	"go/parser"
    17  	"go/token"
    18  	"internal/diff"
    19  	"os"
    20  	"path/filepath"
    21  	"runtime"
    22  	"strings"
    23  	"testing"
    24  )
    25  
    26  var filesToWrite = flag.String("write", "", `go/types files to generate, or "all" for all files`)
    27  
    28  const (
    29  	srcDir = "/src/cmd/compile/internal/types2/"
    30  	dstDir = "/src/go/types/"
    31  )
    32  
    33  // TestGenerate verifies that generated files in go/types match their types2
    34  // counterpart. If -write is set, this test actually writes the expected
    35  // content to go/types; otherwise, it just compares with the existing content.
    36  func TestGenerate(t *testing.T) {
    37  	// If filesToWrite is set, write the generated content to disk.
    38  	// In the special case of "all", write all files in filemap.
    39  	write := *filesToWrite != ""
    40  	var files []string // files to process
    41  	if *filesToWrite != "" && *filesToWrite != "all" {
    42  		files = strings.Split(*filesToWrite, ",")
    43  	} else {
    44  		for file := range filemap {
    45  			files = append(files, file)
    46  		}
    47  	}
    48  
    49  	for _, filename := range files {
    50  		generate(t, filename, write)
    51  	}
    52  }
    53  
    54  func generate(t *testing.T, filename string, write bool) {
    55  	// parse src (cmd/compile/internal/types2)
    56  	srcFilename := filepath.FromSlash(runtime.GOROOT() + srcDir + filename)
    57  	file, err := parser.ParseFile(fset, srcFilename, nil, parser.ParseComments)
    58  	if err != nil {
    59  		t.Fatal(err)
    60  	}
    61  
    62  	// fix package name
    63  	file.Name.Name = strings.ReplaceAll(file.Name.Name, "types2", "types")
    64  
    65  	// rewrite AST as needed
    66  	if action := filemap[filename]; action != nil {
    67  		action(file)
    68  	}
    69  
    70  	// format AST
    71  	var buf bytes.Buffer
    72  	rel, _ := filepath.Rel(dstDir, srcDir)
    73  	fmt.Fprintf(&buf, "// Code generated by \"go test -run=Generate -write=all\"; DO NOT EDIT.\n")
    74  	fmt.Fprintf(&buf, "// Source: %s/%s\n\n", filepath.ToSlash(rel), filename)
    75  	if err := format.Node(&buf, fset, file); err != nil {
    76  		t.Fatal(err)
    77  	}
    78  	generatedContent := buf.Bytes()
    79  
    80  	// read dst (go/types)
    81  	dstFilename := filepath.FromSlash(runtime.GOROOT() + dstDir + filename)
    82  	onDiskContent, err := os.ReadFile(dstFilename)
    83  	if err != nil {
    84  		t.Fatalf("reading %q: %v", filename, err)
    85  	}
    86  
    87  	// compare on-disk dst with buffer generated from src.
    88  	if d := diff.Diff(filename+" (on disk in "+dstDir+")", onDiskContent, filename+" (generated from "+srcDir+")", generatedContent); d != nil {
    89  		if write {
    90  			t.Logf("applying change:\n%s", d)
    91  			if err := os.WriteFile(dstFilename, generatedContent, 0o644); err != nil {
    92  				t.Fatalf("writing %q: %v", filename, err)
    93  			}
    94  		} else {
    95  			t.Errorf("file on disk in %s is stale:\n%s", dstDir, d)
    96  		}
    97  	}
    98  }
    99  
   100  type action func(in *ast.File)
   101  
   102  var filemap = map[string]action{
   103  	"alias.go": fixTokenPos,
   104  	"assignments.go": func(f *ast.File) {
   105  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   106  		renameSelectorExprs(f, "syntax.Name->ast.Ident", "ident.Value->ident.Name", "ast.Pos->token.Pos") // must happen before renaming identifiers
   107  		renameIdents(f, "syntax->ast", "poser->positioner", "nopos->noposn")
   108  	},
   109  	"array.go":          nil,
   110  	"api_predicates.go": nil,
   111  	"basic.go":          nil,
   112  	"builtins.go": func(f *ast.File) {
   113  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   114  		renameIdents(f, "syntax->ast")
   115  		renameSelectors(f, "ArgList->Args")
   116  		fixSelValue(f)
   117  		fixAtPosCall(f)
   118  	},
   119  	"builtins_test.go": func(f *ast.File) {
   120  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`, `"cmd/compile/internal/types2"->"go/types"`)
   121  		renameSelectorExprs(f, "syntax.Name->ast.Ident", "p.Value->p.Name") // must happen before renaming identifiers
   122  		renameIdents(f, "syntax->ast")
   123  	},
   124  	"chan.go":         nil,
   125  	"const.go":        fixTokenPos,
   126  	"context.go":      nil,
   127  	"context_test.go": nil,
   128  	"conversions.go":  nil,
   129  	"cycles.go": func(f *ast.File) {
   130  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   131  		renameSelectorExprs(f, "syntax.Name->ast.Ident", "rhs.Value->rhs.Name")
   132  		renameSelectors(f, "Trace->_Trace")
   133  	},
   134  	"errors_test.go":  func(f *ast.File) { renameIdents(f, "nopos->noposn") },
   135  	"errsupport.go":   nil,
   136  	"gccgosizes.go":   nil,
   137  	"gcsizes.go":      func(f *ast.File) { renameIdents(f, "IsSyncAtomicAlign64->_IsSyncAtomicAlign64") },
   138  	"hilbert_test.go": func(f *ast.File) { renameImportPath(f, `"cmd/compile/internal/types2"->"go/types"`) },
   139  	"infer.go":        func(f *ast.File) { fixTokenPos(f); fixInferSig(f) },
   140  	"initorder.go":    nil,
   141  	// "initorder.go": fixErrErrorfCall, // disabled for now due to unresolved error_ use implications for gopls
   142  	"instantiate.go":      func(f *ast.File) { fixTokenPos(f); fixCheckErrorfCall(f) },
   143  	"instantiate_test.go": func(f *ast.File) { renameImportPath(f, `"cmd/compile/internal/types2"->"go/types"`) },
   144  	"literals.go": func(f *ast.File) {
   145  		insertImportPath(f, `"go/token"`)
   146  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   147  		renameSelectorExprs(f,
   148  			"syntax.IntLit->token.INT", "syntax.FloatLit->token.FLOAT", "syntax.ImagLit->token.IMAG",
   149  			"syntax.Name->ast.Ident", "key.Value->key.Name", "atyp.Elem->atyp.Elt") // must happen before renaming identifiers
   150  		renameIdents(f, "syntax->ast")
   151  		renameSelectors(f, "ElemList->Elts")
   152  	},
   153  	"lookup.go":    fixTokenPos,
   154  	"main_test.go": nil,
   155  	"map.go":       nil,
   156  	"mono.go": func(f *ast.File) {
   157  		fixTokenPos(f)
   158  		insertImportPath(f, `"go/ast"`)
   159  		renameSelectorExprs(f, "syntax.Expr->ast.Expr")
   160  	},
   161  	"named.go":  func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
   162  	"object.go": func(f *ast.File) { fixTokenPos(f); renameIdents(f, "NewTypeNameLazy->_NewTypeNameLazy") },
   163  	// TODO(gri) needs adjustments for TestObjectString - disabled for now
   164  	// "object_test.go": func(f *ast.File) { renameImportPath(f, `"cmd/compile/internal/types2"->"go/types"`) },
   165  	"objset.go": nil,
   166  	"operand.go": func(f *ast.File) {
   167  		insertImportPath(f, `"go/token"`)
   168  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   169  		renameSelectorExprs(f,
   170  			"syntax.Pos->token.Pos", "syntax.LitKind->token.Token",
   171  			"syntax.IntLit->token.INT", "syntax.FloatLit->token.FLOAT",
   172  			"syntax.ImagLit->token.IMAG", "syntax.RuneLit->token.CHAR",
   173  			"syntax.StringLit->token.STRING") // must happen before renaming identifiers
   174  		renameIdents(f, "syntax->ast")
   175  	},
   176  	"package.go":    nil,
   177  	"pointer.go":    nil,
   178  	"predicates.go": nil,
   179  	"range.go": func(f *ast.File) {
   180  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   181  		renameSelectorExprs(f, "syntax.Name->ast.Ident", "syntax.ForStmt->ast.RangeStmt", "ident.Value->ident.Name") // must happen before renaming identifiers
   182  		renameIdents(f, "syntax->ast", "poser->positioner")
   183  	},
   184  	"recording.go": func(f *ast.File) {
   185  		renameImportPath(f, `"cmd/compile/internal/syntax"->"go/ast"`)
   186  		renameSelectorExprs(f, "syntax.Name->ast.Ident") // must happen before renaming identifiers
   187  		renameIdents(f, "syntax->ast")
   188  		fixAtPosCall(f)
   189  	},
   190  	"scope.go":         func(f *ast.File) { fixTokenPos(f); renameIdents(f, "InsertLazy->_InsertLazy") },
   191  	"selection.go":     nil,
   192  	"sizes.go":         func(f *ast.File) { renameIdents(f, "IsSyncAtomicAlign64->_IsSyncAtomicAlign64") },
   193  	"slice.go":         nil,
   194  	"subst.go":         func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
   195  	"termlist.go":      nil,
   196  	"termlist_test.go": nil,
   197  	"trie.go":          nil,
   198  	"trie_test.go":     nil,
   199  	"tuple.go":         nil,
   200  	"typelists.go":     nil,
   201  	"typeset.go":       func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
   202  	"typeparam.go":     nil,
   203  	"typeterm_test.go": nil,
   204  	"typeterm.go":      nil,
   205  	"typestring.go":    nil,
   206  	"under.go":         nil,
   207  	"unify.go":         fixSprintf,
   208  	"universe.go":      fixGlobalTypVarDecl,
   209  	"util_test.go":     fixTokenPos,
   210  	"validtype.go":     func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
   211  }
   212  
   213  // TODO(gri) We should be able to make these rewriters more configurable/composable.
   214  //           For now this is a good starting point.
   215  
   216  // A renameMap maps old strings to new strings.
   217  type renameMap map[string]string
   218  
   219  // makeRenameMap returns a renameMap populates from renames entries of the form "from->to".
   220  func makeRenameMap(renames ...string) renameMap {
   221  	m := make(renameMap)
   222  	for _, r := range renames {
   223  		s := strings.Split(r, "->")
   224  		if len(s) != 2 {
   225  			panic("invalid rename entry: " + r)
   226  		}
   227  		m[s[0]] = s[1]
   228  	}
   229  	return m
   230  }
   231  
   232  // rename renames the given string s if a corresponding rename exists in m.
   233  func (m renameMap) rename(s *string) {
   234  	if r, ok := m[*s]; ok {
   235  		*s = r
   236  	}
   237  }
   238  
   239  // renameSel renames a selector expression of the form a.x to b.x (where a, b are identifiers)
   240  // if m contains the ("a.x" : "b.y") key-value pair.
   241  func (m renameMap) renameSel(n *ast.SelectorExpr) {
   242  	if a, _ := n.X.(*ast.Ident); a != nil {
   243  		a_x := a.Name + "." + n.Sel.Name
   244  		if r, ok := m[a_x]; ok {
   245  			b_y := strings.Split(r, ".")
   246  			if len(b_y) != 2 {
   247  				panic("invalid selector expression: " + r)
   248  			}
   249  			a.Name = b_y[0]
   250  			n.Sel.Name = b_y[1]
   251  		}
   252  	}
   253  }
   254  
   255  // renameIdents renames identifiers: each renames entry is of the form "from->to".
   256  // Note: This doesn't change the use of the identifiers in comments.
   257  func renameIdents(f *ast.File, renames ...string) {
   258  	m := makeRenameMap(renames...)
   259  	ast.Inspect(f, func(n ast.Node) bool {
   260  		switch n := n.(type) {
   261  		case *ast.Ident:
   262  			m.rename(&n.Name)
   263  			return false
   264  		}
   265  		return true
   266  	})
   267  }
   268  
   269  // renameSelectors is like renameIdents but only looks at selectors.
   270  func renameSelectors(f *ast.File, renames ...string) {
   271  	m := makeRenameMap(renames...)
   272  	ast.Inspect(f, func(n ast.Node) bool {
   273  		switch n := n.(type) {
   274  		case *ast.SelectorExpr:
   275  			m.rename(&n.Sel.Name)
   276  			return false
   277  		}
   278  		return true
   279  	})
   280  
   281  }
   282  
   283  // renameSelectorExprs is like renameIdents but only looks at selector expressions.
   284  // Each renames entry must be of the form "x.a->y.b".
   285  func renameSelectorExprs(f *ast.File, renames ...string) {
   286  	m := makeRenameMap(renames...)
   287  	ast.Inspect(f, func(n ast.Node) bool {
   288  		switch n := n.(type) {
   289  		case *ast.SelectorExpr:
   290  			m.renameSel(n)
   291  			return false
   292  		}
   293  		return true
   294  	})
   295  }
   296  
   297  // renameImportPath is like renameIdents but renames import paths.
   298  func renameImportPath(f *ast.File, renames ...string) {
   299  	m := makeRenameMap(renames...)
   300  	ast.Inspect(f, func(n ast.Node) bool {
   301  		switch n := n.(type) {
   302  		case *ast.ImportSpec:
   303  			if n.Path.Kind != token.STRING {
   304  				panic("invalid import path")
   305  			}
   306  			m.rename(&n.Path.Value)
   307  			return false
   308  		}
   309  		return true
   310  	})
   311  }
   312  
   313  // insertImportPath inserts the given import path.
   314  // There must be at least one import declaration present already.
   315  func insertImportPath(f *ast.File, path string) {
   316  	for _, d := range f.Decls {
   317  		if g, _ := d.(*ast.GenDecl); g != nil && g.Tok == token.IMPORT {
   318  			g.Specs = append(g.Specs, &ast.ImportSpec{Path: &ast.BasicLit{ValuePos: g.End(), Kind: token.STRING, Value: path}})
   319  			return
   320  		}
   321  	}
   322  	panic("no import declaration present")
   323  }
   324  
   325  // fixTokenPos changes imports of "cmd/compile/internal/syntax" to "go/token",
   326  // uses of syntax.Pos to token.Pos, and calls to x.IsKnown() to x.IsValid().
   327  func fixTokenPos(f *ast.File) {
   328  	m := makeRenameMap(`"cmd/compile/internal/syntax"->"go/token"`, "syntax.Pos->token.Pos", "IsKnown->IsValid")
   329  	ast.Inspect(f, func(n ast.Node) bool {
   330  		switch n := n.(type) {
   331  		case *ast.ImportSpec:
   332  			// rewrite import path "cmd/compile/internal/syntax" to "go/token"
   333  			if n.Path.Kind != token.STRING {
   334  				panic("invalid import path")
   335  			}
   336  			m.rename(&n.Path.Value)
   337  			return false
   338  		case *ast.SelectorExpr:
   339  			// rewrite syntax.Pos to token.Pos
   340  			m.renameSel(n)
   341  		case *ast.CallExpr:
   342  			// rewrite x.IsKnown() to x.IsValid()
   343  			if fun, _ := n.Fun.(*ast.SelectorExpr); fun != nil && len(n.Args) == 0 {
   344  				m.rename(&fun.Sel.Name)
   345  				return false
   346  			}
   347  		}
   348  		return true
   349  	})
   350  }
   351  
   352  // fixSelValue updates the selector x.Sel.Value to x.Sel.Name.
   353  func fixSelValue(f *ast.File) {
   354  	ast.Inspect(f, func(n ast.Node) bool {
   355  		switch n := n.(type) {
   356  		case *ast.SelectorExpr:
   357  			if n.Sel.Name == "Value" {
   358  				if selx, _ := n.X.(*ast.SelectorExpr); selx != nil && selx.Sel.Name == "Sel" {
   359  					n.Sel.Name = "Name"
   360  					return false
   361  				}
   362  			}
   363  		}
   364  		return true
   365  	})
   366  }
   367  
   368  // fixInferSig updates the Checker.infer signature to use a positioner instead of a token.Position
   369  // as first argument, renames the argument from "pos" to "posn", and updates a few internal uses of
   370  // "pos" to "posn" and "posn.Pos()" respectively.
   371  func fixInferSig(f *ast.File) {
   372  	ast.Inspect(f, func(n ast.Node) bool {
   373  		switch n := n.(type) {
   374  		case *ast.FuncDecl:
   375  			if n.Name.Name == "infer" {
   376  				// rewrite (pos token.Pos, ...) to (posn positioner, ...)
   377  				par := n.Type.Params.List[0]
   378  				if len(par.Names) == 1 && par.Names[0].Name == "pos" {
   379  					par.Names[0] = newIdent(par.Names[0].Pos(), "posn")
   380  					par.Type = newIdent(par.Type.Pos(), "positioner")
   381  					return true
   382  				}
   383  			}
   384  		case *ast.CallExpr:
   385  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil {
   386  				switch selx.Sel.Name {
   387  				case "renameTParams":
   388  					// rewrite check.renameTParams(pos, ... ) to check.renameTParams(posn.Pos(), ... )
   389  					if isIdent(n.Args[0], "pos") {
   390  						pos := n.Args[0].Pos()
   391  						fun := &ast.SelectorExpr{X: newIdent(pos, "posn"), Sel: newIdent(pos, "Pos")}
   392  						arg := &ast.CallExpr{Fun: fun, Lparen: pos, Args: nil, Ellipsis: token.NoPos, Rparen: pos}
   393  						n.Args[0] = arg
   394  						return false
   395  					}
   396  				case "addf":
   397  					// rewrite err.addf(pos, ...) to err.addf(posn, ...)
   398  					if isIdent(n.Args[0], "pos") {
   399  						pos := n.Args[0].Pos()
   400  						arg := newIdent(pos, "posn")
   401  						n.Args[0] = arg
   402  						return false
   403  					}
   404  				case "allowVersion":
   405  					// rewrite check.allowVersion(pos, ...) to check.allowVersion(posn, ...)
   406  					if isIdent(n.Args[0], "pos") {
   407  						pos := n.Args[0].Pos()
   408  						arg := newIdent(pos, "posn")
   409  						n.Args[0] = arg
   410  						return false
   411  					}
   412  				}
   413  			}
   414  		}
   415  		return true
   416  	})
   417  }
   418  
   419  // fixAtPosCall updates calls of the form atPos(x) to x.Pos() in argument lists of (check).dump calls.
   420  // TODO(gri) can we avoid this and just use atPos consistently in go/types and types2?
   421  func fixAtPosCall(f *ast.File) {
   422  	ast.Inspect(f, func(n ast.Node) bool {
   423  		switch n := n.(type) {
   424  		case *ast.CallExpr:
   425  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil && selx.Sel.Name == "dump" {
   426  				for i, arg := range n.Args {
   427  					if call, _ := arg.(*ast.CallExpr); call != nil {
   428  						// rewrite xxx.dump(..., atPos(x), ...) to xxx.dump(..., x.Pos(), ...)
   429  						if isIdent(call.Fun, "atPos") {
   430  							pos := call.Args[0].Pos()
   431  							fun := &ast.SelectorExpr{X: call.Args[0], Sel: newIdent(pos, "Pos")}
   432  							n.Args[i] = &ast.CallExpr{Fun: fun, Lparen: pos, Rparen: pos}
   433  							return false
   434  						}
   435  					}
   436  				}
   437  			}
   438  		}
   439  		return true
   440  	})
   441  }
   442  
   443  // fixErrErrorfCall updates calls of the form err.addf(obj, ...) to err.addf(obj.Pos(), ...).
   444  func fixErrErrorfCall(f *ast.File) {
   445  	ast.Inspect(f, func(n ast.Node) bool {
   446  		switch n := n.(type) {
   447  		case *ast.CallExpr:
   448  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil {
   449  				if isIdent(selx.X, "err") {
   450  					switch selx.Sel.Name {
   451  					case "errorf":
   452  						// rewrite err.addf(obj, ... ) to err.addf(obj.Pos(), ... )
   453  						if ident, _ := n.Args[0].(*ast.Ident); ident != nil && ident.Name == "obj" {
   454  							pos := n.Args[0].Pos()
   455  							fun := &ast.SelectorExpr{X: ident, Sel: newIdent(pos, "Pos")}
   456  							n.Args[0] = &ast.CallExpr{Fun: fun, Lparen: pos, Rparen: pos}
   457  							return false
   458  						}
   459  					}
   460  				}
   461  			}
   462  		}
   463  		return true
   464  	})
   465  }
   466  
   467  // fixCheckErrorfCall updates calls of the form check.errorf(pos, ...) to check.errorf(atPos(pos), ...).
   468  func fixCheckErrorfCall(f *ast.File) {
   469  	ast.Inspect(f, func(n ast.Node) bool {
   470  		switch n := n.(type) {
   471  		case *ast.CallExpr:
   472  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil {
   473  				if isIdent(selx.X, "check") {
   474  					switch selx.Sel.Name {
   475  					case "errorf":
   476  						// rewrite check.errorf(pos, ... ) to check.errorf(atPos(pos), ... )
   477  						if ident := asIdent(n.Args[0], "pos"); ident != nil {
   478  							pos := n.Args[0].Pos()
   479  							fun := newIdent(pos, "atPos")
   480  							n.Args[0] = &ast.CallExpr{Fun: fun, Lparen: pos, Args: []ast.Expr{ident}, Rparen: pos}
   481  							return false
   482  						}
   483  					}
   484  				}
   485  			}
   486  		}
   487  		return true
   488  	})
   489  }
   490  
   491  // fixGlobalTypVarDecl changes the global Typ variable from an array to a slice
   492  // (in types2 we use an array for efficiency, in go/types it's a slice and we
   493  // cannot change that).
   494  func fixGlobalTypVarDecl(f *ast.File) {
   495  	ast.Inspect(f, func(n ast.Node) bool {
   496  		switch n := n.(type) {
   497  		case *ast.ValueSpec:
   498  			// rewrite type Typ = [...]Type{...} to type Typ = []Type{...}
   499  			if len(n.Names) == 1 && n.Names[0].Name == "Typ" && len(n.Values) == 1 {
   500  				n.Values[0].(*ast.CompositeLit).Type.(*ast.ArrayType).Len = nil
   501  				return false
   502  			}
   503  		}
   504  		return true
   505  	})
   506  }
   507  
   508  // fixSprintf adds an extra nil argument for the *token.FileSet parameter in sprintf calls.
   509  func fixSprintf(f *ast.File) {
   510  	ast.Inspect(f, func(n ast.Node) bool {
   511  		switch n := n.(type) {
   512  		case *ast.CallExpr:
   513  			if isIdent(n.Fun, "sprintf") && len(n.Args) >= 4 /* ... args */ {
   514  				n.Args = insert(n.Args, 1, newIdent(n.Args[1].Pos(), "nil"))
   515  				return false
   516  			}
   517  		}
   518  		return true
   519  	})
   520  }
   521  
   522  // asIdent returns x as *ast.Ident if it is an identifier with the given name.
   523  func asIdent(x ast.Node, name string) *ast.Ident {
   524  	if ident, _ := x.(*ast.Ident); ident != nil && ident.Name == name {
   525  		return ident
   526  	}
   527  	return nil
   528  }
   529  
   530  // isIdent reports whether x is an identifier with the given name.
   531  func isIdent(x ast.Node, name string) bool {
   532  	return asIdent(x, name) != nil
   533  }
   534  
   535  // newIdent returns a new identifier with the given position and name.
   536  func newIdent(pos token.Pos, name string) *ast.Ident {
   537  	id := ast.NewIdent(name)
   538  	id.NamePos = pos
   539  	return id
   540  }
   541  
   542  // insert inserts x at list[at] and moves the remaining elements up.
   543  func insert(list []ast.Expr, at int, x ast.Expr) []ast.Expr {
   544  	list = append(list, nil)
   545  	copy(list[at+1:], list[at:])
   546  	list[at] = x
   547  	return list
   548  }
   549  

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