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  	"tuple.go":         nil,
   198  	"typelists.go":     nil,
   199  	"typeset.go":       func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
   200  	"typeparam.go":     nil,
   201  	"typeterm_test.go": nil,
   202  	"typeterm.go":      nil,
   203  	"typestring.go":    nil,
   204  	"under.go":         nil,
   205  	"unify.go":         fixSprintf,
   206  	"universe.go":      fixGlobalTypVarDecl,
   207  	"util_test.go":     fixTokenPos,
   208  	"validtype.go":     func(f *ast.File) { fixTokenPos(f); renameSelectors(f, "Trace->_Trace") },
   209  }
   210  
   211  // TODO(gri) We should be able to make these rewriters more configurable/composable.
   212  //           For now this is a good starting point.
   213  
   214  // A renameMap maps old strings to new strings.
   215  type renameMap map[string]string
   216  
   217  // makeRenameMap returns a renameMap populates from renames entries of the form "from->to".
   218  func makeRenameMap(renames ...string) renameMap {
   219  	m := make(renameMap)
   220  	for _, r := range renames {
   221  		s := strings.Split(r, "->")
   222  		if len(s) != 2 {
   223  			panic("invalid rename entry: " + r)
   224  		}
   225  		m[s[0]] = s[1]
   226  	}
   227  	return m
   228  }
   229  
   230  // rename renames the given string s if a corresponding rename exists in m.
   231  func (m renameMap) rename(s *string) {
   232  	if r, ok := m[*s]; ok {
   233  		*s = r
   234  	}
   235  }
   236  
   237  // renameSel renames a selector expression of the form a.x to b.x (where a, b are identifiers)
   238  // if m contains the ("a.x" : "b.y") key-value pair.
   239  func (m renameMap) renameSel(n *ast.SelectorExpr) {
   240  	if a, _ := n.X.(*ast.Ident); a != nil {
   241  		a_x := a.Name + "." + n.Sel.Name
   242  		if r, ok := m[a_x]; ok {
   243  			b_y := strings.Split(r, ".")
   244  			if len(b_y) != 2 {
   245  				panic("invalid selector expression: " + r)
   246  			}
   247  			a.Name = b_y[0]
   248  			n.Sel.Name = b_y[1]
   249  		}
   250  	}
   251  }
   252  
   253  // renameIdents renames identifiers: each renames entry is of the form "from->to".
   254  // Note: This doesn't change the use of the identifiers in comments.
   255  func renameIdents(f *ast.File, renames ...string) {
   256  	m := makeRenameMap(renames...)
   257  	ast.Inspect(f, func(n ast.Node) bool {
   258  		switch n := n.(type) {
   259  		case *ast.Ident:
   260  			m.rename(&n.Name)
   261  			return false
   262  		}
   263  		return true
   264  	})
   265  }
   266  
   267  // renameSelectors is like renameIdents but only looks at selectors.
   268  func renameSelectors(f *ast.File, renames ...string) {
   269  	m := makeRenameMap(renames...)
   270  	ast.Inspect(f, func(n ast.Node) bool {
   271  		switch n := n.(type) {
   272  		case *ast.SelectorExpr:
   273  			m.rename(&n.Sel.Name)
   274  			return false
   275  		}
   276  		return true
   277  	})
   278  
   279  }
   280  
   281  // renameSelectorExprs is like renameIdents but only looks at selector expressions.
   282  // Each renames entry must be of the form "x.a->y.b".
   283  func renameSelectorExprs(f *ast.File, renames ...string) {
   284  	m := makeRenameMap(renames...)
   285  	ast.Inspect(f, func(n ast.Node) bool {
   286  		switch n := n.(type) {
   287  		case *ast.SelectorExpr:
   288  			m.renameSel(n)
   289  			return false
   290  		}
   291  		return true
   292  	})
   293  }
   294  
   295  // renameImportPath is like renameIdents but renames import paths.
   296  func renameImportPath(f *ast.File, renames ...string) {
   297  	m := makeRenameMap(renames...)
   298  	ast.Inspect(f, func(n ast.Node) bool {
   299  		switch n := n.(type) {
   300  		case *ast.ImportSpec:
   301  			if n.Path.Kind != token.STRING {
   302  				panic("invalid import path")
   303  			}
   304  			m.rename(&n.Path.Value)
   305  			return false
   306  		}
   307  		return true
   308  	})
   309  }
   310  
   311  // insertImportPath inserts the given import path.
   312  // There must be at least one import declaration present already.
   313  func insertImportPath(f *ast.File, path string) {
   314  	for _, d := range f.Decls {
   315  		if g, _ := d.(*ast.GenDecl); g != nil && g.Tok == token.IMPORT {
   316  			g.Specs = append(g.Specs, &ast.ImportSpec{Path: &ast.BasicLit{ValuePos: g.End(), Kind: token.STRING, Value: path}})
   317  			return
   318  		}
   319  	}
   320  	panic("no import declaration present")
   321  }
   322  
   323  // fixTokenPos changes imports of "cmd/compile/internal/syntax" to "go/token",
   324  // uses of syntax.Pos to token.Pos, and calls to x.IsKnown() to x.IsValid().
   325  func fixTokenPos(f *ast.File) {
   326  	m := makeRenameMap(`"cmd/compile/internal/syntax"->"go/token"`, "syntax.Pos->token.Pos", "IsKnown->IsValid")
   327  	ast.Inspect(f, func(n ast.Node) bool {
   328  		switch n := n.(type) {
   329  		case *ast.ImportSpec:
   330  			// rewrite import path "cmd/compile/internal/syntax" to "go/token"
   331  			if n.Path.Kind != token.STRING {
   332  				panic("invalid import path")
   333  			}
   334  			m.rename(&n.Path.Value)
   335  			return false
   336  		case *ast.SelectorExpr:
   337  			// rewrite syntax.Pos to token.Pos
   338  			m.renameSel(n)
   339  		case *ast.CallExpr:
   340  			// rewrite x.IsKnown() to x.IsValid()
   341  			if fun, _ := n.Fun.(*ast.SelectorExpr); fun != nil && len(n.Args) == 0 {
   342  				m.rename(&fun.Sel.Name)
   343  				return false
   344  			}
   345  		}
   346  		return true
   347  	})
   348  }
   349  
   350  // fixSelValue updates the selector x.Sel.Value to x.Sel.Name.
   351  func fixSelValue(f *ast.File) {
   352  	ast.Inspect(f, func(n ast.Node) bool {
   353  		switch n := n.(type) {
   354  		case *ast.SelectorExpr:
   355  			if n.Sel.Name == "Value" {
   356  				if selx, _ := n.X.(*ast.SelectorExpr); selx != nil && selx.Sel.Name == "Sel" {
   357  					n.Sel.Name = "Name"
   358  					return false
   359  				}
   360  			}
   361  		}
   362  		return true
   363  	})
   364  }
   365  
   366  // fixInferSig updates the Checker.infer signature to use a positioner instead of a token.Position
   367  // as first argument, renames the argument from "pos" to "posn", and updates a few internal uses of
   368  // "pos" to "posn" and "posn.Pos()" respectively.
   369  func fixInferSig(f *ast.File) {
   370  	ast.Inspect(f, func(n ast.Node) bool {
   371  		switch n := n.(type) {
   372  		case *ast.FuncDecl:
   373  			if n.Name.Name == "infer" {
   374  				// rewrite (pos token.Pos, ...) to (posn positioner, ...)
   375  				par := n.Type.Params.List[0]
   376  				if len(par.Names) == 1 && par.Names[0].Name == "pos" {
   377  					par.Names[0] = newIdent(par.Names[0].Pos(), "posn")
   378  					par.Type = newIdent(par.Type.Pos(), "positioner")
   379  					return true
   380  				}
   381  			}
   382  		case *ast.CallExpr:
   383  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil {
   384  				switch selx.Sel.Name {
   385  				case "renameTParams":
   386  					// rewrite check.renameTParams(pos, ... ) to check.renameTParams(posn.Pos(), ... )
   387  					if isIdent(n.Args[0], "pos") {
   388  						pos := n.Args[0].Pos()
   389  						fun := &ast.SelectorExpr{X: newIdent(pos, "posn"), Sel: newIdent(pos, "Pos")}
   390  						arg := &ast.CallExpr{Fun: fun, Lparen: pos, Args: nil, Ellipsis: token.NoPos, Rparen: pos}
   391  						n.Args[0] = arg
   392  						return false
   393  					}
   394  				case "addf":
   395  					// rewrite err.addf(pos, ...) to err.addf(posn, ...)
   396  					if isIdent(n.Args[0], "pos") {
   397  						pos := n.Args[0].Pos()
   398  						arg := newIdent(pos, "posn")
   399  						n.Args[0] = arg
   400  						return false
   401  					}
   402  				case "allowVersion":
   403  					// rewrite check.allowVersion(pos, ...) to check.allowVersion(posn, ...)
   404  					if isIdent(n.Args[0], "pos") {
   405  						pos := n.Args[0].Pos()
   406  						arg := newIdent(pos, "posn")
   407  						n.Args[0] = arg
   408  						return false
   409  					}
   410  				}
   411  			}
   412  		}
   413  		return true
   414  	})
   415  }
   416  
   417  // fixAtPosCall updates calls of the form atPos(x) to x.Pos() in argument lists of (check).dump calls.
   418  // TODO(gri) can we avoid this and just use atPos consistently in go/types and types2?
   419  func fixAtPosCall(f *ast.File) {
   420  	ast.Inspect(f, func(n ast.Node) bool {
   421  		switch n := n.(type) {
   422  		case *ast.CallExpr:
   423  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil && selx.Sel.Name == "dump" {
   424  				for i, arg := range n.Args {
   425  					if call, _ := arg.(*ast.CallExpr); call != nil {
   426  						// rewrite xxx.dump(..., atPos(x), ...) to xxx.dump(..., x.Pos(), ...)
   427  						if isIdent(call.Fun, "atPos") {
   428  							pos := call.Args[0].Pos()
   429  							fun := &ast.SelectorExpr{X: call.Args[0], Sel: newIdent(pos, "Pos")}
   430  							n.Args[i] = &ast.CallExpr{Fun: fun, Lparen: pos, Rparen: pos}
   431  							return false
   432  						}
   433  					}
   434  				}
   435  			}
   436  		}
   437  		return true
   438  	})
   439  }
   440  
   441  // fixErrErrorfCall updates calls of the form err.addf(obj, ...) to err.addf(obj.Pos(), ...).
   442  func fixErrErrorfCall(f *ast.File) {
   443  	ast.Inspect(f, func(n ast.Node) bool {
   444  		switch n := n.(type) {
   445  		case *ast.CallExpr:
   446  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil {
   447  				if isIdent(selx.X, "err") {
   448  					switch selx.Sel.Name {
   449  					case "errorf":
   450  						// rewrite err.addf(obj, ... ) to err.addf(obj.Pos(), ... )
   451  						if ident, _ := n.Args[0].(*ast.Ident); ident != nil && ident.Name == "obj" {
   452  							pos := n.Args[0].Pos()
   453  							fun := &ast.SelectorExpr{X: ident, Sel: newIdent(pos, "Pos")}
   454  							n.Args[0] = &ast.CallExpr{Fun: fun, Lparen: pos, Rparen: pos}
   455  							return false
   456  						}
   457  					}
   458  				}
   459  			}
   460  		}
   461  		return true
   462  	})
   463  }
   464  
   465  // fixCheckErrorfCall updates calls of the form check.errorf(pos, ...) to check.errorf(atPos(pos), ...).
   466  func fixCheckErrorfCall(f *ast.File) {
   467  	ast.Inspect(f, func(n ast.Node) bool {
   468  		switch n := n.(type) {
   469  		case *ast.CallExpr:
   470  			if selx, _ := n.Fun.(*ast.SelectorExpr); selx != nil {
   471  				if isIdent(selx.X, "check") {
   472  					switch selx.Sel.Name {
   473  					case "errorf":
   474  						// rewrite check.errorf(pos, ... ) to check.errorf(atPos(pos), ... )
   475  						if ident := asIdent(n.Args[0], "pos"); ident != nil {
   476  							pos := n.Args[0].Pos()
   477  							fun := newIdent(pos, "atPos")
   478  							n.Args[0] = &ast.CallExpr{Fun: fun, Lparen: pos, Args: []ast.Expr{ident}, Rparen: pos}
   479  							return false
   480  						}
   481  					}
   482  				}
   483  			}
   484  		}
   485  		return true
   486  	})
   487  }
   488  
   489  // fixGlobalTypVarDecl changes the global Typ variable from an array to a slice
   490  // (in types2 we use an array for efficiency, in go/types it's a slice and we
   491  // cannot change that).
   492  func fixGlobalTypVarDecl(f *ast.File) {
   493  	ast.Inspect(f, func(n ast.Node) bool {
   494  		switch n := n.(type) {
   495  		case *ast.ValueSpec:
   496  			// rewrite type Typ = [...]Type{...} to type Typ = []Type{...}
   497  			if len(n.Names) == 1 && n.Names[0].Name == "Typ" && len(n.Values) == 1 {
   498  				n.Values[0].(*ast.CompositeLit).Type.(*ast.ArrayType).Len = nil
   499  				return false
   500  			}
   501  		}
   502  		return true
   503  	})
   504  }
   505  
   506  // fixSprintf adds an extra nil argument for the *token.FileSet parameter in sprintf calls.
   507  func fixSprintf(f *ast.File) {
   508  	ast.Inspect(f, func(n ast.Node) bool {
   509  		switch n := n.(type) {
   510  		case *ast.CallExpr:
   511  			if isIdent(n.Fun, "sprintf") && len(n.Args) >= 4 /* ... args */ {
   512  				n.Args = insert(n.Args, 1, newIdent(n.Args[1].Pos(), "nil"))
   513  				return false
   514  			}
   515  		}
   516  		return true
   517  	})
   518  }
   519  
   520  // asIdent returns x as *ast.Ident if it is an identifier with the given name.
   521  func asIdent(x ast.Node, name string) *ast.Ident {
   522  	if ident, _ := x.(*ast.Ident); ident != nil && ident.Name == name {
   523  		return ident
   524  	}
   525  	return nil
   526  }
   527  
   528  // isIdent reports whether x is an identifier with the given name.
   529  func isIdent(x ast.Node, name string) bool {
   530  	return asIdent(x, name) != nil
   531  }
   532  
   533  // newIdent returns a new identifier with the given position and name.
   534  func newIdent(pos token.Pos, name string) *ast.Ident {
   535  	id := ast.NewIdent(name)
   536  	id.NamePos = pos
   537  	return id
   538  }
   539  
   540  // insert inserts x at list[at] and moves the remaining elements up.
   541  func insert(list []ast.Expr, at int, x ast.Expr) []ast.Expr {
   542  	list = append(list, nil)
   543  	copy(list[at+1:], list[at:])
   544  	list[at] = x
   545  	return list
   546  }
   547  

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