ast.go

     1  // Copyright 2009 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  // Parse input AST and prepare Prog structure.
     6  
     7  package main
     8  
     9  import (
    10  	"fmt"
    11  	"go/ast"
    12  	"go/format"
    13  	"go/parser"
    14  	"go/scanner"
    15  	"go/token"
    16  	"os"
    17  	"strings"
    18  )
    19  
    20  func parse(name string, src []byte, flags parser.Mode) *ast.File {
    21  	ast1, err := parser.ParseFile(fset, name, src, flags)
    22  	if err != nil {
    23  		if list, ok := err.(scanner.ErrorList); ok {
    24  			// If err is a scanner.ErrorList, its String will print just
    25  			// the first error and then (+n more errors).
    26  			// Instead, turn it into a new Error that will return
    27  			// details for all the errors.
    28  			for _, e := range list {
    29  				fmt.Fprintln(os.Stderr, e)
    30  			}
    31  			os.Exit(2)
    32  		}
    33  		fatalf("parsing %s: %s", name, err)
    34  	}
    35  	return ast1
    36  }
    37  
    38  func sourceLine(n ast.Node) int {
    39  	return fset.Position(n.Pos()).Line
    40  }
    41  
    42  // ParseGo populates f with information learned from the Go source code
    43  // which was read from the named file. It gathers the C preamble
    44  // attached to the import "C" comment, a list of references to C.xxx,
    45  // a list of exported functions, and the actual AST, to be rewritten and
    46  // printed.
    47  func (f *File) ParseGo(abspath string, src []byte) {
    48  	// Two different parses: once with comments, once without.
    49  	// The printer is not good enough at printing comments in the
    50  	// right place when we start editing the AST behind its back,
    51  	// so we use ast1 to look for the doc comments on import "C"
    52  	// and on exported functions, and we use ast2 for translating
    53  	// and reprinting.
    54  	// In cgo mode, we ignore ast2 and just apply edits directly
    55  	// the text behind ast1. In godefs mode we modify and print ast2.
    56  	ast1 := parse(abspath, src, parser.SkipObjectResolution|parser.ParseComments)
    57  	ast2 := parse(abspath, src, parser.SkipObjectResolution)
    58  
    59  	f.Package = ast1.Name.Name
    60  	f.Name = make(map[string]*Name)
    61  	f.NamePos = make(map[*Name]token.Pos)
    62  
    63  	// In ast1, find the import "C" line and get any extra C preamble.
    64  	sawC := false
    65  	for _, decl := range ast1.Decls {
    66  		switch decl := decl.(type) {
    67  		case *ast.GenDecl:
    68  			for _, spec := range decl.Specs {
    69  				s, ok := spec.(*ast.ImportSpec)
    70  				if !ok || s.Path.Value != `"C"` {
    71  					continue
    72  				}
    73  				sawC = true
    74  				if s.Name != nil {
    75  					error_(s.Path.Pos(), `cannot rename import "C"`)
    76  				}
    77  				cg := s.Doc
    78  				if cg == nil && len(decl.Specs) == 1 {
    79  					cg = decl.Doc
    80  				}
    81  				if cg != nil {
    82  					f.Preamble += fmt.Sprintf("#line %d %q\n", sourceLine(cg), abspath)
    83  					f.Preamble += commentText(cg) + "\n"
    84  					f.Preamble += "#line 1 \"cgo-generated-wrapper\"\n"
    85  				}
    86  			}
    87  
    88  		case *ast.FuncDecl:
    89  			// Also, reject attempts to declare methods on C.T or *C.T.
    90  			// (The generated code would otherwise accept this
    91  			// invalid input; see issue #57926.)
    92  			if decl.Recv != nil && len(decl.Recv.List) > 0 {
    93  				recvType := decl.Recv.List[0].Type
    94  				if recvType != nil {
    95  					t := recvType
    96  					if star, ok := unparen(t).(*ast.StarExpr); ok {
    97  						t = star.X
    98  					}
    99  					if sel, ok := unparen(t).(*ast.SelectorExpr); ok {
   100  						var buf strings.Builder
   101  						format.Node(&buf, fset, recvType)
   102  						error_(sel.Pos(), `cannot define new methods on non-local type %s`, &buf)
   103  					}
   104  				}
   105  			}
   106  		}
   107  
   108  	}
   109  	if !sawC {
   110  		error_(ast1.Package, `cannot find import "C"`)
   111  	}
   112  
   113  	// In ast2, strip the import "C" line.
   114  	if *godefs {
   115  		w := 0
   116  		for _, decl := range ast2.Decls {
   117  			d, ok := decl.(*ast.GenDecl)
   118  			if !ok {
   119  				ast2.Decls[w] = decl
   120  				w++
   121  				continue
   122  			}
   123  			ws := 0
   124  			for _, spec := range d.Specs {
   125  				s, ok := spec.(*ast.ImportSpec)
   126  				if !ok || s.Path.Value != `"C"` {
   127  					d.Specs[ws] = spec
   128  					ws++
   129  				}
   130  			}
   131  			if ws == 0 {
   132  				continue
   133  			}
   134  			d.Specs = d.Specs[0:ws]
   135  			ast2.Decls[w] = d
   136  			w++
   137  		}
   138  		ast2.Decls = ast2.Decls[0:w]
   139  	} else {
   140  		for _, decl := range ast2.Decls {
   141  			d, ok := decl.(*ast.GenDecl)
   142  			if !ok {
   143  				continue
   144  			}
   145  			for _, spec := range d.Specs {
   146  				if s, ok := spec.(*ast.ImportSpec); ok && s.Path.Value == `"C"` {
   147  					// Replace "C" with _ "unsafe", to keep program valid.
   148  					// (Deleting import statement or clause is not safe if it is followed
   149  					// in the source by an explicit semicolon.)
   150  					f.Edit.Replace(f.offset(s.Path.Pos()), f.offset(s.Path.End()), `_ "unsafe"`)
   151  				}
   152  			}
   153  		}
   154  	}
   155  
   156  	// Accumulate pointers to uses of C.x.
   157  	if f.Ref == nil {
   158  		f.Ref = make([]*Ref, 0, 8)
   159  	}
   160  	f.walk(ast2, ctxProg, (*File).validateIdents)
   161  	f.walk(ast2, ctxProg, (*File).saveExprs)
   162  
   163  	// Accumulate exported functions.
   164  	// The comments are only on ast1 but we need to
   165  	// save the function bodies from ast2.
   166  	// The first walk fills in ExpFunc, and the
   167  	// second walk changes the entries to
   168  	// refer to ast2 instead.
   169  	f.walk(ast1, ctxProg, (*File).saveExport)
   170  	f.walk(ast2, ctxProg, (*File).saveExport2)
   171  
   172  	f.Comments = ast1.Comments
   173  	f.AST = ast2
   174  }
   175  
   176  // Like ast.CommentGroup's Text method but preserves
   177  // leading blank lines, so that line numbers line up.
   178  func commentText(g *ast.CommentGroup) string {
   179  	var pieces []string
   180  	for _, com := range g.List {
   181  		c := com.Text
   182  		// Remove comment markers.
   183  		// The parser has given us exactly the comment text.
   184  		switch c[1] {
   185  		case '/':
   186  			//-style comment (no newline at the end)
   187  			c = c[2:] + "\n"
   188  		case '*':
   189  			/*-style comment */
   190  			c = c[2 : len(c)-2]
   191  		}
   192  		pieces = append(pieces, c)
   193  	}
   194  	return strings.Join(pieces, "")
   195  }
   196  
   197  func (f *File) validateIdents(x interface{}, context astContext) {
   198  	if x, ok := x.(*ast.Ident); ok {
   199  		if f.isMangledName(x.Name) {
   200  			error_(x.Pos(), "identifier %q may conflict with identifiers generated by cgo", x.Name)
   201  		}
   202  	}
   203  }
   204  
   205  // Save various references we are going to need later.
   206  func (f *File) saveExprs(x interface{}, context astContext) {
   207  	switch x := x.(type) {
   208  	case *ast.Expr:
   209  		switch (*x).(type) {
   210  		case *ast.SelectorExpr:
   211  			f.saveRef(x, context)
   212  		}
   213  	case *ast.CallExpr:
   214  		f.saveCall(x, context)
   215  	}
   216  }
   217  
   218  // Save references to C.xxx for later processing.
   219  func (f *File) saveRef(n *ast.Expr, context astContext) {
   220  	sel := (*n).(*ast.SelectorExpr)
   221  	// For now, assume that the only instance of capital C is when
   222  	// used as the imported package identifier.
   223  	// The parser should take care of scoping in the future, so
   224  	// that we will be able to distinguish a "top-level C" from a
   225  	// local C.
   226  	if l, ok := sel.X.(*ast.Ident); !ok || l.Name != "C" {
   227  		return
   228  	}
   229  	if context == ctxAssign2 {
   230  		context = ctxExpr
   231  	}
   232  	if context == ctxEmbedType {
   233  		error_(sel.Pos(), "cannot embed C type")
   234  	}
   235  	goname := sel.Sel.Name
   236  	if goname == "errno" {
   237  		error_(sel.Pos(), "cannot refer to errno directly; see documentation")
   238  		return
   239  	}
   240  	if goname == "_CMalloc" {
   241  		error_(sel.Pos(), "cannot refer to C._CMalloc; use C.malloc")
   242  		return
   243  	}
   244  	if goname == "malloc" {
   245  		goname = "_CMalloc"
   246  	}
   247  	name := f.Name[goname]
   248  	if name == nil {
   249  		name = &Name{
   250  			Go: goname,
   251  		}
   252  		f.Name[goname] = name
   253  		f.NamePos[name] = sel.Pos()
   254  	}
   255  	f.Ref = append(f.Ref, &Ref{
   256  		Name:    name,
   257  		Expr:    n,
   258  		Context: context,
   259  	})
   260  }
   261  
   262  // Save calls to C.xxx for later processing.
   263  func (f *File) saveCall(call *ast.CallExpr, context astContext) {
   264  	sel, ok := call.Fun.(*ast.SelectorExpr)
   265  	if !ok {
   266  		return
   267  	}
   268  	if l, ok := sel.X.(*ast.Ident); !ok || l.Name != "C" {
   269  		return
   270  	}
   271  	c := &Call{Call: call, Deferred: context == ctxDefer}
   272  	f.Calls = append(f.Calls, c)
   273  }
   274  
   275  // If a function should be exported add it to ExpFunc.
   276  func (f *File) saveExport(x interface{}, context astContext) {
   277  	n, ok := x.(*ast.FuncDecl)
   278  	if !ok {
   279  		return
   280  	}
   281  
   282  	if n.Doc == nil {
   283  		return
   284  	}
   285  	for _, c := range n.Doc.List {
   286  		if !strings.HasPrefix(c.Text, "//export ") {
   287  			continue
   288  		}
   289  
   290  		name := strings.TrimSpace(c.Text[9:])
   291  		if name == "" {
   292  			error_(c.Pos(), "export missing name")
   293  		}
   294  
   295  		if name != n.Name.Name {
   296  			error_(c.Pos(), "export comment has wrong name %q, want %q", name, n.Name.Name)
   297  		}
   298  
   299  		doc := ""
   300  		for _, c1 := range n.Doc.List {
   301  			if c1 != c {
   302  				doc += c1.Text + "\n"
   303  			}
   304  		}
   305  
   306  		f.ExpFunc = append(f.ExpFunc, &ExpFunc{
   307  			Func:    n,
   308  			ExpName: name,
   309  			Doc:     doc,
   310  		})
   311  		break
   312  	}
   313  }
   314  
   315  // Make f.ExpFunc[i] point at the Func from this AST instead of the other one.
   316  func (f *File) saveExport2(x interface{}, context astContext) {
   317  	n, ok := x.(*ast.FuncDecl)
   318  	if !ok {
   319  		return
   320  	}
   321  
   322  	for _, exp := range f.ExpFunc {
   323  		if exp.Func.Name.Name == n.Name.Name {
   324  			exp.Func = n
   325  			break
   326  		}
   327  	}
   328  }
   329  
   330  type astContext int
   331  
   332  const (
   333  	ctxProg astContext = iota
   334  	ctxEmbedType
   335  	ctxType
   336  	ctxStmt
   337  	ctxExpr
   338  	ctxField
   339  	ctxParam
   340  	ctxAssign2 // assignment of a single expression to two variables
   341  	ctxSwitch
   342  	ctxTypeSwitch
   343  	ctxFile
   344  	ctxDecl
   345  	ctxSpec
   346  	ctxDefer
   347  	ctxCall  // any function call other than ctxCall2
   348  	ctxCall2 // function call whose result is assigned to two variables
   349  	ctxSelector
   350  )
   351  
   352  // walk walks the AST x, calling visit(f, x, context) for each node.
   353  func (f *File) walk(x interface{}, context astContext, visit func(*File, interface{}, astContext)) {
   354  	visit(f, x, context)
   355  	switch n := x.(type) {
   356  	case *ast.Expr:
   357  		f.walk(*n, context, visit)
   358  
   359  	// everything else just recurs
   360  	default:
   361  		f.walkUnexpected(x, context, visit)
   362  
   363  	case nil:
   364  
   365  	// These are ordered and grouped to match ../../go/ast/ast.go
   366  	case *ast.Field:
   367  		if len(n.Names) == 0 && context == ctxField {
   368  			f.walk(&n.Type, ctxEmbedType, visit)
   369  		} else {
   370  			f.walk(&n.Type, ctxType, visit)
   371  		}
   372  	case *ast.FieldList:
   373  		for _, field := range n.List {
   374  			f.walk(field, context, visit)
   375  		}
   376  	case *ast.BadExpr:
   377  	case *ast.Ident:
   378  	case *ast.Ellipsis:
   379  		f.walk(&n.Elt, ctxType, visit)
   380  	case *ast.BasicLit:
   381  	case *ast.FuncLit:
   382  		f.walk(n.Type, ctxType, visit)
   383  		f.walk(n.Body, ctxStmt, visit)
   384  	case *ast.CompositeLit:
   385  		f.walk(&n.Type, ctxType, visit)
   386  		f.walk(n.Elts, ctxExpr, visit)
   387  	case *ast.ParenExpr:
   388  		f.walk(&n.X, context, visit)
   389  	case *ast.SelectorExpr:
   390  		f.walk(&n.X, ctxSelector, visit)
   391  	case *ast.IndexExpr:
   392  		f.walk(&n.X, ctxExpr, visit)
   393  		f.walk(&n.Index, ctxExpr, visit)
   394  	case *ast.SliceExpr:
   395  		f.walk(&n.X, ctxExpr, visit)
   396  		if n.Low != nil {
   397  			f.walk(&n.Low, ctxExpr, visit)
   398  		}
   399  		if n.High != nil {
   400  			f.walk(&n.High, ctxExpr, visit)
   401  		}
   402  		if n.Max != nil {
   403  			f.walk(&n.Max, ctxExpr, visit)
   404  		}
   405  	case *ast.TypeAssertExpr:
   406  		f.walk(&n.X, ctxExpr, visit)
   407  		f.walk(&n.Type, ctxType, visit)
   408  	case *ast.CallExpr:
   409  		if context == ctxAssign2 {
   410  			f.walk(&n.Fun, ctxCall2, visit)
   411  		} else {
   412  			f.walk(&n.Fun, ctxCall, visit)
   413  		}
   414  		f.walk(n.Args, ctxExpr, visit)
   415  	case *ast.StarExpr:
   416  		f.walk(&n.X, context, visit)
   417  	case *ast.UnaryExpr:
   418  		f.walk(&n.X, ctxExpr, visit)
   419  	case *ast.BinaryExpr:
   420  		f.walk(&n.X, ctxExpr, visit)
   421  		f.walk(&n.Y, ctxExpr, visit)
   422  	case *ast.KeyValueExpr:
   423  		f.walk(&n.Key, ctxExpr, visit)
   424  		f.walk(&n.Value, ctxExpr, visit)
   425  
   426  	case *ast.ArrayType:
   427  		f.walk(&n.Len, ctxExpr, visit)
   428  		f.walk(&n.Elt, ctxType, visit)
   429  	case *ast.StructType:
   430  		f.walk(n.Fields, ctxField, visit)
   431  	case *ast.FuncType:
   432  		if tparams := funcTypeTypeParams(n); tparams != nil {
   433  			f.walk(tparams, ctxParam, visit)
   434  		}
   435  		f.walk(n.Params, ctxParam, visit)
   436  		if n.Results != nil {
   437  			f.walk(n.Results, ctxParam, visit)
   438  		}
   439  	case *ast.InterfaceType:
   440  		f.walk(n.Methods, ctxField, visit)
   441  	case *ast.MapType:
   442  		f.walk(&n.Key, ctxType, visit)
   443  		f.walk(&n.Value, ctxType, visit)
   444  	case *ast.ChanType:
   445  		f.walk(&n.Value, ctxType, visit)
   446  
   447  	case *ast.BadStmt:
   448  	case *ast.DeclStmt:
   449  		f.walk(n.Decl, ctxDecl, visit)
   450  	case *ast.EmptyStmt:
   451  	case *ast.LabeledStmt:
   452  		f.walk(n.Stmt, ctxStmt, visit)
   453  	case *ast.ExprStmt:
   454  		f.walk(&n.X, ctxExpr, visit)
   455  	case *ast.SendStmt:
   456  		f.walk(&n.Chan, ctxExpr, visit)
   457  		f.walk(&n.Value, ctxExpr, visit)
   458  	case *ast.IncDecStmt:
   459  		f.walk(&n.X, ctxExpr, visit)
   460  	case *ast.AssignStmt:
   461  		f.walk(n.Lhs, ctxExpr, visit)
   462  		if len(n.Lhs) == 2 && len(n.Rhs) == 1 {
   463  			f.walk(n.Rhs, ctxAssign2, visit)
   464  		} else {
   465  			f.walk(n.Rhs, ctxExpr, visit)
   466  		}
   467  	case *ast.GoStmt:
   468  		f.walk(n.Call, ctxExpr, visit)
   469  	case *ast.DeferStmt:
   470  		f.walk(n.Call, ctxDefer, visit)
   471  	case *ast.ReturnStmt:
   472  		f.walk(n.Results, ctxExpr, visit)
   473  	case *ast.BranchStmt:
   474  	case *ast.BlockStmt:
   475  		f.walk(n.List, context, visit)
   476  	case *ast.IfStmt:
   477  		f.walk(n.Init, ctxStmt, visit)
   478  		f.walk(&n.Cond, ctxExpr, visit)
   479  		f.walk(n.Body, ctxStmt, visit)
   480  		f.walk(n.Else, ctxStmt, visit)
   481  	case *ast.CaseClause:
   482  		if context == ctxTypeSwitch {
   483  			context = ctxType
   484  		} else {
   485  			context = ctxExpr
   486  		}
   487  		f.walk(n.List, context, visit)
   488  		f.walk(n.Body, ctxStmt, visit)
   489  	case *ast.SwitchStmt:
   490  		f.walk(n.Init, ctxStmt, visit)
   491  		f.walk(&n.Tag, ctxExpr, visit)
   492  		f.walk(n.Body, ctxSwitch, visit)
   493  	case *ast.TypeSwitchStmt:
   494  		f.walk(n.Init, ctxStmt, visit)
   495  		f.walk(n.Assign, ctxStmt, visit)
   496  		f.walk(n.Body, ctxTypeSwitch, visit)
   497  	case *ast.CommClause:
   498  		f.walk(n.Comm, ctxStmt, visit)
   499  		f.walk(n.Body, ctxStmt, visit)
   500  	case *ast.SelectStmt:
   501  		f.walk(n.Body, ctxStmt, visit)
   502  	case *ast.ForStmt:
   503  		f.walk(n.Init, ctxStmt, visit)
   504  		f.walk(&n.Cond, ctxExpr, visit)
   505  		f.walk(n.Post, ctxStmt, visit)
   506  		f.walk(n.Body, ctxStmt, visit)
   507  	case *ast.RangeStmt:
   508  		f.walk(&n.Key, ctxExpr, visit)
   509  		f.walk(&n.Value, ctxExpr, visit)
   510  		f.walk(&n.X, ctxExpr, visit)
   511  		f.walk(n.Body, ctxStmt, visit)
   512  
   513  	case *ast.ImportSpec:
   514  	case *ast.ValueSpec:
   515  		f.walk(&n.Type, ctxType, visit)
   516  		if len(n.Names) == 2 && len(n.Values) == 1 {
   517  			f.walk(&n.Values[0], ctxAssign2, visit)
   518  		} else {
   519  			f.walk(n.Values, ctxExpr, visit)
   520  		}
   521  	case *ast.TypeSpec:
   522  		if tparams := typeSpecTypeParams(n); tparams != nil {
   523  			f.walk(tparams, ctxParam, visit)
   524  		}
   525  		f.walk(&n.Type, ctxType, visit)
   526  
   527  	case *ast.BadDecl:
   528  	case *ast.GenDecl:
   529  		f.walk(n.Specs, ctxSpec, visit)
   530  	case *ast.FuncDecl:
   531  		if n.Recv != nil {
   532  			f.walk(n.Recv, ctxParam, visit)
   533  		}
   534  		f.walk(n.Type, ctxType, visit)
   535  		if n.Body != nil {
   536  			f.walk(n.Body, ctxStmt, visit)
   537  		}
   538  
   539  	case *ast.File:
   540  		f.walk(n.Decls, ctxDecl, visit)
   541  
   542  	case *ast.Package:
   543  		for _, file := range n.Files {
   544  			f.walk(file, ctxFile, visit)
   545  		}
   546  
   547  	case []ast.Decl:
   548  		for _, d := range n {
   549  			f.walk(d, context, visit)
   550  		}
   551  	case []ast.Expr:
   552  		for i := range n {
   553  			f.walk(&n[i], context, visit)
   554  		}
   555  	case []ast.Stmt:
   556  		for _, s := range n {
   557  			f.walk(s, context, visit)
   558  		}
   559  	case []ast.Spec:
   560  		for _, s := range n {
   561  			f.walk(s, context, visit)
   562  		}
   563  	}
   564  }
   565  
   566  // If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
   567  func unparen(x ast.Expr) ast.Expr {
   568  	if p, isParen := x.(*ast.ParenExpr); isParen {
   569  		x = unparen(p.X)
   570  	}
   571  	return x
   572  }
   573
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