cmd/cgo: use a named type to indicate syntactic context

We previously used bare strings, which made it difficult to see (and
to cross-reference) the set of allowed context values.

This change is purely cosmetic, but makes it easier for me to
understand how to address #21878.

updates #21878

Change-Id: I9027d94fd5997a0fe857c0055dea8719e1511f03
Reviewed-on: https://go-review.googlesource.com/63830
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/cmd/cgo/ast.go b/src/cmd/cgo/ast.go
index 8ce778cd5ff0df19902e94cade656ec1eddbb030..96cad8050c785c54f4e9f9657fbee66d01af7a3c 100644 (file)
--- a/src/cmd/cgo/ast.go
+++ b/src/cmd/cgo/ast.go
@@ -126,7 +126,7 @@ func (f *File) ParseGo(name string, src []byte) {
        if f.Ref == nil {
                f.Ref = make([]*Ref, 0, 8)
        }
-       f.walk(ast2, "prog", (*File).saveExprs)
+       f.walk(ast2, ctxProg, (*File).saveExprs)
 
        // Accumulate exported functions.
        // The comments are only on ast1 but we need to
@@ -134,8 +134,8 @@ func (f *File) ParseGo(name string, src []byte) {
        // The first walk fills in ExpFunc, and the
        // second walk changes the entries to
        // refer to ast2 instead.
-       f.walk(ast1, "prog", (*File).saveExport)
-       f.walk(ast2, "prog", (*File).saveExport2)
+       f.walk(ast1, ctxProg, (*File).saveExport)
+       f.walk(ast2, ctxProg, (*File).saveExport2)
 
        f.Comments = ast1.Comments
        f.AST = ast2
@@ -166,7 +166,7 @@ func commentText(g *ast.CommentGroup) string {
 }
 
 // Save various references we are going to need later.
-func (f *File) saveExprs(x interface{}, context string) {
+func (f *File) saveExprs(x interface{}, context astContext) {
        switch x := x.(type) {
        case *ast.Expr:
                switch (*x).(type) {
@@ -179,7 +179,7 @@ func (f *File) saveExprs(x interface{}, context string) {
 }
 
 // Save references to C.xxx for later processing.
-func (f *File) saveRef(n *ast.Expr, context string) {
+func (f *File) saveRef(n *ast.Expr, context astContext) {
        sel := (*n).(*ast.SelectorExpr)
        // For now, assume that the only instance of capital C is when
        // used as the imported package identifier.
@@ -189,10 +189,10 @@ func (f *File) saveRef(n *ast.Expr, context string) {
        if l, ok := sel.X.(*ast.Ident); !ok || l.Name != "C" {
                return
        }
-       if context == "as2" {
-               context = "expr"
+       if context == ctxAssign2 {
+               context = ctxExpr
        }
-       if context == "embed-type" {
+       if context == ctxEmbedType {
                error_(sel.Pos(), "cannot embed C type")
        }
        goname := sel.Sel.Name
@@ -223,7 +223,7 @@ func (f *File) saveRef(n *ast.Expr, context string) {
 }
 
 // Save calls to C.xxx for later processing.
-func (f *File) saveCall(call *ast.CallExpr, context string) {
+func (f *File) saveCall(call *ast.CallExpr, context astContext) {
        sel, ok := call.Fun.(*ast.SelectorExpr)
        if !ok {
                return
@@ -231,12 +231,12 @@ func (f *File) saveCall(call *ast.CallExpr, context string) {
        if l, ok := sel.X.(*ast.Ident); !ok || l.Name != "C" {
                return
        }
-       c := &Call{Call: call, Deferred: context == "defer"}
+       c := &Call{Call: call, Deferred: context == ctxDefer}
        f.Calls = append(f.Calls, c)
 }
 
 // If a function should be exported add it to ExpFunc.
-func (f *File) saveExport(x interface{}, context string) {
+func (f *File) saveExport(x interface{}, context astContext) {
        n, ok := x.(*ast.FuncDecl)
        if !ok {
                return
@@ -276,7 +276,7 @@ func (f *File) saveExport(x interface{}, context string) {
 }
 
 // Make f.ExpFunc[i] point at the Func from this AST instead of the other one.
-func (f *File) saveExport2(x interface{}, context string) {
+func (f *File) saveExport2(x interface{}, context astContext) {
        n, ok := x.(*ast.FuncDecl)
        if !ok {
                return
@@ -290,8 +290,30 @@ func (f *File) saveExport2(x interface{}, context string) {
        }
 }
 
+type astContext int
+
+const (
+       ctxProg astContext = iota
+       ctxEmbedType
+       ctxType
+       ctxStmt
+       ctxExpr
+       ctxField
+       ctxParam
+       ctxAssign2 // assignment of a single expression to two variables
+       ctxSwitch
+       ctxTypeSwitch
+       ctxFile
+       ctxDecl
+       ctxSpec
+       ctxDefer
+       ctxCall  // any function call other than ctxCall2
+       ctxCall2 // function call whose result is assigned to two variables
+       ctxSelector
+)
+
 // walk walks the AST x, calling visit(f, x, context) for each node.
-func (f *File) walk(x interface{}, context string, visit func(*File, interface{}, string)) {
+func (f *File) walk(x interface{}, context astContext, visit func(*File, interface{}, astContext)) {
        visit(f, x, context)
        switch n := x.(type) {
        case *ast.Expr:
@@ -306,10 +328,10 @@ func (f *File) walk(x interface{}, context string, visit func(*File, interface{}
 
        // These are ordered and grouped to match ../../go/ast/ast.go
        case *ast.Field:
-               if len(n.Names) == 0 && context == "field" {
-                       f.walk(&n.Type, "embed-type", visit)
+               if len(n.Names) == 0 && context == ctxField {
+                       f.walk(&n.Type, ctxEmbedType, visit)
                } else {
-                       f.walk(&n.Type, "type", visit)
+                       f.walk(&n.Type, ctxType, visit)
                }
        case *ast.FieldList:
                for _, field := range n.List {
@@ -320,163 +342,163 @@ func (f *File) walk(x interface{}, context string, visit func(*File, interface{}
        case *ast.Ellipsis:
        case *ast.BasicLit:
        case *ast.FuncLit:
-               f.walk(n.Type, "type", visit)
-               f.walk(n.Body, "stmt", visit)
+               f.walk(n.Type, ctxType, visit)
+               f.walk(n.Body, ctxStmt, visit)
        case *ast.CompositeLit:
-               f.walk(&n.Type, "type", visit)
-               f.walk(n.Elts, "expr", visit)
+               f.walk(&n.Type, ctxType, visit)
+               f.walk(n.Elts, ctxExpr, visit)
        case *ast.ParenExpr:
                f.walk(&n.X, context, visit)
        case *ast.SelectorExpr:
-               f.walk(&n.X, "selector", visit)
+               f.walk(&n.X, ctxSelector, visit)
        case *ast.IndexExpr:
-               f.walk(&n.X, "expr", visit)
-               f.walk(&n.Index, "expr", visit)
+               f.walk(&n.X, ctxExpr, visit)
+               f.walk(&n.Index, ctxExpr, visit)
        case *ast.SliceExpr:
-               f.walk(&n.X, "expr", visit)
+               f.walk(&n.X, ctxExpr, visit)
                if n.Low != nil {
-                       f.walk(&n.Low, "expr", visit)
+                       f.walk(&n.Low, ctxExpr, visit)
                }
                if n.High != nil {
-                       f.walk(&n.High, "expr", visit)
+                       f.walk(&n.High, ctxExpr, visit)
                }
                if n.Max != nil {
-                       f.walk(&n.Max, "expr", visit)
+                       f.walk(&n.Max, ctxExpr, visit)
                }
        case *ast.TypeAssertExpr:
-               f.walk(&n.X, "expr", visit)
-               f.walk(&n.Type, "type", visit)
+               f.walk(&n.X, ctxExpr, visit)
+               f.walk(&n.Type, ctxType, visit)
        case *ast.CallExpr:
-               if context == "as2" {
-                       f.walk(&n.Fun, "call2", visit)
+               if context == ctxAssign2 {
+                       f.walk(&n.Fun, ctxCall2, visit)
                } else {
-                       f.walk(&n.Fun, "call", visit)
+                       f.walk(&n.Fun, ctxCall, visit)
                }
-               f.walk(n.Args, "expr", visit)
+               f.walk(n.Args, ctxExpr, visit)
        case *ast.StarExpr:
                f.walk(&n.X, context, visit)
        case *ast.UnaryExpr:
-               f.walk(&n.X, "expr", visit)
+               f.walk(&n.X, ctxExpr, visit)
        case *ast.BinaryExpr:
-               f.walk(&n.X, "expr", visit)
-               f.walk(&n.Y, "expr", visit)
+               f.walk(&n.X, ctxExpr, visit)
+               f.walk(&n.Y, ctxExpr, visit)
        case *ast.KeyValueExpr:
-               f.walk(&n.Key, "expr", visit)
-               f.walk(&n.Value, "expr", visit)
+               f.walk(&n.Key, ctxExpr, visit)
+               f.walk(&n.Value, ctxExpr, visit)
 
        case *ast.ArrayType:
-               f.walk(&n.Len, "expr", visit)
-               f.walk(&n.Elt, "type", visit)
+               f.walk(&n.Len, ctxExpr, visit)
+               f.walk(&n.Elt, ctxType, visit)
        case *ast.StructType:
-               f.walk(n.Fields, "field", visit)
+               f.walk(n.Fields, ctxField, visit)
        case *ast.FuncType:
-               f.walk(n.Params, "param", visit)
+               f.walk(n.Params, ctxParam, visit)
                if n.Results != nil {
-                       f.walk(n.Results, "param", visit)
+                       f.walk(n.Results, ctxParam, visit)
                }
        case *ast.InterfaceType:
-               f.walk(n.Methods, "field", visit)
+               f.walk(n.Methods, ctxField, visit)
        case *ast.MapType:
-               f.walk(&n.Key, "type", visit)
-               f.walk(&n.Value, "type", visit)
+               f.walk(&n.Key, ctxType, visit)
+               f.walk(&n.Value, ctxType, visit)
        case *ast.ChanType:
-               f.walk(&n.Value, "type", visit)
+               f.walk(&n.Value, ctxType, visit)
 
        case *ast.BadStmt:
        case *ast.DeclStmt:
-               f.walk(n.Decl, "decl", visit)
+               f.walk(n.Decl, ctxDecl, visit)
        case *ast.EmptyStmt:
        case *ast.LabeledStmt:
-               f.walk(n.Stmt, "stmt", visit)
+               f.walk(n.Stmt, ctxStmt, visit)
        case *ast.ExprStmt:
-               f.walk(&n.X, "expr", visit)
+               f.walk(&n.X, ctxExpr, visit)
        case *ast.SendStmt:
-               f.walk(&n.Chan, "expr", visit)
-               f.walk(&n.Value, "expr", visit)
+               f.walk(&n.Chan, ctxExpr, visit)
+               f.walk(&n.Value, ctxExpr, visit)
        case *ast.IncDecStmt:
-               f.walk(&n.X, "expr", visit)
+               f.walk(&n.X, ctxExpr, visit)
        case *ast.AssignStmt:
-               f.walk(n.Lhs, "expr", visit)
+               f.walk(n.Lhs, ctxExpr, visit)
                if len(n.Lhs) == 2 && len(n.Rhs) == 1 {
-                       f.walk(n.Rhs, "as2", visit)
+                       f.walk(n.Rhs, ctxAssign2, visit)
                } else {
-                       f.walk(n.Rhs, "expr", visit)
+                       f.walk(n.Rhs, ctxExpr, visit)
                }
        case *ast.GoStmt:
-               f.walk(n.Call, "expr", visit)
+               f.walk(n.Call, ctxExpr, visit)
        case *ast.DeferStmt:
-               f.walk(n.Call, "defer", visit)
+               f.walk(n.Call, ctxDefer, visit)
        case *ast.ReturnStmt:
-               f.walk(n.Results, "expr", visit)
+               f.walk(n.Results, ctxExpr, visit)
        case *ast.BranchStmt:
        case *ast.BlockStmt:
                f.walk(n.List, context, visit)
        case *ast.IfStmt:
-               f.walk(n.Init, "stmt", visit)
-               f.walk(&n.Cond, "expr", visit)
-               f.walk(n.Body, "stmt", visit)
-               f.walk(n.Else, "stmt", visit)
+               f.walk(n.Init, ctxStmt, visit)
+               f.walk(&n.Cond, ctxExpr, visit)
+               f.walk(n.Body, ctxStmt, visit)
+               f.walk(n.Else, ctxStmt, visit)
        case *ast.CaseClause:
-               if context == "typeswitch" {
-                       context = "type"
+               if context == ctxTypeSwitch {
+                       context = ctxType
                } else {
-                       context = "expr"
+                       context = ctxExpr
                }
                f.walk(n.List, context, visit)
-               f.walk(n.Body, "stmt", visit)
+               f.walk(n.Body, ctxStmt, visit)
        case *ast.SwitchStmt:
-               f.walk(n.Init, "stmt", visit)
-               f.walk(&n.Tag, "expr", visit)
-               f.walk(n.Body, "switch", visit)
+               f.walk(n.Init, ctxStmt, visit)
+               f.walk(&n.Tag, ctxExpr, visit)
+               f.walk(n.Body, ctxSwitch, visit)
        case *ast.TypeSwitchStmt:
-               f.walk(n.Init, "stmt", visit)
-               f.walk(n.Assign, "stmt", visit)
-               f.walk(n.Body, "typeswitch", visit)
+               f.walk(n.Init, ctxStmt, visit)
+               f.walk(n.Assign, ctxStmt, visit)
+               f.walk(n.Body, ctxTypeSwitch, visit)
        case *ast.CommClause:
-               f.walk(n.Comm, "stmt", visit)
-               f.walk(n.Body, "stmt", visit)
+               f.walk(n.Comm, ctxStmt, visit)
+               f.walk(n.Body, ctxStmt, visit)
        case *ast.SelectStmt:
-               f.walk(n.Body, "stmt", visit)
+               f.walk(n.Body, ctxStmt, visit)
        case *ast.ForStmt:
-               f.walk(n.Init, "stmt", visit)
-               f.walk(&n.Cond, "expr", visit)
-               f.walk(n.Post, "stmt", visit)
-               f.walk(n.Body, "stmt", visit)
+               f.walk(n.Init, ctxStmt, visit)
+               f.walk(&n.Cond, ctxExpr, visit)
+               f.walk(n.Post, ctxStmt, visit)
+               f.walk(n.Body, ctxStmt, visit)
        case *ast.RangeStmt:
-               f.walk(&n.Key, "expr", visit)
-               f.walk(&n.Value, "expr", visit)
-               f.walk(&n.X, "expr", visit)
-               f.walk(n.Body, "stmt", visit)
+               f.walk(&n.Key, ctxExpr, visit)
+               f.walk(&n.Value, ctxExpr, visit)
+               f.walk(&n.X, ctxExpr, visit)
+               f.walk(n.Body, ctxStmt, visit)
 
        case *ast.ImportSpec:
        case *ast.ValueSpec:
-               f.walk(&n.Type, "type", visit)
+               f.walk(&n.Type, ctxType, visit)
                if len(n.Names) == 2 && len(n.Values) == 1 {
-                       f.walk(&n.Values[0], "as2", visit)
+                       f.walk(&n.Values[0], ctxAssign2, visit)
                } else {
-                       f.walk(n.Values, "expr", visit)
+                       f.walk(n.Values, ctxExpr, visit)
                }
        case *ast.TypeSpec:
-               f.walk(&n.Type, "type", visit)
+               f.walk(&n.Type, ctxType, visit)
 
        case *ast.BadDecl:
        case *ast.GenDecl:
-               f.walk(n.Specs, "spec", visit)
+               f.walk(n.Specs, ctxSpec, visit)
        case *ast.FuncDecl:
                if n.Recv != nil {
-                       f.walk(n.Recv, "param", visit)
+                       f.walk(n.Recv, ctxParam, visit)
                }
-               f.walk(n.Type, "type", visit)
+               f.walk(n.Type, ctxType, visit)
                if n.Body != nil {
-                       f.walk(n.Body, "stmt", visit)
+                       f.walk(n.Body, ctxStmt, visit)
                }
 
        case *ast.File:
-               f.walk(n.Decls, "decl", visit)
+               f.walk(n.Decls, ctxDecl, visit)
 
        case *ast.Package:
                for _, file := range n.Files {
-                       f.walk(file, "file", visit)
+                       f.walk(file, ctxFile, visit)
                }
 
        case []ast.Decl:

diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 774786405c0e9ea0a70b3110a4e7777538fe5a85..af0ed216a51865839005780346e709722e7f9684 100644 (file)
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -748,7 +748,7 @@ func (p *Package) rewriteCall(f *File, call *Call, name *Name) bool {
 
                        // If this call expects two results, we have to
                        // adjust the results of the function we generated.
-                       if ref.Context == "call2" {
+                       if ref.Context == ctxCall2 {
                                if ftype.Results == nil {
                                        // An explicit void argument
                                        // looks odd but it seems to
@@ -940,8 +940,8 @@ func (p *Package) checkAddrArgs(f *File, args []ast.Expr, x ast.Expr) []ast.Expr
 // effect is a function call.
 func (p *Package) hasSideEffects(f *File, x ast.Expr) bool {
        found := false
-       f.walk(x, "expr",
-               func(f *File, x interface{}, context string) {
+       f.walk(x, ctxExpr,
+               func(f *File, x interface{}, context astContext) {
                        switch x.(type) {
                        case *ast.CallExpr:
                                found = true
@@ -1080,10 +1080,10 @@ func (p *Package) rewriteRef(f *File) {
                }
                var expr ast.Expr = ast.NewIdent(r.Name.Mangle) // default
                switch r.Context {
-               case "call", "call2":
+               case ctxCall, ctxCall2:
                        if r.Name.Kind != "func" {
                                if r.Name.Kind == "type" {
-                                       r.Context = "type"
+                                       r.Context = ctxType
                                        if r.Name.Type == nil {
                                                error_(r.Pos(), "invalid conversion to C.%s: undefined C type '%s'", fixGo(r.Name.Go), r.Name.C)
                                                break
@@ -1095,7 +1095,7 @@ func (p *Package) rewriteRef(f *File) {
                                break
                        }
                        functions[r.Name.Go] = true
-                       if r.Context == "call2" {
+                       if r.Context == ctxCall2 {
                                if r.Name.Go == "_CMalloc" {
                                        error_(r.Pos(), "no two-result form for C.malloc")
                                        break
@@ -1113,7 +1113,7 @@ func (p *Package) rewriteRef(f *File) {
                                r.Name = n
                                break
                        }
-               case "expr":
+               case ctxExpr:
                        switch r.Name.Kind {
                        case "func":
                                if builtinDefs[r.Name.C] != "" {
@@ -1154,13 +1154,13 @@ func (p *Package) rewriteRef(f *File) {
                        case "macro":
                                expr = &ast.CallExpr{Fun: expr}
                        }
-               case "selector":
+               case ctxSelector:
                        if r.Name.Kind == "var" {
                                expr = &ast.StarExpr{Star: (*r.Expr).Pos(), X: expr}
                        } else {
                                error_(r.Pos(), "only C variables allowed in selector expression %s", fixGo(r.Name.Go))
                        }
-               case "type":
+               case ctxType:
                        if r.Name.Kind != "type" {
                                error_(r.Pos(), "expression C.%s used as type", fixGo(r.Name.Go))
                        } else if r.Name.Type == nil {

diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go
index f2a2d859aa3394adc091e02ad96cb6b672ea378b..8e6bb1f977950cb741a473e945c6bae4871f2a1e 100644 (file)
--- a/src/cmd/cgo/main.go
+++ b/src/cmd/cgo/main.go
@@ -76,7 +76,7 @@ type Call struct {
 type Ref struct {
        Name    *Name
        Expr    *ast.Expr
-       Context string // "type", "expr", "call", or "call2"
+       Context astContext
 }
 
 func (r *Ref) Pos() token.Pos {
@@ -301,7 +301,7 @@ func main() {
                p.Translate(f)
                for _, cref := range f.Ref {
                        switch cref.Context {
-                       case "call", "call2":
+                       case ctxCall, ctxCall2:
                                if cref.Name.Kind != "type" {
                                        break
                                }