This patch enables cgo utility to correctly convert enums in the C source

into consts in the resulting Go source.  Previously known as issue 161047,
which I deleted accidentally.  Fixes issue 207.

R=rsc
https://golang.org/cl/166059

AUTHORS

@@ -35,6 +35,7 @@ Kei Son <hey.calmdown@gmail.com>
 Kevin Ballard <kevin@sb.org>
 Michael Elkins <michael.elkins@gmail.com>
 Michael Hoisie <hoisie@gmail.com>
+Moriyoshi Koizumi <mozo@mozo.jp>
 Môshe van der Sterre <moshevds@gmail.com>
 Peter Froehlich <peter.hans.froehlich@gmail.com>
 Roger Peppe <rogpeppe@gmail.com>

CONTRIBUTORS

@@ -69,6 +69,7 @@ Larry Hosken <lahosken@golang.org>
 Maxim Ushakov <ushakov@google.com>
 Michael Elkins <michael.elkins@gmail.com>
 Michael Hoisie <hoisie@gmail.com>
+Moriyoshi Koizumi <mozo@mozo.jp>
 Môshe van der Sterre <moshevds@gmail.com>
 Nigel Tao <nigeltao@golang.org>
 Peter Froehlich <peter.hans.froehlich@gmail.com>

src/cmd/cgo/ast.go

@@ -35,6 +35,7 @@ type Prog struct {
 	Typedef     map[string]ast.Expr
 	Vardef      map[string]*Type
 	Funcdef     map[string]*FuncType
+	Enumdef     map[string]int64
 	PtrSize     int64
 	GccOptions  []string
 }
@@ -45,6 +46,7 @@ type Type struct {
 	Align      int64
 	C          string
 	Go         ast.Expr
+	EnumValues map[string]int64
 }
 
 // A FuncType collects information about a function type in both the C and Go worlds.

src/cmd/cgo/gcc.go

@@ -120,6 +120,7 @@ func (p *Prog) loadDebugInfo() {
 
 	// Scan DWARF info for top-level TagVariable entries with AttrName __cgo__i.
 	types := make([]dwarf.Type, len(names))
+	enums := make([]dwarf.Offset, len(names))
 	r := d.Reader()
 	for {
 		e, err := r.Next()
@@ -129,16 +130,33 @@ func (p *Prog) loadDebugInfo() {
 		if e == nil {
 			break
 		}
-		if e.Tag != dwarf.TagVariable {
-			goto Continue
+		switch e.Tag {
+		case dwarf.TagEnumerationType:
+			offset := e.Offset
+			for {
+				e, err := r.Next()
+				if err != nil {
+					fatal("reading DWARF entry: %s", err)
 				}
+				if e.Tag == 0 {
+					break
+				}
+				if e.Tag == dwarf.TagEnumerator {
+					entryName := e.Val(dwarf.AttrName).(string)
+					i, ok := m[entryName]
+					if ok {
+						enums[i] = offset
+					}
+				}
+			}
+		case dwarf.TagVariable:
 			name, _ := e.Val(dwarf.AttrName).(string)
 			typOff, _ := e.Val(dwarf.AttrType).(dwarf.Offset)
 			if name == "" || typOff == 0 {
 				fatal("malformed DWARF TagVariable entry")
 			}
 			if !strings.HasPrefix(name, "__cgo__") {
-			goto Continue
+				break
 			}
 			typ, err := d.Type(typOff)
 			if err != nil {
@@ -152,9 +170,16 @@ func (p *Prog) loadDebugInfo() {
 			if err != nil {
 				fatal("malformed __cgo__ name: %s", name)
 			}
+			if enums[i] != 0 {
+				t, err := d.Type(enums[i])
+				if err != nil {
+					fatal("loading DWARF type: %s", err)
+				}
+				types[i] = t
+			} else {
 				types[i] = t.Type
-
-	Continue:
+			}
+		}
 		if e.Tag != dwarf.TagCompileUnit {
 			r.SkipChildren()
 		}
@@ -315,6 +340,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 	t.Size = dtype.Size()
 	t.Align = -1
 	t.C = dtype.Common().Name
+	t.EnumValues = nil
 	c.m[dtype] = t
 	if t.Size < 0 {
 		// Unsized types are [0]byte
@@ -376,6 +402,10 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 			t.Align = c.ptrSize
 		}
 		t.C = "enum " + dt.EnumName
+		t.EnumValues = make(map[string]int64)
+		for _, ev := range dt.Val {
+			t.EnumValues[ev.Name] = ev.Val
+		}
 
 	case *dwarf.FloatType:
 		switch t.Size {

src/cmd/cgo/main.go

@@ -71,6 +71,7 @@ func main() {
 	p.loadDebugInfo()
 	p.Vardef = make(map[string]*Type)
 	p.Funcdef = make(map[string]*FuncType)
+	p.Enumdef = make(map[string]int64)
 
 	for _, cref := range p.Crefs {
 		switch cref.Context {
@@ -86,6 +87,14 @@ func main() {
 			if cref.TypeName {
 				error((*cref.Expr).Pos(), "type C.%s used as expression", cref.Name)
 			}
+			// If the expression refers to an enumerated value, then
+			// place the identifier for the value and add it to Enumdef so
+			// it will be declared as a constant in the later stage.
+			if cref.Type.EnumValues != nil {
+				*cref.Expr = &ast.Ident{Value: cref.Name}
+				p.Enumdef[cref.Name] = cref.Type.EnumValues[cref.Name]
+				break
+			}
 			// Reference to C variable.
 			// We declare a pointer and arrange to have it filled in.
 			*cref.Expr = &ast.StarExpr{X: &ast.Ident{Value: "_C_" + cref.Name}}

src/cmd/cgo/out.go

@@ -69,6 +69,11 @@ func (p *Prog) writeOutput(srcfile string) {
 	}
 	fmt.Fprintf(fc, "\n")
 
+	for name, value := range p.Enumdef {
+		fmt.Fprintf(fgo2, "const %s = %d\n", name, value)
+	}
+	fmt.Fprintf(fgo2, "\n")
+
 	for name, def := range p.Funcdef {
 		// Go func declaration.
 		d := &ast.FuncDecl{