cgo: support export for built-in types

This change doesn't pay attention to structs
so they still cannot be exported, see Issue 2552.

Fixes #2462.

R=dvyukov, rsc, iant
CC=golang-dev
https://golang.org/cl/5487058

misc/cgo/test/Makefile

@@ -16,6 +16,7 @@ CGOFILES=\
 	issue1222.go\
 	issue1328.go\
 	issue1560.go\
+	issue2462.go\
 	duplicate_symbol.go\
 
 CGO_OFILES=\

misc/cgo/test/basic.go

@@ -128,9 +128,9 @@ func testMultipleAssign(t *testing.T) {
 }
 
 var (
-	uint  = (C.uint)(0)
-	ulong C.ulong
-	char  C.char
+	cuint  = (C.uint)(0)
+	culong C.ulong
+	cchar  C.char
 )
 
 type Context struct {

misc/cgo/test/issue2462.go

@@ -0,0 +1,102 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cgotest
+
+import "C"
+
+//export exportbyte
+func exportbyte() byte {
+	return 0
+}
+
+//export exportbool
+func exportbool() bool {
+	return false
+}
+
+//export exportrune
+func exportrune() rune {
+	return 0
+}
+
+//export exporterror
+func exporterror() error {
+	return nil
+}
+
+//export exportint
+func exportint() int {
+	return 0
+}
+
+//export exportuint
+func exportuint() uint {
+	return 0
+}
+
+//export exportuintptr
+func exportuintptr() uintptr {
+	return (uintptr)(0)
+}
+
+//export exportint8
+func exportint8() int8 {
+	return 0
+}
+
+//export exportuint8
+func exportuint8() uint8 {
+	return 0
+}
+
+//export exportint16
+func exportint16() int16 {
+	return 0
+}
+
+//export exportuint16
+func exportuint16() uint16 {
+	return 0
+}
+
+//export exportint32
+func exportint32() int32 {
+	return 0
+}
+
+//export exportuint32
+func exportuint32() uint32 {
+	return 0
+}
+
+//export exportint64
+func exportint64() int64 {
+	return 0
+}
+
+//export exportuint64
+func exportuint64() uint64 {
+	return 0
+}
+
+//export exportfloat32
+func exportfloat32() float32 {
+	return 0
+}
+
+//export exportfloat64
+func exportfloat64() float64 {
+	return 0
+}
+
+//export exportcomplex64
+func exportcomplex64() complex64 {
+	return 0
+}
+
+//export exportcomplex128
+func exportcomplex128() complex128 {
+	return 0
+}

src/cmd/cgo/out.go

@@ -599,8 +599,11 @@ func c(repr string, args ...interface{}) *TypeRepr {
 
 // Map predeclared Go types to Type.
 var goTypes = map[string]*Type{
+	"bool":       {Size: 1, Align: 1, C: c("uchar")},
+	"byte":       {Size: 1, Align: 1, C: c("uchar")},
 	"int":        {Size: 4, Align: 4, C: c("int")},
 	"uint":       {Size: 4, Align: 4, C: c("uint")},
+	"rune":       {Size: 4, Align: 4, C: c("int")},
 	"int8":       {Size: 1, Align: 1, C: c("schar")},
 	"uint8":      {Size: 1, Align: 1, C: c("uchar")},
 	"int16":      {Size: 2, Align: 2, C: c("short")},
@@ -632,7 +635,7 @@ func (p *Package) cgoType(e ast.Expr) *Type {
 	case *ast.FuncType:
 		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
 	case *ast.InterfaceType:
-		return &Type{Size: 3 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
+		return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
 	case *ast.MapType:
 		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoMap")}
 	case *ast.ChanType:
@@ -666,6 +669,9 @@ func (p *Package) cgoType(e ast.Expr) *Type {
 		if t.Name == "string" {
 			return &Type{Size: p.PtrSize + 4, Align: p.PtrSize, C: c("GoString")}
 		}
+		if t.Name == "error" {
+			return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
+		}
 		if r, ok := goTypes[t.Name]; ok {
 			if r.Align > p.PtrSize {
 				r.Align = p.PtrSize