reflect: adjust access to unexported embedded structs

This CL changes reflect to allow access to exported fields and
methods in unexported embedded structs for gccgo and after gc
has been adjusted to disallow access to embedded unexported structs.

Adresses #12367, #7363, #11007, and #7247.

Change-Id: If80536eab35abcd25300d8ddc2d27d5c42d7e78e
Reviewed-on: https://go-review.googlesource.com/14010Reviewed-by: Russ Cox <rsc@golang.org>

src/reflect/export_test.go

@@ -8,13 +8,13 @@ import "unsafe"
 
 // MakeRO returns a copy of v with the read-only flag set.
 func MakeRO(v Value) Value {
-	v.flag |= flagRO
+	v.flag |= flagStickyRO
 	return v
 }
 
 // IsRO reports whether v's read-only flag is set.
 func IsRO(v Value) bool {
-	return v.flag&flagRO != 0
+	return v.flag&flagStickyRO != 0
 }
 
 var CallGC = &callGC

src/reflect/type.go

@@ -496,7 +496,7 @@ func (t *uncommonType) Method(i int) (m Method) {
 	fl := flag(Func)
 	if p.pkgPath != nil {
 		m.PkgPath = *p.pkgPath
-		fl |= flagRO
+		fl |= flagStickyRO
 	}
 	mt := p.typ
 	m.Type = mt

src/reflect/value.go

@@ -44,7 +44,8 @@ type Value struct {
 
 	// flag holds metadata about the value.
 	// The lowest bits are flag bits:
-	//	- flagRO: obtained via unexported field, so read-only
+	//	- flagStickyRO: obtained via unexported not embedded field, so read-only
+	//	- flagEmbedRO: obtained via unexported embedded field, so read-only
 	//	- flagIndir: val holds a pointer to the data
 	//	- flagAddr: v.CanAddr is true (implies flagIndir)
 	//	- flagMethod: v is a method value.
@@ -67,11 +68,13 @@ type flag uintptr
 const (
 	flagKindWidth        = 5 // there are 27 kinds
 	flagKindMask    flag = 1<<flagKindWidth - 1
-	flagRO          flag = 1 << 5
-	flagIndir       flag = 1 << 6
-	flagAddr        flag = 1 << 7
-	flagMethod      flag = 1 << 8
-	flagMethodShift      = 9
+	flagStickyRO    flag = 1 << 5
+	flagEmbedRO     flag = 1 << 6
+	flagIndir       flag = 1 << 7
+	flagAddr        flag = 1 << 8
+	flagMethod      flag = 1 << 9
+	flagMethodShift      = 10
+	flagRO          flag = flagStickyRO | flagEmbedRO
 )
 
 func (f flag) kind() Kind {
@@ -745,11 +748,15 @@ func (v Value) Field(i int) Value {
 	field := &tt.fields[i]
 	typ := field.typ
 
-	// Inherit permission bits from v.
-	fl := v.flag&(flagRO|flagIndir|flagAddr) | flag(typ.Kind())
+	// Inherit permission bits from v, but clear flagEmbedRO.
+	fl := v.flag&(flagStickyRO|flagIndir|flagAddr) | flag(typ.Kind())
 	// Using an unexported field forces flagRO.
 	if field.pkgPath != nil {
-		fl |= flagRO
+		if field.name == nil {
+			fl |= flagEmbedRO
+		} else {
+			fl |= flagStickyRO
+		}
 	}
 	// Either flagIndir is set and v.ptr points at struct,
 	// or flagIndir is not set and v.ptr is the actual struct data.
@@ -1104,7 +1111,7 @@ func (v Value) Method(i int) Value {
 	if v.typ.Kind() == Interface && v.IsNil() {
 		panic("reflect: Method on nil interface value")
 	}
-	fl := v.flag & (flagRO | flagIndir)
+	fl := v.flag & (flagStickyRO | flagIndir) // Clear flagEmbedRO
 	fl |= flag(Func)
 	fl |= flag(i)<<flagMethodShift | flagMethod
 	return Value{v.typ, v.ptr, fl}