cmd/compile, reflect: use field pkgPath if needed

It's possible for the pkgPath of a field to be different than that of
the struct type as a whole. In that case, store the field's pkgPath in
the name field. Use the field's pkgPath when setting PkgPath and when
checking for type identity.

Fixes #17952.

Change-Id: Iebaf92f0054b11427c8f6e4158c3bebcfff06f45
Reviewed-on: https://go-review.googlesource.com/33333
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -494,26 +494,31 @@ func dgopkgpathOffLSym(s *obj.LSym, ot int, pkg *Pkg) int {
 }
 
 // isExportedField reports whether a struct field is exported.
-func isExportedField(ft *Field) bool {
+// It also returns the package to use for PkgPath for an unexported field.
+func isExportedField(ft *Field) (bool, *Pkg) {
 	if ft.Sym != nil && ft.Embedded == 0 {
-		return exportname(ft.Sym.Name)
+		return exportname(ft.Sym.Name), ft.Sym.Pkg
 	} else {
 		if ft.Type.Sym != nil &&
 			(ft.Type.Sym.Pkg == builtinpkg || !exportname(ft.Type.Sym.Name)) {
-			return false
+			return false, ft.Type.Sym.Pkg
 		} else {
-			return true
+			return true, nil
 		}
 	}
 }
 
 // dnameField dumps a reflect.name for a struct field.
-func dnameField(s *Sym, ot int, ft *Field) int {
+func dnameField(s *Sym, ot int, spkg *Pkg, ft *Field) int {
 	var name string
 	if ft.Sym != nil && ft.Embedded == 0 {
 		name = ft.Sym.Name
 	}
-	nsym := dname(name, ft.Note, nil, isExportedField(ft))
+	isExported, fpkg := isExportedField(ft)
+	if isExported || fpkg == spkg {
+		fpkg = nil
+	}
+	nsym := dname(name, ft.Note, fpkg, isExported)
 	return dsymptrLSym(Linksym(s), ot, nsym, 0)
 }
 
@@ -1332,7 +1337,7 @@ ok:
 
 		for _, f := range t.Fields().Slice() {
 			// ../../../../runtime/type.go:/structField
-			ot = dnameField(s, ot, f)
+			ot = dnameField(s, ot, pkg, f)
 			ot = dsymptr(s, ot, dtypesym(f.Type), 0)
 			ot = duintptr(s, ot, uint64(f.Offset))
 		}

src/reflect/all_test.go

@@ -2325,25 +2325,39 @@ func TestFieldPkgPath(t *testing.T) {
 		unexported string
 		OtherPkgFields
 	}{})
-	for _, test := range []struct {
+
+	type pkgpathTest struct {
 		index     []int
 		pkgPath   string
 		anonymous bool
-	}{
+	}
+
+	checkPkgPath := func(name string, s []pkgpathTest) {
+		for _, test := range s {
+			f := typ.FieldByIndex(test.index)
+			if got, want := f.PkgPath, test.pkgPath; got != want {
+				t.Errorf("%s: Field(%d).PkgPath = %q, want %q", name, test.index, got, want)
+			}
+			if got, want := f.Anonymous, test.anonymous; got != want {
+				t.Errorf("%s: Field(%d).Anonymous = %v, want %v", name, test.index, got, want)
+			}
+		}
+	}
+
+	checkPkgPath("testStruct", []pkgpathTest{
 		{[]int{0}, "", false},             // Exported
 		{[]int{1}, "reflect_test", false}, // unexported
 		{[]int{2}, "", true},              // OtherPkgFields
 		{[]int{2, 0}, "", false},          // OtherExported
 		{[]int{2, 1}, "reflect", false},   // otherUnexported
-	} {
-		f := typ.FieldByIndex(test.index)
-		if got, want := f.PkgPath, test.pkgPath; got != want {
-			t.Errorf("Field(%d).PkgPath = %q, want %q", test.index, got, want)
-		}
-		if got, want := f.Anonymous, test.anonymous; got != want {
-			t.Errorf("Field(%d).Anonymous = %v, want %v", test.index, got, want)
-		}
-	}
+	})
+
+	type localOtherPkgFields OtherPkgFields
+	typ = TypeOf(localOtherPkgFields{})
+	checkPkgPath("localOtherPkgFields", []pkgpathTest{
+		{[]int{0}, "", false},        // OtherExported
+		{[]int{1}, "reflect", false}, // otherUnexported
+	})
 }
 
 func TestVariadicType(t *testing.T) {

src/reflect/type.go

@@ -1226,8 +1226,10 @@ func (t *structType) Field(i int) (f StructField) {
 		f.Anonymous = true
 	}
 	if !p.name.isExported() {
-		// Fields never have an import path in their name.
-		f.PkgPath = t.pkgPath.name()
+		f.PkgPath = p.name.pkgPath()
+		if f.PkgPath == "" {
+			f.PkgPath = t.pkgPath.name()
+		}
 	}
 	if tag := p.name.tag(); tag != "" {
 		f.Tag = StructTag(tag)
@@ -1680,7 +1682,6 @@ func haveIdenticalUnderlyingType(T, V *rtype, cmpTags bool) bool {
 		if len(t.fields) != len(v.fields) {
 			return false
 		}
-		allExported := true
 		for i := range t.fields {
 			tf := &t.fields[i]
 			vf := &v.fields[i]
@@ -1696,15 +1697,19 @@ func haveIdenticalUnderlyingType(T, V *rtype, cmpTags bool) bool {
 			if tf.offset != vf.offset {
 				return false
 			}
-			allExported = allExported && tf.name.isExported()
-		}
-		if !allExported && t.pkgPath.name() != v.pkgPath.name() {
-			// An unexported field of a struct is not
-			// visible outside of the package that defines
-			// it, so the package path is implicitly part
-			// of the definition of any struct with an
-			// unexported field.
-			return false
+			if !tf.name.isExported() {
+				tp := tf.name.pkgPath()
+				if tp == "" {
+					tp = t.pkgPath.name()
+				}
+				vp := vf.name.pkgPath()
+				if vp == "" {
+					vp = v.pkgPath.name()
+				}
+				if tp != vp {
+					return false
+				}
+			}
 		}
 		return true
 	}