cmd/compile/internal/gc: export interface embedding information

Fixes #16369.

Change-Id: I23f8c36370d0da37ac5b5126d012d22f78782782
Reviewed-on: https://go-review.googlesource.com/38392
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -753,39 +753,7 @@ func (p *exporter) typ(t *Type) {
 
 	case TINTER:
 		p.tag(interfaceTag)
-		// gc doesn't separate between embedded interfaces
-		// and methods declared explicitly with an interface
-		p.int(0) // no embedded interfaces
-
-		// Because the compiler flattens interfaces containing
-		// embedded interfaces, it is possible to create interface
-		// types that recur through an unnamed type.
-		// If trackAllTypes is disabled, such recursion is not
-		// detected, leading to a stack overflow during export
-		// (issue #16369).
-		// As a crude work-around we terminate deep recursion
-		// through interface types with an empty interface and
-		// report an error.
-		// This will catch endless recursion, but is unlikely
-		// to trigger for valid, deeply nested types given the
-		// high threshold.
-		// It would be ok to continue without reporting an error
-		// since the export format is valid. But a subsequent
-		// import would import an incorrect type. The textual
-		// exporter does not report an error but importing the
-		// resulting package will lead to a syntax error during
-		// import.
-		// TODO(gri) remove this once we have a permanent fix
-		// for the issue.
-		if p.nesting > 100 {
-			p.int(0) // 0 methods to indicate empty interface
-			yyerrorl(t.Pos, "cannot export unnamed recursive interface")
-			break
-		}
-
-		p.nesting++
 		p.methodList(t)
-		p.nesting--
 
 	case TMAP:
 		p.tag(mapTag)
@@ -830,18 +798,44 @@ func (p *exporter) field(f *Field) {
 }
 
 func (p *exporter) methodList(t *Type) {
-	if p.trace && t.NumFields() > 0 {
-		p.tracef("methods {>")
-		defer p.tracef("<\n} ")
+	var embeddeds, methods []*Field
+
+	for _, m := range t.Methods().Slice() {
+		if m.Sym != nil {
+			methods = append(methods, m)
+		} else {
+			embeddeds = append(embeddeds, m)
+		}
 	}
 
-	p.int(t.NumFields())
-	for _, m := range t.Fields().Slice() {
+	if p.trace && len(embeddeds) > 0 {
+		p.tracef("embeddeds {>")
+	}
+	p.int(len(embeddeds))
+	for _, m := range embeddeds {
+		if p.trace {
+			p.tracef("\n")
+		}
+		p.pos(m.Nname)
+		p.typ(m.Type)
+	}
+	if p.trace && len(embeddeds) > 0 {
+		p.tracef("<\n} ")
+	}
+
+	if p.trace && len(methods) > 0 {
+		p.tracef("methods {>")
+	}
+	p.int(len(methods))
+	for _, m := range methods {
 		if p.trace {
 			p.tracef("\n")
 		}
 		p.method(m)
 	}
+	if p.trace && len(methods) > 0 {
+		p.tracef("<\n} ")
+	}
 }
 
 func (p *exporter) method(m *Field) {

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

@@ -526,9 +526,6 @@ func (p *importer) typ() *Type {
 		functypefield0(t, nil, params, result)
 
 	case interfaceTag:
-		if p.int() != 0 {
-			formatErrorf("unexpected embedded interface")
-		}
 		if ml := p.methodList(); len(ml) == 0 {
 			t = Types[TINTER]
 		} else {
@@ -604,12 +601,18 @@ func (p *importer) field() *Field {
 }
 
 func (p *importer) methodList() (methods []*Field) {
-	if n := p.int(); n > 0 {
-		methods = make([]*Field, n)
-		for i := range methods {
-			methods[i] = p.method()
+	for n := p.int(); n > 0; n-- {
+		f := newField()
+		f.Nname = newname(nblank.Sym)
+		f.Nname.Pos = p.pos()
+		f.Type = p.typ()
+		methods = append(methods, f)
 	}
+
+	for n := p.int(); n > 0; n-- {
+		methods = append(methods, p.method())
 	}
+
 	return
 }
 

src/go/internal/gcimporter/bimport.go

@@ -492,12 +492,13 @@ func (p *importer) typ(parent *types.Package) types.Type {
 			p.record(nil)
 		}
 
-		// no embedded interfaces with gc compiler
-		if p.int() != 0 {
-			errorf("unexpected embedded interface")
+		var embeddeds []*types.Named
+		for n := p.int(); n > 0; n-- {
+			p.pos()
+			embeddeds = append(embeddeds, p.typ(parent).(*types.Named))
 		}
 
-		t := types.NewInterface(p.methodList(parent), nil)
+		t := types.NewInterface(p.methodList(parent), embeddeds)
 		if p.trackAllTypes {
 			p.typList[n] = t
 		}

src/go/internal/gcimporter/gcimporter_test.go

@@ -205,7 +205,7 @@ var importedObjectTests = []struct {
 }{
 	{"math.Pi", "const Pi untyped float"},
 	{"io.Reader", "type Reader interface{Read(p []byte) (n int, err error)}"},
-	{"io.ReadWriter", "type ReadWriter interface{Read(p []byte) (n int, err error); Write(p []byte) (n int, err error)}"},
+	{"io.ReadWriter", "type ReadWriter interface{Reader; Writer}"},
 	{"math.Sin", "func Sin(x float64) float64"},
 	// TODO(gri) add more tests
 }

test/fixedbugs/issue16369.go

-// errorcheck
+// compile
 
 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,7 +7,7 @@
 package p
 
 type T interface {
-	M(interface { // ERROR "cannot export unnamed recursive interface"
+	M(interface {
 		T
 	})
 }