diff --git a/src/go/types/exprstring.go b/src/go/types/exprstring.go
index 28d605f5ee..0d9ae58dfc 100644
--- a/src/go/types/exprstring.go
+++ b/src/go/types/exprstring.go
@@ -8,6 +8,7 @@ package types
 
 import (
 	"bytes"
+	"fmt"
 	"go/ast"
 )
 
@@ -31,7 +32,7 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 
 	switch x := x.(type) {
 	default:
-		buf.WriteString("(bad expr)") // nil, ast.BadExpr, ast.KeyValueExpr
+		buf.WriteString(fmt.Sprintf("(ast: %T)", x)) // nil, ast.BadExpr, ast.KeyValueExpr
 
 	case *ast.Ident:
 		buf.WriteString(x.Name)
@@ -97,17 +98,16 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 
 	case *ast.CallExpr:
 		WriteExpr(buf, x.Fun)
-		buf.WriteByte('(')
-		for i, arg := range x.Args {
-			if i > 0 {
-				buf.WriteString(", ")
-			}
-			WriteExpr(buf, arg)
+		var l, r byte = '(', ')'
+		if x.Brackets {
+			l, r = '[', ']'
 		}
+		buf.WriteByte(l)
+		writeExprList(buf, x.Args)
 		if x.Ellipsis.IsValid() {
 			buf.WriteString("...")
 		}
-		buf.WriteByte(')')
+		buf.WriteByte(r)
 
 	case *ast.StarExpr:
 		buf.WriteByte('*')
@@ -134,7 +134,7 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 
 	case *ast.StructType:
 		buf.WriteString("struct{")
-		writeFieldList(buf, x.Fields, "; ", false)
+		writeFieldList(buf, x.Fields.List, "; ", false)
 		buf.WriteByte('}')
 
 	case *ast.FuncType:
@@ -142,8 +142,29 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 		writeSigExpr(buf, x)
 
 	case *ast.InterfaceType:
+		// separate type list types from method list
+		// TODO(gri) we can get rid of this extra code if writeExprList does the separation
+		var types []ast.Expr
+		var methods []*ast.Field
+		for _, f := range x.Methods.List {
+			if len(f.Names) > 1 && f.Names[0].Name == "type" {
+				// type list type
+				types = append(types, f.Type)
+			} else {
+				// method or embedded interface
+				methods = append(methods, f)
+			}
+		}
+
 		buf.WriteString("interface{")
-		writeFieldList(buf, x.Methods, "; ", true)
+		writeFieldList(buf, methods, "; ", true)
+		if len(types) > 0 {
+			if len(methods) > 0 {
+				buf.WriteString("; ")
+			}
+			buf.WriteString("type ")
+			writeExprList(buf, types)
+		}
 		buf.WriteByte('}')
 
 	case *ast.MapType:
@@ -169,7 +190,7 @@ func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
 
 func writeSigExpr(buf *bytes.Buffer, sig *ast.FuncType) {
 	buf.WriteByte('(')
-	writeFieldList(buf, sig.Params, ", ", false)
+	writeFieldList(buf, sig.Params.List, ", ", false)
 	buf.WriteByte(')')
 
 	res := sig.Results
@@ -188,23 +209,18 @@ func writeSigExpr(buf *bytes.Buffer, sig *ast.FuncType) {
 
 	// multiple or named result(s)
 	buf.WriteByte('(')
-	writeFieldList(buf, res, ", ", false)
+	writeFieldList(buf, res.List, ", ", false)
 	buf.WriteByte(')')
 }
 
-func writeFieldList(buf *bytes.Buffer, fields *ast.FieldList, sep string, iface bool) {
-	for i, f := range fields.List {
+func writeFieldList(buf *bytes.Buffer, list []*ast.Field, sep string, iface bool) {
+	for i, f := range list {
 		if i > 0 {
 			buf.WriteString(sep)
 		}
 
 		// field list names
-		for i, name := range f.Names {
-			if i > 0 {
-				buf.WriteString(", ")
-			}
-			buf.WriteString(name.Name)
-		}
+		writeIdentList(buf, f.Names)
 
 		// types of interface methods consist of signatures only
 		if sig, _ := f.Type.(*ast.FuncType); sig != nil && iface {
@@ -222,3 +238,21 @@ func writeFieldList(buf *bytes.Buffer, fields *ast.FieldList, sep string, iface
 		// ignore tag
 	}
 }
+
+func writeIdentList(buf *bytes.Buffer, list []*ast.Ident) {
+	for i, x := range list {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(x.Name)
+	}
+}
+
+func writeExprList(buf *bytes.Buffer, list []ast.Expr) {
+	for i, x := range list {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		WriteExpr(buf, x)
+	}
+}
diff --git a/src/go/types/scope.go b/src/go/types/scope.go
index 8c9d9ab8b8..157b1b7066 100644
--- a/src/go/types/scope.go
+++ b/src/go/types/scope.go
@@ -108,6 +108,40 @@ func (s *Scope) Insert(obj Object) Object {
 	return nil
 }
 
+// Squash merges s with its parent scope p by adding all
+// objects of s to p, adding all children of s to the
+// children of p, and removing s from p's children.
+// The function f is called for each object obj in s which
+// has an object alt in p. s should be discarded after
+// having been squashed.
+func (s *Scope) Squash(err func(obj, alt Object)) {
+	p := s.parent
+	assert(p != nil)
+	for _, obj := range s.elems {
+		obj.setParent(nil)
+		if alt := p.Insert(obj); alt != nil {
+			err(obj, alt)
+		}
+	}
+
+	j := -1 // index of s in p.children
+	for i, ch := range p.children {
+		if ch == s {
+			j = i
+			break
+		}
+	}
+	assert(j >= 0)
+	k := len(p.children) - 1
+	p.children[j] = p.children[k]
+	p.children = p.children[:k]
+
+	p.children = append(p.children, s.children...)
+
+	s.children = nil
+	s.elems = nil
+}
+
 // Pos and End describe the scope's source code extent [pos, end).
 // The results are guaranteed to be valid only if the type-checked
 // AST has complete position information. The extent is undefined
diff --git a/src/go/types/sizes.go b/src/go/types/sizes.go
index 6ab6157b82..e8377a4f92 100644
--- a/src/go/types/sizes.go
+++ b/src/go/types/sizes.go
@@ -48,7 +48,7 @@ type StdSizes struct {
 func (s *StdSizes) Alignof(T Type) int64 {
 	// For arrays and structs, alignment is defined in terms
 	// of alignment of the elements and fields, respectively.
-	switch t := T.Underlying().(type) {
+	switch t := optype(T).(type) {
 	case *Array:
 		// spec: "For a variable x of array type: unsafe.Alignof(x)
 		// is the same as unsafe.Alignof(x[0]), but at least 1."
@@ -118,7 +118,7 @@ var basicSizes = [...]byte{
 }
 
 func (s *StdSizes) Sizeof(T Type) int64 {
-	switch t := T.Underlying().(type) {
+	switch t := optype(T).(type) {
 	case *Basic:
 		assert(isTyped(T))
 		k := t.kind
@@ -148,6 +148,8 @@ func (s *StdSizes) Sizeof(T Type) int64 {
 		}
 		offsets := s.Offsetsof(t.fields)
 		return offsets[n-1] + s.Sizeof(t.fields[n-1].typ)
+	case *Sum:
+		panic("Sizeof unimplemented for type sum")
 	case *Interface:
 		return s.WordSize * 2
 	}
@@ -239,7 +241,7 @@ func (conf *Config) offsetsof(T *Struct) []int64 {
 func (conf *Config) offsetof(typ Type, index []int) int64 {
 	var o int64
 	for _, i := range index {
-		s := typ.Underlying().(*Struct)
+		s := asStruct(typ)
 		o += conf.offsetsof(s)[i]
 		typ = s.fields[i].typ
 	}