cmd/compile/internal/gc: handle recursive interfaces better

Previously, we handled recursive interfaces by deferring typechecking
of interface methods, while eagerly expanding interface embeddings.

This CL switches to eagerly evaluating interface methods, and
deferring expanding interface embeddings to dowidth. This allows us to
detect recursive interface embeddings with the same mechanism used for
detecting recursive struct embeddings.

Updates #16369.

Change-Id: If4c0320058047f8a2d9b52b9a79de47eb9887f95
Reviewed-on: https://go-review.googlesource.com/38391
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/align.go

@@ -4,6 +4,10 @@
 
 package gc
 
+import (
+	"sort"
+)
+
 // machine size and rounding alignment is dictated around
 // the size of a pointer, set in betypeinit (see ../amd64/galign.go).
 var defercalc int
@@ -15,6 +19,47 @@ func Rnd(o int64, r int64) int64 {
 	return (o + r - 1) &^ (r - 1)
 }
 
+// expandiface computes the method set for interface type t by
+// expanding embedded interfaces.
+func expandiface(t *Type) {
+	var fields []*Field
+	for _, m := range t.Methods().Slice() {
+		if m.Sym != nil {
+			fields = append(fields, m)
+			continue
+		}
+
+		if !m.Type.IsInterface() {
+			yyerrorl(m.Nname.Pos, "interface contains embedded non-interface %v", m.Type)
+			m.SetBroke(true)
+			t.SetBroke(true)
+			// Add to fields so that error messages
+			// include the broken embedded type when
+			// printing t.
+			// TODO(mdempsky): Revisit this.
+			fields = append(fields, m)
+			continue
+		}
+
+		// Embedded interface: duplicate all methods
+		// (including broken ones, if any) and add to t's
+		// method set.
+		for _, t1 := range m.Type.Fields().Slice() {
+			f := newField()
+			f.Type = t1.Type
+			f.SetBroke(t1.Broke())
+			f.Sym = t1.Sym
+			f.Nname = m.Nname // preserve embedding position
+			fields = append(fields, f)
+		}
+	}
+	sort.Sort(methcmp(fields))
+
+	// Access fields directly to avoid recursively calling dowidth
+	// within Type.Fields().
+	t.Extra.(*InterType).fields.Set(fields)
+}
+
 func offmod(t *Type) {
 	o := int32(0)
 	for _, f := range t.Fields().Slice() {
@@ -203,9 +248,8 @@ func dowidth(t *Type) {
 
 	case TINTER: // implemented as 2 pointers
 		w = 2 * int64(Widthptr)
-
 		t.Align = uint8(Widthptr)
-		offmod(t)
+		expandiface(t)
 
 	case TCHAN: // implemented as pointer
 		w = int64(Widthptr)
@@ -316,6 +360,14 @@ func dowidth(t *Type) {
 		t.Align = uint8(w)
 	}
 
+	if t.Etype == TINTER {
+		// We defer calling these functions until after
+		// setting t.Width and t.Align so the recursive calls
+		// to dowidth within t.Fields() will succeed.
+		checkdupfields("method", t)
+		offmod(t)
+	}
+
 	lineno = lno
 
 	if defercalc == 1 {

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

@@ -535,7 +535,6 @@ func (p *importer) typ() *Type {
 			t = p.newtyp(TINTER)
 			t.SetInterface(ml)
 		}
-		checkwidth(t)
 
 	case mapTag:
 		t = p.newtyp(TMAP)

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

@@ -7,7 +7,6 @@ package gc
 import (
 	"cmd/internal/src"
 	"fmt"
-	"sort"
 	"strings"
 )
 
@@ -705,24 +704,19 @@ func structfield(n *Node) *Field {
 // checkdupfields emits errors for duplicately named fields or methods in
 // a list of struct or interface types.
 func checkdupfields(what string, ts ...*Type) {
-	lno := lineno
-
 	seen := make(map[*Sym]bool)
 	for _, t := range ts {
 		for _, f := range t.Fields().Slice() {
-			if f.Sym == nil || f.Nname == nil || isblank(f.Nname) {
+			if f.Sym == nil || isblanksym(f.Sym) || f.Nname == nil {
 				continue
 			}
 			if seen[f.Sym] {
-				lineno = f.Nname.Pos
-				yyerror("duplicate %s %s", what, f.Sym.Name)
+				yyerrorl(f.Nname.Pos, "duplicate %s %s", what, f.Sym.Name)
 				continue
 			}
 			seen[f.Sym] = true
 		}
 	}
-
-	lineno = lno
 }
 
 // convert a parsed id/type list into
@@ -805,51 +799,27 @@ func interfacefield(n *Node) *Field {
 		yyerror("interface method cannot have annotation")
 	}
 
-	f := newField()
-	f.SetIsddd(n.Isddd())
+	// MethodSpec = MethodName Signature | InterfaceTypeName .
+	//
+	// If Left != nil, then Left is MethodName and Right is Signature.
+	// Otherwise, Right is InterfaceTypeName.
 
 	if n.Right != nil {
-		if n.Left != nil {
-			// queue resolution of method type for later.
-			// right now all we need is the name list.
-			// avoids cycles for recursive interface types.
-			n.Type = typ(TINTERMETH)
-			n.Type.SetNname(n.Right)
-			n.Left.Type = n.Type
-			queuemethod(n)
-
-			if n.Left.Op == ONAME {
-				f.Nname = n.Left
-				f.Embedded = n.Embedded
-				f.Sym = f.Nname.Sym
-			}
-		} else {
 		n.Right = typecheck(n.Right, Etype)
 		n.Type = n.Right.Type
-
-			if n.Embedded != 0 {
-				checkembeddedtype(n.Type)
+		n.Right = nil
 	}
 
-			if n.Type != nil {
-				switch n.Type.Etype {
-				case TINTER:
-					break
-
-				case TFORW:
-					yyerror("interface type loop involving %v", n.Type)
-					f.SetBroke(true)
-
-				default:
-					yyerror("interface contains embedded non-interface %v", n.Type)
-					f.SetBroke(true)
-				}
-			}
-		}
+	f := newField()
+	if n.Left != nil {
+		f.Nname = n.Left
+		f.Sym = f.Nname.Sym
+	} else {
+		// Placeholder ONAME just to hold Pos.
+		// TODO(mdempsky): Add Pos directly to Field instead.
+		f.Nname = newname(nblank.Sym)
 	}
 
-	n.Right = nil
-
 	f.Type = n.Type
 	if f.Type == nil {
 		f.SetBroke(true)
@@ -876,32 +846,13 @@ func tointerface0(t *Type, l []*Node) *Type {
 	var fields []*Field
 	for _, n := range l {
 		f := interfacefield(n)
-
-		if n.Left == nil && f.Type.IsInterface() {
-			// embedded interface, inline methods
-			for _, t1 := range f.Type.Fields().Slice() {
-				f = newField()
-				f.Type = t1.Type
-				f.SetBroke(t1.Broke())
-				f.Sym = t1.Sym
-				if f.Sym != nil {
-					f.Nname = newname(f.Sym)
-				}
-				fields = append(fields, f)
-			}
-		} else {
-			fields = append(fields, f)
-		}
 		if f.Broke() {
 			t.SetBroke(true)
 		}
+		fields = append(fields, f)
 	}
-	sort.Sort(methcmp(fields))
 	t.SetInterface(fields)
 
-	checkdupfields("method", t)
-	checkwidth(t)
-
 	return t
 }
 

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

@@ -642,7 +642,6 @@ var etnames = []string{
 	TBLANK:      "TBLANK",
 	TFUNCARGS:   "TFUNCARGS",
 	TCHANARGS:   "TCHANARGS",
-	TINTERMETH:  "TINTERMETH",
 	TDDDFIELD:   "TDDDFIELD",
 }
 

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

@@ -65,7 +65,6 @@ const (
 	// pseudo-types for frame layout
 	TFUNCARGS
 	TCHANARGS
-	TINTERMETH
 
 	// pseudo-types for import/export
 	TDDDFIELD // wrapper: contained type is a ... field
@@ -420,8 +419,6 @@ func typ(et EType) *Type {
 		t.Extra = new(ForwardType)
 	case TFUNC:
 		t.Extra = new(FuncType)
-	case TINTERMETH:
-		t.Extra = InterMethType{}
 	case TSTRUCT:
 		t.Extra = new(StructType)
 	case TINTER:
@@ -807,8 +804,6 @@ func (t *Type) Nname() *Node {
 	switch t.Etype {
 	case TFUNC:
 		return t.Extra.(*FuncType).Nname
-	case TINTERMETH:
-		return t.Extra.(InterMethType).Nname
 	}
 	Fatalf("Type.Nname %v %v", t.Etype, t)
 	return nil
@@ -819,8 +814,6 @@ func (t *Type) SetNname(n *Node) {
 	switch t.Etype {
 	case TFUNC:
 		t.Extra.(*FuncType).Nname = n
-	case TINTERMETH:
-		t.Extra = InterMethType{Nname: n}
 	default:
 		Fatalf("Type.SetNname %v %v", t.Etype, t)
 	}
@@ -846,6 +839,7 @@ func (t *Type) Fields() *Fields {
 	case TSTRUCT:
 		return &t.Extra.(*StructType).fields
 	case TINTER:
+		dowidth(t)
 		return &t.Extra.(*InterType).fields
 	}
 	Fatalf("Fields: type %v does not have fields", t)
@@ -882,7 +876,7 @@ func (t *Type) SetFields(fields []*Field) {
 
 func (t *Type) SetInterface(methods []*Field) {
 	t.wantEtype(TINTER)
-	t.Fields().Set(methods)
+	t.Methods().Set(methods)
 }
 
 func (t *Type) isDDDArray() bool {

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

@@ -3571,8 +3571,15 @@ func copytype(n *Node, t *Type) {
 	if n.Name != nil {
 		t.Vargen = n.Name.Vargen
 	}
+
+	// spec: "The declared type does not inherit any methods bound
+	// to the existing type, but the method set of an interface
+	// type [...] remains unchanged."
+	if !t.IsInterface() {
 		t.methods = Fields{}
 		t.allMethods = Fields{}
+	}
+
 	t.nod = n
 	t.SetDeferwidth(false)
 	t.ptrTo = ptrTo

test/fixedbugs/bug195.go

@@ -14,14 +14,14 @@ type I3 interface { int }	// ERROR "interface"
 type S struct {
 	x interface{ S }	// ERROR "interface"
 }
-type I4 interface {
-	I4	// ERROR "interface"
+type I4 interface { // GC_ERROR "invalid recursive type"
+	I4	// GCCGO_ERROR "interface"
 }
 
 type I5 interface {
 	I6	// GCCGO_ERROR "interface"
 }
 
-type I6 interface {
-	I5	// ERROR "interface"
+type I6 interface { // GC_ERROR "invalid recursive type"
+	I5	// GCCGO_ERROR "interface"
 }

test/fixedbugs/bug251.go

@@ -6,13 +6,17 @@
 
 package main
 
-type I1 interface {
+type I1 interface { // GC_ERROR "invalid recursive type"
 	m() I2
-	I2 // GCCGO_ERROR "loop|interface"
+	// TODO(mdempsky): The duplicate method error is silly
+	// and redundant, but tricky to prevent as it's actually
+	// being emitted against the underlying interface type
+	// literal, not I1 itself.
+	I2 // ERROR "loop|interface|duplicate method m"
 }
 
 type I2 interface {
-	I1 // ERROR "loop|interface"
+	I1 // GCCGO_ERROR "loop|interface"
 }
 
 

test/fixedbugs/issue18392.go

@@ -7,5 +7,8 @@
 package p
 
 type A interface {
-	Fn(A.Fn) // ERROR "type A has no method A.Fn"
+	// TODO(mdempsky): This should be an error, but this error is
+	// nonsense. The error should actually mention that there's a
+	// type loop.
+	Fn(A.Fn) // ERROR "type A has no method Fn"
 }