cmd/compile: delay fillinMethods to deal with mutually-recursive types

We need to delay fillinMethods until we get to a top-level type, so we
know all the TFORW types have been filled in, and we can do the
substitutions required by fillinMethods.

Fixes #47710

Change-Id: I298de7e7753ed31a2c2b1ff04f35177a8afc7a66
Reviewed-on: https://go-review.googlesource.com/c/go/+/345149
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/noder/irgen.go

@@ -149,6 +149,9 @@ type irgen struct {
 	// statements yet.
 	exprStmtOK bool
 
+	// types which we need to finish, by doing g.fillinMethods.
+	typesToFinalize []*typeDelayInfo
+
 	// Fully-instantiated generic types whose methods should be instantiated
 	instTypeList []*types.Type
 
@@ -184,6 +187,11 @@ type delayInfo struct {
 	off   int
 }
 
+type typeDelayInfo struct {
+	typ  *types2.Named
+	ntyp *types.Type
+}
+
 func (g *irgen) generate(noders []*noder) {
 	types.LocalPkg.Name = g.self.Name()
 	types.LocalPkg.Height = g.self.Height()

src/cmd/compile/internal/noder/types.go

@@ -35,6 +35,16 @@ func (g *irgen) typ(typ types2.Type) *types.Type {
 	types.DeferCheckSize()
 	res := g.typ1(typ)
 	types.ResumeCheckSize()
+
+	// Finish up any types on typesToFinalize, now that we are at the top of a
+	// fully-defined (possibly recursive) type. fillinMethods could create more
+	// types to finalize.
+	for len(g.typesToFinalize) > 0 {
+		l := len(g.typesToFinalize)
+		info := g.typesToFinalize[l-1]
+		g.typesToFinalize = g.typesToFinalize[:l-1]
+		g.fillinMethods(info.typ, info.ntyp)
+	}
 	return res
 }
 
@@ -151,10 +161,19 @@ func (g *irgen) typ0(typ types2.Type) *types.Type {
 			ntyp.SetRParams(rparams)
 			//fmt.Printf("Saw new type %v %v\n", instName, ntyp.HasTParam())
 
-			ntyp.SetUnderlying(g.typ1(typ.Underlying()))
-			g.fillinMethods(typ, ntyp)
 			// Save the symbol for the base generic type.
 			ntyp.OrigSym = g.pkg(typ.Obj().Pkg()).Lookup(typ.Obj().Name())
+			ntyp.SetUnderlying(g.typ1(typ.Underlying()))
+			if typ.NumMethods() != 0 {
+				// Save a delayed call to g.fillinMethods() (once
+				// potentially recursive types have been fully
+				// resolved).
+				g.typesToFinalize = append(g.typesToFinalize,
+					&typeDelayInfo{
+						typ:  typ,
+						ntyp: ntyp,
+					})
+			}
 			return ntyp
 		}
 		obj := g.obj(typ.Obj())
@@ -266,11 +285,11 @@ func (g *irgen) typ0(typ types2.Type) *types.Type {
 	}
 }
 
-// fillinMethods fills in the method name nodes and types for a defined type. This
-// is needed for later typechecking when looking up methods of instantiated types,
-// and for actually generating the methods for instantiated types.
+// fillinMethods fills in the method name nodes and types for a defined type with at
+// least one method. This is needed for later typechecking when looking up methods of
+// instantiated types, and for actually generating the methods for instantiated
+// types.
 func (g *irgen) fillinMethods(typ *types2.Named, ntyp *types.Type) {
-	if typ.NumMethods() != 0 {
 	targs2 := typ.TArgs()
 	targs := make([]*types.Type, targs2.Len())
 	for i := range targs {
@@ -336,7 +355,6 @@ func (g *irgen) fillinMethods(typ *types2.Named, ntyp *types.Type) {
 		// Generate all the methods for a new fully-instantiated type.
 		g.instTypeList = append(g.instTypeList, ntyp)
 	}
-	}
 }
 
 func (g *irgen) signature(recv *types.Field, sig *types2.Signature) *types.Type {

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

@@ -927,7 +927,7 @@ func formalType(t *types.Type) *types.Type {
 
 func writeType(t *types.Type) *obj.LSym {
 	t = formalType(t)
-	if t.IsUntyped() {
+	if t.IsUntyped() || t.HasTParam() {
 		base.Fatalf("writeType %v", t)
 	}
 

test/typeparam/issue47710.go

@@ -0,0 +1,19 @@
+// compile -G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type FooType[t any] interface {
+	Foo(BarType[t])
+}
+type BarType[t any] interface {
+	Int(IntType[t]) FooType[int]
+}
+
+type IntType[t any] int
+
+func (n IntType[t]) Foo(BarType[t]) {}
+func (n IntType[_]) String()    {}