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>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/typeparam/issue47710.go b/test/typeparam/issue47710.go
new file mode 100644
index 0000000000..0882cb4137
--- /dev/null
+++ b/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()    {}