cmd/compile: delay transformAssign if lhs/rhs have typeparam

This also requires that we sometimes delay transformSelect(), if the
assignments in the Comm part of the select have not been transformed.

Fixes #48137

Change-Id: I163aa1f999d1e63616280dca807561b12b2aa779
Reviewed-on: https://go-review.googlesource.com/c/go/+/347915
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/test/typeparam/issue48137.go b/test/typeparam/issue48137.go
new file mode 100644
index 0000000000..3dd7810482
--- /dev/null
+++ b/test/typeparam/issue48137.go
@@ -0,0 +1,25 @@
+// run -gcflags=-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 main
+
+type Constraint[T any] interface {
+	~func() T
+}
+
+func Foo[T Constraint[T]]() T {
+	var t T
+
+	t = func() T {
+		return t
+	}
+	return t
+}
+
+func main() {
+	type Bar func() Bar
+	Foo[Bar]()
+}