cmd/compile: fix stencil call expression.

Fixes: #47878

Change-Id: I369350813726fd518b4eab2b98f43bf031a6dee6
Reviewed-on: https://go-review.googlesource.com/c/go/+/344210
Reviewed-by: Dan Scales <danscales@google.com>
Trust: Dan Scales <danscales@google.com>
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

2 files changed, 53 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 18a0506036..b3ff4b8855 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -1048,6 +1048,13 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			case ir.OCLOSURE:
 				transformCall(call)
 
+			case ir.ODEREF, ir.OINDEX, ir.OINDEXMAP, ir.ORECV:
+				// Transform a call that was delayed because of the
+				// use of typeparam inside an expression that required
+				// a pointer dereference, array indexing, map indexing,
+				// or channel receive to compute function value.
+				transformCall(call)
+
 			case ir.OFUNCINST:
 				// A call with an OFUNCINST will get transformed
 				// in stencil() once we have created & attached the
diff --git a/test/typeparam/issue47878.go b/test/typeparam/issue47878.go
new file mode 100644
index 0000000000..cb1043a440
--- /dev/null
+++ b/test/typeparam/issue47878.go
@@ -0,0 +1,46 @@
+// 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 main
+
+type Src1[T any] func() Src1[T]
+
+func (s *Src1[T]) Next() {
+	*s = (*s)()
+}
+
+type Src2[T any] []func() Src2[T]
+
+func (s Src2[T]) Next() {
+	_ = s[0]()
+}
+
+type Src3[T comparable] map[T]func() Src3[T]
+
+func (s Src3[T]) Next() {
+	var a T
+	_ = s[a]()
+}
+
+type Src4[T any] chan func() T
+
+func (s Src4[T]) Next() {
+	_ = (<-s)()
+}
+
+func main() {
+	var src1 Src1[int]
+	src1.Next()
+
+	var src2 Src2[int]
+	src2.Next()
+
+	var src3 Src3[string]
+	src3.Next()
+
+	var src4 Src4[int]
+	src4.Next()
+}