cmd/compile: fix function contains no TParam in generic function

Fixes #47948

Change-Id: I446a9548265d195ae4d88aff6b1361474d1b6214
Reviewed-on: https://go-review.googlesource.com/c/go/+/344910
Trust: Alexander Rakoczy <alex@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

2 files changed, 20 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index b9cdcf10f2..8d05356543 100644
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -1051,7 +1051,8 @@ func (ts *Tsubster) typ1(t *types.Type) *types.Type {
 	var targsChanged bool
 	var forw *types.Type
 
-	if t.Sym() != nil {
+	if t.Sym() != nil && t.HasTParam() {
+		// Need to test for t.HasTParam() again because of special TFUNC case above.
 		// Translate the type params for this type according to
 		// the tparam/targs mapping from subst.
 		neededTargs = make([]*types.Type, len(t.RParams()))
diff --git a/test/typeparam/issue47948.go b/test/typeparam/issue47948.go
new file mode 100644
index 0000000000..8e5df81f6d
--- /dev/null
+++ b/test/typeparam/issue47948.go
@@ -0,0 +1,18 @@
+// 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 fun func()
+
+func F[T any]() {
+	_ = fun(func() {
+
+	})
+}
+func main() {
+	F[int]()
+}