cmd/compile: accept string|[]byte-constrained 2nd argument in append

Similarly to what we do for the built-in function `copy`,
where we allow a string as 2nd argument to append, also
permit a type parameter constrained by string|[]byte.

While at it, change date in the manual.go2 test files so
that we don't need to constantly correct it when copying
a test case from that file into a proper test file.

Fixes #50281.

Change-Id: I23fed66736aa07bb3c481fe97313e828425ac448
Reviewed-on: https://go-review.googlesource.com/c/go/+/376214
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/test/typeparam/issue376214.go b/test/typeparam/issue376214.go
new file mode 100644
index 00000000000..8f94f4107d4
--- /dev/null
+++ b/test/typeparam/issue376214.go
@@ -0,0 +1,20 @@
+// run -gcflags=-G=3
+
+// Copyright 2022 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
+
+func add[S ~string | ~[]byte](buf *[]byte, s S) {
+	*buf = append(*buf, s...)
+}
+
+func main() {
+	var buf []byte
+	add(&buf, "foo")
+	add(&buf, []byte("bar"))
+	if string(buf) != "foobar" {
+		panic("got " + string(buf))
+	}
+}