test: add test of select inside generic function

Make sure that we can import/export selects for generics.

Change-Id: Ibf36e98fc574ce9275820aa426b3e6703b0aae6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/369101
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

test/typeparam/select.dir/a.go

@@ -0,0 +1,15 @@
+// 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 a
+
+func F[T any](c, d chan T) T {
+	select {
+	case x := <- c:
+		return x
+	case x := <- d:
+		return x
+	}
+}
+

test/typeparam/select.dir/main.go

@@ -0,0 +1,28 @@
+// 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
+
+import (
+	"sort"
+
+	"./a"
+)
+
+func main() {
+	c := make(chan int, 1)
+	d := make(chan int, 1)
+
+	c <- 5
+	d <- 6
+
+	var r [2]int
+	r[0] = a.F(c, d)
+	r[1] = a.F(c, d)
+	sort.Ints(r[:])
+
+	if r != [2]int{5, 6} {
+		panic("incorrect results")
+	}
+}

test/typeparam/select.go

@@ -0,0 +1,7 @@
+// rundir -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 ignored