[dev.typeparams] cmd/compile: handle interface type parameters in type switches

Change-Id: I9bba21a64d7e9f42395b6fcdf8aa3ca01cf131dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/340912
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

4 files changed, 75 insertions, 0 deletions

diff --git a/test/typeparam/typeswitch6.go b/test/typeparam/typeswitch6.go
new file mode 100644
index 0000000000..574f4aa819
--- /dev/null
+++ b/test/typeparam/typeswitch6.go
@@ -0,0 +1,30 @@
+// 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
+
+func f[T any](i interface{}) {
+	switch i.(type) {
+	case T:
+		println("T")
+	case int:
+		println("int")
+	default:
+		println("other")
+	}
+}
+
+type myint int
+func (myint) foo() {
+}
+
+func main() {
+	f[interface{}](nil)
+	f[interface{}](6)
+	f[interface{foo()}](nil)
+	f[interface{foo()}](7)
+	f[interface{foo()}](myint(8))
+}
diff --git a/test/typeparam/typeswitch6.out b/test/typeparam/typeswitch6.out
new file mode 100644
index 0000000000..441add5ec5
--- /dev/null
+++ b/test/typeparam/typeswitch6.out
@@ -0,0 +1,5 @@
+other
+T
+other
+int
+T
diff --git a/test/typeparam/typeswitch7.go b/test/typeparam/typeswitch7.go
new file mode 100644
index 0000000000..f2e1279fb4
--- /dev/null
+++ b/test/typeparam/typeswitch7.go
@@ -0,0 +1,37 @@
+// 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
+
+func f[T any](i interface{foo()}) {
+	switch i.(type) {
+	case interface{bar() T}:
+		println("barT")
+	case myint:
+		println("myint")
+	case myfloat:
+		println("myfloat")
+	default:
+		println("other")
+	}
+}
+
+type myint int
+func (myint) foo() {
+}
+func (x myint) bar() int {
+	return int(x)
+}
+
+type myfloat float64
+func (myfloat) foo() {
+}
+
+func main() {
+	f[int](nil)
+	f[int](myint(6))
+	f[int](myfloat(7))
+}
diff --git a/test/typeparam/typeswitch7.out b/test/typeparam/typeswitch7.out
new file mode 100644
index 0000000000..d7fcad4fee
--- /dev/null
+++ b/test/typeparam/typeswitch7.out
@@ -0,0 +1,3 @@
+other
+barT
+myfloat