Initial commit: Go 1.23 release state

test/typeparam/issue50002.go

@@ -0,0 +1,64 @@
+// run
+
+// 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.
+
+// Test for cases where certain instantiations of a generic function (F in this
+// example) will always fail on a type assertion or mismatch on a type case.
+
+package main
+
+import "fmt"
+
+type S struct{}
+
+func (S) M() byte {
+	return 0
+}
+
+type I[T any] interface {
+	M() T
+}
+
+func F[T, A any](x I[T], shouldMatch bool) {
+	switch x.(type) {
+	case A:
+		if !shouldMatch {
+			fmt.Printf("wanted mis-match, got match")
+		}
+	default:
+		if shouldMatch {
+			fmt.Printf("wanted match, got mismatch")
+		}
+	}
+
+	_, ok := x.(A)
+	if ok != shouldMatch {
+		fmt.Printf("ok: got %v, wanted %v", ok, shouldMatch)
+	}
+
+	if !shouldMatch {
+		defer func() {
+			if shouldMatch {
+				fmt.Printf("Shouldn't have panicked")
+			}
+			recover()
+		}()
+	}
+	_ = x.(A)
+	if !shouldMatch {
+		fmt.Printf("Should have panicked")
+	}
+}
+
+func main() {
+	// Test instantiation where the type switch/type asserts can't possibly succeed
+	// (since string does not implement I[byte]).
+	F[byte, string](S{}, false)
+
+	// Test instantiation where the type switch/type asserts should succeed
+	// (since S does implement I[byte])
+	F[byte, S](S{}, true)
+	F[byte, S](I[byte](S{}), true)
+}