reflect: add TypeFor[T]

This function was added in Go 1.22. See:
https://github.com/golang/go/commit/42d2dfb4305aecb3a6e5494db6b8f6e48a09b420

2 files changed, 41 insertions, 0 deletions

diff --git a/src/reflect/type.go b/src/reflect/type.go
index bc45a41e4..56d4767f7 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -1313,3 +1313,9 @@ func uvarint32(buf []byte) (uint32, int) {
 	}
 	return 0, 0
 }
+
+// TypeFor returns the [Type] that represents the type argument T.
+func TypeFor[T any]() Type {
+	// This function was copied from the Go 1.22 source tree.
+	return TypeOf((*T)(nil)).Elem()
+}
diff --git a/src/reflect/type_test.go b/src/reflect/type_test.go
new file mode 100644
index 000000000..75784f966
--- /dev/null
+++ b/src/reflect/type_test.go
@@ -0,0 +1,35 @@
+// Copyright 2023 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 reflect_test
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestTypeFor(t *testing.T) {
+	type (
+		mystring string
+		myiface  interface{}
+	)
+
+	testcases := []struct {
+		wantFrom any
+		got      reflect.Type
+	}{
+		{new(int), reflect.TypeFor[int]()},
+		{new(int64), reflect.TypeFor[int64]()},
+		{new(string), reflect.TypeFor[string]()},
+		{new(mystring), reflect.TypeFor[mystring]()},
+		{new(any), reflect.TypeFor[any]()},
+		{new(myiface), reflect.TypeFor[myiface]()},
+	}
+	for _, tc := range testcases {
+		want := reflect.ValueOf(tc.wantFrom).Elem().Type()
+		if want != tc.got {
+			t.Errorf("unexpected reflect.Type: got %v; want %v", tc.got, want)
+		}
+	}
+}