rollup merge of #20039: barosl/if-let-friendly-error

Fixes #19991.

src/test/compile-fail/issue-19991.rs

@@ -0,0 +1,18 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test if the sugared if-let construct correctly prints "missing an else clause" when an else
+// clause does not exist, instead of the unsympathetic "match arms have incompatible types"
+
+fn main() {
+    if let Some(homura) = Some("madoka") { //~ ERROR missing an else clause: expected `()`
+        765i32
+    };
+}