Rollup merge of #48033 - GuillaumeGomez:better-char-cast-message, r=estebank

Show better warning for trying to cast non-u8 scalar to char

Fixes #44201.

src/test/ui/cast_char.rs

@@ -0,0 +1,20 @@
+// Copyright 2018 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.
+
+#![deny(overflowing_literals)]
+
+fn main() {
+    const XYZ: char = 0x1F888 as char;
+    //~^ ERROR only u8 can be casted into char
+    const XY: char = 129160 as char;
+    //~^ ERROR only u8 can be casted into char
+    const ZYX: char = '\u{01F888}';
+    println!("{}", XYZ);
+}

src/test/ui/cast_char.stderr

@@ -0,0 +1,20 @@
+error: only u8 can be casted into char
+  --> $DIR/cast_char.rs:14:23
+   |
+14 |     const XYZ: char = 0x1F888 as char;
+   |                       ^^^^^^^^^^^^^^^ help: use a char literal instead: `'/u{1F888}'`
+   |
+note: lint level defined here
+  --> $DIR/cast_char.rs:11:9
+   |
+11 | #![deny(overflowing_literals)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: only u8 can be casted into char
+  --> $DIR/cast_char.rs:16:22
+   |
+16 |     const XY: char = 129160 as char;
+   |                      ^^^^^^^^^^^^^^ help: use a char literal instead: `'/u{1F888}'`
+
+error: aborting due to 2 previous errors
+