Auto merge of #4418 - euclio:byte-lit-suggestion, r=flip1995

use a structured suggestion for char-lit-as-u8

changelog: use a structured suggestion for char-lit-as-u8

tests/ui/char_lit_as_u8.rs

@@ -1,5 +1,5 @@
 #![warn(clippy::char_lit_as_u8)]
-#![allow(unused_variables)]
+
 fn main() {
-    let c = 'a' as u8;
+    let _ = '❤' as u8; // no suggestion, since a byte literal won't work.
 }

tests/ui/char_lit_as_u8.stderr

@@ -1,12 +1,11 @@
-error: casting character literal to u8. `char`s are 4 bytes wide in rust, so casting to u8 truncates them
+error: casting a character literal to `u8` truncates
   --> $DIR/char_lit_as_u8.rs:4:13
    |
-LL |     let c = 'a' as u8;
+LL |     let _ = '❤' as u8; // no suggestion, since a byte literal won't work.
    |             ^^^^^^^^^
    |
    = note: `-D clippy::char-lit-as-u8` implied by `-D warnings`
-   = help: Consider using a byte literal instead:
-           b'a'
+   = note: `char` is four bytes wide, but `u8` is a single byte
 
 error: aborting due to previous error
 

tests/ui/char_lit_as_u8_suggestions.fixed

@@ -0,0 +1,10 @@
+// run-rustfix
+
+#![warn(clippy::char_lit_as_u8)]
+
+fn main() {
+    let _ = b'a';
+    let _ = b'\n';
+    let _ = b'\0';
+    let _ = b'\x01';
+}

tests/ui/char_lit_as_u8_suggestions.rs

@@ -0,0 +1,10 @@
+// run-rustfix
+
+#![warn(clippy::char_lit_as_u8)]
+
+fn main() {
+    let _ = 'a' as u8;
+    let _ = '\n' as u8;
+    let _ = '\0' as u8;
+    let _ = '\x01' as u8;
+}

tests/ui/char_lit_as_u8_suggestions.stderr

@@ -0,0 +1,35 @@
+error: casting a character literal to `u8` truncates
+  --> $DIR/char_lit_as_u8_suggestions.rs:6:13
+   |
+LL |     let _ = 'a' as u8;
+   |             ^^^^^^^^^ help: use a byte literal instead: `b'a'`
+   |
+   = note: `-D clippy::char-lit-as-u8` implied by `-D warnings`
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: casting a character literal to `u8` truncates
+  --> $DIR/char_lit_as_u8_suggestions.rs:7:13
+   |
+LL |     let _ = '/n' as u8;
+   |             ^^^^^^^^^^ help: use a byte literal instead: `b'/n'`
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: casting a character literal to `u8` truncates
+  --> $DIR/char_lit_as_u8_suggestions.rs:8:13
+   |
+LL |     let _ = '/0' as u8;
+   |             ^^^^^^^^^^ help: use a byte literal instead: `b'/0'`
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: casting a character literal to `u8` truncates
+  --> $DIR/char_lit_as_u8_suggestions.rs:9:13
+   |
+LL |     let _ = '/x01' as u8;
+   |             ^^^^^^^^^^^^ help: use a byte literal instead: `b'/x01'`
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: aborting due to 4 previous errors
+