Fix invalid suggestions for non-ASCII characters in byte constants

1 files changed, 29 insertions, 8 deletions

diff --git a/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs b/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
index a580f0c55d0..0f76898a912 100644
--- a/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
+++ b/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
@@ -153,16 +153,37 @@ pub(crate) fn emit_unescape_error(
         EscapeError::NonAsciiCharInByte => {
             assert!(mode.is_bytes());
             let (c, span) = last_char();
-            handler
-                .struct_span_err(span, "non-ASCII character in byte constant")
-                .span_label(span, "byte constant must be ASCII")
-                .span_suggestion(
+            let mut err = handler.struct_span_err(span, "non-ASCII character in byte constant");
+            err.span_label(span, "byte constant must be ASCII");
+            if (c as u32) <= 0xFF {
+                err.span_suggestion(
                     span,
-                    "use a \\xHH escape for a non-ASCII byte",
+                    &format!(
+                        "if you meant to use the unicode code point for '{}', use a \\xHH escape",
+                        c
+                    ),
                     format!("\\x{:X}", c as u32),
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+                    Applicability::MaybeIncorrect,
+                );
+            } else if matches!(mode, Mode::Byte) {
+                err.span_label(span, "this multibyte character does not fit into a single byte");
+            } else if matches!(mode, Mode::ByteStr) {
+                let mut utf8 = String::new();
+                utf8.push(c);
+                err.span_suggestion(
+                    span,
+                    &format!(
+                        "if you meant to use the UTF-8 encoding of '{}', use \\xHH escapes",
+                        c
+                    ),
+                    utf8.as_bytes()
+                        .iter()
+                        .map(|b: &u8| format!("\\x{:X}", *b))
+                        .fold("".to_string(), |a, c| a + &c),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            err.emit();
         }
         EscapeError::NonAsciiCharInByteString => {
             assert!(mode.is_bytes());