Implement suggested fix and update test

Author: LFS6502

compiler/rustc_parse/src/lexer/unescape_error_reporting.rs

@@ -159,11 +159,18 @@ pub(crate) fn emit_unescape_error(
                      version control settings",
                 );
             } else if looks_like_quote(c) {
+                diag.span_suggestion(
+                    err_span,
+                    "if you meant to use a unicode quote; \
+                    consider using its escaped form for clarity",
+                    // lit.replace(c, &ec[1..]),
+                    &ec,
+                    Applicability::MaybeIncorrect,
+                );
+
                 diag.help(format!(
-                    "{ec} is not an ascii quote, \
-                             but may look like one in some fonts.\n\
-                             consider writing it in its \
-                             escaped form for clarity."
+                    "{ec} is not an ascii quote, but may look like one in some fonts; \
+                     consider writing it in its escaped form for clarity."
                 ));
             } else {
                 if mode == Mode::Str || mode == Mode::Char {

tests/ui/unicode-quote.rs

@@ -1,3 +1,5 @@
 fn main() {
-    dbg!("since when is \“THIS\” not allowed in a string literal");
+    dbg!("Is this \“ a small sized quote or a big sized quote. \“ ");
+    //~^ 2:20: 2:21: unknown character escape: `\u{201c}`
+    //~^^ 2:65: 2:66: unknown character escape: `\u{201c}`
 }

tests/ui/unicode-quote.stderr

@@ -1,20 +1,28 @@
 error: unknown character escape: `\u{201c}`
-  --> $DIR/unicode-quote.rs:2:26
+  --> $DIR/unicode-quote.rs:2:20
    |
-LL |     dbg!("since when is \“THIS\” not allowed in a string literal");
-   |                          ^ unknown character escape
+LL |     dbg!("Is this \“ a small sized quote or a big sized quote. \“ ");
+   |                    ^ unknown character escape
+   |
+   = help: \u{201c} is not an ascii quote, but may look like one in some fonts; consider writing it in its escaped form for clarity.
+help: if you meant to use a unicode quote; consider using its escaped form for clarity
+   |
+LL -     dbg!("Is this \“ a small sized quote or a big sized quote. \“ ");
+LL +     dbg!("Is this \u{201c} a small sized quote or a big sized quote. \“ ");
    |
-   = help: \u{201c} is not an ascii quote, but may look like one in some fonts.
-           consider writing it in its escaped form for clarity.
 
-error: unknown character escape: `\u{201d}`
-  --> $DIR/unicode-quote.rs:2:32
+error: unknown character escape: `\u{201c}`
+  --> $DIR/unicode-quote.rs:2:65
+   |
+LL |     dbg!("Is this \“ a small sized quote or a big sized quote. \“ ");
+   |                                                                 ^ unknown character escape
+   |
+   = help: \u{201c} is not an ascii quote, but may look like one in some fonts; consider writing it in its escaped form for clarity.
+help: if you meant to use a unicode quote; consider using its escaped form for clarity
    |
-LL |     dbg!("since when is \“THIS\” not allowed in a string literal");
-   |                                ^ unknown character escape
+LL -     dbg!("Is this \“ a small sized quote or a big sized quote. \“ ");
+LL +     dbg!("Is this \“ a small sized quote or a big sized quote. \u{201c} ");
    |
-   = help: \u{201d} is not an ascii quote, but may look like one in some fonts.
-           consider writing it in its escaped form for clarity.
 
 error: aborting due to 2 previous errors