Replace ZWJ with nothing in terminal output

Author: estebank

compiler/rustc_errors/src/emitter.rs

@@ -2081,6 +2081,7 @@ fn num_decimal_digits(num: usize) -> usize {
 // We replace some characters so the CLI output is always consistent and underlines aligned.
 const OUTPUT_REPLACEMENTS: &[(char, &str)] = &[
     ('\t', "    "),   // We do our own tab replacement
+    ('\u{200D}', ""), // Replace ZWJ with nothing for consistent terminal output of grapheme clusters.
     ('\u{202A}', ""), // The following unicode text flow control characters are inconsistently
     ('\u{202B}', ""), // supported accross CLIs and can cause confusion due to the bytes on disk
     ('\u{202D}', ""), // not corresponding to the visible source code, so we replace them always.

src/test/ui/parser/emoji-identifiers.stderr

@@ -48,10 +48,10 @@ error: identifiers cannot contain emojis: `i_like_to_😅_a_lot`
 LL | fn i_like_to_😅_a_lot() -> 👀 {
    |    ^^^^^^^^^^^^^^^^^^
 
-error: identifiers cannot contain emojis: `ABig👩‍👩‍👧‍👧Family`
+error: identifiers cannot contain emojis: `ABig👩👩👧👧Family`
   --> $DIR/emoji-identifiers.rs:1:8
    |
-LL | struct ABig👩‍👩‍👧‍👧Family;
+LL | struct ABig👩👩👧👧Family;
    |        ^^^^^^^^^^^^^^^^^^
 
 error[E0599]: no function or associated item named `full_of✨` found for struct `👀` in the current scope