fix(rust) emoji supported in single quote strings (#4156)

Author: joshgoebel

CHANGES.md

@@ -7,6 +7,7 @@ CAVEATS / POTENTIALLY BREAKING CHANGES
 
 Core Grammars:
 
+- fix(rust) - adds emoji support in single quote strings [joshgoebel][]
 - fix(apache) - support line continuation via `\` [Josh Goebel][]
 - fix(makefile) - allow strings inside `$()` expressions [aneesh98][]
 - enh(arcade) updated to ArcGIS Arcade version 1.29 [Kristian Ekenes][]

src/languages/rust.js

@@ -199,10 +199,19 @@ export default function(hljs) {
         illegal: null
       }),
       {
-        className: 'string',
+        scope: 'string',
         variants: [
           { begin: /b?r(#*)"(.|\n)*?"\1(?!#)/ },
-          { begin: /b?'\\?(x\w{2}|u\w{4}|U\w{8}|.)'/ }
+          {
+            begin: /b?'/,
+            end: /'/,
+            contains: [
+              {
+                scope: "char.escape",
+                match: /\\(\w|x\w{2}|u\w{4}|U\w{8})/
+              }
+            ]
+          }
         ]
       },
       {

test/markup/rust/strings.expect.txt

@@ -1,8 +1,8 @@
 <span class="hljs-string">&#x27;a&#x27;</span>;
-<span class="hljs-string">&#x27;\n&#x27;</span>;
-<span class="hljs-string">&#x27;\x1A&#x27;</span>;
-<span class="hljs-string">&#x27;\u12AS&#x27;</span>;
-<span class="hljs-string">&#x27;\U1234ASDF&#x27;</span>;
+<span class="hljs-string">&#x27;<span class="hljs-char escape_">\n</span>&#x27;</span>;
+<span class="hljs-string">&#x27;<span class="hljs-char escape_">\x</span>1A&#x27;</span>;
+<span class="hljs-string">&#x27;<span class="hljs-char escape_">\u</span>12AS&#x27;</span>;
+<span class="hljs-string">&#x27;<span class="hljs-char escape_">\U</span>1234ASDF&#x27;</span>;
 <span class="hljs-string">b&#x27;a&#x27;</span>;
 
 <span class="hljs-string">&quot;hello&quot;</span>;