enh(erlang) highlight character literals (#3970)

* highlight erlang character literals

* fix regex, add extra markup test cases

* 3 digits are only allowed after backslash

* add char literal into basic modes to fix nesting issues

* adopt modern code standard

* improve markup tests

src/languages/erlang.js

@@ -76,6 +76,10 @@ export default function(hljs) {
       }
     ]
   };
+  const CHAR_LITERAL = {
+    scope: 'string',
+    match: /\$(\\([^0-9]|[0-9]{1,3}|)|.)/,
+  };
 
   const BLOCK_STATEMENTS = {
     beginKeywords: 'fun receive if try case',
@@ -93,7 +97,8 @@ export default function(hljs) {
     TUPLE,
     VAR1,
     VAR2,
-    RECORD_ACCESS
+    RECORD_ACCESS,
+    CHAR_LITERAL
   ];
 
   const BASIC_MODES = [
@@ -106,7 +111,8 @@ export default function(hljs) {
     TUPLE,
     VAR1,
     VAR2,
-    RECORD_ACCESS
+    RECORD_ACCESS,
+    CHAR_LITERAL
   ];
   FUNCTION_CALL.contains[1].contains = BASIC_MODES;
   TUPLE.contains = BASIC_MODES;
@@ -142,6 +148,7 @@ export default function(hljs) {
     end: '\\)',
     contains: BASIC_MODES
   };
+
   return {
     name: 'Erlang',
     aliases: [ 'erl' ],
@@ -183,6 +190,7 @@ export default function(hljs) {
       VAR1,
       VAR2,
       TUPLE,
+      CHAR_LITERAL,
       { begin: /\.$/ } // relevance booster
     ]
   };

test/markup/erlang/char_literal.expect.txt

@@ -0,0 +1,23 @@
+Character = <span class="hljs-string">$a</span>
+TabCharacter = <span class="hljs-string">$\t</span>
+TabCharacterDecimal = <span class="hljs-string">$\011</span>
+TextWithDollar = <span class="hljs-string">&quot;This is just a normal text with a $ in the middle&quot;</span>
+StringStart = <span class="hljs-string">$&quot;</span>
+Backslash = <span class="hljs-string">$\\</span>
+ListStart = <span class="hljs-string">$[</span>
+ListEnd = <span class="hljs-string">$]</span>
+SpaceChar = <span class="hljs-string">$ </span> <span class="hljs-comment">% yes, that works</span>
+<span class="hljs-function"><span class="hljs-title">fun_takes_literal</span><span class="hljs-params">(<span class="hljs-string">$a</span>)</span> -&gt;</span> ok.
+<span class="hljs-function"><span class="hljs-title">fun_takes_literal_list</span><span class="hljs-params">([<span class="hljs-string">$a</span>|Rest])</span> -&gt;</span> ok.
+<span class="hljs-function"><span class="hljs-title">fun_takes_literal_binary</span><span class="hljs-params">(&lt;&lt;<span class="hljs-string">$a</span>, Rest/binary&gt;&gt;)</span> -&gt;</span> ok.
+<span class="hljs-function"><span class="hljs-title">convert_escape_sequence</span><span class="hljs-params">(&lt;&lt;<span class="hljs-string">$\\</span>, Escaped, Rest/binary&gt;&gt;)</span> -&gt;</span>
+    C = <span class="hljs-keyword">case</span> Escaped <span class="hljs-keyword">of</span>
+        <span class="hljs-string">$b</span> -&gt; <span class="hljs-string">$\b</span>;
+        <span class="hljs-string">$f</span> -&gt; <span class="hljs-string">$\f</span>;
+        <span class="hljs-string">$n</span> -&gt; <span class="hljs-string">$\n</span>;
+        <span class="hljs-string">$r</span> -&gt; <span class="hljs-string">$\r</span>;
+        <span class="hljs-string">$t</span> -&gt; <span class="hljs-string">$\t</span>;
+        <span class="hljs-string">$&quot;</span> -&gt; <span class="hljs-string">$&quot;</span>;
+        <span class="hljs-string">$\\</span> -&gt; <span class="hljs-string">$\\</span>;
+        _  -&gt; error
+    <span class="hljs-keyword">end</span>

test/markup/erlang/char_literal.txt

@@ -0,0 +1,23 @@
+Character = $a
+TabCharacter = $\t
+TabCharacterDecimal = $\011
+TextWithDollar = "This is just a normal text with a $ in the middle"
+StringStart = $"
+Backslash = $\\
+ListStart = $[
+ListEnd = $]
+SpaceChar = $  % yes, that works
+fun_takes_literal($a) -> ok.
+fun_takes_literal_list([$a|Rest]) -> ok.
+fun_takes_literal_binary(<<$a, Rest/binary>>) -> ok.
+convert_escape_sequence(<<$\\, Escaped, Rest/binary>>) ->
+    C = case Escaped of
+        $b -> $\b;
+        $f -> $\f;
+        $n -> $\n;
+        $r -> $\r;
+        $t -> $\t;
+        $" -> $";
+        $\\ -> $\\;
+        _  -> error
+    end