fix(rust) Add negative-lookahead for fn like keywords (#3883)

Author: omalk98

CHANGES.md

@@ -20,6 +20,7 @@ New Grammars:
 
 Core Grammars:
 
+- fix(rust) added negative-lookahead for callable keywords `if` `while` `for` [Omar Hussein][]
 - enh(armasm) added `x0-x30` and `w0-w30` ARMv8 registers [Nicholas Thompson][]
 - enh(haxe) added `final`, `is`, `macro` keywords and `$` identifiers [Robert Borghese][]
 - enh(haxe) support numeric separators and suffixes [Robert Borghese][]

src/languages/rust.js

@@ -14,7 +14,7 @@ export default function(hljs) {
     relevance: 0,
     begin: regex.concat(
       /\b/,
-      /(?!let\b)/,
+      /(?!let|for|while|if|else|match\b)/,
       hljs.IDENT_RE,
       regex.lookahead(/\s*\(/))
   };

test/detect/rust/default.txt

@@ -12,5 +12,12 @@ impl From<&'a str> for State {
             "closed" => State::Closed,
             _ => unreachable!(),
         }
+
+        if (str == "trans") {
+            State::Transient;
+        }
+        else if str == "start" {
+            State::Start;
+        }
     }
 }

test/markup/rust/invoked-keywords.expect.txt

@@ -0,0 +1,9 @@
+<span class="hljs-keyword">if</span> (<span class="hljs-literal">true</span>) {}
+<span class="hljs-keyword">if</span> <span class="hljs-literal">true</span> {}
+<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (<span class="hljs-literal">true</span>) {}
+<span class="hljs-keyword">while</span> (<span class="hljs-literal">true</span>) {}
+<span class="hljs-keyword">while</span> <span class="hljs-literal">true</span> {}
+<span class="hljs-keyword">for</span> (a, b) <span class="hljs-title function_ invoke__">in</span> (<span class="hljs-number">0</span>..<span class="hljs-number">10</span>).<span class="hljs-title function_ invoke__">enumerate</span>() {}
+<span class="hljs-keyword">for</span> <span class="hljs-variable">a</span> <span class="hljs-keyword">in</span> <span class="hljs-number">0</span>..<span class="hljs-number">10</span> {}
+<span class="hljs-keyword">match</span> <span class="hljs-type">str</span> {}
+<span class="hljs-keyword">match</span> (<span class="hljs-type">str</span>) {}

test/markup/rust/invoked-keywords.txt

@@ -0,0 +1,9 @@
+if (true) {}
+if true {}
+else if (true) {}
+while (true) {}
+while true {}
+for (a, b) in (0..10).enumerate() {}
+for a in 0..10 {}
+match str {}
+match (str) {}