Support for ruby's squiggly heredoc (#2049)

* Support for ruby's squiggly heredoc

Ruby has the squiggly heredoc notation to insert indented multiline
strings. This should be supported in addition to the existing heredoc
notation.

+ Improved heredoc regexp so that the closing tag must match the open tag

src/languages/ruby.js

@@ -65,8 +65,16 @@ function(hljs) {
         // is the last character of a preceding identifier, as in: `func?4`
         begin: /\B\?(\\\d{1,3}|\\x[A-Fa-f0-9]{1,2}|\\u[A-Fa-f0-9]{4}|\\?\S)\b/
       },
-      {
-        begin: /<<(-?)\w+$/, end: /^\s*\w+$/,
+      { // heredocs
+        begin: /<<[-~]?'?(\w+)(?:.|\n)*?\n\s*\1\b/,
+        returnBegin: true,
+        contains: [
+          { begin: /<<[-~]?'?/ },
+          { begin: /\w+/,
+            endSameAsBegin: true,
+            contains: [hljs.BACKSLASH_ESCAPE, SUBST],
+          }
+        ]
       }
     ]
   };

test/markup/ruby/heredoc.expect.txt

@@ -4,5 +4,12 @@
     &lt;h4&gt;<span class="hljs-subst">#{bar}</span>&lt;/h4&gt;
   &lt;/div&gt;
   HTML</span>
+<span class="hljs-keyword">end</span>
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">baz</span><span class="hljs-params">()</span></span>
+  msg = <span class="hljs-string">&lt;&lt;~FOO
+  &lt;div&gt;
+    &lt;h4&gt;<span class="hljs-subst">#{bar}</span>&lt;/h4&gt;
+  &lt;/div&gt;
+  FOO</span>
+<span class="hljs-keyword">end</span>

test/markup/ruby/heredoc.txt

@@ -4,5 +4,12 @@ def foo()
     <h4>#{bar}</h4>
   </div>
   HTML
+end
 
 def baz()
+  msg = <<~FOO
+  <div>
+    <h4>#{bar}</h4>
+  </div>
+  FOO
+end