(objectivec) Sync preprocessor highlighting with cpp (#2265)

The objectivec highlighting had a few bugs and was missing a few
features:

- Expressions with < were misidentified as a string like <stdio.h>
  (fixes #1964).
- Keywords like if, else, endif, etc. were not highlighted.
- The escape sequences in string literals were not parsed.
- Line continuations were not parsed.
- Comments were not parsed.

Fix all these by adapting cpp's preprocessor definition. Pull in the
preprocessor test from cpp. (This is actually objectivec's first markup
test. It probably could do with tests beyond just this feature.)

CHANGES.md

@@ -20,6 +20,7 @@ Improvements:
 - fix(parser): Look-ahead regex now work for end matches also (#2237) [Josh Goebel][]
 - fix(parser): Better errors when a language is missing (#2236) [Josh Goebel][]
 - fix(go): Fix escaped character literals (#2266) [David Benjamin][]
+- fix(objectivec): Fix various preprocessor highlighting issues (#2265) [David Benjamin][]
 - fix(objectivec): Handle multibyte character literals (#2268) [David Benjamin][]
 
 [Josh Goebel]: https://github.com/yyyc514

src/languages/cpp.js

@@ -56,7 +56,7 @@ function(hljs) {
       hljs.inherit(STRINGS, {className: 'meta-string'}),
       {
         className: 'meta-string',
-        begin: /<[^\n>]*>/, end: /$/,
+        begin: /<.*?>/, end: /$/,
         illegal: '\\n',
       },
       hljs.C_LINE_COMMENT_MODE,

src/languages/objectivec.js

@@ -66,16 +66,24 @@ function(hljs) {
       },
       {
         className: 'meta',
-        begin: '#',
-        end: '$',
+        begin: /#\s*[a-z]+\b/, end: /$/,
+        keywords: {
+          'meta-keyword':
+            'if else elif endif define undef warning error line ' +
+            'pragma ifdef ifndef include'
+        },
         contains: [
+          {
+            begin: /\\\n/, relevance: 0
+          },
+          hljs.inherit(hljs.QUOTE_STRING_MODE, {className: 'meta-string'}),
           {
             className: 'meta-string',
-            variants: [
-              { begin: '\"', end: '\"' },
-              { begin: '<', end: '>' }
-            ]
-          }
+            begin: /<.*?>/, end: /$/,
+            illegal: '\\n',
+          },
+          hljs.C_LINE_COMMENT_MODE,
+          hljs.C_BLOCK_COMMENT_MODE
         ]
       },
       {

test/markup/cpp/preprocessor.expect.txt

@@ -11,3 +11,9 @@
 <span class="hljs-meta">#<span class="hljs-meta-keyword">define</span> x(v) ((v))</span>
 <span class="hljs-meta"># <span class="hljs-meta-keyword">define</span> x(v) ((v))</span>
 <span class="hljs-meta">#  <span class="hljs-meta-keyword">define</span> x(v) ((v))</span>
+
+<span class="hljs-meta">#<span class="hljs-meta-keyword">if</span> MACRO_WITH_STRING_ARG(<span class="hljs-meta-string">"hello \"world\""</span>)</span>
+<span class="hljs-meta">#<span class="hljs-meta-keyword">elif</span> MULTI_LINE <span class="hljs-comment">/* comment */</span> &lt; \
+    EXPRESSION</span>
+<span class="hljs-keyword">int</span> bar;
+<span class="hljs-meta">#<span class="hljs-meta-keyword">endif</span>  <span class="hljs-comment">// comment</span></span>

test/markup/cpp/preprocessor.txt

@@ -11,3 +11,9 @@ int foo(void)
 #define x(v) ((v))
 # define x(v) ((v))
 #  define x(v) ((v))
+
+#if MACRO_WITH_STRING_ARG("hello \"world\"")
+#elif MULTI_LINE /* comment */ < \
+    EXPRESSION
+int bar;
+#endif  // comment

test/markup/objectivec/preprocessor.expect.txt

@@ -0,0 +1,19 @@
+<span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;iostream&gt;</span></span>
+<span class="hljs-meta">#<span class="hljs-meta-keyword">define</span> foo 1&lt;&lt;16</span>
+
+<span class="hljs-meta">#<span class="hljs-meta-keyword">ifdef</span> DEBUG</span>
+TYPE1 foo(<span class="hljs-keyword">void</span>)
+<span class="hljs-meta">#<span class="hljs-meta-keyword">else</span></span>
+<span class="hljs-keyword">int</span> foo(<span class="hljs-keyword">void</span>)
+<span class="hljs-meta">#<span class="hljs-meta-keyword">endif</span></span>
+{ }
+
+<span class="hljs-meta">#<span class="hljs-meta-keyword">define</span> x(v) ((v))</span>
+<span class="hljs-meta"># <span class="hljs-meta-keyword">define</span> x(v) ((v))</span>
+<span class="hljs-meta">#  <span class="hljs-meta-keyword">define</span> x(v) ((v))</span>
+
+<span class="hljs-meta">#<span class="hljs-meta-keyword">if</span> MACRO_WITH_STRING_ARG(<span class="hljs-meta-string">"hello \"world\""</span>)</span>
+<span class="hljs-meta">#<span class="hljs-meta-keyword">elif</span> MULTI_LINE <span class="hljs-comment">/* comment */</span> &lt; \
+    EXPRESSION</span>
+<span class="hljs-keyword">int</span> bar;
+<span class="hljs-meta">#<span class="hljs-meta-keyword">endif</span>  <span class="hljs-comment">// comment</span></span>

test/markup/objectivec/preprocessor.txt

@@ -0,0 +1,19 @@
+#include <iostream>
+#define foo 1<<16
+
+#ifdef DEBUG
+TYPE1 foo(void)
+#else
+int foo(void)
+#endif
+{ }
+
+#define x(v) ((v))
+# define x(v) ((v))
+#  define x(v) ((v))
+
+#if MACRO_WITH_STRING_ARG("hello \"world\"")
+#elif MULTI_LINE /* comment */ < \
+    EXPRESSION
+int bar;
+#endif  // comment