enh(csharp) add generic modifiers

CHANGES.md

@@ -14,6 +14,7 @@ Core Changes:
 
 Language Improvements:
 
+- enh(csharp) Add generic modifiers (in, out) (#2378) [Josh Goebel][]
 - (fortran) Add Fortran 2018 keywords and coarray intrinsics (#2361) [Sam Miller][]
 - (delphi) highlight hexadecimal, octal, and binary numbers (#2370) [Robert Riebisch]()
 - enh(plaintext) added `text` and `txt` as alias (#2360) [Taufik Nurrohman][]
@@ -22,6 +23,7 @@ Developer Tools:
 
 - none.
 
+[Josh Goebel]: https://github.com/yyyc514
 [Sam Miller]: https://github.com/smillerc
 [Robert Riebisch]: https://github.com/bttrx
 [Taufik Nurrohman]: https://github.com/taufik-nurrohman

src/languages/csharp.js

@@ -18,7 +18,9 @@ function(hljs) {
       'uint ulong unchecked unsafe ushort using virtual void volatile while ' +
       // Contextual keywords.
       'add alias ascending async await by descending dynamic equals from get global group into join ' +
-      'let nameof on orderby partial remove select set value var when where yield',
+      'let nameof on orderby partial remove select set value var when where yield ' +
+      // generic modifiers
+      'in out',
     literal:
       'null false true'
   };
@@ -86,6 +88,11 @@ function(hljs) {
     ]
   };
 
+  GENERIC_var MODIFIER = {
+    begin: "<",
+    end: ">",
+    keywords: "in out"
+  };
   var TYPE_IDENT_RE = hljs.IDENT_RE + '(<' + hljs.IDENT_RE + '(\\s*,\\s*' + hljs.IDENT_RE + ')*>)?(\\[\\])?';
 
   return {
@@ -131,6 +138,7 @@ function(hljs) {
         beginKeywords: 'class interface', end: /[{;=]/,
         illegal: /[^\s:,]/,
         contains: [
+          GENERIC_MODIFIER,
           hljs.TITLE_MODE,
           hljs.C_LINE_COMMENT_MODE,
           hljs.C_BLOCK_COMMENT_MODE

test/markup/csharp/generic_modifiers.expect.txt

@@ -0,0 +1,7 @@
+<span class="hljs-keyword">interface</span> <span class="hljs-title">IObserver</span>&lt;<span class="hljs-keyword">in</span> T&gt;;
+{}
+
+<span class="hljs-keyword">interface</span> <span class="hljs-title">IObservable</span>&lt;<span class="hljs-keyword">out</span> T&gt;;
+{}
+
+<span class="hljs-keyword">public</span> <span class="hljs-keyword">delegate</span> <span class="hljs-keyword">void</span> DContravariant&lt;<span class="hljs-keyword">in</span> A&gt;(A argument);

test/markup/csharp/generic_modifiers.txt

@@ -0,0 +1,7 @@
+interface IObserver<in T>;
+{}
+
+interface IObservable<out T>;
+{}
+
+public delegate void DContravariant<in A>(A argument);