clang-format: [JS] Support for EC6 arrow functions.

Before:
  var b = a.map((x) = > x + 1);

After:
  var b = a.map((x) => x + 1);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209112 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/Format.cpp

@@ -1244,6 +1244,7 @@ private:
       static tok::TokenKind JSNotIdentity[] = { tok::exclaimequal, tok::equal };
       static tok::TokenKind JSShiftEqual[] = { tok::greater, tok::greater,
                                                tok::greaterequal };
+      static tok::TokenKind JSRightArrow[] = { tok::equal, tok::greater };
       // FIXME: We probably need to change token type to mimic operator with the
       // correct priority.
       if (tryMergeTokens(JSIdentity))
@@ -1252,6 +1253,8 @@ private:
         return;
       if (tryMergeTokens(JSShiftEqual))
         return;
+      if (tryMergeTokens(JSRightArrow))
+        return;
     }
   }
 

unittests/Format/FormatTestJS.cpp

@@ -77,6 +77,8 @@ TEST_F(FormatTestJS, UnderstandsJavaScriptOperators) {
                "            bbbbbb :\n"
                "            ccc;",
                getGoogleJSStyleWithColumns(20));
+
+  verifyFormat("var b = a.map((x) => x + 1);");
 }
 
 TEST_F(FormatTestJS, SpacesInContainerLiterals) {