[clang-format] don't break between function and function name in JS

The patch https://reviews.llvm.org/D105964 (llvm@58494c8)
updated detection of function declaration names. It had the unfortunate
consequence that it started breaking between `function` and the function
name in some cases in JavaScript code.

This patch addresses this.

Reviewed By: MyDeveloperDay, owenpan

Differential Revision: https://reviews.llvm.org/D107267

Author: krasimirgg

clang/lib/Format/ContinuationIndenter.cpp

@@ -495,7 +495,10 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
   if (((Current.is(TT_FunctionDeclarationName) &&
         // Don't break before a C# function when no break after return type
         (!Style.isCSharp() ||
-         Style.AlwaysBreakAfterReturnType != FormatStyle::RTBS_None)) ||
+         Style.AlwaysBreakAfterReturnType != FormatStyle::RTBS_None) &&
+        // Don't always break between a JavaScript `function` and the function
+        // name.
+        Style.Language != FormatStyle::LK_JavaScript) ||
        (Current.is(tok::kw_operator) && !Previous.is(tok::coloncolon))) &&
       !Previous.is(tok::kw_template) && State.Stack.back().BreakBeforeParameter)
     return true;

clang/unittests/Format/FormatTestJS.cpp

@@ -692,6 +692,13 @@ TEST_F(FormatTestJS, FormatsFreestandingFunctions) {
                "  let x = 1;\n"
                "  console.log(x);\n"
                "}\n");
+  EXPECT_EQ("a = function(x) {}\n"
+            "\n"
+            "function f(x) {}",
+            format("a = function(x) {}\n"
+                   "\n"
+                   "function f(x) {}",
+                   getGoogleJSStyleWithColumns(20)));
 }
 
 TEST_F(FormatTestJS, GeneratorFunctions) {