clang-format: [JS] parse async function declarations.

[mprobst]

Summary

Previously, clang-format would accidentally parse an async function
declaration as a function expression, and thus not insert an unwrapped
line for async functions, causing subsequent functions to run into the
function:

async function f() {
  x();
} function g() { ...

With this change, async functions get parsed as top level function
declarations and get their own unwrapped line context.

[djasper]

Looks good.

lib/Format/UnwrappedLineParser.cpp

1043–1047

Nit: I'd start this and the next sentence upper case.

[mprobst]

• capitalization

lib/Format/UnwrappedLineParser.cpp

case tok::kw_try:
       parseTryCatch();
       return;
     case tok::identifier: {
       if (FormatTok->is(TT_MacroBlockEnd)) {
         addUnwrappedLine();
         return;
       }
 
-      // Parse function literal unless 'function' is the first token in a line
-      // in which case this should be treated as a free-standing function.
+      // Function declarations (as opposed to function expressions) are parsed
+      // on their own unwrapped line by continuing this loop. Function
+      // expressions (functions that are not on their own line) must not create
+      // a new unwrapped line, so they are special cased below.
+      size_t TokenCount = Line->Tokens.size();
       if (Style.Language == FormatStyle::LK_JavaScript &&
-          (FormatTok->is(Keywords.kw_function) ||
-           FormatTok->startsSequence(Keywords.kw_async,
-                                     Keywords.kw_function)) &&
-          Line->Tokens.size() > 0) {
+          FormatTok->is(Keywords.kw_function) &&
+          (TokenCount > 1 || (TokenCount == 1 && !Line->Tokens.front().Tok->is(
+                                                     Keywords.kw_async)))) {
         tryToParseJSFunction();
         break;
       }
       if ((Style.Language == FormatStyle::LK_JavaScript ||
            Style.Language == FormatStyle::LK_Java) &&
           FormatTok->is(Keywords.kw_interface)) {
         if (Style.Language == FormatStyle::LK_JavaScript) {
           // In JavaScript/TypeScript, "interface" can be used as a standalone

unittests/Format/FormatTestJS.cpp

verifyFormat("var x = {\n"
                "}\n");
 }
 
 TEST_F(FormatTestJS, AsyncFunctions) {
   verifyFormat("async function f() {\n"
                "  let x = 1;\n"
                "  return fetch(x);\n"
                "}");
+  verifyFormat("async function f() {\n"
+               "  return 1;\n"
+               "}\n"
+               "\n"
+               "function a() {\n"
+               "  return 1;\n"
+               "}\n",
+               "  async   function f() {\n"
+               "   return 1;\n"
+               "}\n"
+               "\n"
+               "   function a() {\n"
+               "  return   1;\n"
+               "}  \n");
   verifyFormat("async function* f() {\n"
                "  yield fetch(x);\n"
                "}");
   verifyFormat("export async function f() {\n"
                "  return fetch(x);\n"
                "}");
   verifyFormat("let x = async () => f();");
+  verifyFormat("let x = async function() {\n"
+               "  f();\n"
+               "};");
   verifyFormat("let x = async();");
   verifyFormat("class X {\n"
                "  async asyncMethod() {\n"
                "    return fetch(1);\n"
                "  }\n"
                "}");
   verifyFormat("function initialize() {\n"
                "  // Comment.\n"