clang-format: [JS] fix incorrectly collapsed lines after export statement.

[mprobst]

Summary

When an exported function would follow a class declaration, it would not be recognized as a stand-alone function. That would then collapse the following line with the current one, e.g.

class C {}
export function f() {} var x;

This change recognizes functions as free standing even when the line starts with an export keyword.

[mprobst]

kw_import is unneeded, there is no "import function ..." statement.

[djasper]

Fixed with a different fix in r239592.

lib/Format/UnwrappedLineParser.cpp

case tok::l_brace:
       // element continues.
       break;
     case tok::kw_try:
       // We arrive here when parsing function-try blocks.
       parseTryCatch();
       return;
     case tok::identifier: {
       // Parse function literal unless 'function' is the first token in a line
-      // in which case this should be treated as a free-standing function.
+      // (or it is part of an export statement) in which case this should be
+      // treated as a free-standing function.
       if (Style.Language == FormatStyle::LK_JavaScript &&
-          FormatTok->is(Keywords.kw_function) && Line->Tokens.size() > 0) {
+          FormatTok->is(Keywords.kw_function) && Line->Tokens.size() > 0 &&
+          (true ||
+           !(Line->Tokens.size() == 1 &&
+             Line->Tokens.begin()->Tok->is(tok::kw_export)))) {
         tryToParseJSFunction();
         break;
       }
       if ((Style.Language == FormatStyle::LK_JavaScript ||
            Style.Language == FormatStyle::LK_Java) &&
           FormatTok->is(Keywords.kw_interface)) {
         parseRecord();
         break;

unittests/Format/FormatTestJS.cpp

TEST_F(FormatTestJS, Modules) {
   verifyFormat("export class C {\n"
                "  x: number;\n"
                "  y: string;\n"
                "}");
   verifyFormat("export class X { y: number; }");
   verifyFormat("export default class X { y: number }");
   verifyFormat("export default function() {\n  return 1;\n}");
   verifyFormat("export var x = 12;");
+  verifyFormat("class C {}\n"
+               "export function f() {}\n"
+               "var v;");
   verifyFormat("export var x: number = 12;");
   verifyFormat("export const y = {\n"
                "  a: 1,\n"
                "  b: 2\n"
                "};");
 }
 
 TEST_F(FormatTestJS, TemplateStrings) {