[clang-format] Fix lambda with ellipsis in return type

[johnchen902]

Summary

BTW my actual code that hit this issue is like

[a, b = std::move(b)](auto &&... c) mutable -> std::invoke_result_t<decltype(b), decltype(c)...> { /* omitted */ }

where this explicit return type is required for SFINAE.

[krasimir]

Could you please update the patch with full context: https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface
This helps out when reviewing.

[johnchen902]

Rebased to HEAD.

[krasimir]

Thank you!

I think this is OK as-is.

[MyDeveloperDay]

Me too LGTM

[johnchen902]

Well... I don't know how to land this. I guess I don't have commit access anyway.

clang/lib/Format/UnwrappedLineParser.cpp

while (FormatTok->isNot(tok::l_brace)) {
     case tok::ampamp:
     case tok::caret:
     case tok::equalequal:
     case tok::exclaimequal:
     case tok::greaterequal:
     case tok::lessequal:
     case tok::question:
     case tok::colon:
+    case tok::ellipsis:
     case tok::kw_true:
     case tok::kw_false:
       if (SeenArrow) {
         nextToken();
         break;
       }
       return true;
     case tok::arrow:

clang/unittests/Format/FormatTest.cpp

verifyFormat(
       "    [](aaaaaaaaaaaaaaaaaaaaaaaaaaa &aaa) -> aaaaaaaaaaaaaaaa {\n"
       "      return aaaaaaaaaaaaaaaaa;\n"
       "    });",
       getLLVMStyleWithColumns(70));
   verifyFormat("[]() //\n"
                "    -> int {\n"
                "  return 1; //\n"
                "};");
+  verifyFormat("[]() -> Void<T...> {};");
+  verifyFormat("[a, b]() -> Tuple<T...> { return {}; };");
 
   // Lambdas with explicit template argument lists.
   verifyFormat(
       "auto L = []<template <typename> class T, class U>(T<U> &&a) {};\n");
 
   // Multiple lambdas in the same parentheses change indentation rules. These
   // lambdas are forced to start on new lines.
   verifyFormat("SomeFunction(\n"