[clang-format] Mark constexpr lambdas as lambda

[HazardyKnusperkeks]

Summary

Otherwise the brace was detected as a function brace, not wrong per se, but when directly calling the lambda the calling parens were put on the next line.

[owenpan]

clang/lib/Format/UnwrappedLineParser.cpp

2131

Maybe move it up so that it's grouped with kw_const?

[HazardyKnusperkeks]

clang/lib/Format/UnwrappedLineParser.cpp

2131

Will do before submit.

clang/lib/Format/UnwrappedLineParser.cpp

case tok::kw_typename:
       assert(FormatTok->Previous);
       if (FormatTok->Previous->is(tok::less))
         InTemplateParameterList = true;
       nextToken();
       break;
     case tok::amp:
     case tok::star:
     case tok::kw_const:
+    case tok::kw_constexpr:
     case tok::comma:
     case tok::less:
     case tok::greater:
     case tok::identifier:
     case tok::numeric_constant:
     case tok::coloncolon:
     case tok::kw_mutable:
     case tok::kw_noexcept:
       nextToken();
       break;
     // Specialization of a template with an integer parameter can contain
     // arithmetic, logical, comparison and ternary operators.
     //
     // FIXME: This also accepts sequences of operators that are not in the scope
     // of a template argument list.
     //
     // In a C++ lambda a template type can only occur after an arrow. We use

clang/unittests/Format/TokenAnnotatorTest.cpp

TEST_F(TokenAnnotatorTest, UnderstandsObjCBlock) {
 
   Tokens = annotate("int *p = ^int*(){ //\n"
                     "  return nullptr;\n"
                     "}();");
   ASSERT_EQ(Tokens.size(), 19u) << Tokens;
   EXPECT_TOKEN(Tokens[9], tok::l_brace, TT_ObjCBlockLBrace);
 }
 
+TEST_F(TokenAnnotatorTest, UnderstandsLambdas) {
+  auto Tokens = annotate("[]() constexpr {}");
+  ASSERT_EQ(Tokens.size(), 8u) << Tokens;
+  EXPECT_TOKEN(Tokens[0], tok::l_square, TT_LambdaLSquare);
+  EXPECT_TOKEN(Tokens[5], tok::l_brace, TT_LambdaLBrace);
+}
+
 } // namespace
 } // namespace format
 } // namespace clang