[clang-format] Fix lambdas returning template specialization that contains operator in parameter

[jkorous]

Summary

Inspired by https://reviews.llvm.org/D58922

Since this code compiles I assume we should add those tokens to switch:

template<int> struct foo {};

int main() {
  { auto lambda = []() -> foo<5+2> { return {}; }; }
  { auto lambda = []() -> foo<5-2> { return {}; }; }
  { auto lambda = []() -> foo<5/3> { return {}; }; }
  { auto lambda = []() -> foo<5%2> { return {}; }; }
  { auto lambda = []() -> foo<5<<2> { return {}; }; }
  { auto lambda = []() -> foo<!false> { return {}; }; }
  { auto lambda = []() -> foo<~5> { return {}; }; }
  { auto lambda = []() -> foo<5|2> { return {}; }; }
  { auto lambda = []() -> foo<5||2> { return {}; }; }
  { auto lambda = []() -> foo<5&2> { return {}; }; }
  { auto lambda = []() -> foo<5&&2> { return {}; }; }
  { auto lambda = []() -> foo<5==2> { return {}; }; }
  { auto lambda = []() -> foo<5!=2> { return {}; }; }
  { auto lambda = []() -> foo<5>=2> { return {}; }; }
  { auto lambda = []() -> foo<5<2> { return {}; }; }
  { auto lambda = []() -> foo<5<=2> { return {}; }; }
  { auto lambda = []() -> foo<2 ? 1 : 0> { return {}; }; }
}

[MyDeveloperDay]

I'm not sure I personally would ever write code like that ;-) , but if its legal C++ and it compiles we should handle it the same as foo<1>,foo<true>,foo<!true>

As there are a number of reviews out there for formatting Lambdas I think its a good idea for us to add corner cases like this to the unit tests, but it does get me thinking if this shouldn't be handled by a piece of code which knows about trailing return types (template or otherwise) and not be in the general Lambda parsing code

I suspect that given that the switch statement handles

tok::identifier, tok::less, tok::numeric_constant, tok::greater
foo            <                          1              >

We are effectively just consuming the return type tokens.

But to handle what you have here it LGTM and handles more use cases that https://bugs.llvm.org/show_bug.cgi?id=40910 would throw up.

Thanks for helping out

[jkorous]

In D58934#1418043, @MyDeveloperDay wrote:

I'm not sure I personally would ever write code like that ;-) , but if its legal C++ and it compiles we should handle it the same as foo<1>,foo<true>,foo<!true>

I hear you :D

As there are a number of reviews out there for formatting Lambdas I think its a good idea for us to add corner cases like this to the unit tests, but it does get me thinking if this shouldn't be handled by a piece of code which knows about trailing return types (template or otherwise) and not be in the general Lambda parsing code

I suspect that given that the switch statement handles

tok::identifier, tok::less, tok::numeric_constant, tok::greater
foo            <                          1              >

We are effectively just consuming the return type tokens.

But to handle what you have here it LGTM and handles more use cases that https://bugs.llvm.org/show_bug.cgi?id=40910 would throw up.

Thanks for helping out

I had the same exact idea but since I wasn't able to find any existing function I just followed your lead for now. But I assume we can just factor out this later.

clang/lib/Format/UnwrappedLineParser.cpp

while (FormatTok->isNot(tok::l_brace)) {
     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:
+    // Specialization of a template with an integer parameter can contain
+    // arithmetic, logical, comparison and ternary operators.
+    case tok::plus:
+    case tok::minus:
+    case tok::exclaim:
+    case tok::tilde:
+    case tok::slash:
+    case tok::percent:
+    case tok::lessless:
+    case tok::pipe:
+    case tok::pipepipe:
+    case tok::ampamp:
+    case tok::caret:
+    case tok::equalequal:
+    case tok::exclaimequal:
+    case tok::greaterequal:
+    case tok::lessequal:
+    case tok::question:
+    case tok::colon:
       nextToken();
       break;
     case tok::arrow:
       // This might or might not actually be a lambda arrow (this could be an
       // ObjC method invocation followed by a dereferencing arrow). We might
       // reset this back to TT_Unknown in TokenAnnotator.
       FormatTok->Type = TT_LambdaArrow;
       nextToken();

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, FormatsLambdas) {
   verifyFormat("int c = []() -> int * { return 2; }();\n");
   verifyFormat("int c = []() -> vector<int> { return {2}; }();\n");
   verifyFormat("Foo([]() -> std::vector<int> { return {2}; }());");
   verifyGoogleFormat("auto a = [&b, c](D* d) -> D* {};");
   verifyGoogleFormat("auto a = [&b, c](D* d) -> pair<D*, D*> {};");
   verifyGoogleFormat("auto a = [&b, c](D* d) -> D& {};");
   verifyGoogleFormat("auto a = [&b, c](D* d) -> const D* {};");
   verifyFormat("[a, a]() -> a<1> {};");
+  verifyFormat("[]() -> foo<5 + 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 - 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 / 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 * 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 % 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 << 2> { return {}; };");
+  verifyFormat("[]() -> foo<!5> { return {}; };");
+  verifyFormat("[]() -> foo<~5> { return {}; };");
+  verifyFormat("[]() -> foo<5 | 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 || 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 & 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 && 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 == 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 != 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 >= 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 <= 2> { return {}; };");
+  verifyFormat("[]() -> foo<5 < 2> { return {}; };");
+  verifyFormat("[]() -> foo<2 ? 1 : 0> { return {}; };");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 + 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 - 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 / 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 * 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 % 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 << 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<!5> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<~5> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 | 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 || 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 & 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 && 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 == 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 != 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 >= 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 <= 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<5 < 2> { return {}; }};\n"
+              "} // namespace bar");
+  verifyFormat("namespace bar {\n"
+              "// broken:\n"
+              "auto foo{[]() -> foo<2 ? 1 : 0> { return {}; }};\n"
+              "} // namespace bar");
   verifyFormat("auto aaaaaaaa = [](int i, // break for some reason\n"
                "                   int j) -> int {\n"
                "  return ffffffffffffffffffffffffffffffffffffffffffff(i * j);\n"
                "};");
   verifyFormat(
       "aaaaaaaaaaaaaaaaaaaaaa(\n"
       "    [](aaaaaaaaaaaaaaaaaaaaaaaaaaa &aaa) -> aaaaaaaaaaaaaaaa {\n"
       "      return aaaaaaaaaaaaaaaaa;\n"