[PATCH] D155064: [clang][SemaCXX] Diagnose tautological uses of consteval if and is_constant_evaluated

[Sam McCall via Phabricator via cfe-commits]

sammccall added a comment.

Hi, I'm afraid this breaks valid code with false diagnostics, I need to revert.

Specifically it complains about missing lambda captures for values that are in fact arguments to the lambda:

  template <typename F>
  constexpr void inner(F f) {
    return f(0);
  }
  
  template <typename F>
  void outer(F f) {
    inner([](auto I) {
      constexpr auto kFuncs = [](F& g) { return g(); };
      (void) kFuncs;
    });
  }
  
  void entry() {
    outer([&] {});
  }



  $ bin/clang++ -fsyntax-only ~/test.cc
  
  /usr/local/google/home/sammccall/test.cc:9:47: error: variable 'g' cannot be implicitly captured in a lambda with no capture-default specified
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                                               ^
  /usr/local/google/home/sammccall/test.cc:9:29: note: while substituting into a lambda expression here
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                             ^
  /usr/local/google/home/sammccall/test.cc:3:10: note: in instantiation of function template specialization 'outer((lambda at /usr/local/google/home/sammccall/test.cc:15:9))::(anonymous class)::operator()<int>' requested here
      3 |   return f(0);
        |          ^
  /usr/local/google/home/sammccall/test.cc:8:3: note: in instantiation of function template specialization 'inner<(lambda at /usr/local/google/home/sammccall/test.cc:8:9)>' requested here
      8 |   inner([](auto I) {
        |   ^
  /usr/local/google/home/sammccall/test.cc:15:3: note: in instantiation of function template specialization 'outer<(lambda at /usr/local/google/home/sammccall/test.cc:15:9)>' requested here
     15 |   outer([&] {});
        |   ^
  /usr/local/google/home/sammccall/test.cc:9:35: note: 'g' declared here
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                                   ^
  /usr/local/google/home/sammccall/test.cc:9:29: note: lambda expression begins here
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                             ^
  /usr/local/google/home/sammccall/test.cc:9:30: note: capture 'g' by value
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                              ^
        |                              g
  /usr/local/google/home/sammccall/test.cc:9:30: note: capture 'g' by reference
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                              ^
        |                              &g
  /usr/local/google/home/sammccall/test.cc:9:30: note: default capture by value
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                              ^
        |                              =
  /usr/local/google/home/sammccall/test.cc:9:30: note: default capture by reference
      9 |     constexpr auto kFuncs = [](F& g) { return g(); };
        |                              ^
        |                              &
  1 error generated.


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