clang/test/SemaTemplate/trailing-return-short-circuit.cpp

   1 // RUN: %clang_cc1 -std=c++20 -verify %s
   2
   3 template <class T>
   4   requires(sizeof(T) > 2) || T::value // #FOO_REQ
   5 void Foo(T){};                        // #FOO
   6
   7 template <class T>
   8 void TrailingReturn(T)       // #TRAILING
   9   requires(sizeof(T) > 2) || // #TRAILING_REQ
  10           T::value           // #TRAILING_REQ_VAL
  11 {};
  12 template <bool B>
  13 struct HasValue {
  14   static constexpr bool value = B;
  15 };
  16 static_assert(sizeof(HasValue<true>) <= 2);
  17
  18 template <bool B>
  19 struct HasValueLarge {
  20   static constexpr bool value = B;
  21   int I;
  22 };
  23 static_assert(sizeof(HasValueLarge<true>) > 2);
  24
  25 void usage() {
  26   // Passes the 1st check, short-circuit so the 2nd ::value is not evaluated.
  27   Foo(1.0);
  28   TrailingReturn(1.0);
  29
  30   // Fails the 1st check, but has a ::value, so the check happens correctly.
  31   Foo(HasValue<true>{});
  32   TrailingReturn(HasValue<true>{});
  33
  34   // Passes the 1st check, but would have passed the 2nd one.
  35   Foo(HasValueLarge<true>{});
  36   TrailingReturn(HasValueLarge<true>{});
  37
  38   // Fails the 1st check, fails 2nd because there is no ::value.
  39   Foo(true);
  40   // expected-error@-1{{no matching function for call to 'Foo'}}
  41   // expected-note@#FOO{{candidate template ignored: constraints not satisfied [with T = bool]}}
  42   // expected-note@#FOO_REQ{{because 'sizeof(_Bool) > 2' (1 > 2) evaluated to false}}
  43   // expected-note@#FOO_REQ{{because substituted constraint expression is ill-formed: type 'bool' cannot be used prior to '::' because it has no members}}
  44
  45   TrailingReturn(true);
  46   // expected-error@-1{{no matching function for call to 'TrailingReturn'}}
  47   // expected-note@#TRAILING{{candidate template ignored: constraints not satisfied [with T = bool]}}
  48   // expected-note@#TRAILING_REQ{{because 'sizeof(_Bool) > 2' (1 > 2) evaluated to false}}
  49   // expected-note@#TRAILING_REQ_VAL{{because substituted constraint expression is ill-formed: type 'bool' cannot be used prior to '::' because it has no members}}
  50
  51   // Fails the 1st check, fails 2nd because ::value is false.
  52   Foo(HasValue<false>{});
  53   // expected-error@-1 {{no matching function for call to 'Foo'}}
  54   // expected-note@#FOO{{candidate template ignored: constraints not satisfied [with T = HasValue<false>]}}
  55   // expected-note@#FOO_REQ{{because 'sizeof(HasValue<false>) > 2' (1 > 2) evaluated to false}}
  56   // expected-note@#FOO_REQ{{and 'HasValue<false>::value' evaluated to false}}
  57   TrailingReturn(HasValue<false>{});
  58   // expected-error@-1 {{no matching function for call to 'TrailingReturn'}}
  59   // expected-note@#TRAILING{{candidate template ignored: constraints not satisfied [with T = HasValue<false>]}}
  60   // expected-note@#TRAILING_REQ{{because 'sizeof(HasValue<false>) > 2' (1 > 2) evaluated to false}}
  61   // expected-note@#TRAILING_REQ_VAL{{and 'HasValue<false>::value' evaluated to false}}
  62 }