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// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify %s
namespace GH85667 {
template <class T>
struct identity {
using type = T;
};
template <class> using ElementType = int;
template <class = void> void f() {
static_assert([]<class... Is>(Is... x) {
return ([I(x)] {
return I;
}() + ...);
}(1, 2) == 3);
[]<class... Is>(Is... x) {
return ([](auto y = Is()) { return y + 1; }() + ...); // expected-error {{no matching function}} \
// expected-note {{couldn't infer template argument 'y:auto'}} \
// expected-note@-1 {{requested here}}
// expected-note@#instantiate-f {{requested here}}
}(1);
[]<class... Is>() {
([]<class = Is>(Is)
noexcept(bool(Is()))
{}(Is()),
...);
}.template operator()<char, int, float>();
static_assert(__is_same(decltype([]<class... Is>() {
return ([]() -> decltype(Is()) { return {}; }(),
...);
}.template operator()<int, char>()),
char));
[]<class... Is>() {
return ([]<class... Ts>() -> decltype(Is()) { return Ts(); }() + ...);
// expected-error@-1 {{unexpanded parameter pack 'Ts'}}
}.template operator()<int, int>();
// https://github.com/llvm/llvm-project/issues/56852
[]<class... Is>(Is...) {
([] {
using T = identity<Is>::type;
}(), ...);
}(1, 2);
[]<class... Is>(Is...) {
([] { using T = ElementType<Is>; }(), ...);
}(1);
[](auto ...y) {
([y] { }(), ...);
}();
[](auto ...x) {
([&](auto ...y) {
([x..., y] { }(), ...);
})(1);
}(2, 'b');
#if 0
// FIXME: https://github.com/llvm/llvm-project/issues/18873
[](auto ...x) { // #1
([&](auto ...y) { // #2
([x, y] { }(), ...); // #3
})(1, 'a'); // #4
}(2, 'b'); // #5
// We run into another crash for the above lambda because of the absence of a
// mechanism that rebuilds an unexpanded pack from an expanded Decls.
//
// Basically, this happens after `x` at #1 being expanded when the template
// arguments at #5, deduced as <int, char>, are ready. When we want to
// instantiate the body of #1, we first instantiate the CallExpr at #4, which
// boils down to the lambda's instantiation at #2. To that end, we have to
// instantiate the body of it, which turns out to be #3. #3 is a CXXFoldExpr,
// and we immediately have to hold off on the expansion because we don't have
// corresponding template arguments (arguments at #4 are not transformed yet) for it.
// Therefore, we want to rebuild a CXXFoldExpr, which requires another pattern
// transformation of the lambda inside #3. Then we need to find an unexpanded form
// of such a Decl of x at the time of transforming the capture, which is impossible
// because the instantiated form has been expanded at #1!
[](auto ...x) { // #outer
([&](auto ...y) { // #inner
([x, y] { }(), ...);
// expected-error@-1 {{parameter pack 'y' that has a different length (4 vs. 3) from outer parameter packs}}
// expected-note-re@#inner {{function template specialization {{.*}} requested here}}
// expected-note-re@#outer {{function template specialization {{.*}} requested here}}
// expected-note-re@#instantiate-f {{function template specialization {{.*}} requested here}}
})('a', 'b', 'c');
}(0, 1, 2, 3);
#endif
}
template void f(); // #instantiate-f
} // namespace GH85667
namespace GH99877 {
struct tuple {
int x[3];
};
template <class F> int apply(F f, tuple v) { return f(v.x[0], v.x[1], v.x[2]); }
int Cartesian1(auto x, auto y) {
return apply(
[&](auto... xs) {
return (apply([xs](auto... ys) { return (ys + ...); }, y) + ...);
},
x);
}
int Cartesian2(auto x, auto y) {
return apply(
[&](auto... xs) {
return (apply([zs = xs](auto... ys) { return (ys + ...); }, y) + ...);
},
x);
}
template <int...> struct Ints {};
template <int> struct Choose {
template <class> struct Templ;
};
template <int... x> int Cartesian3(auto y) {
return [&]<int... xs>(Ints<xs...>) {
// check in default template arguments for
// - type template parameters,
(void)(apply([]<class = decltype(xs)>(auto... ys) { return (ys + ...); },
y) +
...);
// - template template parameters.
(void)(apply([]<template <class> class = Choose<xs>::template Templ>(
auto... ys) { return (ys + ...); },
y) +
...);
// - non-type template parameters,
return (apply([]<int = xs>(auto... ys) { return (ys + ...); }, y) + ...);
}(Ints<x...>());
}
template <int... x> int Cartesian4(auto y) {
return [&]<int... xs>(Ints<xs...>) {
return (
apply([]<decltype(xs) xx = 1>(auto... ys) { return (ys + ...); }, y) +
...);
}(Ints<x...>());
}
// FIXME: Attributes should preserve the ContainsUnexpandedPack flag.
#if 0
int Cartesian5(auto x, auto y) {
return apply(
[&](auto... xs) {
return (apply([](auto... ys) __attribute__((
diagnose_if(!__is_same(decltype(xs), int), "message",
"error"))) { return (ys + ...); },
y) +
...);
},
x);
}
#endif
void foo() {
auto x = tuple({1, 2, 3});
auto y = tuple({4, 5, 6});
Cartesian1(x, y);
Cartesian2(x, y);
Cartesian3<1, 2, 3>(y);
Cartesian4<1, 2, 3>(y);
#if 0
Cartesian5(x, y);
#endif
}
} // namespace GH99877
namespace GH101754 {
template <typename... Ts> struct Overloaded : Ts... {
using Ts::operator()...;
};
template <typename... Ts> Overloaded(Ts...) -> Overloaded<Ts...>;
template <class T, class U>
concept same_as = __is_same(T, U); // #same_as
template <typename... Ts> constexpr auto foo() {
return Overloaded{[](same_as<Ts> auto value) { return value; }...}; // #lambda
}
static_assert(foo<int, double>()(123) == 123);
static_assert(foo<int, double>()(2.718) == 2.718);
static_assert(foo<int, double>()('c'));
// expected-error@-1 {{no matching function}}
// expected-note@#lambda {{constraints not satisfied}}
// expected-note@#lambda {{'same_as<char, int>' evaluated to false}}
// expected-note@#same_as {{evaluated to false}}
// expected-note@#lambda {{constraints not satisfied}}
// expected-note@#lambda {{'same_as<char, double>' evaluated to false}}
// expected-note@#same_as {{evaluated to false}}
template <class T, class U, class V>
concept C = same_as<T, U> && same_as<U, V>; // #C
template <typename... Ts> constexpr auto bar() {
return ([]<class Up>() {
return Overloaded{[](C<Up, Ts> auto value) { // #bar
return value;
}...};
}.template operator()<Ts>(), ...);
}
static_assert(bar<int, float>()(3.14f)); // OK, bar() returns the last overload i.e. <float>.
static_assert(bar<int, float>()(123));
// expected-error@-1 {{no matching function}}
// expected-note@#bar {{constraints not satisfied}}
// expected-note@#bar {{'C<int, float, int>' evaluated to false}}
// expected-note@#C {{evaluated to false}}
// expected-note@#bar {{constraints not satisfied}}
// expected-note@#bar {{'C<int, float, float>' evaluated to false}}
// expected-note@#C {{evaluated to false}}
// expected-note@#same_as 2{{evaluated to false}}
} // namespace GH101754
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