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[Clang] Treat default template argument as constant expressions #107073

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Merged
merged 5 commits into from
Sep 4, 2024
Merged

[Clang] Treat default template argument as constant expressions #107073

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5edd9a9
[Clang] Treat default template argument as constant expressions
cor3ntin Sep 3, 2024
b98c94e
address review comments
cor3ntin Sep 3, 2024
00672c5
add tests
cor3ntin Sep 4, 2024
51ccc13
Merge branch 'main' into corentin/gh107048
cor3ntin Sep 4, 2024
5e1efac
Merge branch 'main' into corentin/gh107048
cor3ntin Sep 4, 2024
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1 change: 1 addition & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -346,6 +346,7 @@ Bug Fixes to C++ Support
- Fix handling of ``_`` as the name of a lambda's init capture variable. (#GH107024)
- Fix an issue with dependent source location expressions (#GH106428), (#GH81155), (#GH80210), (#GH85373)
- Fixed a bug in the substitution of empty pack indexing types. (#GH105903)
- Clang no longer tries to capture non-odr used default arguments of template parameters of generic lambdas (#GH107048)

Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
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2 changes: 1 addition & 1 deletion clang/lib/Parse/ParseTemplate.cpp
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Expand Up @@ -959,7 +959,7 @@ Parser::ParseNonTypeTemplateParameter(unsigned Depth, unsigned Position) {
++CurTemplateDepthTracker;
EnterExpressionEvaluationContext ConstantEvaluated(
Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated);
DefaultArg = Actions.CorrectDelayedTyposInExpr(ParseInitializer());
DefaultArg = Actions.ActOnConstantExpression(ParseInitializer());
if (DefaultArg.isInvalid())
SkipUntil(tok::comma, tok::greater, StopAtSemi | StopBeforeMatch);
}
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34 changes: 34 additions & 0 deletions clang/test/SemaCXX/cxx2a-template-lambdas.cpp
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Expand Up @@ -97,3 +97,37 @@ void foo() {

}
#endif

#if __cplusplus >= 202002L
namespace {
struct S {};
constexpr S gs;
void f() {
constexpr int x{};
const int y{};
auto b = []<int=x, int=y>{};
using A = decltype([]<int=x>{});

int z; // expected-note {{'z' declared here}}
auto c = []<int t=z>{
// expected-error@-1 {{no matching function for call to object of type}} \
// expected-error@-1 {{variable 'z' cannot be implicitly captured in a lambda with no capture-default specified}} \
// expected-note@-1 {{lambda expression begins here}} \
// expected-note@-1 4{{capture}} \
// expected-note@-1 {{candidate template ignored: substitution failure: reference to local variable 'z' declared in enclosing function}}
return t;
}();

auto class_type_global = []<S=gs>{};

static constexpr S static_s;
auto class_type_static = []<S=static_s>{};

constexpr S s; // expected-note {{'s' declared here}}
auto class_type = []<S=s>{};
// expected-error@-1 {{variable 's' cannot be implicitly captured in a lambda with no capture-default specified}} \
// expected-note@-1 {{lambda expression begins here}} \
// expected-note@-1 4{{capture}}
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Curious about these cases: https://godbolt.org/z/xWbWYfnf3

struct S {};
constexpr S s; 

void f() {
  auto class_type = []<S=s>{};
}

void h() {
  static constexpr S s;
  auto class_type = []<S=s>{};
}

template <S=s>
void g() {}

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All of these work (because they are not local entities so don't need capturing https://eel.is/c++draft/basic#pre-7)

}
}
#endif
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