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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 @@ -339,6 +339,7 @@ Bug Fixes to C++ Support
- Template parameter names are considered in the name lookup of out-of-line class template
specialization right before its declaration context. (#GH64082)
- Fixed a constraint comparison bug for friend declarations. (#GH78101)
- Clang no longer tries to capture default argument of template arguments 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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26 changes: 26 additions & 0 deletions clang/test/SemaCXX/cxx2a-template-lambdas.cpp
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Expand Up @@ -97,3 +97,29 @@ void foo() {

}
#endif

#if __cplusplus >= 202002L
void GH107048() {
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;
}();

struct 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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