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[clang] stop error recovery in SFINAE for narrowing in converted constant expressions #183614

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Merged
mizvekov merged 1 commit into from
Feb 27, 2026
Merged

[clang] stop error recovery in SFINAE for narrowing in converted constant expressions #183614

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8 changes: 8 additions & 0 deletions clang/lib/Sema/SemaOverload.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6470,6 +6470,12 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From,
S.Diag(From->getBeginLoc(), diag::ext_cce_narrowing)
<< CCE << /*Constant*/ 1
<< PreNarrowingValue.getAsString(S.Context, PreNarrowingType) << T;
// If this is an SFINAE Context, treat the result as invalid so it stops
// substitution at this point, respecting C++26 [temp.deduct.general]p7.

@zyn0217 zyn0217 Feb 27, 2026

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Can we expand what temp.deduct.general.p7 says?

@mizvekov mizvekov Feb 27, 2026

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That is a giant paragraph with multiple bullets, and the only relevant part is "The substitution proceeds in lexical order and stops when a condition that causes deduction to fail is encountered".
But that seems well explained enough by the comment?

@mizvekov mizvekov Feb 27, 2026

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Anyway, I am going to merge, we can adjust the comment later with something sensible if we come up with it.

// FIXME: Should do this whenever the above diagnostic is an error, but
// without further changes this would degrade some other diagnostics.
if (S.isSFINAEContext())
return ExprError();
break;

case NK_Dependent_Narrowing:
Expand All @@ -6485,6 +6491,8 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From,
// constant expression.
S.Diag(From->getBeginLoc(), diag::ext_cce_narrowing)
<< CCE << /*Constant*/ 0 << From->getType() << T;
if (S.isSFINAEContext())
return ExprError();
break;
}
if (!ReturnPreNarrowingValue)
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11 changes: 10 additions & 1 deletion clang/test/SemaTemplate/temp_arg_nontype_cxx11.cpp
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Expand Up @@ -43,7 +43,7 @@ void TempFunc() {}

void Useage() {
//expected-error@+2 {{no matching function}}
//expected-note@-4 {{candidate template ignored: substitution failure [with a = 1, b = 4294967295, c = 1]: non-type template argument evaluates to -1, which cannot be narrowed to type 'unsigned int'}}
//expected-note@-4 {{candidate template ignored: invalid explicitly-specified argument for template parameter 'b'}}
TempFunc<1, -1, 1>();
}
}
Expand Down Expand Up @@ -114,3 +114,12 @@ void lookup() {
Kolumn<&container::a>().ls(); // expected-error {{<&container::a}}
Kolumn<nullptr>().ls(); // expected-error {{<nullptr}}
}

namespace GH167709 {
template <unsigned I> struct A {
static_assert(false, "shouldn't instantiate this");
};
template <int> void f() {}
template <int I> typename A<I>::type f() = delete;
template void f<-1>();
} // namespace GH167709