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[clang] fix nondeduced mismatch with nullptr template arguments #124498

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Merged
merged 1 commit into from
Jan 28, 2025
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[clang] fix nondeduced mismatch with nullptr template arguments #124498

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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 @@ -1037,6 +1037,7 @@ Bug Fixes to C++ Support
- Fix template argument checking so that converted template arguments are
converted again. This fixes some issues with partial ordering involving
template template parameters with non-type template parameters.
- Fix nondeduced mismatch with nullptr template arguments.
- Clang now rejects declaring an alias template with the same name as its template parameter. (#GH123423)
- Fixed the rejection of valid code when referencing an enumerator of an unscoped enum member with a prior declaration. (#GH124405)
- Fixed immediate escalation of non-dependent expressions. (#GH123405)
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7 changes: 4 additions & 3 deletions clang/lib/Sema/SemaTemplateDeduction.cpp
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Expand Up @@ -2541,10 +2541,9 @@ DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
return TemplateDeductionResult::NonDeducedMismatch;

case TemplateArgument::NullPtr:
if (A.getKind() == TemplateArgument::NullPtr &&
S.Context.hasSameType(P.getNullPtrType(), A.getNullPtrType()))
// 'nullptr' has only one possible value, so it always matches.
if (A.getKind() == TemplateArgument::NullPtr)
return TemplateDeductionResult::Success;

Info.FirstArg = P;
Info.SecondArg = A;
return TemplateDeductionResult::NonDeducedMismatch;
Expand All @@ -2559,6 +2558,8 @@ DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
return TemplateDeductionResult::NonDeducedMismatch;

case TemplateArgument::StructuralValue:
// FIXME: structural equality will also compare types,
// but they should match iff they have the same value.
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@cor3ntin cor3ntin Jan 27, 2025

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Suggested change
// but they should match iff they have the same value.
// FIXME: Arguments of structural types should match when their values are the same,
// even when their types are different.

if (A.getKind() == TemplateArgument::StructuralValue &&
A.structurallyEquals(P))
return TemplateDeductionResult::Success;
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4 changes: 0 additions & 4 deletions clang/test/SemaTemplate/cwg2398.cpp
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Expand Up @@ -697,15 +697,11 @@ namespace nttp_partial_order {
template void f<B>(B<&A::m>);
} // namespace t5
namespace t6 {
// FIXME: This should pick the second overload.
struct A {};
using nullptr_t = decltype(nullptr);
template<template<nullptr_t> class TT2> void f(TT2<nullptr>);
// new-note@-1 {{here}}
template<template<A*> class TT1> void f(TT1<nullptr>) {}
// new-note@-1 {{here}}
template<A*> struct B {};
template void f<B>(B<nullptr>);
// new-error@-1 {{ambiguous}}
} // namespace t6
} // namespace nttp_partial_order