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[clang] ODR hashes depth+index and not name of TemplateTypeParm #144796

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[clang] ODR hashes depth+index and not name of TemplateTypeParm #144796

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2fd016f
[clang] ODR hashes depth+index and not name of TemplateTypeParm
emaxx-google Jun 18, 2025
4f800c8
fix assert line number
emaxx-google Jun 18, 2025
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18 changes: 17 additions & 1 deletion clang/lib/AST/ODRHash.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -828,7 +828,23 @@ void ODRHash::AddDecl(const Decl *D) {
return;
}

AddDeclarationName(ND->getDeclName());
// For template parameters, use depth+index instead of name, because type
// canonicalization can change the name of the template parameter.
if (auto *TTPD = dyn_cast<TemplateTypeParmDecl>(ND)) {
ID.AddInteger(TTPD->getDepth());
ID.AddInteger(TTPD->getIndex());
AddBoolean(TTPD->isParameterPack());
} else if (auto *NTTPD = dyn_cast<NonTypeTemplateParmDecl>(ND)) {
ID.AddInteger(NTTPD->getDepth());
ID.AddInteger(NTTPD->getIndex());
AddBoolean(NTTPD->isParameterPack());
} else if (auto *TTPD = dyn_cast<TemplateTemplateParmDecl>(ND)) {
ID.AddInteger(TTPD->getDepth());
ID.AddInteger(TTPD->getIndex());
AddBoolean(TTPD->isParameterPack());
} else {
AddDeclarationName(ND->getDeclName());
}

// If this was a specialization we should take into account its template
// arguments. This helps to reduce collisions coming when visiting template
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23 changes: 23 additions & 0 deletions clang/test/Modules/odr_hash.cpp
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Expand Up @@ -5164,6 +5164,29 @@ namespace A {
A::X x;
#endif

namespace TemplateDecltypeOperator {

#if defined(FIRST) || defined(SECOND)
template <class T6>
T6 func();
#endif

#if defined(SECOND)
template <class UnrelatedT>
using UnrelatedAlias = decltype(func<UnrelatedT>())();
#endif

#if defined(FIRST) || defined(SECOND)
class A {
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Without the changes in this PR, this test would fail with this message:

'TemplateDecltypeOperator::A' with definition in module 'SecondModule' has different definitions in different modules; first difference is this function template
but in 'FirstModule' found different function template

template <class T6>
operator decltype(func<T6>()) () {}
};
#else
A a;
#endif

}

// Keep macros contained to one file.
#ifdef FIRST
#undef FIRST
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11 changes: 6 additions & 5 deletions clang/test/PCH/race-condition.cpp
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Expand Up @@ -31,11 +31,12 @@ constexpr enable_if_t<meta<F>::value == 2, void> midpoint(F) {}

#else

// expected-error@27{{'N::midpoint' has different definitions in different modules; defined here first difference is 1st parameter with type 'F'}}
// expected-error@24{{'N::midpoint' has different definitions in different modules; defined here first difference is 1st parameter with type 'U'}}
// expected-note@21{{but in '' found 1st parameter with type 'T'}}
// FIXME: Change the test to trigger a suitable error: previously the test
// asserted the ODR error ("'N::midpoint' has different definitions in different
// modules"), which isn't fully correct as there's only one module, and since a
// change in the ODR hash calculation this error isn't triggered anymore.

int x = N::something;
// expected-error@37{{no member named 'something' in namespace 'N'}}
// expected-note@21{{but in '' found 1st parameter with type 'T'}}
// expected-error@39{{no member named 'something' in namespace 'N'}}

#endif
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