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[Clang][Sema] Use StructuralValues to model dependent NTTP arguments #93556

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Merged
merged 3 commits into from
May 29, 2024
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[Clang][Sema] Use StructuralValues to model dependent NTTP arguments #93556

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[Clang][Sema] Use StructuralValues to model dependent NTTP arguments
zyn0217 May 28, 2024
c87457e
Merge branch 'main' into GH84052
zyn0217 May 29, 2024
9443bd4
Fix changelog
zyn0217 May 29, 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 @@ -810,6 +810,7 @@ Bug Fixes to C++ Support
- Clang now diagnoses unexpanded parameter packs in attributes. (Fixes #GH93269).
- Clang now allows ``@$``` in raw string literals. Fixes (#GH93130).
- Fix an assertion failure when checking invalid ``this`` usage in the wrong context. (Fixes #GH91536).
- Clang no longer models dependent NTTP arguments as ``TemplateParamObjectDecl`` s. Fixes (#GH84052).

Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
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7 changes: 6 additions & 1 deletion clang/lib/AST/TemplateBase.cpp
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Expand Up @@ -221,8 +221,13 @@ static const ValueDecl *getAsSimpleValueDeclRef(const ASTContext &Ctx,

// We model class non-type template parameters as their template parameter
// object declaration.
if (V.isStruct() || V.isUnion())
if (V.isStruct() || V.isUnion()) {
// Dependent types are not supposed to be described as
// TemplateParamObjectDecls.
if (T->isDependentType() || T->isInstantiationDependentType())
return nullptr;
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What do we end up modeling them as instead?

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The only caller of getAsSimpleValueDeclRef is TemplateArgument's constructor (for an NTTP establishment), where we basically try the following things in order, IIUC:

  1. integral type
  2. nullptrs
  3. declarations (this is where we called getAsSimpleValueDeclRef and built up a TemplateParamObjectDecl if the function does return a value)

otherwise, a structural type.

llvm-project/clang/lib/AST/TemplateBase.cpp

Lines 237 to 249 in 74ed79f

TemplateArgument::TemplateArgument(const ASTContext &Ctx, QualType Type,
const APValue &V, bool IsDefaulted) {
if (Type->isIntegralOrEnumerationType() && V.isInt())
initFromIntegral(Ctx, V.getInt(), Type, IsDefaulted);
else if ((V.isLValue() && V.isNullPointer()) ||
(V.isMemberPointer() && !V.getMemberPointerDecl()))
initFromType(Type, /*isNullPtr=*/true, IsDefaulted);
else if (const ValueDecl *VD = getAsSimpleValueDeclRef(Ctx, Type, V))
// FIXME: The Declaration form should expose a const ValueDecl*.
initFromDeclaration(const_cast<ValueDecl *>(VD), Type, IsDefaulted);
else
initFromStructural(Ctx, Type, V, IsDefaulted);
}

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Ah! Thanks! That explains it.

return Ctx.getTemplateParamObjectDecl(T, V);
}

// Pointers and references with an empty path use the special 'Declaration'
// representation.
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23 changes: 22 additions & 1 deletion clang/test/SemaTemplate/temp_arg_nontype_cxx2c.cpp
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@@ -1,4 +1,4 @@
// RUN: %clang_cc1 -fsyntax-only -std=c++20 -Wconversion -verify %s
// RUN: %clang_cc1 -fsyntax-only -std=c++2c -Wconversion -verify %s

struct Test {
int a = 0;
Expand Down Expand Up @@ -102,3 +102,24 @@ void bar() {
}

}

namespace GH84052 {

template <class... T>
concept C = sizeof(T...[1]) == 1; // #C

struct A {};

template <class T, C<T> auto = A{}> struct Set {}; // #Set

template <class T> void foo() {
Set<T> unrelated;
}

Set<bool> sb;
Set<float> sf;
// expected-error@-1 {{constraints not satisfied for class template 'Set'}}
// expected-note@#Set {{because 'C<decltype(GH84052::A{}), float>' evaluated to false}}
// expected-note@#C {{evaluated to false}}

} // namespace GH84052
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