https://github.com/sdkrystian created
https://github.com/llvm/llvm-project/pull/92425
When the argument passed to `ASTContext::getUnconstrainedType` is an
unconstrained `AutoType`, will return the argument unchanged. However, when
called with a constrained `AutoType`, an unconstrained, non-dependent
`AutoType` will be returned even if the argument was dependent. Consider the
following:
```cpp
template<typename T>
concept C = sizeof(T) == sizeof(int);
template<auto N>
struct A;
template<C auto N>
struct A<N> { }; // error: class template partial specialization is not more
specialized than the primary template
```
When comparing the template parameters for equivalence,
`ASTContext::getUnconstrainedType` is used to remove the constraints per
[[temp.over.link] p6 sentence
2](http://eel.is/c++draft/temp.over.link#6.sentence-2). For the template
parameter `N` of the class template, it returns a dependent `AutoType`. For the
template parameter `N` of the class template partial specialization, it returns
a non-dependent `AutoType`. We subsequently compare the adjusted types and find
they are not equivalent, thus we consider the partial specialization to not be
more specialized than the primary template per [[temp.func.order]
p6.2.2](http://eel.is/c++draft/temp.func.order#6.2.2).
This patch changes `ASTContext::getUnconstrainedType` such that the dependence
of a constrained `AutoType` will propagate to the returned unconstrained
`AutoType`. This causes the above example to be correctly accepted, fixing
#77377.
>From 7905c01b3501f211c044649052d7556b6cacd4a3 Mon Sep 17 00:00:00 2001
From: Krystian Stasiowski <sdkryst...@gmail.com>
Date: Thu, 16 May 2024 10:59:03 -0400
Subject: [PATCH] [Clang][Sema] ASTContext::getUnconstrainedType propagates
dependence
---
clang/docs/ReleaseNotes.rst | 1 +
clang/lib/AST/ASTContext.cpp | 3 ++-
.../temp/temp.decls/temp.fct/temp.func.order/p2.cpp | 11 +++++++++++
3 files changed, 14 insertions(+), 1 deletion(-)
create mode 100644
clang/test/CXX/temp/temp.decls/temp.fct/temp.func.order/p2.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index be4cded276321..21f273cf8f54e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -723,6 +723,7 @@ Bug Fixes to C++ Support
- Clang now ignores template parameters only used within the exception
specification of candidate function
templates during partial ordering when deducing template arguments from a
function declaration or when
taking the address of a function template.
+- Fix a bug with checking constrained non-type template parameters for
equivalence.
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 4475f399a120b..8fc2bb8c401c2 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -5910,7 +5910,8 @@ QualType ASTContext::getUnconstrainedType(QualType T)
const {
if (auto *AT = CanonT->getAs<AutoType>()) {
if (!AT->isConstrained())
return T;
- return getQualifiedType(getAutoType(QualType(), AT->getKeyword(), false,
+ return getQualifiedType(getAutoType(QualType(), AT->getKeyword(),
+ AT->isDependentType(),
AT->containsUnexpandedParameterPack()),
T.getQualifiers());
}
diff --git a/clang/test/CXX/temp/temp.decls/temp.fct/temp.func.order/p2.cpp
b/clang/test/CXX/temp/temp.decls/temp.fct/temp.func.order/p2.cpp
new file mode 100644
index 0000000000000..5c908d789d511
--- /dev/null
+++ b/clang/test/CXX/temp/temp.decls/temp.fct/temp.func.order/p2.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
+// expected-no-diagnostics
+
+template<typename T>
+concept C = sizeof(T) == sizeof(int);
+
+template<auto N>
+struct A;
+
+template<C auto N>
+struct A<N> { };
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