llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Krystian Stasiowski (sdkrystian)
<details>
<summary>Changes</summary>
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.
---
Full diff: https://github.com/llvm/llvm-project/pull/92425.diff
3 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+1)
- (modified) clang/lib/AST/ASTContext.cpp (+2-1)
- (added) clang/test/CXX/temp/temp.decls/temp.fct/temp.func.order/p2.cpp (+11)
``````````diff
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> { };
``````````
</details>
https://github.com/llvm/llvm-project/pull/92425
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