[all-commits] [llvm/llvm-project] da928c: [Clang][Sema] ASTContext::getUnconstrainedType pro...

[Krystian Stasiowski via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: da928c6d6e0e2f619fdaef71cea8747d9aef188d
      https://github.com/llvm/llvm-project/commit/da928c6d6e0e2f619fdaef71cea8747d9aef188d
  Author: Krystian Stasiowski <sdkrystian at gmail.com>
  Date:   2024-05-16 (Thu, 16 May 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/AST/ASTContext.cpp
    A clang/test/CXX/temp/temp.decls/temp.fct/temp.func.order/p2.cpp

  Log Message:
  -----------
  [Clang][Sema] ASTContext::getUnconstrainedType propagates dependence (#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:
```
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. 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.

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.



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