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decltype(&(C::member)) yields pointer-to-member type #40906

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llvmbot opened this issue Apr 22, 2019 · 3 comments · Fixed by #89713
Closed

decltype(&(C::member)) yields pointer-to-member type #40906

llvmbot opened this issue Apr 22, 2019 · 3 comments · Fixed by #89713
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accepts-invalid bugzilla Issues migrated from bugzilla c++ clang:frontend Language frontend issues, e.g. anything involving "Sema" confirmed Verified by a second party

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@llvmbot
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llvmbot commented Apr 22, 2019

Bugzilla Link 41561
Version trunk
OS All
Reporter LLVM Bugzilla Contributor
CC @hfinkel,@randomnetcat,@darkbuck,@riccibruno,@zygoloid

Extended Description

In some contexts, decltype(&(C::member)) yields a pointer to member type, but according to [expr.unary.op]/4, no pointer to member should be formed when the operand of the & operator is enclosed in parentheses.

http://eel.is/c++draft/expr.unary.op#4

The code below demonstrates this behavior. It compiles on all Clang versions I have tried between 3.2 and HEAD, even though I don't think it should.

#include <type_traits>
 
struct S {
    int x;

    static_assert(std::is_same<decltype(&(S::x)), int S::*>::value, ""); // !

    void foo() {
        static_assert(std::is_same<decltype(&(S::x)), int*>::value, ""); // OK
    }
};

static_assert(std::is_same<decltype(&(S::x)), int S::*>::value, ""); // !

int main() {
}
@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
@llvmbot llvmbot added the confirmed Verified by a second party label Jan 26, 2022
@AaronBallman AaronBallman added c++ clang:frontend Language frontend issues, e.g. anything involving "Sema" accepts-invalid and removed clang Clang issues not falling into any other category labels Jun 20, 2023
@AaronBallman
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Issue still reproduces as of Clang 16.0.0: https://gcc.godbolt.org/z/1r93K5KTa

@llvmbot
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llvmbot commented Jun 20, 2023

@llvm/issue-subscribers-clang-frontend

@llvmbot
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llvmbot commented Jun 20, 2023

@llvm/issue-subscribers-c-1

@zwuis zwuis mentioned this issue Apr 23, 2024
Merged
cor3ntin added a commit that referenced this issue May 3, 2024
@zwuis @cor3ntin
[clang] pointer to member with qualified-id enclosed in parentheses i…
8480c93 
…n unevaluated context should be invalid (#89713)

clang don't check whether the operand of the & operator is enclosed in
parantheses when pointer to member is formed in unevaluated context, for
example:

```cpp
struct foo { int val; };

int main() { decltype(&(foo::val)) ptr; }
```

`decltype(&(foo::val))` should be invalid, but clang accepts it. This PR
fixes this issue.

Fixes #40906.

---------

Co-authored-by: cor3ntin <corentinjabot@gmail.com>
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accepts-invalid bugzilla Issues migrated from bugzilla c++ clang:frontend Language frontend issues, e.g. anything involving "Sema" confirmed Verified by a second party
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