[llvm-bugs] [Bug 37279] New: Unexpected internal linkage when using an alias to an private class

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37279

            Bug ID: 37279
           Summary: Unexpected internal linkage when using an alias to an
                    private class
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: oliver at apple.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

I am not sure if clang's behaviour is wrong, but the behaviour is unexpected.
The basic issue is that I can have a public alias to a private type, but if the
alias appears in a method declaration the method is given internal linkage.

Here's a trivial example (compile with clang++ -c):

namespace Foo {
    namespace {
         struct _X {
             int y;
        };
    }
    using X = _X;
}
namespace Foo {
    struct Bar {
        X womp();
    };
}
Foo::Bar *thing();
int main() {
    thing()->womp();
    return 0;
}

Bug 20296 seems to be similar, but that seems to be related to class protection
rather than anonymous namespaces

Given that the X alias public it seems expected that the method should not
receive internal linkage. That would be my /expectation/, if the actual
specification is different, it would be great if the warning actually said why
a method got internal linkage.

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