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    Bug 
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    Resolution: Fixed
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    P1: Critical 
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    6.9
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    None
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        d9d4d15aef
When compiling the dev branch with clang-cl 19.1, Clang emits the following warning:
G:/Dev/qt-build/qtbase/src/corelib/text/qstring.h(1018,45): warning: '= delete' with a message is a C++2c extension [-Wc++26-extensions]
 1018 |     QString &operator=(const QByteArray &a) QSTRING_DECL_DELETED_ASCII_OP;
      |                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
G:/Dev/qt-build/qtbase/src/corelib/text/qstring.h(1012,58): note: expanded from macro 'QSTRING_DECL_DELETED_ASCII_OP'
 1012 | #define QSTRING_DECL_DELETED_ASCII_OP Q_DECL_EQ_DELETE_X("This function is not available under QT_NO_CAST_FROM_ASCII")
      |                                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
G:/Dev/qt-build/qtbase/src/corelib/global/qcompilerdetection.h(1028,49): note: expanded from macro 'Q_DECL_EQ_DELETE_X'
 1028 | #    define Q_DECL_EQ_DELETE_X(reason) = delete(reason)
      |                                                 ^~~~~~
I didn't test it on Linux/macOS, but I'd guess it emits the same warning. Support for = delete(reason) is detected through __cpp_deleted_function >= 202403L. This might be a Clang bug.
Since this is in qstring.h, the whole output is filled with this error.