When converting an implicitly-shared Qt container to QSpan, the QSpan
ctor would call .data(), which detaches said Qt container (if it's not
const). This is what must happen for mutable spans (QSpan<int>), but
is not necessary for non-mutable spans (QSpan<const int>).
Fix by copying the potential const from QSpan::element_type to the
Range object in the resp. QSpan ctor. This makes a QSpan over a const
element_type mark the range const before passing it to adl_data() (=
member-data()). For a non-const element_type, nothing changes.
[ChangeLog][QtCore][QSpan] No longer detaches implicitly-shared Qt
containers converted to QSpan<const T, N>. Note that std::span<const
T, N> will, however, detach such containers, so we recommend to use
std::as_const() with implcitly-shared Qt containers, as always.
Fixes: QTBUG-132133
Pick-to: 6.9
Change-Id: I9fdae20994d2c900bc5b45b44db3901d10f8838a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
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