QString has several functions taking a QRegularExpression: indexOf(),
contains(), and so on. Some of those have an out-argument of type
QRegularExpressionMatch, to report the details of the match (if any).
For instance:
QRegularExpression re(...);
QRegularExpressionMatch match;
if (string.contains(re, &match))
use(match);
The code used to route the implementation of these functions through
QStringView (which has the very same functions). This however opens
up a lifetime problem with temporary strings:
if (getString().contains(re, &match))
use(match); // match is dangling
Here `match` is dangling because it is referencing data into the
destroyed temporary -- nothing is keeping the string alive. This is
against the rules we've decided for Qt, and it's also asymmetric with
the corresponding code that uses QRegularExpression directly instead:
match = re.match(getString());
if (match.hasMatch())
use(match); // not dangling
... although we've documented not to do this. (In light of the decision
we've made w.r.t. temporaries, the documentation is wrong anyways.)
Here QRE takes a copy of the string and stores it in the match object,
thus keeping it alive.
Hence, extend the implementation of the QString functions to keep a
(shallow) copy of the string. To keep the code shared as much as
possible with QStringView, in theory one could have a function taking a
std::variant<QString, QStringView> and that uses the currently active
member. However I've found that std::variant here creates some abysmal
codegen, so instead I went for a simpler approach -- pass a QStringView
and an optional pointer to a QString. Use the latter if it's loaded.
QStringView has some inline code that calls into exported functions, so
I can't change the signature of them without breaking BC; I'm instead
adding new unexported functions and a Qt 7 note to unify them.
Change-Id: I7c65885a84069d0fbb902dcc96ddff543ca84562
Fixes: QTBUG-103940
Pick-to: 6.2 6.3 6.4
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
6f852935e0