[Development] Requesting feature freeze exception to container-assign epic

[Marc Mutz]

Hi,

The container-assign epic is partially merged. What's left is 
QString::assign(), and there only the assign(it, it) part. If we release 
as-is (with step 1, cf. below), there's a gap in the QString::assign() 
overload set vis-a-vis all other container classes (Qt or STL).

The QString::assign() overload set is constructed in four steps:
- 1: non-(it,it) overloads (approved before the FF, but still doing its 
rounds on the CI for actual merging)
- 2: (it, it) for QChar, QLatin1Char, char16_t (on Gerrit for review)
- 3: ditto for char32_t (ditto, on Gerrit)
- 4: ditto for (signed,unsigned) char, char8_t (not on Gerrit, yet)

Each step adds value: Step 1 gives QString at least a contiguous-range 
overload. Step 2 makes QString pass tst_containerapisymmetry tests for 
assign(). Step 3 enables assign() functionality for UCS4-encoded data 
and Step 4 for UTF-8 encoded data that's not contiguous.

The fourth step ran into a cyclic dependency issue with QStringDecoder, 
which depends on QString, and we need it vice versa. Given that 
non-contiguous UTF-8 data should be pretty rare, I'd be fine with 
cutting off after Step 3 for Qt 6.6 and adding Step 4 after the 
necessary refactorings (if any) for 6.7.

I wouldn't like to stop after Step 2, because in that state the 
assign(it,it) function has an implied post-condition of result.size() == 
std::distance(first, last), which users should not come to rely on 
(Hyrum's Law), and Step 3 breaks that.

Chain ends in https://codereview.qt-project.org/c/qt/qtbase/+/481544.
Epic: https://bugreports.qt.io/browse/QTBUG-106165

Thanks,
Marc

-- 
Marc Mutz <marc.mutz at qt.io>
Principal Software Engineer

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