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This commit adds an opt-in mechanism to kill type-unsafe functions
and implicit conversions of QFlags, therefore removing an entire
category of bugs that QFlags itself is supposed to protect against:
QFlags<E> f;
f == 3.14; // OK; f->int, int->double, then operator==(double,double)
f & UnrelatedEnum; // OK if of unscoped enum, calls operator&(int)
f &= 123; // calls QFlags::operator&=(int)
int i = f * 42; // f->int, then operator*(int, int)
Thankfully, operator+ and operator- had already been deleted.
By defining QT_TYPESAFE_FLAGS one:
* disables operators taking (u)int, forcing the usage of an enumeration
or another QFlags object;
* turns the implicit conversions towards integers/bool in explicit
(one can always use fromInt/toInt instead);
* adds a convenience set of (in)equality operators against literal 0,
in order to keep code like `(flag & bit) == 0` compile. This set can't
be added normally otherwise it would add ambiguity;
* adds the unary operator~(Enum), turning it into a flag. This is
a source incompatible change, in general, so it's opt-in.
This is a Qt-internal macro at this point. It can't be offered to users
yet because we need to fix some public API flaws first: in some places
(e.g. QPainter::drawText) we ask users to do type-unsafe manipulation
of flags. A user enabling the macro wouldn't be able to properly use the
functions in question.
This macro will be enabled in a follow-up commit.
Change-Id: I796f2256b446bafc12cdcbaf7de417d12bd3619e
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
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