[cfe-dev] Warning when calling virtual functions from constructor/desctructor?

[Arnaud Bienner via cfe-dev]

> There's a fairly substantial difference between warnings that target
patterns
> that are *inarguably* bad, like the std::move problem (which in some
sense is
> a language defect that people just need to be taught how to work around),
and
> warnings that target code patterns that might be confusing or which have a
> higher-than-normal chance of being a typo. -Wparentheses is the classic
> example here

Yes, and this warning is definitely like -Wparentheses: something that
could be wrong, but is not necessarily.
Still, I think it will catch tricky bugs.

What should we do about this warning/patch?
Deactivate it by default, with its own flag? without putting it in
Wall/extra?
Or wait for something like your proposal to be implemented?
Or just forget about it for now and simply wait for more feedback from the
mailing before deciding?

Arnaud





Le mer. 9 janv. 2019 à 01:14, John McCall <jmccall at apple.com> a écrit :

> On 8 Jan 2019, at 15:03, Arthur O'Dwyer wrote:
>
> I was thinking of `-Wreturn-std-move`, which is -Wmove/-Wmost/-Wall but not
> always-on.
>
> I honestly don't know why this isn't default-on.
>
> Grepping the code for DefaultIgnore, I see that -Wfor-loop-analysis is
> another example (but 4 years old).
>
> This is a harder call. At any rate, I think my point stands that this is
> not
> "frequent".
>
> There's a fairly substantial difference between warnings that target
> patterns
> that are *inarguably* bad, like the std::move problem (which in some
> sense is
> a language defect that people just need to be taught how to work around),
> and
> warnings that target code patterns that might be confusing or which have a
> higher-than-normal chance of being a typo. -Wparentheses is the classic
> example here: it unquestionably catches a common mistake that C
> unfortunately
> otherwise masks, but it's still perennially controversial because the
> assign-and-test idiom is so common in C programming, and there are a lot of
> people who still swear by reversing the equality test (0 == foo) instead
> of
> relying on the warning.
>
> John.
>
> On Tue, Jan 8, 2019 at 2:37 PM John McCall <jmccall at apple.com> wrote:
>
> On 8 Jan 2019, at 13:45, Arthur O'Dwyer wrote:
>
> On Tue, Jan 8, 2019 at 1:05 PM John McCall via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
> On 8 Jan 2019, at 8:37, Arnaud Bienner wrote:
>
> I realized I didn't put "DefaultIgnore" on this warning.
> I'm not experienced enough with clang to know what's the best way to
> deal
> with new warnings, but my feeling is that it would be sensible to
> have
>
> this
>
> new warning DefaultIgnore for now, in -Wall, and make it default
> once we
> have some feedback from the community: while not all C++ projects
> use
>
> -Wall
>
> (or -Wextra) I believe enough do to give us a chance to get some
>
> feedback.
>
> What do you think?
>
> We generally don't add things to -Wall. That's why I went into my
> whole
> spiel
> about versioning: I think it's a conversation we need to have before
> we're
> ready to accept this as a warning that's anything but hidden
> permanently
> behind its own opt-in flag.
>
> John: Wha? Clang *frequently* adds things to -Wall! -Wall includes
> -Wmost
> which includes a bunch of other categories, so while we don't often
> put new
> diagnostics *directly* under -Wall, pretty much every "reasonable"
> diagnostic eventually winds up in there somehow — which is the
> intent.
>
> I don't think we "frequently" add things to -Wall or -Wmost. We do
> somewhat
> frequently add warnings that are unconditionally default-on, but the
> groups
> have a conventional meaning that we don't generally touch. What
> recently-added
> warnings are you thinking of that are not default-on but which are
> included
> in a group like -Wall or -Wmost?
>
> John.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20190111/cee0f523/attachment.html>