We also have a static analysis attribute MOZ_MUST_USE_TYPE which can be added to class declarations to ensure that those declarations are always used when they are returned. We currently are using it to annotate already_AddRefed values. If there are other types which universally should be checked when used as a return value, that annotation may be a useful shortcut.
On Thu, Nov 3, 2016 at 3:42 AM, Wei-Cheng Pan <w...@mozilla.com> wrote: > Hi, > > As :njn announced before [1], we are trying to add MOZ_MUST_USE to all > fail-able functions, which is tracking in bug 1268766 [2]. > > We have bugs to track the progress for each directory. > If anyone is interested, please feel free to take any of the bugs. > > We hope all reviewers also mind the following rules, so that new code > may benefit by the static checking. > I'll update the style guide to reflect these rules later. > > The attribute is meant to avoid possible fatal failure. > All failure should be handled, reported, asserted, or at least caught by > Unused (and better leave a comment, see bug 1301574 [3]). > > You can find the rule proposed by :njn in the bug comment [4]. > Because now we don't need to worry about NS_IMETHOD (see bug 1295825 > [5]), we have updated rules: > > 1. search all *.h and *.idl > 2. add [must_use] for *.idl > 3. add MOZ_MUST_USE for all functions that return |nsresult| or |bool| > in *.h > > Also with some exceptions: > > 1. Predicates, getters which return |bool|. > > 2. IPC method implementation (e.g. bool RecvSomeMessage()). > > 3. Most callers just check the output parameter. e.g.: > > nsresult > SomeMap::GetValue(const nsString& key, nsString& value); > > nsString value; > rv = map->GetValue(key, value); > > If it failed, of course |value| will be empty. > But if it succeed, |value| may still be empty because the stored value > is empty in the first place. > So just check |value| is a common idiom. > This was also discussed in thread [1], and seems we still have no > conclusion. > > Such grey zone will depend on each reviewers' own judgement. > > Wei-Cheng Pan > > [1] > https://groups.google.com/forum/#!msg/mozilla.dev.platform/dS5Dz6SfO3w/ > avzIxb7CBAAJ > [2] https://bugzilla.mozilla.org/show_bug.cgi?id=MOZ_MUST_USE > [3] https://bugzilla.mozilla.org/show_bug.cgi?id=1301574 > [4] https://bugzilla.mozilla.org/show_bug.cgi?id=1268766#c5 > [5] https://bugzilla.mozilla.org/show_bug.cgi?id=1295825 > > _______________________________________________ > dev-platform mailing list > dev-platform@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-platform > _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
