malcolm.parsons added inline comments.
================
Comment at: test/SemaCXX/warn-unused-lambda-capture.cpp:17
+ auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture
'i' is not used}}
+ auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; //
expected-warning{{lambda capture 'i' is not used}}
+
----------------
Quuxplusone wrote:
> malcolm.parsons wrote:
> > Quuxplusone wrote:
> > > aaron.ballman wrote:
> > > > This does not match the behavior for other -Wunused flags. e.g.,
> > > > ```
> > > > void f() {
> > > > int i;
> > > > (void)sizeof(i);
> > > > }
> > > > ```
> > > > I don't think diagnosing this test case is correct.
> > > I see some value to maybe diagnosing *something* here. For example, `[] {
> > > return sizeof(i); }` would produce the same result as `[i] { return
> > > sizeof(i); }` but with one fewer capture, so removing the `i` might be
> > > seen as an improvement.
> > >
> > > But I'm not sure how to convey this information to the user. You could
> > > say "variable `i` used in unevaluated context refers to the `i` in the
> > > outer scope, not the captured `i`"... except that I think that would be
> > > false. Given that you *have* captured an `i`, `sizeof(i)` definitely
> > > refers to the captured one AFAIK. The fact that the captured `i` shadows
> > > an `i` in the outer scope is irrelevant --- in fact the user is
> > > *expecting* to shadow the outer `i`.
> > >
> > > Perhaps it would be appropriate to reword the diagnostic to "lambda
> > > captures variable `i` unnecessarily". I would also lean toward splitting
> > > it into two diagnostics — one for "this capture is unnecessary" (as in
> > > this example) and one for "this capture doesn't even appear lexically in
> > > the body of the lambda". Not sure how other people would feel about that.
> > >
> > > You should add some test cases with `decltype(i)` for the same reason as
> > > `sizeof(i)`.
> > Does "lambda capture 'i' is not odr-used" make more sense?
> > Does "lambda capture 'i' is not odr-used" make more sense?
>
> That would completely satisfy *me*, for what that's worth. It admittedly
> doesn't match the other -Wunused diagnostics, but it is concise and correct —
> at least I assume it's correct. :)
C++14 [expr.prim.lambda]p18:
> [ Note: An id-expression that is not an odr-use refers to the original
> entity, never to a member
> of the closure type. Furthermore, such an id-expression does not cause the
> implicit capture of the entity.
> — end note ]
https://reviews.llvm.org/D28467
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
