Quuxplusone 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}}
+
----------------
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. :)
https://reviews.llvm.org/D28467
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