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No warning for unused function using impl Trait on beta and nightly #54754
Description
The following code only warns that f is unused on stable, not on beta or nightly:
trait Trait {}
impl<T> Trait for T {}
fn f() -> impl Trait {}(apologies if this is a duplicate, but a quick search didn't turn anything up)
Activity
jonas-schievink commentedon Oct 2, 2018
This has appeared between 63d6649 and d41f21f (commits in that range).
Likely culprit is #53545 (cc @FelixMcFelix). It introduces a new reachability level to rustc (
ReachableFromImplTrait), which marks any function with animpl Traitreturn type with that level. Maybe the level required by the lint to consider an item reachable needs to be higher than that?FelixMcFelix commentedon Oct 4, 2018
Yeah, the likely fix for this is to create a query for lints that removes all levels under
AccessLevel::Reachable, or manually strip the entries each time. The former probably makes more sense. I wasn't sure we'd need to do this at the time, it shouldn't take too long.jonas-schievink commentedon Oct 4, 2018
I've implemented a more minimal fix at #54810. It should be safe to backport to beta, if this is wanted at all.
pnkfelix commentedon Oct 4, 2018
(assigning self just to make sure everything gets followed up on here)
pnkfelix commentedon Oct 4, 2018
tagged as P-high since it was a regression.