Fix too restrictive checks on Drop impls #67059

TommasoBianchi · 2019-12-05T17:31:24Z

This PR completes and extends #59497 (which has been inactive for a while now).
The problem generating both issues was that when checking that the Predicates of the Drop impl are exactly the same as the ones of the struct definition, the check was essentially performed by a simple == operator, which was not handling correctly HRTBs and involved Fn types.

The implemented solution relies on the relate machinery to more correctly equate Predicates, and on anonymize_late_bound_regions to handle HRTB in a more general way. As the Relate trait currently is implemented only for TraitPredicate and ProjectionPredicate (and as they were the ones generating problems), relate is used only for them while for other Predicates the equality check is kept. I'm currently considering whether it would make sense to implement the Relate trait also for all other Predicates to render the proposed solution more general.

rust-highfive · 2019-12-05T17:31:28Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @zackmdavis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

Centril · 2019-12-05T17:58:21Z

r? @pnkfelix

Centril · 2019-12-05T17:58:31Z

cc @arielb1 @matthewjasper

pnkfelix · 2019-12-11T22:30:04Z

src/librustc_typeck/check/dropck.rs

@@ -83,10 +87,7 @@ fn ensure_drop_params_and_item_params_correspond<'tcx>(
        let fresh_impl_self_ty = drop_impl_ty.subst(tcx, fresh_impl_substs);

        let cause = &ObligationCause::misc(drop_impl_span, drop_impl_hir_id);
-        match infcx


please try to avoid making pure-formatting changes in the same commit that has effectual semantic changes.

(If the reformatting is being injected by e.g. running rustfmt, then try to do those runs in a separate commit, please.)

(the reason I'm asking for it to be in a separate commit is that it eases review: It allows the reviewer to just quickly skim the commits that are formatting fixes, while diving into the commits that have the real meat!)

Btw, ticking the "hide whitespace changes" checkbox usually helps a bit with this when reviewing.

pnkfelix · 2019-12-11T22:32:47Z

src/librustc_typeck/check/dropck.rs

                    item_span,
                    "Use same sequence of generic type and region \
                     parameters that is on the struct/enum definition",
                )
-                    .emit();
+                .emit();


follow-up to other note about formatting changes: while I stand by my claim that I prefer formatting changes to be segregated into their own commits, I will say that if the formatting "fixes" were solely to formatting "bugs" that are this egregious, I myself would probably leave them in the same commit too.

pnkfelix · 2019-12-11T22:35:59Z

src/librustc_typeck/check/dropck.rs

@@ -212,20 +216,40 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
        // the analysis together via the fulfill , rather than the
        // repeated `contains` calls.


there is comment here that only makes sense based on the prior version of the code that called .contains(..). Can you update the comment accordingly for future code readers?

pnkfelix · 2019-12-11T22:38:19Z

this looks good. r=me once the formatting changes are factored out and the noted comment about contains is updated in some reasonable way.

TommasoBianchi · 2019-12-16T16:34:57Z

r=@pnkfelix thank you for the review, I should have fixed both problems.
I am still curious about whether it would be beneficial to implement equality for all Predicates using the Relate trait; probably it is better to just be conservative and change as little as possible while still fixing the open issues.

pnkfelix · 2019-12-21T10:31:41Z

@bors r+

bors · 2019-12-21T10:31:43Z

📌 Commit b08d697 has been approved by pnkfelix

bors · 2019-12-21T10:31:44Z

🌲 The tree is currently closed for pull requests below priority 100, this pull request will be tested once the tree is reopened

…felix Fix too restrictive checks on Drop impls Fixes rust-lang#34426. Fixes rust-lang#58311. This PR completes and extends rust-lang#59497 (which has been inactive for a while now). The problem generating both issues was that when checking that the `Predicate`s of the `Drop` impl are exactly the same as the ones of the struct definition, the check was essentially performed by a simple `==` operator, which was not handling correctly HRTBs and involved `Fn` types. The implemented solution relies on the `relate` machinery to more correctly equate `Predicate`s, and on `anonymize_late_bound_regions` to handle HRTB in a more general way. As the `Relate` trait currently is implemented only for `TraitPredicate` and `ProjectionPredicate` (and as they were the ones generating problems), `relate` is used only for them while for other `Predicate`s the equality check is kept. I'm currently considering whether it would make sense to implement the `Relate` trait also for all other `Predicate`s to render the proposed solution more general.

@ghost

Rollup of 7 pull requests Successful merges: - #67059 (Fix too restrictive checks on Drop impls) - #67355 (Merge `ast::Mutability` and `mir::Mutability`) - #67393 (Enable opting out of specific default LLVM arguments.) - #67422 (Cleanup err codes) - #67462 (Make ptr::slice_from_raw_parts a const fn available under a feature flag) - #67467 (Test slice patterns more) - #67478 (Fix src/libcore/str/mod.rs doc comments) Failed merges: r? @ghost

Add regression tests

2bd28d9

rust-highfive assigned zackmdavis Dec 5, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 5, 2019

rust-highfive assigned pnkfelix and unassigned zackmdavis Dec 5, 2019

jonas-schievink mentioned this pull request Dec 5, 2019

Impossible to Specify Appropriate Lifetime with for<'a> &'a ... #67067

Closed

pnkfelix reviewed Dec 11, 2019

View reviewed changes

TommasoBianchi added 2 commits December 16, 2019 11:27

Fix too restrictive checks on Drop impls

042d855

Formatting fixes

b08d697

TommasoBianchi force-pushed the dropck_fix_pr branch from e02de5c to b08d697 Compare December 16, 2019 16:29

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 21, 2019

Centril mentioned this pull request Dec 21, 2019

Rollup of 5 pull requests #67479

Closed

Centril mentioned this pull request Dec 21, 2019

Rollup of 7 pull requests #67485

Merged

bors merged commit b08d697 into rust-lang:master Dec 21, 2019

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Fix too restrictive checks on Drop impls #67059

Fix too restrictive checks on Drop impls #67059

TommasoBianchi commented Dec 5, 2019

rust-highfive commented Dec 5, 2019

Centril commented Dec 5, 2019

Centril commented Dec 5, 2019

pnkfelix Dec 11, 2019

pnkfelix Dec 11, 2019

Centril Dec 21, 2019

pnkfelix Dec 11, 2019 •

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pnkfelix Dec 11, 2019

pnkfelix commented Dec 11, 2019

TommasoBianchi commented Dec 16, 2019

pnkfelix commented Dec 21, 2019

bors commented Dec 21, 2019

bors commented Dec 21, 2019

		@@ -212,20 +216,40 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
		// the analysis together via the fulfill , rather than the
		// repeated `contains` calls.

Fix too restrictive checks on Drop impls #67059

Fix too restrictive checks on Drop impls #67059

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