Use fulfillment to check `Drop` impl compatibility #110577

compiler-errors · 2023-04-20T04:21:24Z

Use an ObligationCtxt to ensure that a Drop impl does not have stricter requirements than the ADT that it's implemented for, rather than using a SimpleEqRelation to (more or less) syntactically equate predicates on an ADT with predicates on an impl.

r? types

Some background

The old code reads:

// An earlier version of this code attempted to do this checking
// via the traits::fulfill machinery. However, it ran into trouble
// since the fulfill machinery merely turns outlives-predicates
// 'a:'b and T:'b into region inference constraints. It is simpler
// just to look for all the predicates directly.

I'm not sure what this means, but perhaps in the 8 years since that this comment was written (cc #23638) it's gotten easier to process region constraints after doing fulfillment? I don't know how this logic differs from anything we do in the compare_impl_item module. Ironically, later on it says:

// However, it may be more efficient in the future to batch
// the analysis together via the fulfill (see comment above regarding
// the usage of the fulfill machinery), rather than the
// repeated `.iter().any(..)` calls.

Also:

Removes SimpleEqRelation which was far too syntactical in its relation.
Fixes ICE: bound types encountered in super_relate_tys #110557

compiler/rustc_hir_analysis/src/check/dropck.rs

lcnr · 2023-04-20T06:09:46Z

r? @lcnr

lcnr

r=me after nits

compiler/rustc_hir_analysis/src/check/dropck.rs

lcnr · 2023-04-21T08:26:11Z

wait, not r=me 😅 time for fcp 😁

lcnr

can you add some tests showing how we now check Drop semantically

thinking of some interesting cases:

adding a 'static: 'a bound
explicitly require a super trait
have an additional Vec<T>: Clone bound implied by T: Clone
explicitly state transitive dependency for outlives, 'a, 'b: 'a, 'c: 'b, adding 'c: 'a in the Drop impül
different way to specify equality of a group of lifetimes, e.g. 'a: 'b, 'b: 'c, 'c: 'a vs 'a: 'b + 'c, 'b: 'a, 'c: 'a
implied lt bound in the definition, explicit one in the impl

with this we need an FCP as reverting this change will be breaking. I do really prefer this over the status quo. We already need some hacks here as e.g. unevaluated constants are never structurally eqiual so we need at least some sort of semantic equality her.

compiler-errors · 2023-04-21T18:17:16Z

Added tests.

Per description and lcnr's comment above, this PR changes the way we do the Drop impl check to no longer require syntactic correspondence between every impl bound and a bound on the ADT, but instead use fulfillment to ensure that the Drop impl's bounds are semantically implied by the ADT it's being implemented for.

Since we now accept more Drop impls, this represents a committment to a larger set of accepted Drop impls, but in reality, this makes the Drop impl check align with the way we check predicate entailment for other items such as methods and associated types.

I can't see any reason why we would prefer the check that we have right now or ever move back to it-- it's both fragile to experimental and future trait system features (constification, changes to implied bounds, non-lifetime-binders, generic const exprs) and also more confusing to understand since it's one of the only places in the type-checking layer that we actually care about syntactic rather than semantic implication.

So with that...

@rfcbot fcp merge

compiler-errors · 2023-04-21T18:19:23Z

Oh, lol, it didn't start a compiler fcp luckily.

@rfcbot fcp merge

rfcbot · 2023-04-21T18:19:25Z

Team member @compiler-errors has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

oli-obk · 2023-04-21T22:26:56Z

@bors try @rust-timer queue

bors · 2023-04-21T22:27:06Z

⌛ Trying commit f302ed27f4c28968f630ef1edd12aba3675ebcf5 with merge 516aada95cba5f300f9ea07f80a58cd961ea7736...

bors · 2023-04-22T00:07:19Z

☀️ Try build successful - checks-actions
Build commit: 516aada95cba5f300f9ea07f80a58cd961ea7736 (516aada95cba5f300f9ea07f80a58cd961ea7736)

rust-timer · 2023-04-22T01:22:59Z

Finished benchmarking commit (516aada95cba5f300f9ea07f80a58cd961ea7736): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.3%	[1.6%, 3.1%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

nikomatsakis · 2023-04-22T04:15:57Z

@rfcbot fcp reviewed

cc @spastorino this is relevant to the "always applicable negative impls" discussion we were having recently

lcnr

r=me after oli's review

compiler-errors · 2023-05-04T15:31:21Z

@bors r=lcnr

bors · 2023-05-04T15:31:25Z

📌 Commit f4c77b8f45098ba57cf99a7850c752847cb6ba1f has been approved by lcnr

It is now in the queue for this repository.

bors · 2023-05-04T17:49:21Z

☔ The latest upstream changes (presumably #111174) made this pull request unmergeable. Please resolve the merge conflicts.

compiler-errors · 2023-05-04T21:17:39Z

@bors r=lcnr

bors · 2023-05-04T21:17:41Z

📌 Commit 2e346b6 has been approved by lcnr

It is now in the queue for this repository.

compiler-errors · 2023-05-04T22:32:42Z

@bors rollup=maybe

… r=lcnr Use fulfillment to check `Drop` impl compatibility Use an `ObligationCtxt` to ensure that a `Drop` impl does not have stricter requirements than the ADT that it's implemented for, rather than using a `SimpleEqRelation` to (more or less) syntactically equate predicates on an ADT with predicates on an impl. r? types ### Some background The old code reads: ```rust // An earlier version of this code attempted to do this checking // via the traits::fulfill machinery. However, it ran into trouble // since the fulfill machinery merely turns outlives-predicates // 'a:'b and T:'b into region inference constraints. It is simpler // just to look for all the predicates directly. ``` I'm not sure what this means, but perhaps in the 8 years since that this comment was written (cc rust-lang#23638) it's gotten easier to process region constraints after doing fulfillment? I don't know how this logic differs from anything we do in the `compare_impl_item` module. Ironically, later on it says: ```rust // However, it may be more efficient in the future to batch // the analysis together via the fulfill (see comment above regarding // the usage of the fulfill machinery), rather than the // repeated `.iter().any(..)` calls. ``` Also: * Removes `SimpleEqRelation` which was far too syntactical in its relation. * Fixes rust-lang#110557

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#110577 (Use fulfillment to check `Drop` impl compatibility) - rust-lang#110610 (Add Terminator conversion from MIR to SMIR, part #1) - rust-lang#110985 (Fix spans in LLVM-generated inline asm errors) - rust-lang#110989 (Make the BUG_REPORT_URL configurable by tools ) - rust-lang#111167 (debuginfo: split method declaration and definition) - rust-lang#111230 (add hint for =< as <=) - rust-lang#111279 (More robust debug assertions for `Instance::resolve` on built-in traits with non-standard trait items) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned spastorino Apr 20, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 20, 2023

rust-cloud-vms bot force-pushed the drop-impl-fulfill branch from 06d9150 to 85d8079 Compare April 20, 2023 04:49

lcnr reviewed Apr 20, 2023

View reviewed changes

compiler/rustc_hir_analysis/src/check/dropck.rs Show resolved Hide resolved

rustbot assigned lcnr and unassigned spastorino Apr 20, 2023

lcnr reviewed Apr 20, 2023

View reviewed changes

compiler/rustc_hir_analysis/src/check/dropck.rs Outdated Show resolved Hide resolved

rust-cloud-vms bot force-pushed the drop-impl-fulfill branch from 85d8079 to c691133 Compare April 21, 2023 04:27

lcnr reviewed Apr 21, 2023

View reviewed changes

This comment was marked as duplicate.

Sign in to view

compiler-errors added T-types Relevant to the types team, which will review and decide on the PR/issue. and removed T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 21, 2023

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Apr 21, 2023

This comment has been minimized.

Sign in to view

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 21, 2023

This comment has been minimized.

Sign in to view

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 22, 2023

lcnr reviewed May 4, 2023

View reviewed changes

lcnr added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-fcp Status: PR is in FCP and is awaiting for FCP to complete. labels May 4, 2023

rust-cloud-vms bot force-pushed the drop-impl-fulfill branch from f302ed2 to f4c77b8 Compare May 4, 2023 15:01

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 4, 2023

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels May 4, 2023

compiler-errors added 3 commits May 4, 2023 18:05

Use fulfillment to check Drop impl compatibility

964fb67

Add test for rust-lang#110557

9d44f9b

Even more tests

2e346b6

compiler-errors force-pushed the drop-impl-fulfill branch from f4c77b8 to 2e346b6 Compare May 4, 2023 18:06

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 4, 2023

matthiaskrgr mentioned this pull request May 6, 2023

Rollup of 7 pull requests #111283

Closed

matthiaskrgr mentioned this pull request May 6, 2023

Rollup of 7 pull requests #111287

Merged

bors merged commit bcc9aa0 into rust-lang:master May 6, 2023
11 checks passed

rustbot added this to the 1.71.0 milestone May 6, 2023

apiraino removed the to-announce Announce this issue on triage meeting label May 25, 2023

compiler-errors deleted the drop-impl-fulfill branch August 11, 2023 19:59

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Use fulfillment to check `Drop` impl compatibility #110577

Use fulfillment to check `Drop` impl compatibility #110577

compiler-errors commented Apr 20, 2023

lcnr commented Apr 20, 2023

lcnr left a comment

lcnr commented Apr 21, 2023

lcnr left a comment

compiler-errors commented Apr 21, 2023

This comment was marked as duplicate.

compiler-errors commented Apr 21, 2023

rfcbot commented Apr 21, 2023 •

edited by spastorino

oli-obk commented Apr 21, 2023

This comment has been minimized.

bors commented Apr 21, 2023

bors commented Apr 22, 2023

This comment has been minimized.

rust-timer commented Apr 22, 2023

nikomatsakis commented Apr 22, 2023

lcnr left a comment

compiler-errors commented May 4, 2023

bors commented May 4, 2023

bors commented May 4, 2023

compiler-errors commented May 4, 2023

bors commented May 4, 2023

compiler-errors commented May 4, 2023

Use fulfillment to check Drop impl compatibility #110577

Use fulfillment to check Drop impl compatibility #110577

Conversation

compiler-errors commented Apr 20, 2023

Some background

lcnr commented Apr 20, 2023

lcnr left a comment

Choose a reason for hiding this comment

lcnr commented Apr 21, 2023

lcnr left a comment

Choose a reason for hiding this comment

compiler-errors commented Apr 21, 2023

This comment was marked as duplicate.

compiler-errors commented Apr 21, 2023

rfcbot commented Apr 21, 2023 • edited by spastorino

oli-obk commented Apr 21, 2023

This comment has been minimized.

bors commented Apr 21, 2023

bors commented Apr 22, 2023

This comment has been minimized.

rust-timer commented Apr 22, 2023

Overall result: no relevant changes - no action needed

Instruction count

Max RSS (memory usage)

Cycles

nikomatsakis commented Apr 22, 2023

lcnr left a comment

Choose a reason for hiding this comment

compiler-errors commented May 4, 2023

bors commented May 4, 2023

bors commented May 4, 2023

compiler-errors commented May 4, 2023

bors commented May 4, 2023

compiler-errors commented May 4, 2023

Use fulfillment to check `Drop` impl compatibility #110577

Use fulfillment to check `Drop` impl compatibility #110577

rfcbot commented Apr 21, 2023 •

edited by spastorino