Implement T-types suggested logic for perfect non-local impl detection #122747

Urgau · 2024-03-19T21:04:20Z

This implement T-types suggested logic for perfect non-local impl detection:

for each impl, instantiate all local types with inference vars and then assemble candidates for that goal, if there are more than 1 (non-private impls), it does not leak

This extension to the current logic is meant to address issues reported in #121621.

This PR also re-enables the lint non_local_definitions to warn-by-default.

Implementation was discussed in this zulip thread.

Fixes #121621
Fixes #121746

r? @lcnr (feel free to re-roll)

compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs

compiler/rustc_lint/src/non_local_def.rs

lcnr

i'd like some style changes, apart from this r=me after perf

compiler/rustc_lint/src/non_local_def.rs

lcnr · 2024-03-21T08:25:13Z

@bors try @rust-timer queue

…=<try> Implement T-types suggested logic for perfect non-local impl detection This implement [T-types suggested logic](rust-lang#121621 (comment)) for perfect non-local impl detection: > for each impl, instantiate all local types with inference vars and then assemble candidates for that goal, if there are more than 1 (non-private impls), it does not leak This extension to the current logic is meant to address issues reported in rust-lang#121621. This PR also re-enables the lint `non_local_definitions` to warn-by-default. Implementation was discussed in this [zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/144729-t-types/topic/Implementing.20new.20non-local.20impl.20defs.20logic). r? `@lcnr` *(feel free to re-roll)*

bors · 2024-03-21T08:26:24Z

⌛ Trying commit eed8e95 with merge c5a16cd...

bors · 2024-03-21T09:58:19Z

☀️ Try build successful - checks-actions
Build commit: c5a16cd (c5a16cd81a23f6f21bfed93b321b2d9f3420fe10)

rust-timer · 2024-03-21T11:59:31Z

Finished benchmarking commit (c5a16cd): comparison URL.

Overall result: ❌ regressions - 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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.2%	[0.6%, 4.2%]	12
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.2%	[0.6%, 4.2%]	12

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)	3.3%	[2.1%, 5.9%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
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)	2.7%	[0.6%, 3.4%]	7
Regressions ❌ (secondary)	3.0%	[3.0%, 3.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.7%	[0.6%, 3.4%]	7

Binary size

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

Bootstrap: 669.21s -> 669.518s (0.05%)
Artifact size: 312.83 MiB -> 315.05 MiB (0.71%)

Urgau · 2024-03-21T13:06:19Z

I've looked locally (with callgrind) at the perf regression and it's the same symptom as in the first implementation #120393 (comment), the version of diesel (v1.4.8) we embed trigger the warnings more than 300 times leading to some unavoidable perf regression.

I have checked that at least from version 2.1.0 (May 2023) and onwards of the crate there is no warnings, I suspect there are no warnings in any >=2 of diesel (but could check due to MSRV issues).

One question through, I haven't update the diagnostic message, but I would like to do so before we merge this PR however I don't know what phrasing we should use, the one you proposed (@lcnr), seems a bit to "technical" for users:

An item nested inside an expression-containing item (through any level of nesting) may not define an impl<T0..Tn> [Trait<P1..Pn> for] P0 if it has an observable impact outside of this item

Any suggestion for what to replace it instead ?

Also, should we suggest or mention the 2 or more impls rule ?

lcnr · 2024-03-22T10:59:56Z

something like the following 🤔

Impls inside of an item body should not impact code outside of that item.

and that this is the case if there are more than 1 other global impls is just an implementation detail imo

Urgau · 2024-03-23T13:44:25Z

I've addressed all the review comments (expect for #122747 (comment)), as well as adding a conservative message for "not impacting code outside the item".

I believe this is ready for another review or approval (which I cannot do since I don't have r+ rights).

Urgau · 2024-03-30T12:49:55Z

@lcnr, all the reviews comments have been addressed, but I can't r=you since I don't have r+ rights.
could you give a quick look at the PR again, thks

lcnr

final nits, then r=me

compiler/rustc_lint/src/non_local_def.rs

tests/ui/lint/non_local_definitions.rs

lcnr · 2024-04-05T13:16:38Z

compiler/rustc_lint/messages.ftl

@@ -443,7 +443,7 @@ lint_non_local_definitions_impl = non-local `impl` definition, they should be av
            [one] `{$body_name}`
           *[other] `{$body_name}` and up {$depth} bodies
        }
-    .non_local = an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block
+    .non_local = an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block and should not impact code outside of that item


that sentence seems off to me 🤔

Suggested change

.non_local = an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block and should not impact code outside of that item

.non_local = an `impl` definition is non-local if it is nested inside an item and may impact type checking outside of that item. This can be the case if neither the trait or the self type are at the same nesting level as the `impl`

or even ignoring the second sentence, simply using " an impl definition is non-local if it is nested inside an item and may impact type checking outside of that item."

The sentence also seemed a bit weird to me. Thanks for the suggestions, I ended up using the first one, since it gives a bit more details.

compiler/rustc_lint/src/non_local_def.rs

lcnr · 2024-04-05T13:18:12Z

compiler/rustc_lint/src/non_local_def.rs

                }
+
+                let const_anon = if self.body_depth == 1


please explain what this if chain is doing? getting the span for an anon const suggestion?

Yes, it's getting the span of the parent const item ident (if there is one) for the const anon suggestion.

I changed to variable name to span_for_const_anon_suggestion and added a comment to explain what it is doing.

lcnr · 2024-04-05T13:19:19Z

@bors delegate+

bors · 2024-04-05T13:19:23Z

✌️ @Urgau, you can now approve this pull request!

If @lcnr told you to "r=me" after making some further change, please make that change, then do @bors r=@lcnr

Urgau · 2024-04-05T18:19:21Z

@bors r=@lcnr

bors · 2024-04-05T18:19:24Z

📌 Commit 2f2d5cc has been approved by lcnr

It is now in the queue for this repository.

bors · 2024-04-05T20:10:00Z

⌛ Testing commit 2f2d5cc with merge 9d79cd5...

bors · 2024-04-05T22:11:36Z

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing 9d79cd5 to master...

rust-timer · 2024-04-05T23:31:03Z

Finished benchmarking commit (9d79cd5): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.3%	[0.6%, 4.4%]	12
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.2%]	9
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.2%	[-0.4%, 4.4%]	21

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)	-	-	0
Improvements ✅ (primary)	-3.2%	[-3.8%, -2.6%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.2%	[-3.8%, -2.6%]	2

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)	2.7%	[1.2%, 3.5%]	7
Regressions ❌ (secondary)	3.1%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.7%	[1.2%, 3.5%]	7

Binary size

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

Bootstrap: 667.559s -> 670.251s (0.40%)
Artifact size: 318.06 MiB -> 318.26 MiB (0.06%)

Urgau · 2024-04-05T23:51:17Z

The perf regressions in diesel are due to the lint being triggered and producing nearly 300 warnings (with 155 actually shown). See #122747 (comment) and #120393 (comment) for more details.

@rustbot label: +perf-regression-triaged

rustbot assigned lcnr Mar 19, 2024

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 Mar 19, 2024

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 21, 2024

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Mar 21, 2024

Urgau force-pushed the non-local-defs_perfect_impl branch from eed8e95 to 3c8cadc Compare March 21, 2024 18:19

Urgau force-pushed the non-local-defs_perfect_impl branch from 3c8cadc to ba7f52d Compare March 23, 2024 11:45

Urgau mentioned this pull request Apr 2, 2024

Update non-local-defns regarding parameterized traits and types rust-lang/rfcs#3581

Open

lcnr reviewed Apr 5, 2024

View reviewed changes

Urgau added 2 commits April 5, 2024 18:39

Take the polarity into account in compute_applicable_impls

524f3c9

Expose rustc_trait_selection::error_reporting::ambiguity module

6173240

Urgau added 3 commits April 5, 2024 19:25

Eliminate false-positives in the non-local lint with the type-system

a1d7bff

Update non-local impl definition lint rule note

8edf255

Put non_local_definitions lint back to warn-by-default

2f2d5cc

Urgau force-pushed the non-local-defs_perfect_impl branch from ba7f52d to 2f2d5cc Compare April 5, 2024 17:26

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 Apr 5, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Apr 5, 2024

bors merged commit 9d79cd5 into rust-lang:master Apr 5, 2024
12 checks passed

rustbot added this to the 1.79.0 milestone Apr 5, 2024

rustbot added the perf-regression-triaged The performance regression has been triaged. label Apr 5, 2024

apiraino mentioned this pull request Apr 6, 2024

False positives for the new non_local_definitions lint #121746

Closed

dtolnay mentioned this pull request Apr 7, 2024

nightly-2024-04-05 regression: error[E0275]: overflow evaluating the requirement #123573

Closed

ChayimFriedman2 mentioned this pull request Apr 26, 2024

False positive and highly misleading suggestions for the non-local-definitions lint #124396

Closed

wesleywiser mentioned this pull request May 10, 2024

Make non-local-def lint Allow by default #124950

Closed

lqd mentioned this pull request Jun 27, 2024

Switch back non_local_definitions lint to allow-by-default #127015

Merged

This was referenced Jul 11, 2024

Tracking Issue for RFC 3373: Avoid non-local definitions in functions #120363

Closed

non_local_definitions lint fires for impl Trait for NonLocalType<SomeLocalType>, probably shouldn't #126768

Closed

lcnr mentioned this pull request Sep 4, 2024

Tracking Issue for -Znext-solver #107374

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Implement T-types suggested logic for perfect non-local impl detection #122747

Implement T-types suggested logic for perfect non-local impl detection #122747

Urgau commented Mar 19, 2024 •

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Urgau commented Apr 5, 2024

	.non_local = an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block and should not impact code outside of that item
	.non_local = an `impl` definition is non-local if it is nested inside an item and may impact type checking outside of that item. This can be the case if neither the trait or the self type are at the same nesting level as the `impl`

Implement T-types suggested logic for perfect non-local impl detection #122747

Implement T-types suggested logic for perfect non-local impl detection #122747

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Overall result: ❌ regressions - ACTION NEEDED

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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Urgau commented Mar 19, 2024 •

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