delegation: fix cycles during delayed lowering by aerooneqq · Pull Request #154368 · rust-lang/rust

aerooneqq · 2026-03-25T12:59:15Z

This PR forces lowering of delayed owners after hir_crate_items, as some diagnostics use hir_crate_items which results in query cycle which is then hangs calling def_path_str again and again. Fixes #154169. Part of #118212.

r? @petrochenkov

petrochenkov · 2026-03-25T14:30:19Z

What specific uses of def_path_str cause the infinite recursion?
Perhaps using something like with_reduced_queries will allow to break the recursion locally, and avoid global changes that this PR does.

petrochenkov · 2026-03-26T10:02:29Z

Relevant - #154387, #154389.

jyn514 · 2026-03-26T13:25:58Z

This should really have a reviewer with a lot of query system experience.

r? @Zoxc

rustbot · 2026-03-26T13:26:04Z

Failed to set assignee to zoxc: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

rustbot · 2026-03-27T09:41:52Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

…ering in print

aerooneqq · 2026-03-27T10:00:44Z

So the reason of this cycle was that this function wants to iterate over all free items, however they were not available during delayed lowering as it was executed before hir_crate_items(()), now delayed lowering is executed after hir_crate_items(()), and we use available-without-lowering information to fill hir_crate_items with information about delayed owners.

rust/compiler/rustc_middle/src/ty/print/pretty.rs

Line 3393 in e3691a5

for id in tcx.hir_free_items() {

Next, there is one more problem in this function, which is maybe not that actual now, but it will be during supporting inherent impls, as during function resolution we will do coherence check, and in cases like:

struct X<T> { t: T }

// No generics provided
impl X {
  pub fn foo() {}
}

reuse X::foo;

we would still come to for_each_def function, but this time this line will be a problem, as we would call delayed lowering during resolution of delegation, so I stored identifier which is needed by this loop in delayed owners, as it once again information that can be accessed without lowering.

rust/compiler/rustc_middle/src/ty/print/pretty.rs

Line 3398 in e3691a5

let item = tcx.hir_item(id);

@rustbot ready

compiler/rustc_hir/src/hir.rs

compiler/rustc_middle/src/hir/mod.rs

petrochenkov · 2026-03-27T10:52:12Z

compiler/rustc_middle/src/hir/map.rs

-            node => node.ident(),
-        }
+    pub fn hir_opt_ident(self, id: HirId) -> Option<Ident> {
+        self.hir_crate(()).opt_ident(self, id)


This use of hir_crate looks like it may be a source of perf regressions in incremental mode, I'll run benchmarks.

petrochenkov · 2026-03-27T11:05:03Z

compiler/rustc_middle/src/hir/map.rs

+        };
+
+        let delayed_kinds = tcx.hir_crate(()).delayed_owners_kinds();
+        let delayed_kinds = delayed_kinds.filter(|(id, _)| match collection_kind {


So calls like tcx.hir_module_items(specific_module) now need to walk the whole crate instead of just specific_module.
Ideally, delayed_ids should perhaps be per-module to fit best into the current setup.
(Not sure if this needs to be addressed right now, perhaps we'll see after running benchmarks.)

aerooneqq · 2026-03-27T11:28:15Z

@rustbot ready
For perf.

petrochenkov · 2026-03-27T11:34:03Z

@bors try @rust-timer queue

…<try> delegation: fix cycles during delayed lowering

rust-bors · 2026-03-27T13:44:31Z

☀️ Try build successful (CI)
Build commit: 40807f4 (40807f47e0044fa8a906be6caefbfcebd878e621, parent: e3691a5bd58e92999bcbffedf640ecd61e02c29e)

rust-timer · 2026-03-27T14:24:52Z

Finished benchmarking commit (40807f4): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	6.9%	[0.3%, 43.4%]	63
Regressions ❌ (secondary)	0.6%	[0.0%, 1.1%]	16
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	2
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	6.7%	[-0.2%, 43.4%]	65

Max RSS (memory usage)

Results (primary 6.6%, secondary 2.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	6.6%	[1.2%, 24.4%]	64
Regressions ❌ (secondary)	5.3%	[1.4%, 19.8%]	12
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.2%	[-6.1%, -3.5%]	5
All ❌✅ (primary)	6.6%	[1.2%, 24.4%]	64

Cycles

Results (primary 13.2%, secondary 3.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	13.2%	[2.0%, 61.2%]	51
Regressions ❌ (secondary)	3.1%	[2.7%, 3.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	13.2%	[2.0%, 61.2%]	51

Binary size

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

Bootstrap: 483.294s -> 485.596s (0.48%)
Artifact size: 395.05 MiB -> 395.15 MiB (0.03%)

jyn514 · 2026-03-27T14:31:12Z

regressions are mostly in evaluate_obligation and typeck. probably they call either ItemCollector::new or hir_opt_ident a lot?

rust-bors · 2026-03-28T17:14:38Z

☔ The latest upstream changes (presumably #154503) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot assigned petrochenkov Mar 25, 2026

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. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Mar 25, 2026

aerooneqq changed the title ~~delegation: invoke hir_crate_items before force_delayed_lowering~~ delegation: invoke hir_crate_items before force_delayed_owners_lowering Mar 25, 2026

petrochenkov added the F-fn_delegation `#![feature(fn_delegation)]` label Mar 25, 2026

petrochenkov 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-review Status: Awaiting review from the assignee but also interested parties. labels Mar 25, 2026

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aerooneqq force-pushed the delegation-force-lowering-later branch from f32739b to f50159f Compare March 27, 2026 09:41

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Invoke hir_crate_items before force_delayed_lowering, don't force low…

5afd6e4

…ering in print

aerooneqq force-pushed the delegation-force-lowering-later branch from f50159f to 5afd6e4 Compare March 27, 2026 09:50

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 27, 2026

jyn514 mentioned this pull request Mar 27, 2026

Automated pull from upstream HEAD ferrocene/ferrocene#2239

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aerooneqq added 2 commits March 27, 2026 13:37

Fix tests

2c40717

Add FIXME for bad error message

08de547

aerooneqq changed the title ~~delegation: invoke hir_crate_items before force_delayed_owners_lowering~~ delegation: fix cycles during delayed lowering Mar 27, 2026

petrochenkov reviewed Mar 27, 2026

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petrochenkov 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-review Status: Awaiting review from the assignee but also interested parties. labels Mar 27, 2026

Review: inline delayed_owners_kinds

de0bc7d

aerooneqq added 3 commits March 27, 2026 14:18

Review: &self -> self

1502ad8

Review: Option<Ident> -> Ident

00a49a0

Rename kind -> owner

3574b92

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 27, 2026

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rust-bors bot pushed a commit that referenced this pull request Mar 27, 2026

Auto merge of #154368 - aerooneqq:delegation-force-lowering-later, r=…

40807f4

…<try> delegation: fix cycles during delayed lowering

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 27, 2026

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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 27, 2026

petrochenkov added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Mar 27, 2026

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rust-timer commented Mar 27, 2026

Overall result: ❌ regressions - please read the text below

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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