obligations_for_self_ty: skip irrelevant goals (recompute sub_root from stalled_vars) by inq · Pull Request #156187 · rust-lang/rust

inq · 2026-05-05T12:01:03Z

Supersedes #146759. Since the original PR is having conflict now, I've rebased.

This includes 2 commit

the original one with rebase
above that, I've changed:

if stalled_on is Some: ignore sub_roots -> walk stalled_vars -> re-evaluate sub_root 
else: same with this PR

Why:
cached sub_roots can be stale if there is a sub-unification merge after stalling (lcnr proposed on the original PR)
so re-evaluating when reads ---> so more conservative

Testing:

next-solver / traits tests
we can follow after merging Implement a new flag -Zdisable-fast-paths in trait solving #156172 with -Zdisable-fast-paths

Style question:

In my preference, inside filter, I used filter_map - matches, but do you prefer if-let chain?

Original author: lcnr #146759

r? @lcnr

rustbot · 2026-05-05T12:01:07Z

changes to inspect_obligations.rs

cc @lcnr

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

lcnr · 2026-05-05T12:41:11Z

+            .filter(|(_, stalled_on)| {
+                let Some(stalled_on) = stalled_on else { return true };
+                stalled_on.stalled_vars.iter().filter_map(|arg| arg.as_type()).any(|ty| {
+                    matches!(*ty.kind(), ty::Infer(ty::TyVar(tv)) if infcx.sub_unification_table_root_var(tv) == vid)


please shallow_resolve the stalled_var here and if it is not an inference variable, always return true for now.

View changes since the review

also, please add a comment explaining that we are conservative here and want to handle cases where a goal is no longer stalled

added! thank you!

lcnr · 2026-05-05T12:41:47Z

@bors try @rust-timer queue

…=<try> obligations_for_self_ty: skip irrelevant goals (recompute sub_root from stalled_vars)

rust-bors · 2026-05-05T14:50:36Z

☀️ Try build successful (CI)
Build commit: 1a8e5b7 (1a8e5b75d2437597d5622146fe1d722a41e373c6, parent: 4feb7221f4d445120a5061b16ce7222adbfdf6f6)

lcnr · 2026-05-05T15:06:19Z

r? BoxyUwU

given that it's largely my PR, let's give it to somebody else to review

rust-timer · 2026-05-05T15:52:48Z

Finished benchmarking commit (1a8e5b7): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-17.6%	[-51.4%, -0.5%]	9
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -2.4%, secondary -67.8%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-67.8%	[-90.8%, -0.5%]	4
All ❌✅ (primary)	-2.4%	[-2.4%, -2.4%]	1

Cycles

Results (secondary -25.7%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.7%	[0.7%, 0.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-29.4%	[-67.4%, -0.6%]	7
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 495.518s -> 495.667s (0.03%)
Artifact size: 394.42 MiB -> 394.40 MiB (-0.00%)

BoxyUwU · 2026-06-03T11:42:25Z

    fn pending_obligations(&self) -> PredicateObligations<'tcx>;

+    /// Returning all pending obligations which reference an inference
+    /// variable with `_sub_root`.


should explicitly state that this can be conservative and return obligations which don't reference sub root

View changes since the review

Sorry for late update! Fixed, thank you!!

BoxyUwU · 2026-06-03T11:43:03Z

+                // Conservative here: if any of its stalled vars are not infer var anymore,
+                // some unification happened, so this goal is no longer stalled.
+                // So include it to re-evaluate in the downstream.
+                stalled_on.stalled_vars.iter().filter_map(|arg| arg.as_type()).any(


can you add a comment about how we don't just use the sub roots from stalled_on as they may be out of date

View changes since the review

Fixed! sorry for my bad english T.T

BoxyUwU · 2026-06-07T21:15:41Z

@rustbot author

rustbot · 2026-06-07T21:15:45Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

rustbot · 2026-06-09T05:14:41Z

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.

inq · 2026-06-09T05:19:58Z

@rustbot ready

lcnr · 2026-06-09T09:01:19Z

@bors r=BoxyUwU,lcnr

rust-bors · 2026-06-09T09:01:22Z

📌 Commit 6287f19 has been approved by BoxyUwU,lcnr

It is now in the queue for this repository.

JonathanBrouwer · 2026-06-09T09:05:14Z

Scheduling this before the next rollup, since there's few rollupable prs
@bors p=6

rust-bors · 2026-06-09T15:23:30Z

☀️ Test successful - CI
Approved by: BoxyUwU,lcnr
Duration: 3h 32m 20s
Pushing beae781 to main...

github-actions · 2026-06-09T15:26:43Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 057ed8b (parent) -> beae781 (this PR)

Test differences

Show 1 test diff

Stage 2

[run-make] tests/run-make/compressed-debuginfo-zstd: ignore (ignored if LLVM wasn't build with zstd for ELF section compression or LLVM is not the default codegen backend) -> pass (J0)

Job group index

J0: x86_64-gnu-nopt

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard beae781308e9ddef13074a03faf57ca2fac59a5b --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-gnu-gcc-core-tests: 20m 54s -> 12m 51s (-38.5%)
armhf-gnu: 1h 8m -> 1h 33m (+36.4%)
dist-x86_64-llvm-mingw: 1h 54m -> 1h 14m (-35.0%)
x86_64-gnu-stable: 3h 16m -> 2h 21m (-27.8%)
dist-android: 23m 18s -> 29m 34s (+26.9%)
pr-check-1: 43m 9s -> 31m 43s (-26.5%)
pr-check-2: 54m 41s -> 42m 29s (-22.3%)
x86_64-msvc-1: 2h 37m -> 2h 4m (-20.7%)
x86_64-gnu: 3h 4m -> 2h 30m (-18.5%)
aarch64-apple: 2h 55m -> 3h 25m (+17.6%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2026-06-09T16:04:54Z

Finished benchmarking commit (beae781): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-14.2%	[-69.4%, -0.2%]	15
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -53.5%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-53.5%	[-87.1%, -1.4%]	5
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -48.4%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-48.4%	[-79.2%, -2.1%]	5
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 517.542s -> 523.273s (1.11%)
Artifact size: 400.80 MiB -> 400.81 MiB (0.00%)

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. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels May 5, 2026

rustbot assigned lcnr May 5, 2026

This comment has been minimized.

Sign in to view

inq force-pushed the obligations-self-ty-recompute-sub-root branch from 90c0853 to 596f7e9 Compare May 5, 2026 12:03

lcnr reviewed May 5, 2026

View reviewed changes

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 May 5, 2026

This comment has been minimized.

Sign in to view

rust-bors Bot pushed a commit that referenced this pull request May 5, 2026

Auto merge of #156187 - inq:obligations-self-ty-recompute-sub-root, r…

1a8e5b7

…=<try> obligations_for_self_ty: skip irrelevant goals (recompute sub_root from stalled_vars)

This comment has been minimized.

Sign in to view

rustbot assigned BoxyUwU and unassigned lcnr May 5, 2026

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label May 5, 2026

lcnr mentioned this pull request May 5, 2026

obligations_for_self_ty: skip irrelevant goals #146759

Closed

BoxyUwU reviewed Jun 3, 2026

View reviewed changes

Comment thread compiler/rustc_trait_selection/src/solve/fulfill.rs

rustbot 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 Jun 7, 2026

lcnr and others added 2 commits June 9, 2026 11:05

obligations_for_self_ty: skip irrelevant goals

67fdef4

walk stalled_vars at read time for sub_root filter

b02a6b7

inq added 3 commits June 9, 2026 11:05

shallow_resolve stalled vars + conservative include

dbde6a6

format fix

d9cf1ae

gate sub_root fast path on -Zdisable-fast-paths

6287f19

inq force-pushed the obligations-self-ty-recompute-sub-root branch from 38cdf1c to 6287f19 Compare June 9, 2026 05:14

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 Jun 9, 2026

rust-bors Bot 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 Jun 9, 2026

This comment has been minimized.

Sign in to view

rust-bors Bot added merged-by-bors This PR was explicitly merged by bors. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jun 9, 2026

rust-bors Bot merged commit beae781 into rust-lang:main Jun 9, 2026
13 checks passed

rustbot added this to the 1.98.0 milestone Jun 9, 2026

rust-bors Bot mentioned this pull request Jun 9, 2026

-Znext-solver Less normalizes-to janks #156619

Open

Uh oh!

Conversation

inq commented May 5, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented May 5, 2026

Uh oh!

This comment has been minimized.

lcnr May 5, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

lcnr commented May 5, 2026

Uh oh!

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

rust-bors Bot commented May 5, 2026

Uh oh!

This comment has been minimized.

lcnr commented May 5, 2026

Uh oh!

rust-timer commented May 5, 2026

Overall result: ✅ improvements - no action needed

Uh oh!

BoxyUwU Jun 3, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

BoxyUwU Jun 3, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

BoxyUwU commented Jun 7, 2026

Uh oh!

rustbot commented Jun 7, 2026

Uh oh!

rustbot commented Jun 9, 2026

Uh oh!

inq commented Jun 9, 2026

Uh oh!

lcnr commented Jun 9, 2026

Uh oh!

rust-bors Bot commented Jun 9, 2026

Uh oh!

JonathanBrouwer commented Jun 9, 2026

Uh oh!

This comment has been minimized.

rust-bors Bot commented Jun 9, 2026

Uh oh!

Uh oh!

github-actions Bot commented Jun 9, 2026

Test differences

Stage 2

Job duration changes

Uh oh!

rust-timer commented Jun 9, 2026

Overall result: ✅ improvements - no action needed

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

inq commented May 5, 2026 •

edited by rustbot

Loading

lcnr May 5, 2026 •

edited by rustbot

Loading

BoxyUwU Jun 3, 2026 •

edited by rustbot

Loading

BoxyUwU Jun 3, 2026 •

edited by rustbot

Loading