Remove `QueryDispatcher` #152371

nnethercote · 2026-02-09T02:54:11Z

QueryDispatcher is a trait that existed purely because rustc_query_system had code that didn't have access to TyCtxt. That is no longer the case, so the trait can be removed.

r? @Zalathar

Query keys must be stably hashable. Currently this requirement is expressed as a where-clause on `impl QueryDispatcher for SemiDynamicQueryDispatcher` and a where-clause on `create_deferred_query_stack_frame`. This commit removes those where-clause bounds and adds a single bound to `QueryCache::Key`, which already has some other bounds. I.e. it consolidates the bounds. It also gives them a name (`QueryCacheKey`) to avoid repeating them. There is also a related `Key` trait in `rustc_middle`; it should probably be merged with `QueryCacheKey` in the future, but not today. This cleanup helps with the next two commits, which do bigger rearrangements, and where the where-clauses caused me some difficulties.

It's always `SemiDynamicQueryDispatcher`, so we can just use that type directly. (This requires adding some explicit generic params to `QueryDispatcherUnerased`.) Less indirection makes the code clearer, and this is a prerequisite for the next commit, which is a much bigger simplification.

nnethercote · 2026-02-09T02:54:26Z

@bors try @rust-timer queue

Remove `QueryDispatcher`

nnethercote · 2026-02-09T02:55:56Z

Best reviewed one commit at a time.

This code uses generics and trait bounds heavily and getting everything compiling took some effort. The changes I made make sense to me but there might be better ways of doing things.

compiler/rustc_query_system/src/query/caches.rs

Zalathar · 2026-02-09T04:13:05Z

compiler/rustc_query_impl/src/lib.rs

        self.vtable.will_cache_on_disk_for_key_fn.map_or(false, |f| f(tcx, key))
    }

+    // Don't use this method to access query results, instead use the methods on TyCtxt.


Note for future reference: These are existing comments, being migrated over from QueryDispatcher.

compiler/rustc_query_impl/src/plumbing.rs

rust-bors · 2026-02-09T05:05:19Z

☀️ Try build successful (CI)
Build commit: a7cede3 (a7cede3634626a3af8d24e7a615fb2390494a786, parent: 1c316d34610a3cd31831d2ae8e5dd454f26de430)

rust-timer · 2026-02-09T05:46:01Z

Finished benchmarking commit (a7cede3): comparison URL.

Overall result: ❌ regressions - no action needed

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.

@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)	2.9%	[2.9%, 2.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -4.3%, secondary -4.4%)

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)	-4.3%	[-4.3%, -4.3%]	1
Improvements ✅ (secondary)	-4.4%	[-4.9%, -4.0%]	3
All ❌✅ (primary)	-4.3%	[-4.3%, -4.3%]	1

Cycles

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

Binary size

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

Bootstrap: 475.432s -> 478.527s (0.65%)
Artifact size: 397.82 MiB -> 397.89 MiB (0.02%)

It takes an `is_anon` argument, but it's now generic over `QueryFlags`, which contains the same `is_anon` field. So the argument is no longer necessary.

It existed only to bridge the divide between `rustc_query_system` and `rustc_query_impl`. But enough pieces have been moved from the former to the latter that the trait is no longer needed. Less indirection and abstraction makes the code easier to understand.

It's the only thing left in `rustc_query_system::query::dispatcher`.

Zalathar · 2026-02-09T09:32:14Z

@bors r+ rollup=maybe

rust-bors · 2026-02-09T09:32:17Z

📌 Commit f995804 has been approved by Zalathar

It is now in the queue for this repository.

rust-bors · 2026-02-09T13:14:38Z

☀️ Test successful - CI
Approved by: Zalathar
Duration: 3h 40m 19s
Pushing c6936c3 to main...

github-actions · 2026-02-09T13:17:59Z

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 4cd4c18 (parent) -> c6936c3 (this PR)

Test differences

Show 4 test diffs

4 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard c6936c309add33a7008747866aee081ff5289946 --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

aarch64-apple: 2h 15m -> 3h 32m (+56.7%)
dist-apple-various: 1h 5m -> 1h 31m (+39.6%)
dist-aarch64-linux: 2h 43m -> 1h 48m (-33.3%)
dist-aarch64-msvc: 1h 30m -> 1h 42m (+13.1%)
dist-i586-gnu-i586-i686-musl: 1h 36m -> 1h 25m (-11.8%)
i686-gnu-nopt-1: 2h 18m -> 2h 5m (-9.5%)
arm-android: 1h 46m -> 1h 37m (-8.8%)
aarch64-gnu-debug: 1h 17m -> 1h 10m (-8.3%)
dist-aarch64-apple: 1h 52m -> 2h (+6.9%)
i686-msvc-1: 2h 58m -> 2h 45m (-6.9%)

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 · 2026-02-09T13:57:02Z

Finished benchmarking commit (c6936c3): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (secondary 4.8%)

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)	4.8%	[4.8%, 4.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 4.8%)

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)	4.8%	[4.8%, 4.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.0%, secondary -0.1%)

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)	-0.0%	[-0.1%, -0.0%]	15
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	20
All ❌✅ (primary)	-0.0%	[-0.1%, -0.0%]	15

Bootstrap: 473.075s -> 474.574s (0.32%)
Artifact size: 397.90 MiB -> 397.79 MiB (-0.03%)

nnethercote added 2 commits February 9, 2026 10:23

rustbot assigned Zalathar Feb 9, 2026

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rust-bors bot pushed a commit that referenced this pull request Feb 9, 2026

Auto merge of #152371 - nnethercote:rm-QueryDispatcher, r=<try>

a7cede3

Remove `QueryDispatcher`

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 9, 2026

Zalathar reviewed Feb 9, 2026

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compiler/rustc_query_system/src/query/caches.rs Show resolved Hide resolved

Zalathar reviewed Feb 9, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 9, 2026

nnethercote added 3 commits February 9, 2026 20:00

Adjust make_dep_kind_vtable_for_query.

f91c808

It takes an `is_anon` argument, but it's now generic over `QueryFlags`, which contains the same `is_anon` field. So the argument is no longer necessary.

Move HashResult.

f995804

It's the only thing left in `rustc_query_system::query::dispatcher`.

nnethercote force-pushed the rm-QueryDispatcher branch from 08c239a to f995804 Compare February 9, 2026 09:03

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 Feb 9, 2026

This was referenced Feb 9, 2026

Rollup of 1 pull requests #152380

Closed

Rename the query system's JobOwner to ActiveJobGuard, and include key_hash #152377

Merged

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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 Feb 9, 2026

rust-bors bot merged commit c6936c3 into rust-lang:main Feb 9, 2026
12 checks passed

rustbot added this to the 1.95.0 milestone Feb 9, 2026

rust-bors bot mentioned this pull request Feb 9, 2026

Remove HasDepContext by merging it into QueryContext #151968

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nnethercote deleted the rm-QueryDispatcher branch February 10, 2026 01:20

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Remove QueryDispatcher #152371

Remove QueryDispatcher #152371

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Overall result: ❌ regressions - no action needed

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Test differences

Job duration changes

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Overall result: no relevant changes - no action needed

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Remove `QueryDispatcher` #152371

Remove `QueryDispatcher` #152371