Rewrite `query_ensure_result`. by nnethercote · Pull Request #154075 · rust-lang/rust

nnethercote · 2026-03-19T04:07:05Z

It currently uses chaining which is concise but hard to read. There are up to four implicit matches occurring after the call to execute_query_fn.

The first map on Option<Erased<Result<T, ErrorGuaranteed>>>.
The second map on Option<Result<T, ErrorGuaranteed>>.
The third map on Result<T, ErrorGuaranteed>.
The unwrap_or on Option<Result<(), ErrorGuaranteed>>.

This commit rewrites it to use at most two matches.

An explicit match on Option<Erased<Result<T, ErrorGuaranteed>>>.
An explicit match on Result<T, ErrorGuaranteed>.

This is easier to read. It's also more efficient, though the code isn't hot enough for that to matter.

r? @Zalathar

rustbot · 2026-03-19T04:07:11Z

Zalathar is not on the review rotation at the moment.
They may take a while to respond.

compiler/rustc_middle/src/query/inner.rs

rustbot · 2026-03-19T07:53:38Z

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.

nnethercote · 2026-03-19T07:54:33Z

Let's run perf just in case.

@bors try @rust-timer queue

Rewrite `query_ensure_result`.

Zalathar · 2026-03-19T08:57:56Z

compiler/rustc_middle/src/query/inner.rs

+                QueryMode::Ensure { ensure_mode: EnsureMode::Ok },
+            ) {
+                // We executed the query. Convert the successful result.
+                Some(res) => convert(res),


Style: I think value is better than res here (and above), as it’s consistent with the other cache lookups on this file, and we can’t treat the value as a Result without unerasing it first anyway.

Zalathar · 2026-03-19T08:58:49Z

r=me after considering the res/value feedback, assuming perf is good.

It currently uses chaining which is concise but hard to read. There are up to four implicit matches occurring after the call to `execute_query_fn`. - The first `map` on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - The second `map` on `Option<Result<T, ErrorGuaranteed>>`. - The third `map` on `Result<T, ErrorGuaranteed>`. - The `unwrap_or` on `Option<Result<(), ErrorGuaranteed>>`. This commit rewrites it to use at most two matches. - An explicit match on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - An explicit match on `Result<T, ErrorGuaranteed>`. This is easier to read. It's also more efficient, though the code isn't hot enough for that to matter.

rust-bors · 2026-03-19T10:04:15Z

☀️ Try build successful (CI)
Build commit: 936d6e3 (936d6e3bcbc7a2764e21d35c7e1d90ab67157121, parent: fd0c901b00ee1e08a250039cdb90258603497e20)

rust-timer · 2026-03-19T11:07:09Z

Finished benchmarking commit (936d6e3): comparison URL.

Overall result: no relevant changes - 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

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

Max RSS (memory usage)

Results (secondary -4.5%)

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)	-4.5%	[-4.5%, -4.5%]	1
All ❌✅ (primary)	-	-	0

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: 481.003s -> 479.608s (-0.29%)
Artifact size: 396.91 MiB -> 394.93 MiB (-0.50%)

nnethercote · 2026-03-19T11:36:30Z

@bors r=Zalathar rollup

rust-bors · 2026-03-19T11:36:33Z

📌 Commit 74776c4 has been approved by Zalathar

It is now in the queue for this repository.

@Zalathar

…esult, r=Zalathar Rewrite `query_ensure_result`. It currently uses chaining which is concise but hard to read. There are up to four implicit matches occurring after the call to `execute_query_fn`. - The first `map` on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - The second `map` on `Option<Result<T, ErrorGuaranteed>>`. - The third `map` on `Result<T, ErrorGuaranteed>`. - The `unwrap_or` on `Option<Result<(), ErrorGuaranteed>>`. This commit rewrites it to use at most two matches. - An explicit match on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - An explicit match on `Result<T, ErrorGuaranteed>`. This is easier to read. It's also more efficient, though the code isn't hot enough for that to matter. r? @Zalathar

…uwer Rollup of 9 pull requests Successful merges: - #153556 (`impl` restriction lowering) - #153992 (bootstrap: Optionally print a backtrace if a command fails) - #154019 (two smaller feature cleanups) - #154059 (tests: Activate `must_not_suspend` test for `MutexGuard` dropped before `await`) - #154075 (Rewrite `query_ensure_result`.) - #154082 (Updates derive_where and removes workaround) - #154084 (Preserve braces around `self` in use tree pretty printing) - #154086 (Insert space after float literal ending with `.` in pretty printer) - #154087 (Fix whitespace after fragment specifiers in macro pretty printing)

@Zalathar

…esult, r=Zalathar Rewrite `query_ensure_result`. It currently uses chaining which is concise but hard to read. There are up to four implicit matches occurring after the call to `execute_query_fn`. - The first `map` on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - The second `map` on `Option<Result<T, ErrorGuaranteed>>`. - The third `map` on `Result<T, ErrorGuaranteed>`. - The `unwrap_or` on `Option<Result<(), ErrorGuaranteed>>`. This commit rewrites it to use at most two matches. - An explicit match on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - An explicit match on `Result<T, ErrorGuaranteed>`. This is easier to read. It's also more efficient, though the code isn't hot enough for that to matter. r? @Zalathar

@Zalathar

…esult, r=Zalathar Rewrite `query_ensure_result`. It currently uses chaining which is concise but hard to read. There are up to four implicit matches occurring after the call to `execute_query_fn`. - The first `map` on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - The second `map` on `Option<Result<T, ErrorGuaranteed>>`. - The third `map` on `Result<T, ErrorGuaranteed>`. - The `unwrap_or` on `Option<Result<(), ErrorGuaranteed>>`. This commit rewrites it to use at most two matches. - An explicit match on `Option<Erased<Result<T, ErrorGuaranteed>>>`. - An explicit match on `Result<T, ErrorGuaranteed>`. This is easier to read. It's also more efficient, though the code isn't hot enough for that to matter. r? @Zalathar

…uwer Rollup of 12 pull requests Successful merges: - #152909 (sess: `-Zbranch-protection` is a target modifier) - #153556 (`impl` restriction lowering) - #154048 (Don't emit rustdoc `missing_doc_code_examples` lint on impl items) - #153992 (bootstrap: Optionally print a backtrace if a command fails) - #154019 (two smaller feature cleanups) - #154059 (tests: Activate `must_not_suspend` test for `MutexGuard` dropped before `await`) - #154075 (Rewrite `query_ensure_result`.) - #154082 (Updates derive_where and removes workaround) - #154084 (Preserve braces around `self` in use tree pretty printing) - #154086 (Insert space after float literal ending with `.` in pretty printer) - #154087 (Fix whitespace after fragment specifiers in macro pretty printing) - #154109 (tests: Add regression test for async closures involving HRTBs)

Rollup of 15 pull requests Successful merges: - #152909 (sess: `-Zbranch-protection` is a target modifier) - #153556 (`impl` restriction lowering) - #154048 (Don't emit rustdoc `missing_doc_code_examples` lint on impl items) - #150935 (Introduce #[diagnostic::on_move(message)]) - #152973 (remove -Csoft-float) - #153862 (Rename `cycle_check` to `find_cycle`) - #153992 (bootstrap: Optionally print a backtrace if a command fails) - #154019 (two smaller feature cleanups) - #154059 (tests: Activate `must_not_suspend` test for `MutexGuard` dropped before `await`) - #154075 (Rewrite `query_ensure_result`.) - #154082 (Updates derive_where and removes workaround) - #154084 (Preserve braces around `self` in use tree pretty printing) - #154086 (Insert space after float literal ending with `.` in pretty printer) - #154087 (Fix whitespace after fragment specifiers in macro pretty printing) - #154109 (tests: Add regression test for async closures involving HRTBs)

rustbot assigned Zalathar Mar 19, 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. labels Mar 19, 2026

nnethercote mentioned this pull request Mar 19, 2026

Two small query improvements #154067

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Zalathar reviewed Mar 19, 2026

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compiler/rustc_middle/src/query/inner.rs Outdated Show resolved Hide resolved

nnethercote force-pushed the rewrite-query_ensure_result branch from cf1ff55 to d7ba9ed Compare March 19, 2026 07:53

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rust-bors bot pushed a commit that referenced this pull request Mar 19, 2026

Auto merge of #154075 - nnethercote:rewrite-query_ensure_result, r=<try>

936d6e3

Rewrite `query_ensure_result`.

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 19, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 19, 2026

nnethercote force-pushed the rewrite-query_ensure_result branch from d7ba9ed to 74776c4 Compare March 19, 2026 11:35

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 Mar 19, 2026

JonathanBrouwer mentioned this pull request Mar 19, 2026

Rollup of 9 pull requests #154102

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JonathanBrouwer mentioned this pull request Mar 19, 2026

Rollup of 12 pull requests #154116

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JonathanBrouwer mentioned this pull request Mar 19, 2026

Rollup of 12 pull requests #154117

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Zalathar mentioned this pull request Mar 20, 2026

Rollup of 15 pull requests #154123

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rust-bors bot merged commit 3cabafe into rust-lang:main Mar 20, 2026
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rustbot added this to the 1.96.0 milestone Mar 20, 2026

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Rewrite `query_ensure_result`.#154075

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Overall result: no relevant changes - no action needed

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