Improve diagnostic deduplication - #163461

nnethercote · 2026-09-28T23:22:54Z

Diagnostic deduplication currently considers Span::parent, which can lead to some surprising results. Details in individual commits.

Fixes #106571.
Fixes #162901.

r? @JonathanBrouwer

nnethercote · 2026-09-28T23:23:08Z

cc @oli-obk @bjorn3

nnethercote · 2026-09-28T23:24:26Z

LLM disclosure: an LLM came up with the idea of using Encoder/SpanEncoder for the hashing traversal. (My initial version used a new DedupHasher trait that was more verbose and error-prone.) I wrote all the code and text myself.

bjorn3 · 2026-09-29T11:53:40Z

Does this also fix #106571?

nnethercote · 2026-09-30T03:12:10Z

Does this also fix #106571?

I just checked: yes!

JonathanBrouwer · 2026-09-30T08:56:57Z

@bors try @rust-timer queue

Improve diagnostic deduplication

JonathanBrouwer

r=me after changing to my suggestion, or adding a comment to the code explaining why the code is like this

View changes since this review

rust-bors · 2026-09-30T09:56:35Z

☀️ Try build successful (CI)
Build commit: 333c7cd (333c7cd08a99be5fc1d1001dfc2a7bbb674af48d)
Base parent: c1bf6e1 (c1bf6e13fa5ff2c753a49fd5ef37371c6fed729f)

rust-timer · 2026-09-30T11:16:57Z

Finished benchmarking commit (333c7cd): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (secondary 4.6%)

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)	4.6%	[3.2%, 5.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.9%, secondary 2.2%)

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

	mean	range	count
Regressions ❌ (primary)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.9%	[2.9%, 2.9%]	1

Binary size

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

Bootstrap: 489.184s -> 489.472s (0.06%)
Artifact size: 406.44 MiB -> 406.45 MiB (0.00%)

- Introduce `Subdiag::dedup_hash`, which mirrors `DiagInner::dedup_hash` and is necessary for the subsequent commits. - Change the name and structure of `not_yet_emitted` to be clearer. - Change `retain_mut` to `retain`; mutability isn't required.

Currently deduplication erroneously has no effect with incremental enabled because the span parent gets included in the hash used for deduplication.

So it applies the `#[inline]` to every method, not just the first one.

By making it ignore the parent field of spans within the diagnostic. This is done with a new `DedupHashEncoder` type that uses the existing `Encoder`/`SpanEncoder` traits to traverse the fields within `DiagInner` and `Subdiag`. Fixes rust-lang#162901.

rustbot · 2026-10-01T11:47:04Z

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.

rustbot · 2026-10-01T11:47:05Z

⚠️ Warning ⚠️

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Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtrees.
- 4341575

nnethercote · 2026-10-01T11:47:17Z

@bors r=JonathanBrouwer

rust-bors · 2026-10-01T11:47:21Z

📌 Commit 4341575 has been tentatively approved by JonathanBrouwer

It will be put into the queue for this repository once PR CI succeeds.

@JonathanBrouwer

…Brouwer Improve diagnostic deduplication Diagnostic deduplication currently considers `Span::parent`, which can lead to some surprising results. Details in individual commits. Fixes rust-lang#106571. Fixes rust-lang#162901. r? @JonathanBrouwer

…uwer Rollup of 9 pull requests Successful merges: - #163461 (Improve diagnostic deduplication) - #159021 (windows-gnu: enable native TLS) - #161467 (wfcheck: name the item that discards an unused type parameter) - #162618 (trait_selection: Preserve eager normalization failures) - #163064 (Avoid computing overflowed goal chains for crate dependencies) - #163360 ([rustdoc] Correctly handle rustc_allow_incoherent_impl on primitive methods) - #163385 (GVN transmutes of Immediate::Uninit to Immediate::Uninit) - #163590 (Make `AllocatorNightly` less clever) - #163599 (Add union pattern reference change to relnotes)

…uwer Rollup of 20 pull requests Successful merges: - #163483 (Bump bootstrap compiler to 1.100.0 beta) - #161380 (only rerun const eval in next-solver if the const actually references opaques) - #162900 (Some refactorings around metadata encoding) - #163461 (Improve diagnostic deduplication) - #163580 (Provide better doc code example for `UnixDatagram::bind_addr` and `UnixListener::bind_addr`) - #163584 ([triagebot] Ping me for debugger visualizer changes) - #159021 (windows-gnu: enable native TLS) - #161467 (wfcheck: name the item that discards an unused type parameter) - #162618 (trait_selection: Preserve eager normalization failures) - #162904 (Fix ICE for ambiguous candidates on method probing) - #163064 (Avoid computing overflowed goal chains for crate dependencies) - #163281 (Add `f16` inline ASM support to `spirv.rs`) - #163314 (move `#[macro_export]` on declarative macro check to `rustc_attr_parsing`) - #163360 ([rustdoc] Correctly handle rustc_allow_incoherent_impl on primitive methods) - #163385 (GVN transmutes of Immediate::Uninit to Immediate::Uninit) - #163405 (Remove some #[linkage] options) - #163530 (`const impl PartialEq` for `f16b`) - #163581 (do not suggest precise capturing when the opaque span is in a macro expansion) - #163590 (Make `AllocatorNightly` less clever) - #163599 (Add union pattern reference change to relnotes)

@JonathanBrouwer

Rollup merge of #163461 - nnethercote:fix-162901, r=JonathanBrouwer Improve diagnostic deduplication Diagnostic deduplication currently considers `Span::parent`, which can lead to some surprising results. Details in individual commits. Fixes #106571. Fixes #162901. r? @JonathanBrouwer

…uwer Rollup of 20 pull requests Successful merges: - rust-lang/rust#163483 (Bump bootstrap compiler to 1.100.0 beta) - rust-lang/rust#161380 (only rerun const eval in next-solver if the const actually references opaques) - rust-lang/rust#162900 (Some refactorings around metadata encoding) - rust-lang/rust#163461 (Improve diagnostic deduplication) - rust-lang/rust#163580 (Provide better doc code example for `UnixDatagram::bind_addr` and `UnixListener::bind_addr`) - rust-lang/rust#163584 ([triagebot] Ping me for debugger visualizer changes) - rust-lang/rust#159021 (windows-gnu: enable native TLS) - rust-lang/rust#161467 (wfcheck: name the item that discards an unused type parameter) - rust-lang/rust#162618 (trait_selection: Preserve eager normalization failures) - rust-lang/rust#162904 (Fix ICE for ambiguous candidates on method probing) - rust-lang/rust#163064 (Avoid computing overflowed goal chains for crate dependencies) - rust-lang/rust#163281 (Add `f16` inline ASM support to `spirv.rs`) - rust-lang/rust#163314 (move `#[macro_export]` on declarative macro check to `rustc_attr_parsing`) - rust-lang/rust#163360 ([rustdoc] Correctly handle rustc_allow_incoherent_impl on primitive methods) - rust-lang/rust#163385 (GVN transmutes of Immediate::Uninit to Immediate::Uninit) - rust-lang/rust#163405 (Remove some #[linkage] options) - rust-lang/rust#163530 (`const impl PartialEq` for `f16b`) - rust-lang/rust#163581 (do not suggest precise capturing when the opaque span is in a macro expansion) - rust-lang/rust#163590 (Make `AllocatorNightly` less clever) - rust-lang/rust#163599 (Add union pattern reference change to relnotes)

rustbot assigned JonathanBrouwer Sep 28, 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 Sep 28, 2026