Use `LocalDefId` as an index in metadata encoding by aerooneqq · Pull Request #163321 · rust-lang/rust

aerooneqq · 2026-09-25T10:54:13Z

The goal of this PR to eliminate encoding of a raw DefIndex, instead we should encode something (LocalDefId) that certainly indicates that index belongs to the local crate. The implementation of DefIndex encoding should always panic to prevent accidental remappings of non-local DefIndexes in #162809.

So the plan is as follows:

Use LocalDefId as a writing index in tables for metadata encoding, use LocalDefId instead of DefIndex everywhere, specialize encode/decode methods to correctly process it,
Replace implementation of encode_def_index in EncodeContext with panic, so we never remap and encode def index,
Make tables' keys two-sided: we can read and write using different index types, in this case we will write using LocalDefId and read using DefIndex (done in Allow using different index types when reading and writing to tables #163447).

Blocked by #162900.

r? @petrochenkov

petrochenkov · 2026-09-25T11:52:04Z

@bors try @rust-timer queue

Create `LocalDefIndex` for metadata encoding

rust-bors · 2026-09-25T12:50:30Z

☀️ Try build successful (CI)
Build commit: 2fa5a47 (2fa5a472bd28122b86b69706e673d2b3704e5c27)
Base parent: 4e701dc (4e701dc6ba63a40c908a173df269a55e1fd6297e)

rust-timer · 2026-09-25T13:48:43Z

Finished benchmarking commit (2fa5a47): comparison URL.

Overall result: ❌ regressions - 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

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)	0.8%	[0.8%, 0.9%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -0.5%)

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)	-0.5%	[-0.5%, -0.5%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -1.6%, secondary 3.8%)

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)	3.8%	[3.8%, 3.8%]	1
Improvements ✅ (primary)	-1.6%	[-1.6%, -1.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.6%	[-1.6%, -1.6%]	1

Binary size

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

Bootstrap: 488.984s -> 488.935s (-0.01%)
Artifact size: 406.31 MiB -> 406.32 MiB (0.00%)

@petrochenkov

…ata, r=petrochenkov Allow using different index types when reading and writing to tables Make tables of metadata two-sided: one can write with one index type and read with another, as long as both those types are indexes. That will be used in rust-lang#163321 when we will have `LocalDefIndex` or similar type. r? @petrochenkov

@petrochenkov

…ata, r=petrochenkov Allow using different index types when reading and writing to tables Make tables of metadata two-sided: one can write with one index type and read with another, as long as both those types are indexes. That will be used in rust-lang#163321 when we will have `LocalDefIndex` or similar type. r? @petrochenkov

@petrochenkov

…ata, r=petrochenkov Allow using different index types when reading and writing to tables Make tables of metadata two-sided: one can write with one index type and read with another, as long as both those types are indexes. That will be used in rust-lang#163321 when we will have `LocalDefIndex` or similar type. r? @petrochenkov

@petrochenkov

…ata, r=petrochenkov Allow using different index types when reading and writing to tables Make tables of metadata two-sided: one can write with one index type and read with another, as long as both those types are indexes. That will be used in rust-lang#163321 when we will have `LocalDefIndex` or similar type. r? @petrochenkov

aerooneqq · 2026-09-29T11:44:50Z

After some experiments with LocalDefIndex and LocalDefId it seems that LocalDefId is a better option, so now waiting for #162900 to merge and after that this will be ready.

rust-bors · 2026-10-07T06:54:14Z

This pull request was unapproved.

View changes since this unapproval

aerooneqq · 2026-10-07T08:12:59Z

Removed default decode_local_def_id impl and specialization for DefKey encoding.
@rustbot ready

oli-obk

@bors delegate+

r=me,petrochenkov with changes applied and commits squashed

View changes since this review

rust-bors · 2026-10-07T08:27:14Z

✌️ @aerooneqq, you can now approve this pull request!

If @oli-obk told you to "r=me" after making some further change, then please make that change and post @bors r=oli-obk.

View changes since this delegation.

rustbot · 2026-10-07T08:27:17Z

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

aerooneqq · 2026-10-07T08:36:44Z

@bors squash msg="Use LocalDefId instead of DefIndex in metadata encoding"

rust-bors · 2026-10-07T08:37:08Z

🔨 3 commits were squashed into b92cb3e.

aerooneqq · 2026-10-07T08:38:47Z

@bors r=oli-obk,petrochenkov

rust-bors · 2026-10-07T08:38:51Z

📌 Commit b92cb3e has been tentatively approved by oli-obk,petrochenkov

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

@petrochenkov

…nkov Use `LocalDefId` as an index in metadata encoding The goal of this PR to eliminate encoding of a raw `DefIndex`, instead we should encode something (`LocalDefId`) that certainly indicates that index belongs to the local crate. The implementation of `DefIndex` encoding should always panic to prevent accidental remappings of non-local `DefIndex`es in #162809. So the plan is as follows: - Use `LocalDefId` as a writing index in tables for metadata encoding, use `LocalDefId` instead of `DefIndex` everywhere, specialize encode/decode methods to correctly process it, - Replace implementation of `encode_def_index` in `EncodeContext` with panic, so we never remap and encode def index, - Make tables' keys two-sided: we can read and write using different index types, in this case we will write using `LocalDefId` and read using `DefIndex` (done in #163447). Blocked by #162900. r? @petrochenkov

rust-log-analyzer · 2026-10-08T07:25:11Z

The job dist-aarch64-freebsd failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

rust-bors · 2026-10-08T07:26:06Z

💔 Test for fcbcce8 failed: CI. Failed job:

auto - dist-aarch64-freebsd (web logs, enhanced plaintext logs)

JonathanBrouwer · 2026-10-08T07:59:40Z

@bors retry

rust-bors · 2026-10-08T10:25:16Z

⌛ Testing commit b92cb3e with merge 65efa19...

Workflow: https://github.com/rust-lang/rust/actions/runs/37763351175

@petrochenkov

…nkov Use `LocalDefId` as an index in metadata encoding The goal of this PR to eliminate encoding of a raw `DefIndex`, instead we should encode something (`LocalDefId`) that certainly indicates that index belongs to the local crate. The implementation of `DefIndex` encoding should always panic to prevent accidental remappings of non-local `DefIndex`es in #162809. So the plan is as follows: - Use `LocalDefId` as a writing index in tables for metadata encoding, use `LocalDefId` instead of `DefIndex` everywhere, specialize encode/decode methods to correctly process it, - Replace implementation of `encode_def_index` in `EncodeContext` with panic, so we never remap and encode def index, - Make tables' keys two-sided: we can read and write using different index types, in this case we will write using `LocalDefId` and read using `DefIndex` (done in #163447). Blocked by #162900. r? @petrochenkov

rustbot assigned petrochenkov Sep 25, 2026

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 25, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 25, 2026

Auto merge of #163321 - aerooneqq:local-def-index, r=<try>

2fa5a47

Create `LocalDefIndex` for metadata encoding

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 25, 2026

aerooneqq force-pushed the local-def-index branch from 3b195e0 to 2b5f330 Compare September 28, 2026 10:37

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aerooneqq force-pushed the local-def-index branch from 2b5f330 to 012aa52 Compare September 28, 2026 11:03

petrochenkov mentioned this pull request Sep 28, 2026

Promoting Parallel Front End rust-lang/goals#121

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aerooneqq mentioned this pull request Sep 28, 2026

Allow using different index types when reading and writing to tables #163447

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Comment thread compiler/rustc_hir_id/src/definitions.rs

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aerooneqq force-pushed the local-def-index branch 2 times, most recently from d3319be to 68c2396 Compare September 29, 2026 10:11

rustbot added the A-query-system Area: The rustc query system (https://rustc-dev-guide.rust-lang.org/query.html) label Sep 29, 2026

aerooneqq force-pushed the local-def-index branch from 68c2396 to 52b92f8 Compare September 29, 2026 10:15

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aerooneqq changed the title ~~Create LocalDefIndex for metadata encoding~~ Use LocalDefId as an index in metadata encoding Sep 29, 2026

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 Oct 7, 2026

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Use LocalDefId instead of DefIndex in metadata encoding

b92cb3e

rust-bors Bot force-pushed the local-def-index branch from a32d487 to b92cb3e Compare October 7, 2026 08:37

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aerooneqq mentioned this pull request Oct 7, 2026

parallel compiler: generics_of encoding not reproducible #163878

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Overall result: ❌ regressions - no action needed

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