THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data #150788

Zalathar · 2026-01-08T02:29:39Z

This PR removes the AscribeUserType and ExpandedConstant variants from thir::PatKind, and replaces them with an Option<Box<PatExtra>> field attached to every thir::Pat.

Why remove these variants?

Unlike other THIR pattern kinds, these variants are mere “wrappers” that exist to attach some additional information to an underlying pattern node.

There are several places where code that consumes THIR patterns needs to carefully “unpeel” any wrapper nodes, in order to match on the underlying pattern. This is clunky, and easy to forget to do, especially since it's not always obvious where the wrapper nodes can and can't appear.

Attaching the data to an optional per-node field makes it easier for consuming code to simply ignore the extra data when it is not relevant.

(One downside is that it is now easier to accidentally ignore the extra data when it is relevant, but I think that's generally a favourable tradeoff.)

Impact

After this change, THIR pattern trees should be “logically identical” to the previous THIR pattern trees, in the sense that information that was carried by wrapper nodes should now be directly attached to the non-wrapper nodes that were being wrapped. Types and spans associated with THIR pattern nodes should (hopefully!) still be accurate.

There should be no change to the output of THIR-based checks or MIR building.

rustbot · 2026-01-08T02:29:42Z

Some changes occurred in exhaustiveness checking

cc @Nadrieril

Some changes occurred in match lowering

cc @Nadrieril

Some changes occurred in match checking

cc @Nadrieril

rustbot · 2026-01-08T02:29:44Z

r? @davidtwco

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Zalathar · 2026-01-08T02:31:51Z

I don't expect any measurable perf impact, but let's check.

@bors try @rust-timer queue

THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data

rust-bors · 2026-01-08T04:55:04Z

☀️ Try build successful (CI)
Build commit: aaf4488 (aaf4488e6255bbdeeff8e4c003177b5941dddfa0, parent: fecb335cbad3d84ef3da39191ba094e6c726a5b4)

rust-timer · 2026-01-08T05:35:46Z

Finished benchmarking commit (aaf4488): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.2%, secondary 2.6%)

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

	mean	range	count
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-1.6%	[-1.6%, -1.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-1.6%, 2.0%]	2

Cycles

Results (primary 3.0%, secondary -3.1%)

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

	mean	range	count
Regressions ❌ (primary)	3.0%	[2.3%, 3.6%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.1%	[-3.4%, -2.9%]	2
All ❌✅ (primary)	3.0%	[2.3%, 3.6%]	2

Binary size

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

Bootstrap: 473.64s -> 475.633s (0.42%)
Artifact size: 390.86 MiB -> 390.86 MiB (-0.00%)

Zalathar · 2026-01-08T06:34:43Z

Perf changes look like the usual noise to me.

@bors rollup=maybe

rustbot · 2026-01-09T05:29:10Z

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.

This will allow extra data to be attached to the `Pat` before it is returned.

Nadrieril · 2026-01-10T04:53:56Z

Nice, those wrappers were indeed a hassle to deal with.

r? me

@bors r+

rust-bors · 2026-01-10T04:54:00Z

📌 Commit 8516c64 has been approved by Nadrieril

It is now in the queue for this repository.

THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data This PR removes the `AscribeUserType` and `ExpandedConstant` variants from `thir::PatKind`, and replaces them with an `Option<Box<PatExtra>>` field attached to every `thir::Pat`. ### Why remove these variants? Unlike other THIR pattern kinds, these variants are mere “wrappers” that exist to attach some additional information to an underlying pattern node. There are several places where code that consumes THIR patterns needs to carefully “unpeel” any wrapper nodes, in order to match on the underlying pattern. This is clunky, and easy to forget to do, especially since it's not always obvious where the wrapper nodes can and can't appear. Attaching the data to an optional per-node field makes it easier for consuming code to simply ignore the extra data when it is not relevant. (One downside is that it is now easier to accidentally ignore the extra data when it *is* relevant, but I think that's generally a favourable tradeoff.) ### Impact After this change, THIR pattern trees should be “logically identical” to the previous THIR pattern trees, in the sense that information that was carried by wrapper nodes should now be directly attached to the non-wrapper nodes that were being wrapped. Types and spans associated with THIR pattern nodes should (hopefully!) still be accurate. There should be no change to the output of THIR-based checks or MIR building.

@ghost

Rollup of 11 pull requests Successful merges: - #148196 (Implement create_dir_all() to operate iteratively instead of recursively) - #150494 ( Fix dso_local for external statics with linkage) - #150788 (THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data) - #150799 (Fix ICE: can't type-check body of DefId for issue #148729) - #150804 (Remove std_detect_file_io and std_detect_dlsym_getauxval features) - #150852 (std: sys: fs: uefi: Implement File::write) - #150871 (Use f64 NaN in documentation instead of sqrt(-1.0)) - #150878 (Emit an error for linking staticlibs on BPF) - #150911 (Add missing documentation for globs feature) - #150913 (compiler: Forward attributes to eii-expanded macros) - #150916 (Once again, reorganize the EII tests a bit) r? @ghost

@ghost

Rollup of 12 pull requests Successful merges: - #150947 (alloctests: Don't run the longer partial-sort tests under Miri) - #148196 (Implement create_dir_all() to operate iteratively instead of recursively) - #150494 ( Fix dso_local for external statics with linkage) - #150788 (THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data) - #150799 (Fix ICE: can't type-check body of DefId for issue #148729) - #150804 (Remove std_detect_file_io and std_detect_dlsym_getauxval features) - #150852 (std: sys: fs: uefi: Implement File::write) - #150871 (Use f64 NaN in documentation instead of sqrt(-1.0)) - #150878 (Emit an error for linking staticlibs on BPF) - #150911 (Add missing documentation for globs feature) - #150913 (compiler: Forward attributes to eii-expanded macros) - #150916 (Once again, reorganize the EII tests a bit) r? @ghost

Rollup merge of #150788 - thir-pat, r=Nadrieril THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data This PR removes the `AscribeUserType` and `ExpandedConstant` variants from `thir::PatKind`, and replaces them with an `Option<Box<PatExtra>>` field attached to every `thir::Pat`. ### Why remove these variants? Unlike other THIR pattern kinds, these variants are mere “wrappers” that exist to attach some additional information to an underlying pattern node. There are several places where code that consumes THIR patterns needs to carefully “unpeel” any wrapper nodes, in order to match on the underlying pattern. This is clunky, and easy to forget to do, especially since it's not always obvious where the wrapper nodes can and can't appear. Attaching the data to an optional per-node field makes it easier for consuming code to simply ignore the extra data when it is not relevant. (One downside is that it is now easier to accidentally ignore the extra data when it *is* relevant, but I think that's generally a favourable tradeoff.) ### Impact After this change, THIR pattern trees should be “logically identical” to the previous THIR pattern trees, in the sense that information that was carried by wrapper nodes should now be directly attached to the non-wrapper nodes that were being wrapped. Types and spans associated with THIR pattern nodes should (hopefully!) still be accurate. There should be no change to the output of THIR-based checks or MIR building.

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 Jan 8, 2026

rustbot assigned davidtwco Jan 8, 2026

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rust-bors bot added a commit that referenced this pull request Jan 8, 2026

Auto merge of #150788 - Zalathar:thir-pat, r=<try>

aaf4488

THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 8, 2026

Zalathar mentioned this pull request Jan 8, 2026

mir_build: Remove several remnants of #![feature(inline_const_pat)] #150498

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 8, 2026

Zalathar force-pushed the thir-pat branch from 5bdc19a to 9c96cd1 Compare January 9, 2026 05:29

Zalathar added 4 commits January 9, 2026 16:32

Prepare for thir::Pat nodes having multiple user-type ascriptions

0495a73

Prefer to return Box<thir::Pat> instead of thir::PatKind

f85b898

This will allow extra data to be attached to the `Pat` before it is returned.

Initial plumbing for thir::PatExtra

bd77048

Replace AscribeUserType and ExpandedConstant with per-node data

8516c64

Zalathar force-pushed the thir-pat branch from 9c96cd1 to 8516c64 Compare January 9, 2026 05:47

rust-bors bot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Jan 10, 2026

rustbot assigned Nadrieril Jan 10, 2026

rust-bors bot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 10, 2026

rustbot unassigned davidtwco Jan 10, 2026

Zalathar mentioned this pull request Jan 10, 2026

Rollup of 15 pull requests #150914

Closed

matthiaskrgr mentioned this pull request Jan 10, 2026

Rollup of 11 pull requests #150923

Closed

JonathanBrouwer mentioned this pull request Jan 10, 2026

Rollup of 14 pull requests #150924

Closed

Zalathar mentioned this pull request Jan 11, 2026

Rollup of 12 pull requests #150951

Merged

rust-bors bot merged commit 8a5c66e into rust-lang:main Jan 11, 2026
11 checks passed

rustbot added this to the 1.94.0 milestone Jan 11, 2026

Zalathar deleted the thir-pat branch January 11, 2026 06:48

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THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data #150788

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Zalathar commented Jan 8, 2026

Why remove these variants?

Impact

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Overall result: ❌✅ regressions and improvements - no action needed

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THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data #150788

THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data #150788