Clean up AST visitor some more by nnethercote · Pull Request #162315 · rust-lang/rust

nnethercote · 2026-09-04T23:07:57Z

A sequel to #162226. Details in individual commits.

`visit_test_binder_constraints` is the only `visit_foo` method in `impl_visitable_calling_walkable!` without a corresponding `walk_foo` method in `define_named_walk!`. I confirmed with the original author (khyperia) that this is an unintentional oversight.

There is currently a big list of `visit_*` methods in one macro call and another list of `walk_*` method in another macro call. The previous commit showed these can unintentionally get out of sync. This commit introduces a higher-order macro that puts all the information in a single place. This will make it impossible for the `visit_*` and `walk_*` methods to get out of sync (as we saw in the previous commit). It will also facilitate another cleanup in the next commit.

Currently various `Visitable` impls are defined within functions even though `Visitable` is defined at the top level, which is weird and requires `allow(non_local_definitions)`. This commit uses `for_each_ast_visit_hook` to move them out. It also renames a couple of the existing macros to give them simpler names.

Use `$ty` and `$extra` and `$extra_ty` consistently in macros, rather than `$Ty` and `$ExtraTy` and `$ParamTy`. Also fix some spacing.

They fit the pattern. Also remove `#[inline]` from `impl_visitable_list` for consistency. The visitor is generic so the methods are monomorphized into the calling crate and probably inlined anyway.

The AST visitor code uses `($($extra_ty)?)` which expands to `()` in some cases and `(T)` in others, which requires `allow(unused_parens)` to avoid warnings. This commit splits the two `impl_visitable!` macros into two rules: one for the "no-extra" case and one for the "with-extra" case. There's a small amount of duplication between the two rules but there are multiple advantages. - The `allow(unused_parens)` is removed. - `impl_visitable!` callers can omit the extra param if it's `()`. - When the extra argument might or might not be present, a more standard `$(, $extra: $extra_ty)?` is now used. - No weird `let ($($extra)?) = extra;` destructuring. The `Visitable` derive also gets a tweak to avoid unnecessary parens around extra args.

These macros aren't needed outside the crate.

We can just hardwire `'a` and `Visitor`/`MutVisitor`. This simplifies the inputs for these macros from "leading thing + repeating elements" to just "repeating elements".

A lot of these lists are already almost in alphabetical order.

nnethercote · 2026-09-04T23:08:13Z

LLM disclosure: most of these clean-ups were suggested by an LLM. I made all the code and text changes myself.

nnethercote · 2026-09-04T23:08:57Z

Shouldn't affect perf, but just in case:

@bors try @rust-timer queue

…=<try> Clean up AST visitor some more

rust-bors · 2026-09-05T05:09:39Z

💥 Test timed out after 21600s

nnethercote · 2026-09-05T06:07:54Z

💥 Test timed out after 21600s

Not sure what happened. Let's try again:

@bors try @rust-timer queue

…=<try> Clean up AST visitor some more

rust-bors · 2026-09-05T11:42:13Z

☀️ Try build successful (CI)
Build commit: d804d79 (d804d7975d767ccd03c93b9f34541ae4bc41c8ee)
Base parent: 0ed41eb (0ed41eb4142dda2df61eb1145a312c1a9d62eb56)

rust-timer · 2026-09-05T12:25:39Z

Finished benchmarking commit (d804d79): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@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)	0.2%	[0.2%, 0.3%]	7
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	2
All ❌✅ (primary)	0.2%	[0.2%, 0.3%]	7

Max RSS (memory usage)

Results (primary 2.2%, secondary 6.8%)

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

	mean	range	count
Regressions ❌ (primary)	7.7%	[7.7%, 7.7%]	1
Regressions ❌ (secondary)	6.8%	[6.8%, 6.8%]	1
Improvements ✅ (primary)	-3.3%	[-3.3%, -3.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.2%	[-3.3%, 7.7%]	2

Cycles

Results (secondary -2.0%)

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)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 476.718s -> 480.953s (0.89%)
Artifact size: 403.29 MiB -> 403.40 MiB (0.03%)

nnethercote · 2026-09-05T13:16:56Z

Slight regressions on html5ever. I'll investigate on Monday.

rust-bors · 2026-09-05T13:53:32Z

☔ The latest upstream changes (presumably #162310) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

nnethercote added 9 commits September 5, 2026 07:57

Improve naming consistency

fc96817

Use `$ty` and `$extra` and `$extra_ty` consistently in macros, rather than `$Ty` and `$ExtraTy` and `$ParamTy`. Also fix some spacing.

Use impl_visitable! for the generate_*_fns macros

a83c52f

They fit the pattern. Also remove `#[inline]` from `impl_visitable_list` for consistency. The visitor is generic so the methods are monomorphized into the calling crate and probably inlined anyway.

Avoid #[macro_export]

89f9acb

These macros aren't needed outside the crate.

Don't pass in $Visitor/$lt to various macros

1a276b1

We can just hardwire `'a` and `Visitor`/`MutVisitor`. This simplifies the inputs for these macros from "leading thing + repeating elements" to just "repeating elements".

Use tidy-alphabetical markers on various lists

f9e5acf

A lot of these lists are already almost in alphabetical order.

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 4, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 4, 2026

Auto merge of #162315 - nnethercote:clean-up-AST-visitor-some-more, r…

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…=<try> Clean up AST visitor some more

rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 5, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 5, 2026

Auto merge of #162315 - nnethercote:clean-up-AST-visitor-some-more, r…

d804d79

…=<try> Clean up AST visitor some more

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Sep 5, 2026

nnethercote marked this pull request as draft September 5, 2026 13:16

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Clean up AST visitor some more - #162315

Clean up AST visitor some more#162315
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rust-timer commented Sep 5, 2026

Overall result: ❌✅ regressions and improvements - please read:

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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