Simplify `TypeFreshener` methods. by nnethercote · Pull Request #150239 · rust-lang/rust

nnethercote · 2025-12-22T06:24:05Z

freshen_{ty,const} take a Result and just do a fold if the input is Ok. It's simpler to do those folds at the call site, and only call freshen_{ty,const} in the Err case. That way we can also avoid useless fold operations on the results of new_{int,uint,float}.

Also, make some bug! calls more concise.

r? @lcnr

`freshen_{ty,const}` take a `Result` and just do a fold if the input is `Ok`. It's simpler to do those folds at the call site, and only call `freshen_{ty,const}` in the `Err` case. That way we can also avoid useless fold operations on the results of `new_{int,uint,float}`. Also, make some `bug!` calls more concise.

I have always found this confusingly named, because it creates a new freshener rather than returning an existing one. We can remove it and just use `TypeFreshener::new()` at the two call sites, avoiding this confusion.

lcnr

r=me, but would love for u to look into a related refactor

View changes since this review

Sometimes we freshen using a new `TypeFreshener`, and sometimes we freshen with an existing `TypeFreshener`. For the former we have the method `InferCtxt::freshen`. For the latter we just call `fold_with`. This asymmetry has been confusing to me. This commit removes `InferCtxt::freshen` so that all the freshening sites consistently use `fold_with` and it's obvious if each one is using a new or existing `TypeFreshener`.

Because `fresh_trait_pred` is the name of the field/argument. The `_ref` suffix appears to be a typo, or left over from earlier versions of the code.

It never happens in practice.

lcnr · 2025-12-22T15:18:27Z

    #[inline(never)]
-    fn fold_infer_ty(&mut self, v: ty::InferTy) -> Option<Ty<'tcx>> {
-        match v {
+    fn fold_infer_ty(&mut self, ty: ty::InferTy) -> Option<Ty<'tcx>> {


now always returns Some?

Yes! I have added a commit to remove the Option.

It's no longer needed.

nnethercote · 2025-12-22T21:02:52Z

Thanks for the suggestions, this has ended up much nicer than the first version.

lcnr · 2025-12-23T09:38:48Z

@bors try @rust-timer queue

freshening should be at least somewhat hot?

…=<try> Simplify `TypeFreshener` methods.

nnethercote · 2025-12-23T10:05:52Z

Freshening is definitely hot, but freshening of inference variables is much less so. Local measurements indicated that the perf effects were negligible, but it doesn't hurt to double check.

rust-bors · 2025-12-23T15:42:12Z

💥 Test timed out after 21600s

lcnr · 2025-12-23T20:01:17Z

@bors try

…=<try> Simplify `TypeFreshener` methods.

rust-bors · 2025-12-23T22:15:41Z

☀️ Try build successful (CI)
Build commit: d1d7c44 (d1d7c443a2cb57b25b43cf0031489c133be86cff, parent: 99ff3fbb86658b427f5dd7daaae8db5626a63c26)

rust-timer · 2025-12-23T22:56:33Z

Finished benchmarking commit (d1d7c44): 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)

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

Cycles

Results (primary 2.1%, secondary 2.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[1.7%, 2.6%]	4
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.1%	[1.7%, 2.6%]	4

Binary size

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

Bootstrap: 482.582s -> 480.862s (-0.36%)
Artifact size: 390.35 MiB -> 390.37 MiB (0.00%)

lcnr · 2025-12-30T09:20:54Z

@bors r+ rollup

bors · 2025-12-30T09:20:57Z

📌 Commit ec5e96e has been approved by lcnr

It is now in the queue for this repository.

…uwer Rollup of 2 pull requests Successful merges: - #150239 (Simplify `TypeFreshener` methods.) - #150344 (Cleanup linked list) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #150239 - nnethercote:simplify-TypeFreshener-methods, r=lcnr Simplify `TypeFreshener` methods. `freshen_{ty,const}` take a `Result` and just do a fold if the input is `Ok`. It's simpler to do those folds at the call site, and only call `freshen_{ty,const}` in the `Err` case. That way we can also avoid useless fold operations on the results of `new_{int,uint,float}`. Also, make some `bug!` calls more concise. r? `@lcnr`

rustbot assigned lcnr Dec 22, 2025

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 Dec 22, 2025

Remove InferCtxt::freshener.

1bb9ff0

I have always found this confusingly named, because it creates a new freshener rather than returning an existing one. We can remove it and just use `TypeFreshener::new()` at the two call sites, avoiding this confusion.

lcnr reviewed Dec 22, 2025

View reviewed changes

Comment thread compiler/rustc_infer/src/infer/freshen.rs Outdated

lcnr reviewed Dec 22, 2025

View reviewed changes

nnethercote added 3 commits December 22, 2025 23:32

s/fresh_trait_ref/fresh_trait_pred.

63d30f1

Because `fresh_trait_pred` is the name of the field/argument. The `_ref` suffix appears to be a typo, or left over from earlier versions of the code.

Disallow freshening an already-freshened type/const.

2d10f47

It never happens in practice.

nnethercote force-pushed the simplify-TypeFreshener-methods branch from 0d4649d to 2d10f47 Compare December 22, 2025 12:47

lcnr reviewed Dec 22, 2025

View reviewed changes

Remove Option from fold_infer_ty return type.

ec5e96e

It's no longer needed.

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rust-bors Bot added a commit that referenced this pull request Dec 23, 2025

Auto merge of #150239 - nnethercote:simplify-TypeFreshener-methods, r…

1f5b4d4

…=<try> Simplify `TypeFreshener` methods.

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 23, 2025

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rust-bors Bot added a commit that referenced this pull request Dec 23, 2025

Auto merge of #150239 - nnethercote:simplify-TypeFreshener-methods, r…

d1d7c44

…=<try> Simplify `TypeFreshener` methods.

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 23, 2025

bors 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 Dec 30, 2025

JonathanBrouwer mentioned this pull request Dec 30, 2025

Rollup of 2 pull requests #150503

Merged

bors merged commit be715d4 into rust-lang:main Dec 30, 2025
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rustbot added this to the 1.94.0 milestone Dec 30, 2025

nnethercote deleted the simplify-TypeFreshener-methods branch January 1, 2026 21:41

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rust-timer commented Dec 23, 2025

Overall result: no relevant changes - no action needed

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