Rename `lazy_type_alias` feature gate to `checked_type_aliases` by josetorrs · Pull Request #158758 · rust-lang/rust

josetorrs · 2026-07-04T02:37:36Z

there's not an open issue for it, though happy to create one if desired, but this is the zulip thread. basically just did a cmd+shift+F on VSCode

r? @lcnr

cc: @BoxyUwU

josetorrs · 2026-07-04T02:44:40Z

+#![feature(checked_free_type_aliases)]



for these, the directory is tests/ui/lazy-type-alias/... but I wasn't sure if I should rename this TBH

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Ideally, yes, since I named this directory after the feature name. It currently exercises both the "checkedness" and the "laziness" ("retainedness") of LTA.

rustbot · 2026-07-04T03:13:44Z

HIR ty lowering was modified

cc @fmease

rustc-dev-guide is developed in its own repository. If possible, consider making this change to rust-lang/rustc-dev-guide instead.

cc @BoxyUwU, @tshepang

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

fmease · 2026-07-04T07:34:57Z

            let ty = tcx.type_of(def_id).instantiate_identity();
            let span = tcx.def_span(def_id);
-            if tcx.type_alias_is_lazy(def_id) {
+            if tcx.type_alias_is_free(def_id) {


All type aliases are free, that's their very nature. This function is returning (1) whether to check the type alias for well-formedness (2) whether to lower its use sites to an alias type instead of eagerly expanding them to the aliased type during HIR ty lowering.

This should probably say type_alias_is_checked.

If I split this feature into unchecked & checked in the future I guess I need to come up with a new way of expressing eager vs. lazy, maybe unretained vs. retained 🤔

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fmease · 2026-07-04T08:18:44Z

                }
                self.check_type_no_bounds(bounds, "this context");

-                if self.features.lazy_type_alias() {


(Personally speaking, I'm voting for checked_type_aliases, cc #t-types/lazy-type-alias > name bikeshed @ 💬)

View changes since the review

let's wait ~2-3 days on https://rust-lang.zulipchat.com/#narrow/channel/609192-t-types.2Flazy-type-alias/topic/name.20bikeshed/near/608438367

the poll is unanimous with renaming to checked_type_alias. I think I should be good with changing it along with renaming the test directory per #158758 (comment) to tests/ui/checked-type-alias/... (?) and this rename

I didn't vote in the poll as I didn't want to pretend I 100% fully understood everything haha

fmease · 2026-07-04T08:20:59Z

+#![feature(checked_free_type_aliases)]



Ideally, yes, since I named this directory after the feature name. It currently exercises both the "checkedness" and the "laziness" ("retainedness") of LTA.

ChayimFriedman2 · 2026-07-04T17:40:26Z

        deny_since: None,
    },
    Lint {
-        label: "lazy_type_alias",


Please do not change this file. It is auto-generated.

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Could you please remove the changes to this file completely, e.g., by interactive rebase-editing the commit 49c4377 or squashing commits rather than adding another commit undoing it?
We do sync this repository with rust-lang/rust-analyzer bidirectionally and the cleaner history helps it being done automatically without hassle 😄

rustbot · 2026-07-04T17:40:34Z

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

rustbot · 2026-07-13T14:19:12Z

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.

…t directory

josetorrs · 2026-07-13T19:20:56Z

@rustbot ready

rust-bors · 2026-07-15T03:22:47Z

☔ The latest upstream changes (presumably #159293) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

lcnr

r=me after minor issue

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lcnr · 2026-07-15T06:25:34Z


+## `tests/ui/checked-type-alias/`
+
+Tests for `#![feature(checked_type_aliases)]`. See [Tracking issue for lazy type aliases #112792](https://github.com/rust-lang/rust/issues/112792).


Suggested change

Tests for `#![feature(checked_type_aliases)]`. See [Tracking issue for lazy type aliases #112792](https://github.com/rust-lang/rust/issues/112792).

Tests for `#![feature(checked_type_aliases)]`. See [Tracking issue for checked type aliases](https://github.com/rust-lang/rust/issues/112792).

lcnr · 2026-07-15T06:26:20Z

also needs a rebase

rustbot assigned lcnr Jul 4, 2026

josetorrs commented Jul 4, 2026

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josetorrs changed the title ~~Rename lazy_type_alias to checked_free_type_aliases~~ Rename lazy_type_alias feature gate to checked_free_type_aliases Jul 4, 2026

josetorrs marked this pull request as ready for review July 4, 2026 03:13

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 Jul 4, 2026

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rustbot 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 Jul 4, 2026

josetorrs force-pushed the rename-lazy-type-alias branch from 06051f4 to e47a599 Compare July 7, 2026 02:04

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ChayimFriedman2 approved these changes Jul 7, 2026

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josetorrs force-pushed the rename-lazy-type-alias branch from e47a599 to d6a0757 Compare July 7, 2026 02:09

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josetorrs force-pushed the rename-lazy-type-alias branch from d6a0757 to c3cbfbe Compare July 7, 2026 12:18

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rename from lazy_type_alias to checked_free_type_alias

583deec

josetorrs force-pushed the rename-lazy-type-alias branch from c3cbfbe to 583deec Compare July 13, 2026 14:19

rename from free_lazy_type_alias to checked_type_alias, including tes…

2e8f8a4

…t directory

josetorrs changed the title ~~Rename lazy_type_alias feature gate to checked_free_type_aliases~~ Rename lazy_type_alias feature gate to checked_type_aliases Jul 13, 2026

rename from type_alias_is_lazy to type_alias_is_checked

a8d4284

josetorrs force-pushed the rename-lazy-type-alias branch from 6e62d29 to a8d4284 Compare July 13, 2026 15:59

fixing some typos

0d8bbee

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 Jul 13, 2026

lcnr reviewed Jul 15, 2026

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		## `tests/ui/checked-type-alias/`

		Tests for `#![feature(checked_type_aliases)]`. See [Tracking issue for lazy type aliases #112792](https://github.com/rust-lang/rust/issues/112792).

		#![feature(checked_free_type_aliases)]

		#![feature(checked_free_type_aliases)]

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