Enable build-dir layout v2 on nightly by default by ranger-ross · Pull Request #17258 · rust-lang/cargo

ranger-ross · 2026-07-23T12:09:11Z

What does this PR try to resolve?

This PR enables the new build-dir on nightly by default.

The majority of changes were taken/adapted from #16807

Tracked in #15010

How to test and review this PR?

Same as the original stabilization PR.
The notable changes are:

A handful of tests may recompile crates when test's p.cargo() use a mixture of stable and nightly
- For checksum freshness specifically, I enabled nightly on all of the p.cargo() as the tests are specifically testing for rebuilds.

rustbot · 2026-07-23T17:01:05Z

r? @epage

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Owners of files modified in this PR: @epage, @weihanglo
@epage, @weihanglo expanded to epage, weihanglo
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ranger-ross · 2026-07-23T17:05:39Z

Marking this as ready to review.

I spent some time trying to reproduce sccache failures with argfiles on windows, and couldn't get a failure. (tested on zed again, with __CARGO_TEST_FORCE_ARGFILE but it just worked)
I still wanna tinker on it some more, but I think it should at least be okay on the happy path which makes me more comfortable at least trying it on nightly.

epage · 2026-07-23T19:17:24Z

        /// gating unstable functionality to Cargo. These flags are only available on
        /// the nightly channel of Cargo.
-        #[derive(Default, Debug, Deserialize)]
+        #[derive(Debug, Deserialize)]


Is there a way to do this without removing Default? This makes it more invasive to undo and redo.

View changes since the review

Ehh its get awkward to avoid, specially due to #[serde(default)].

I split out a refactor commit and manually impl'd Default in the macro to reduce the bloat and need to update the Default impl when adding new features.
It's still not ideal but maybe a bit better?

rustbot · 2026-07-24T01:50:38Z

This PR was rebased onto a different master 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.

weihanglo · 2026-07-24T03:35:25Z

+                // Defaults to enabled on nightly unless explicitly opted out.
+                let c = &channel();
+                unstable.build_dir_new_layout =
+                    (c == "nightly" || c == "dev") && !is_new_build_dir_layout_opt_out();


Josh (or someone I don't remember) has mentioned there are people using stable toolchains but enable RUSTC_BOOTSTRAP=1 for enabling some unstable features. Should we avoid enable it if the toolchain is stable/beta?

View changes since the review

It was @Mark-Simulacrum that mentioned it here.
Yeah, I think that makes sense. When that comment was made it kind of went over my head (we have so many bespoke config options 😆)

If I understand it correctly, enabling RUSTC_BOOTSTRAP=1 will result in Cargo using the dev channel.

cargo/src/workspace/features.rs

Lines 1602 to 1605 in 5b6fca7

if let Ok(staging) = env::var("RUSTC_BOOTSTRAP") {

if staging == "1" {

return "dev".to_string();

}

So the logic should be updated to

let is_rustc_bootstrap = env::var("RUSTC_BOOTSTRAP").map(|o| &o == "1"); unstable.build_dir_new_layout = (c == "nightly" || c == "dev") && !is_new_build_dir_layout_opt_out() && !is_rustc_bootstrap;

Will this cause an issues in bootstrap? I guess not since bootstrap explicitly passes -Zbuild-dir-new-layout and this is just for the defaults.

Does that all sound correct?

Either that or just something like crate::version().release_channel == Some("nightly" | "dev")?

ah yeah that should work. I wish I had thought of this before updating all of the tests again. 🫠

Since this skips __CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS none of the tests need to be updated

weihanglo

Thanks

View changes since this review

Cargo enables build-dir layout v2 by default on nightly (rust-lang/cargo#17258). Intermediate build artifacts no longer live in `<target-dir>/<triple>/<profile>/deps/` but in per-unit `build/<pkg>/<hash>/out/` directories. Search the target directory recursively instead of hardcoding the artifact location, so these tests pass under both the old and the new layout.

Cargo enables build-dir layout v2 by default on nightly (rust-lang/cargo#17258). Intermediate build artifacts no longer live in `<target-dir>/<triple>/<profile>/deps/` but in per-unit `build/<pkg>/<hash>/out/` directories.

Update cargo submodule 17 commits in 3efb1f477e99b42974b982d939fd100303cdf7db..54b61f13a4eea47ec3ee95237d4107976d7909ed 2026-07-17 23:53:19 +0000 to 2026-07-24 13:23:18 +0000 - chore: bump to `libgit2-sys@0.18.7+1.9.6` (rust-lang/cargo#17259) - Enable build-dir layout v2 on nightly by default (rust-lang/cargo#17258) - fix(path): clarify error message when path dependency has wrong package (rust-lang/cargo#16927) - fix(toml): warn on hyphenated lint names and duplicates (rust-lang/cargo#17051) - fix(test): gate trim-paths tests on split debuginfo support (rust-lang/cargo#17256) - test(git): Explicitly test for git injection attacks (rust-lang/cargo#17253) - fix(git): Suggest libgit2 if git-cli fails (rust-lang/cargo#17252) - fix(diag): bound transitive unused dependency traversal (rust-lang/cargo#17251) - fix(git): Hide git fetch output without progress (rust-lang/cargo#17243) - revert(lint): Remove `new_implicit_minimum_version_req` (rust-lang/cargo#16321) (rust-lang/cargo#17249) - fix: Add haiku's dylib path (rust-lang/cargo#17248) - Zsh completion: Add `-p` and `--package` flags for `cargo add` (rust-lang/cargo#17247) - refactor(source): Clarify the name of the remote git registry (rust-lang/cargo#17240) - fix(timings): only report units the job queue actually ran (rust-lang/cargo#17238) - Do not include proc-macro deps in rustc search path args (rust-lang/cargo#17236) - chore(deps): update cargo-semver-checks to v0.49.0 (rust-lang/cargo#17237) - rustdoc: rename the doc parts metadata params (rust-lang/cargo#17234) r? ghost

rustbot added the A-unstable Area: nightly unstable support label Jul 23, 2026

ranger-ross force-pushed the enable-build-dir-layout-nightly branch 7 times, most recently from 3f297a4 to d34b4b3 Compare July 23, 2026 15:27

ranger-ross marked this pull request as ready for review July 23, 2026 17:01

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 23, 2026

rustbot assigned epage Jul 23, 2026

epage reviewed Jul 23, 2026

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ranger-ross force-pushed the enable-build-dir-layout-nightly branch from d34b4b3 to 4bb796b Compare July 24, 2026 01:49

rustbot added the A-dependency-resolution Area: dependency resolution and the resolver label Jul 24, 2026

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refactor: Don't derive Default on CliUnstable

c9d7310

ranger-ross force-pushed the enable-build-dir-layout-nightly branch from 4bb796b to 7b66084 Compare July 24, 2026 01:50

weihanglo reviewed Jul 24, 2026

View reviewed changes

feat: Enable build-dir layout v2 on nightly

d035da6

ranger-ross force-pushed the enable-build-dir-layout-nightly branch from 7b66084 to d035da6 Compare July 24, 2026 04:53

weihanglo approved these changes Jul 24, 2026

View reviewed changes

weihanglo added this pull request to the merge queue Jul 24, 2026

Merged via the queue into rust-lang:master with commit 95303e6 Jul 24, 2026
29 checks passed

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 24, 2026

weihanglo mentioned this pull request Jul 24, 2026

Update cargo submodule rust-lang/rust#159857

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Enable build-dir layout v2 on nightly by default#17258

Enable build-dir layout v2 on nightly by default#17258
weihanglo merged 2 commits into
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ranger-ross:enable-build-dir-layout-nightly

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	if let Ok(staging) = env::var("RUSTC_BOOTSTRAP") {
	if staging == "1" {
	return "dev".to_string();
	}

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ranger-ross commented Jul 23, 2026

What does this PR try to resolve?

How to test and review this PR?

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