feat(config): Add build.profile, install.profile by epage · Pull Request #17215 · rust-lang/cargo

epage · 2026-07-14T20:23:21Z

What does this PR try to resolve?

This adds build.profile to smooth out the transition for #15931 by allowing users to change to the debug profile by default.

This also adds install.profile

to further clarify that build.profile does not apply
to allow users to create a custom profile for their tools without affecting the rest of their development

How to test and review this PR?

This is part of #15931

dev profile changes are deferred for 1+ releases

How should test and bench be handled? We went with cargo test having build.profile override the default test so users will get consistent behavior between cargo build and cargo test. Alternatively, we could have told users to set profile.test.inherits = "debug". Changing the inheritance is even less obvious though it is likely to run into fewer issues if projects change the test profile.

rustbot · 2026-07-14T20:23:25Z

r? @weihanglo

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Owners of files modified in this PR: @ehuss, @epage, @weihanglo
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### What does this PR try to resolve? Key points: - It inherits from `dev` - Conceptually, debugging is part of the development process - The hope is this will smooth out the transition for people - `cargo install --debug` now uses `debug` instead of `dev` - `debug` changes nothing from `dev` right now. `dev` will evolve in the future (with `debug` overriding those values to leave it effectively unchanged) but that is deferred out to offer a transition period where `debug` can be used without but isn't required for debugging as people deal with multiple Rust versions. This also shrinks the change and decouples what the conversation around what the settings should be. - `dev` still uses `target/debug`: this does not change any calculation for the transition cost and any conflicts between the profiles should mostly be in the artifact-dir (which are just hard links), especially once the new build layout lands - `--dev`/`--debug` flags are deferred out, needing more evaluation to decide if they are worth it See also https://github.com/rust-lang/cargo-team/blob/main/meetings/sync-meeting/2026-07-14.md#splitting-dev-and-debug-profiles ### How to test and review this PR? This is part of #15931 - `build.profile` will be a follow up (#17215) - `dev` profile changes are deferred for 1+ releases

weihanglo

This needs FCP

View changes since this review

weihanglo · 2026-08-19T18:50:42Z

How should test and bench be handled? We went with cargo test having build.profile override the default test so users will get consistent behavior between cargo build and cargo test. Alternatively, we could have told users to set profile.test.inherits = "debug". Changing the inheritance is even less obvious though it is likely to run into fewer issues if projects change the test profile.

How do we communicate and document this? Do we need to decide before proceeding?

View changes since the review

My assumption is that this will behave as people expect and the only documentation burden is on the fields. If there is something I'm overlooking, let me know!

Commented in other threads.

weihanglo · 2026-08-21T21:01:15Z

+* Default: `"dev"`
+* Environment: `CARGO_BUILD_PROFILE`
+
+The default [profile] to compile with.


I think this might need to be expanded. For example, explaing what scope it apply to, and the relationship with bench and test profiles. The tricky part is the default is not always dev for different scope. We should point that one.

(It's okay to be a bit vague, if we plan to change it in the future)

View changes since the review

I'm cautious about getting into test and bench profiles because I expect most people don't know about them and could cause more confusion.

Unsure how to handle the install/bench nuance. “for development tasks"?

I'm cautious about getting into test and bench profiles because I expect most people don't know about them and could cause more confusion.

I got a different impression that because people tend to tweak profile.test profile for either a faster test execution time, or just want to coerce that to match release profile in order to reuse cache.

For bench, yeah people just don't care about it, as keeping the same as release is pretty reasonable.

I've at least changed the default. Still a bit unsure what else to say here.

weihanglo · 2026-08-21T21:01:36Z

Commented in other threads.

weihanglo · 2026-08-31T23:47:54Z

Before kicking off the FCP, would you mind sharing the complete transition plan with this feature?

rustbot · 2026-09-02T23:59:26Z

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.

epage · 2026-09-03T00:01:18Z

Before kicking off the FCP, would you mind sharing the complete transition plan with this feature?

Not too sure what more you are looking for. The PR description talks about this easing the transition to the split dev/debug profiles by allowing people to choose to switch to debug exclusively to get the old behavior back.

weihanglo · 2026-09-03T00:24:39Z

Before kicking off the FCP, would you mind sharing the complete transition plan with this feature?

Not too sure what more you are looking for. The PR description talks about this easing the transition to the split dev/debug profiles by allowing people to choose to switch to debug exclusively to get the old behavior back.

I actually forgot what I was looking for.

@rfcbot fcp merge

This insta-stabilizes two new configs: build.profile and install.profile. See PR description and the proposed doc update for details.

rust-rfcbot · 2026-09-03T00:24:42Z

@weihanglo has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

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rustbot assigned weihanglo Jul 14, 2026

epage marked this pull request as draft July 14, 2026 20:23

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 14, 2026

epage mentioned this pull request Jul 14, 2026

feat(profile): Add built-in profile debug #17214

Merged

epage force-pushed the config-profile branch 4 times, most recently from 1127b1e to 2add9e9 Compare July 16, 2026 14:08