cargo clean: Add target directory validation by TanmayArya-1p · Pull Request #16712 · rust-lang/cargo

TanmayArya-1p · 2026-03-05T23:20:32Z

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What does this PR try to resolve?

Fixes #9192

Implements the checks mentioned in this comment

To summarise, when cargo clean is run with a specified target directory:

If a target directory is explicitly passed via --target-dir: check if a valid CACHEDIR.TAG exists in the target directory and hard error otherwise.
In other cases where target directory is specified(via env vars or build config): emit a future incompat warning if the target directory does not contain a valid CACHEDIR.TAG

Tests

I've added 3 sets of unit tests for:

When --target-dir is used explicitly
When target directory is specified via the build config
When target directory is specified via the CARGO_TARGET_DIR env variable

Let me know if there is a case I've missed or if i need to merge multiple tests into a single one.

TanmayArya-1p · 2026-03-05T23:22:38Z

I also noticed that if a file path is passed via --target-dir, it gets deleted without validation. I was wondering if we require checks for this as well?

rustbot · 2026-03-05T23:27:20Z

r? @weihanglo

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The reviewer was selected based on:

Owners of files modified in this PR: @ehuss, @epage, @weihanglo
@ehuss, @epage, @weihanglo expanded to ehuss, epage, weihanglo
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weihanglo

Some nitpicks but general good. Thank you!

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src/cargo/ops/cargo_clean.rs

TanmayArya-1p · 2026-03-06T12:44:44Z

thanks for the review :)
I made a few changes and fixed the things you pointed out, let me know if theres anything else that needs to be changed.

Also I noticed that the CI keeps failing in something totally unrelated. I see it's happening in other PRs as well. Any idea why this is happening?
Edit: Nevermind, I see #16714 addresses this

weihanglo · 2026-03-06T17:09:52Z

Also I noticed that the CI keeps failing in something totally unrelated. I see it's happening in other PRs as well. Any idea why this is happening?
Edit: Nevermind, I see #16714 addresses this

Feel free to rebase onto master!
Edit: actually you need to do that in order to make CI green and in a mergeable state

weihanglo

While this has been discussed within the team, this is a behavior change so I may start an FCP. Just FYI

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src/cargo/ops/cargo_clean.rs

TanmayArya-1p · 2026-03-07T21:06:12Z

Added a check(and test) to make sure target_dir is a directory when it is specified. Also, I wasnt happy with how the code looked so i refactored it a bit.

weihanglo

Thanks!

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weihanglo · 2026-03-11T01:10:20Z

I knew we discussed this during a meeting last year, but for a behavior change it is still better to have a formal record and give members time to think about it offline. Hence

@rfcbot fcp merge cargo

This implements the target-dir validation described in #9192 (comment).

If --target-dir is passed, cargo clean now hard-errors unless the directory contains a valid CACHEDIR.TAG.
~~Otherwise, if the explicit target-dir comes from config, cargo clean emits a future-incompat warning if it doesn't contain a valid CACHEDIR.TAG~~ See cargo clean: Add target directory validation #16712 (comment)

~~This also adds an extra validation that if target-dir points to a file, errors out.~~ We decided to split this out to its own PR #16765 as it is less controversial.

rust-rfcbot · 2026-03-11T01:10:22Z

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

Concerns:

future-incompat (cargo clean: Add target directory validation #16712 (comment))

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!

See this document for info about what commands tagged team members can give me.

epage · 2026-03-11T15:12:47Z

Otherwise, if the explicit target-dir comes from config, cargo clean emits a future-incompat warning if it doesn't contain a valid CACHEDIR.TAG

From #9192 (comment)

There was some uncertainty if that should also include setting target dir via environment variables and config files. One idea is to issue a future-incompatible warning that those situations may not be allowed in the future too, and then collect any feedback if people have issues with that.

What led to deciding in the direction of the future-incompat warning?

weihanglo · 2026-03-11T17:29:21Z

What led to deciding in the direction of the future-incompat warning?

For myself, to be conservative. I remembered rust-analyzer may create target-dir before running any cargo command, and that there will be no CACHEDIR.TAG. But probably this doesn't matter for this case.

weihanglo · 2026-03-17T14:44:14Z

@TanmayArya-1p While this is still in FCP, we were discussing whether the target-dir-is-file check can be a separate commit, or even a separate PR. That one turns out to be less controversial within the Cargo team.

TanmayArya-1p · 2026-03-17T23:52:41Z

cool, i'll open another pr for the file validation.

As discussed in #16712 , this is a separate PR that adds validation to `cargo clean` to make sure target-dir is not a file #### Tests: - Added unit tests for when target-dir is found to be a file. - I also noticed that there was no unit test asserting the expected behaviour discussed in <#7510 (comment)> when the target-dir is a symlink. I added a unit test that asserts that when the target-dir is a symlink, cargo should just delete the symlink and should not delete the content it is pointing to.

rustbot · 2026-03-21T00:45:31Z

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 · 2026-03-24T14:06:17Z

What led to deciding in the direction of the future-incompat warning?

For myself, to be conservative. I remembered rust-analyzer may create target-dir before running any cargo command, and that there will be no CACHEDIR.TAG. But probably this doesn't matter for this case.

The choice when we last discussed this wasn't between future-incompat OR error but do-nothing OR future-incompat.

weihanglo · 2026-03-24T16:22:53Z

What led to deciding in the direction of the future-incompat warning?

For myself, to be conservative. I remembered rust-analyzer may create target-dir before running any cargo command, and that there will be no CACHEDIR.TAG. But probably this doesn't matter for this case.

The choice when we last discussed this wasn't between future-incompat OR error but do-nothing OR future-incompat.

I was re-reading #9192 (comment) and the meeting note. My understanding is that, for the env/config cases, the conclusion was not to hard-error right away. Instead the direction was to use a future-incompat warning first and then revisit based on user feedback.

I wasn't in the meeting, though I feel like without a warning there is no action we can take in the future. The drawback of the warning is no way to suppress it though.

0xPoe

Do we need to consider the new build directory layout here? I am not sure if this is out of scope. However, for the new build dir layout, I believe cargo clean also deletes the build directory. Should we perform the same check for the build directory?

Even if it is out of scope, it may be better to create an issue to track it if necessary.

cc: @ranger-ross @weihanglo

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ranger-ross · 2026-03-25T21:41:12Z

Should we perform the same check for the build directory?

I think that seems reasonable to also check the build-dir assuming target-dir != build-dir.
Note that for build-dir there is no --build-dir CLI flag, so if we matched the target-dir behavior in this PR Cargo would only warn.
Perhaps this could be added in a separate PR?

Do we need to consider the new build directory layout here?

The validation performed by validate_target_dir_tag() should be compatible for both the v1 and v2 build-dir layouts as it does not change anything outside <build-dir>/{platform-profile}/. The layout changes do not touch CACHEDIR.TAG so I don't think there should be any issues here.

weihanglo · 2026-03-26T01:11:53Z

Note that for build-dir there is no --build-dir CLI flag, so if we matched the target-dir behavior in this PR Cargo would only warn.
Perhaps this could be added in a separate PR?

Either in this or a separate PR is fine for me, though I would suggest doing it after the FCP concludes

rust-rfcbot · 2026-03-26T07:31:15Z

🔔 This is now entering its final comment period, as per the review above. 🔔

epage · 2026-03-26T17:07:49Z

@rfcbot fcp concern future-incompat

See thread starting at #16712 (comment)

epage · 2026-03-26T17:12:34Z

My understanding is that, for the env/config cases, the conclusion was not to hard-error right away. Instead the direction was to use a future-incompat warning first and then revisit based on user feedback.

While there, I'm mostly going off the notes at this point and that isn't what I got from them.

From https://github.com/rust-lang/cargo-team/blob/main/meetings/sync-meeting/2025-11-11.md

ehuss: Sounds to me like detecting the use of target-dir as the CLI flag and detecting the cache dir is not there, then error out. And we can add the rest later.

From #9192 (comment)

There was some uncertainty if that should also include setting target dir via environment variables and config files

The reason for the discrepancy with how things are called from https://github.com/rust-lang/cargo-team/blob/main/meetings/sync-meeting/2025-11-11.md

epage: Would we only do this if you specify --target-dir or for all target dirs?
Josh: I'd only do it if you specify it. Because at that point it's equivalent to rm -rf

epage: There's a lot of people who go the configuration route for caching purposes, changing drives etc. I think if they'er manually configuring something they're more likely to create the directory manually.

epage: The highest risk one is the --target-dir flag -- there we can error out. With the other ones, there's still chances where people could be creating the directory manually. And our tools haven't been good about creating target dir.

epage · 2026-03-26T17:13:22Z

Should we perform the same check for the build directory?

build-dir doesn't have a CLI flag. Anything we do for target-dir config, we should probably do for build-dir config.

weihanglo · 2026-03-26T18:36:47Z

Yeah, as the warning is non-suppressible, we would like to have further discussion and plan around it in order not to annoy people.

@TanmayArya-1p would you mind take the future incompatible warning out to help resolve the concern?

TanmayArya-1p · 2026-03-26T20:48:58Z

Yeah, as the warning is non-suppressible, we would like to have further discussion and plan around it in order not to annoy people.

@TanmayArya-1p would you mind take the future incompatible warning out to help resolve the concern?

Alright makes sense, sorry for misinterpreting the comment there. Since we should not do anything different in the config-target-dir case, should I leave in the tests for config-target-dir or do i remove them completely since there is no behaviour change in that case?

weihanglo · 2026-03-26T20:55:16Z

Can add those also for capturing the current behavior.

weihanglo

Thanks for the update!

@epage the warning is removed. We defer it to future discussion. I think the concern is addressed :)

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weihanglo · 2026-03-27T17:47:49Z

tests/testsuite/clean.rs


-"#]]).run();
+"#]])
+        .run();


nit: This formatting change should be in the first commit

rustbot added A-cli Area: Command-line interface, option parsing, etc. Command-clean labels Mar 5, 2026

TanmayArya-1p marked this pull request as ready for review March 5, 2026 23:27

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 5, 2026

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cargo clean: Validate that target_dir is not a file #16765

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TanmayArya-1p added 2 commits March 28, 2026 01:59

add tests showing cargo clean does not validate target dir

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cargo clean: add target dir validation

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