Vendoring can lead to corrupt files

[mortenmj]

Description of the bug:

Occasionally, when vendoring all dependencies in our repository, file content can be written to the wrong file, leading to corrupt dependencies. Other than stress testing the system by vendoring a large number of dependencies, which is when I generally see this, I am not sure how to reproduce this reliably.
In the specific example I'm seeing now, a partial golang source file has been written to a BUILD.bazel file.

Which category does this issue belong to?

Core

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Run bazel vendor //... in a repository with many external dependencies, potentially several times in order to trigger the issue

Which operating system are you running Bazel on?

Linux

What is the output of bazel info release?

release 7.3.1

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

No response

If this is a regression, please try to identify the Bazel commit where the bug was introduced with bazelisk --bisect.

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

Running in a GitHub Codespace. May or may not matter w.r.t. the reliability of the underlying platform

[meisterT]

cc @meteorcloudy

[meteorcloudy]

This is so weird, the way a repo is vendored is by moving its source from the external root to the vendor directory, we are not even copying any files around:

bazel/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/VendorManager.java

Lines 94 to 96 in 5209ce7

	// 3. Move the external repo to vendor dir. It's fine if this step fails or is interrupted,
	// because the marker file under external is gone anyway.
	FileSystemUtils.moveTreesBelow(repoUnderExternal, repoUnderVendor);

It'll be really helpful if you can somehow construct a potential reproducible case.