Description of the feature request:

An important use case for Starlark repositories is configuring the build for the local machine.

This sometimes requires reading files, calling readdir(), i.e. interacting with the local file system. In some cases, it's desirable that the repository is not re-fetched if the local state changes (if it's expensive to do so), but in some other case, it is and we currently don't provide a good mechanism to do so:

• rctx.read() and friends can only declare dependencies on files in other repositories
• local_repository() and new_local_repository() are only invalidated when the top-level directory of the repository changes and they can't pull in individual files (this matters for large directories e.g. /etc). The rationale behind the first limitation is that one would glob() in the repository and declare dependencies on the files below the first level that way, but that doesn't work for other repository rules.

The only workaround at the moment is to declare a dependency on an environment variable that always changes, which has other undesirable effects (see #20951).

There is a separate, ancient feature request to always re-run a repository rule (#3041) but I think that's dangerous because it results in sloppiness with declaring dependencies.

Which category does this issue belong to?

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What underlying problem are you trying to solve with this feature?

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Which operating system are you running Bazel on?

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What is the output of bazel info release?

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

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

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Have you found anything relevant by searching the web?

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

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