Read aspect providers in cquery

[matts1]

Description of the feature request:

Cquery should be able to read providers that were created by an aspect.

I tested, and the aspects already run during cquery (see #16310 (comment)). So all I'm asking is that we surface that via cquery. I suspect that this will likely be a relatively simple change, since the aspects already run, but it depends on how it's implemented.

Which category does this issue belong to?

Rules API

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

Aspects are very useful for allowing IDEs access to metadata about the build. However, at the moment, IIUC, the way you have to use them is to:

1. run bazel build <something> --aspects=...
2. Read from the output file generated by your aspect.

Sometimes, however, you don't need anything other than the providers created by the aspect. In cases like this, cquery should be sufficient. For example, generating rust-project.json in rust can be done without building a single target.

The use case that I was trying to do for this is that if I run cquery on the following target:

cc_binary(
    name = "foo",
    deps = ["//path/to:rust_library"],
)

Then I want cquery to attach a RustAnalyzerInfo object to :foo. This can then be picked up on by the rust-analyzer vscode extension. At the moment we use bazel build instead of bazel cquery, which means that if any bazel target fails to build, then we can't run get IDE support for our rust code.

Which operating system are you running Bazel on?

Linux

What is the output of bazel info release?

7.1.1

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

Have you found anything relevant by searching the web?

I commented on #16310 (comment) last week

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

No response

[comius]

cc @mai93

[mai93]

Can specifying only the output group containing the file with aspect provider data via --output_groups in the bazel build <something> --aspects=... invocation help with that? IIUC this will not execute the rest of the actions in the build that may fail.

[matts1]

That's a good point. I just tried it out, and it does appear to work. I still think this suggestion has value, but it can be achieved via other means, so it's probably not a priority.

[kilian-funk]

The bazel build <something> --aspect=... workaround is only practical for a few targets. It is not helpful if I want to use this approach to harvest more detailed information on a complete region of my workspace. In my use case, I need to process certain information from an attribute of many targets. Since cquery Starlark does not give me access to the attributes, I need to use an aspect. Using output groups in combination with bazel build would mean reading thousands of files to collect the results.

So I would be very happy if this issue got fixed soon 👍