Incompatible targets with selects on a label flag config produce spurious "is not a valid select() condition" errors, are not skipped

[tpudlik]

Description of the bug:

A target with a select statement referencing a config_setting based on a label_flag will not be correctly detected as incompatible with the target platform. Instead, you get the message <config setting> is not a valid select() condition for //:library_with_select.

This is particularly severe because it breaks incompatible target skipping. Instead of skipping the incompatible target, Bazel prints the error message above.

This bug is a little hard to understand based on this description, but it's easy to reproduce. See https://github.com/tpudlik/not_a_valid_select for a simple BUILD.bazel file and repro steps.

Which category does this issue belong to?

Configurability

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

https://github.com/tpudlik/not_a_valid_select

Which operating system are you running Bazel on?

Linux

What is the output of bazel info release?

release 8.0.0-pre.20240618.2

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.

I don't believe this ever worked. I get the same error on Bazel 7.2.1, too.

Have you found anything relevant by searching the web?

No response

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

This bug may sound a little academic, but it's not! We've run into this in a real project (http://pwrev.dev/221036).

[tpudlik]

@katre FYI

[katre]

Also @gregestren and @AustinSchuh

[gregestren]

Weird. It's got to be something with label_flag acting alias-like and somehow not propagating the right info.

I'll dig in and diagnose.

[gregestren]

@aranguyen is looking now.

[aranguyen]

Hi all, the error is being thrown here due to null ConfigMatchingProvider from ConfiguredTarget.getProvider(ConfigMatchingProvider.class)

The ConfiguredTarget is being produced by ConfiguredTargetAndDataProducer which has been noted to possibly produced a different configuration for alias. And Bazel treatslabel_flag as an alias. In addition, the current implementation of ConfigSettings probably also needs modification to work with label_flag. Tracing back to a few previous release, this issue was also observed.

For immediate usage, please use constraint_setting as a workaround. I will lower the priority of this issue but we're planning to pick them up in the future as this seems to be an oversight and there aren't obvious reason why label_flag can't be used with config_setting.