Only run PR checks on Ubuntu by default

[henrymercer]

Continue running ones on macOS and Windows too where it's useful, but the default should be Linux only as most functionality is platform independent.

This should reduce unnecessary compute usage and help avoid rate limiting.

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Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
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[Copilot]

Pull Request Overview

This PR changes the default operating systems for CI tests from all platforms (Ubuntu, macOS, Windows) to Ubuntu only. The goal is to reduce compute usage and avoid rate limiting by running most tests exclusively on Linux, while preserving cross-platform testing for specific tests where it provides meaningful coverage.

• Removes Ubuntu-only OS specifications from many test files since Ubuntu is now the default
• Updates the default OS list in the sync script from all platforms to Ubuntu only
• Preserves multi-platform testing for specific tests like autobuild and file baseline export where platform differences matter
• Removes Windows-specific conditional logic that's no longer needed

Reviewed Changes

Copilot reviewed 41 out of 41 changed files in this pull request and generated no comments.

File	Description
pr-checks/sync.py	Changes default OS from all platforms to Ubuntu only and removes exclusion logic
pr-checks/checks/*.yml	Removes redundant Ubuntu-only OS specifications from 25+ test files
.github/workflows/*.yml	Removes macOS/Windows entries from generated workflow matrices

[mbg]

Makes sense. I have added a few comments for where we might be able to make further improvements, but they can all be handled separately.

[mbg]

Should the other two autobuild- workflows also run on macos? Or was there a specific reason those only run on linux and windows?

[henrymercer]

I think just because it's very unlikely to run Java analysis on macOS.

[mbg]

If the tests are mainly for direct tracing, would it make sense to switch to a different traced language where we're more likely to run on all platforms (e.g. C#)?

Or alternatively, if the main goal is to test direct tracing, does it matter that it's unlikely to run Java analysis on macOS?

[henrymercer]

Can you open an issue about this? We want testing of both indirect and direct tracing, and I'd like to understand better why we disable the CLR tracer in this job.

[mbg]

Could this test be combined with one of autobuild-direct-tracing*? Seems similar.

Alternatively, maybe we could combine the three build-mode tests in one workflow with a matrix (and conditional steps based on the build-mode) / sequential jobs.

[henrymercer]

Could this test be combined with one of autobuild-direct-tracing*? Seems similar.

I've combined with autobuild-direct-tracing now that we will use direct tracing by default. But with the specific working directory it might still be useful to check build-mode: autobuild respects the working directory.

Alternatively, maybe we could combine the three build-mode tests in one workflow with a matrix (and conditional steps based on the build-mode) / sequential jobs.

We could, but we could no longer generate the workflow, so won't do for now.

[mbg]

This seems like it could be useful across all platforms because of difference in how IO behaves. That said, it feels like this could easily just be tacked on to another test that already runs on all platforms.

[henrymercer]

I'll preserve the existing behaviour here. It seems unlikely that this would break.

[mbg]

Feels like this could be added on to some other test.

[henrymercer]

True, but I'll leave this for future work.

[mbg]

This can probably be removed in favour of unit test coverage (which may already exist).

[henrymercer]

I think a test is useful, particularly since default setup relies on language aliases.

[mbg]

Do we need this specific one for Rust?

[henrymercer]

It provides some coverage against specific older versions. I'll keep for now.