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--project-matrix or three -b flags? What is the difference in practice?

3 answers

• 19votes✓

  Accepted answer

  --project-matrix means "every browser declared in the project YAML". Your three -b flags mean "these three, whatever the project says".

  Prefer the matrix flag for a nightly: when someone adds a browser to the project, the nightly picks it up without an edit to your CI file. Prefer explicit -b where the point is that this job runs one specific engine — a pull request check on chromium, say.

  Note that -b is checked against the project's allow-list either way:

  textCopy

  Browser "webkit" is not enabled for project demo-shop (browsers: chromium, firefox).

  Exit 2, before anything runs.

  SKanswered by Sunita Kale982 · 11 Feb 2025

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• 10votes

  If you pass both, --project-matrix wins — it is read first and the -b values are ignored. Not an error, which is arguably too quiet, so do not write both and expect an intersection.

  The full precedence for browsers is: --project-matrix, then explicit -b, then the browsers of a --process, then the project default.

  RNanswered by Reeta Nandalmaintainer41,280 · 12 Feb 2025

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• 7votes

  From the release side: put the browser list in the process rather than in either flag. release-gate names its browsers in YAML, so the gate cannot drift because someone edited a workflow, and the list is reviewable in the same place as the pass-rate gate.

  RHanswered by Rasha Halabi572 · 2 Sept 2025

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