GeezerVison

This PR introduces support for merging the config inputs that are provided by Default Setup with custom configuration files. That can be the case if, for example, a configuration file is configured by the corresponding repository property. With the change in this PR, a supported scenario is that e.g.:

• A CodeQL workflow runs in Default Setup on a repository where the github-codeql-config-file is set.
• getConfigFileInput returns the value from the repository property.
• getOptionalInput("config") returns the configuration provided by Default Setup.
• In determineUserConfig, the two configurations are merged if the corresponding FF is enabled.

Notes for reviewers / deliberate implementation aspects

• determineUserConfig is refactored out of initConfig. This PR does not make any changes to the refactored code that aren't required for the objective of this PR.
• inputs.configFile is mutated to the resulting configuration file path as in initConfig before. No change in behaviour. The new tests for determineUserConfig check that this behaves as expected in relevant cases.
• No new validation of the inputs properties is performed. Just like initConfig before, determineUserConfig assumes that the necessary validation before this step has taken place. Further validation may occur in e.g. loadUserConfig.
• The new tests do not cover Feature.ValidateDbConfig. This is deliberate because there are already tests exercising loadUserConfig's behaviour if that FF is enabled. In any case, Feature.ValidateDbConfig needs more work to work correctly that is not in the scope of this PR.
• The tests make use of the framework merged in Allow abstracting over process.env #3993 to allow the tests to run in parallel.
• The tests do not cover cases with remote files, because whether a file is or is not remote does not matter to determineUserConfig. That's for the existing loadUserConfig function and its tests.

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Which use cases does this change impact?

Workflow types:

• Advanced setup - Impacts users who have custom CodeQL workflows.
• Managed - Impacts users with dynamic workflows (Default Setup, Code Quality, ...).

Products:

• Code Scanning - The changes impact analyses when analysis-kinds: code-scanning.
• Code Quality - The changes impact analyses when analysis-kinds: code-quality.
• Other first-party - The changes impact other first-party analyses.

Environments:

• Dotcom - Impacts CodeQL workflows on github.com and/or GitHub Enterprise Cloud with Data Residency.

How did/will you validate this change?

• Unit tests - I am depending on unit test coverage (i.e. tests in .test.ts files).
• End-to-end tests - I am depending on PR checks (i.e. tests in pr-checks).

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Feature flags - All new or changed code paths can be fully disabled with corresponding feature flags.

How will you know if something goes wrong after this change is released?

• Telemetry - I rely on existing telemetry or have made changes to the telemetry.
  • Dashboards - I will watch relevant dashboards for issues after the release. Consider whether this requires this change to be released at a particular time rather than as part of a regular release.
  • Alerts - New or existing monitors will trip if something goes wrong with this change.

Are there any special considerations for merging or releasing this change?

• No special considerations - This change can be merged at any time.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.