Improve dockerfile inputs detection

[Prucek]

This PR adds:

• getting the right path when in rehearsal to fix:

{"error":"failed to read Dockerfile at ./Dockerfile: open ./Dockerfile: no such file or directory","image":"leader-elector","level":"debug","msg":"Failed to read Dockerfile for input detection, skipping","time":"2026-01-30T08:13:52Z"}

• build_root to base_images so that when it is detected in a dockerfile it does not have to be reimported again

[openshift-ci-robot]

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[coderabbitai]

Walkthrough

The changes refactor how build root paths are handled for repository-based builds. A new helper function getPath() extracts path calculation logic previously inlined. Two internal functions—detectDockerfileInputs() and readDockerfileForImage()—are updated to accept an explicit path parameter, with all call sites updated accordingly. Dockerfile resolution and base image detection logic are adjusted to use the provided path parameter.

Changes

Cohort / File(s)	Summary
Path-aware Dockerfile handling pkg/defaults/defaults.go	Introduced new getPath() helper function to compute working directory paths. Updated detectDockerfileInputs() and readDockerfileForImage() signatures to accept a path parameter. Modified Dockerfile path construction to join provided path with Dockerfile components. Updated runtimeStepConfigsForBuild() to use the new helper. Enhanced logic to propagate baseImages mapping with root/Alias entries.
Test coverage for path-based Dockerfile resolution pkg/defaults/defaults_test.go	Added two new test cases to TestStepConfigsForBuild exercising dockerfile-driven image building with input and output step generation. Updated TestReadDockerfileForImage call site to pass path parameter (".").

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

pkg/defaults/defaults.go (1)

1103-1108: ⚠️ Potential issue | 🔴 Critical

Fix ContextDir path construction to account for computed path parameter.

When image.ContextDir is set, the current code at line 1106 completely replaces the computed path parameter. This causes failures in rehearsal scenarios where path is an absolute directory like /home/prow/go/src/github.com/org/repo. The ContextDir would become a relative path when it should be absolute.

The correct logic should be:

if image.ContextDir != "" {
    dockerfilePath = fmt.Sprintf("%s/%s/%s", path, image.ContextDir, details.path)
}

This treats ContextDir as relative to the computed path, ensuring consistent behavior whether path is "." or an absolute directory.

[hector-vido]

/lgtm
/retest

[Prucek]

/lgtm cancel

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hector-vido

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[openshift-ci-robot]

Scheduling required tests:
/test e2e

[openshift-ci]

@Prucek: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/breaking-changes	7eeab25	link	false	/test breaking-changes

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