Propagate errors when probing for generated schemas

[stevendborrelli]

Description of your changes

Four probes for a generated schemas directory discarded their error and treated the failure as "no schemas". An unreadable schemas directory therefore produced a silently degraded result instead of an error:

Location	Silent failure
generatePythonFiles	Scaffolds a function without the local schema dependency
generateGoFiles	Omits the dev.crossplane.io/models replace directive
generateGoTemplatingFiles	Omits the model index path
pythonBuilder.buildVenv	Builds an image without the project's python schemas

In each case the user sees the real fault much later and in a misleading form — generated code that doesn't compile, or a function image missing its models — with nothing pointing at the schemas directory.

afero.DirExists and afero.Exists already report a missing directory as (false, nil), so a non-nil error here is a genuine I/O or permission fault and is worth surfacing rather than discarding.

Found while reviewing feedback on #170, which flags the same pattern in the TypeScript paths that PR introduces. Those instances live in code that only exists on that branch, so they're fixed there; this PR covers the pre-existing ones on main.

Deliberately not changed

internal/schemas/generator/python.go:769 uses the same if exists, _ := afero.Exists(...) shape when creating __init__.py files, but the error is not truly lost there: a failing probe falls through to afero.WriteFile, which reports its own wrapped error. Happy to include it if a reviewer would rather have it consistent.

I have:

• Read and followed Crossplane's contribution process.
• Run ./nix.sh flake check to ensure this PR is ready for review.
• Added or updated unit tests.
• Linked a PR or a docs tracking issue to document this change.
• Added backport release-x.y labels to auto-backport this PR.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3d72f93 and ad553f9.

📒 Files selected for processing (2)

• cmd/crossplane/function/generate.go
• internal/project/functions/python.go

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📝 Walkthrough

Walkthrough

Schema filesystem checks now propagate errors with contextual messages during function file generation and Python virtual-environment setup.

Changes

Schema error propagation

Layer / File(s)	Summary
Generation schema checks cmd/crossplane/function/generate.go	Python, Go, and Go templating generation now return wrapped errors when schema directory or index checks fail.
Python environment schema check internal/project/functions/python.go	buildVenv now returns a wrapped error when checking the Python schemas directory fails.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to ad553

The change makes schema-directory I/O failures surface immediately instead of silently generating incomplete artifacts. No actionable merge-blocking risk remains after normal checks and review.

Suggested reviewers: bobh66

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error)

Check name	Status	Explanation	Resolution
Breaking Changes	❌ Error	cmd/crossplane/function/generate.go removes existing behavior without a breaking-change label. Before this change, a schema probe error was ignored and the command generated files without the sche…	Add the breaking-change label to the pull request. Alternatively, preserve the previous fallback behavior if this change is not intended to be treated as breaking.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is descriptive, directly related to the error-propagation changes, and is under 72 characters at 51 characters.
Description check	✅ Passed	The description clearly explains the affected schema probes, the previous silent failures, the new error behavior, validation performed, and the deliberate scope.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Feature Gate Requirement	✅ Passed	PASS. The pull request introduces no new experimental feature. The verified commit changes only cmd/crossplane/function/generate.go and internal/project/functions/python.go; no files under `apis/*…

Full details: Breaking Changes

Explanation

cmd/crossplane/function/generate.go removes existing behavior without a breaking-change label. Before this change, a schema probe error was ignored and the command generated files without the schema dependency or model path. The new code returns the probe error, and Run stops at the generator error path before writing files. The diff does not remove or rename public fields or flags and adds no required public fields or flags, but this is still a behavior removal under the check's explicit condition. No breaking-change marker appears in the commit metadata or description.

Full details: Feature Gate Requirement

Explanation

PASS. The pull request introduces no new experimental feature. The verified commit changes only cmd/crossplane/function/generate.go and internal/project/functions/python.go; no files under apis/** changed. The four added branches only return existing filesystem probe errors instead of treating probe failures as missing schemas. This is corrective error handling, not an experimental feature that requires a feature flag.

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