Update the codegen script to be vendor-aware

[jinbum-kim]

Why are these changes needed?

This PR is related to #4352

Currently, hack/update-codegen.sh relies solely on go list -m to locate k8s.io/code-generator.

This can break in vendor mode (-mod=vendor), where module resolution may be restricted.

This PR makes the script vendor-aware: when running in vendor mode it uses the vendored path (./vendor/k8s.io/code-generator), and otherwise it resolves the path in module mode via go list -m.

This ensures code generation works reliably in both module and vendor workflows.

Related issue number

Closes #4352

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[jinbum-kim]

Hi @win5923
I updated the relative path to an absolute path—could you please take a look when you get a chance? Thanks!

[jinbum-kim]

@win5923 I fixed a ShellCheck lint issue in a previous PR and verified that all checks have passed. It was a bit of change, but I should’ve been more careful. 😅

[win5923]

Thanks for the PR! I'm wondering if we need this level of complexity. Could we simplify this using Shell Parameter Expansion like:

CODEGEN_PKG=$(go list -m -f "{{.Dir}}" k8s.io/code-generator 2>/dev/null || true)
CODEGEN_PKG=${CODEGEN_PKG:-$(cd "${SCRIPT_ROOT}"; ls -d -1 ./vendor/k8s.io/code-generator 2>/dev/null || echo ../code-generator)}

if [[ ! -d ${CODEGEN_PKG} ]]; then
    echo "${CODEGEN_PKG} is missing. Running 'go mod download'."
    go mod download
    CODEGEN_PKG=$(go list -m -f "{{.Dir}}" k8s.io/code-generator)
fi

This way we don't need to explicitly detect vendor mode, the behavior is determined by the result, not by pre-checking the mode.

[win5923]

For example, if someone has a stale vendor/ directory but isn't using vendor mode

Doesn't CODEGEN_PKG=$(go list -m -f "{{.Dir}}" k8s.io/code-generator 2>/dev/null || true) cover that?

I think we can just follow the official Kubernetes sample-controller pattern.

[jinbum-kim]

You're right. I misinterpreted what was happening in my local env.

Reviewing the logs, my local vendor/modules.txt was corrupted during testing, so go list failed and CODEGEN_PKG ended up empty.

I’ll remove complex logic and update the script to follow the sample-controller pattern.

[jinbum-kim]

@win5923 PTAL, thank you!

[win5923]

LGTM! I tested both vendor and non-vendor mode, thanks!