feat(v2/app): add build metadata vars with automatic logger enrichment

Elliot Forbesrequested to merge
worktree-feat-app-build-metadata into master

What this MR does

Adds three exported, ldflag-injectable package-level variables (Version, Commit, Date) to the gitlab.com/gitlab-org/labkit/v2/app package, and enriches the structured logger in NewWithConfig with those values automatically.

Services that link with:

-X 'gitlab.com/gitlab-org/labkit/v2/app.Version=<version>'
-X 'gitlab.com/gitlab-org/labkit/v2/app.Commit=<commit>'
-X 'gitlab.com/gitlab-org/labkit/v2/app.Date=<date>'

will get version, commit, and date fields on every log line with no per-service boilerplate.

Without ldflags (local/dev builds) the defaults are "dev", "unknown", "unknown".

Why

Every Go service at GitLab currently duplicates the same var version/commit/date block and logger.With(...) enrichment in main.go. This moves that concern into LabKit so it is consistent across all consumers and cannot be accidentally omitted.

Files changed

File Change
v2/app/buildinfo.go New — exported Version, Commit, Date vars
v2/app/buildinfo_test.go New — tests for defaults and overridability
v2/app/app.go NewWithConfig now calls logger.With(...) after constructing the logger
v2/app/app_test.go TestNewWithConfigEnrichesLogger asserts all three fields appear in JSON output

How to test

  1. cd v2 && go test ./app/... -v — all tests should pass
  2. Build any consumer binary with the new ldflags and observe version/commit/date in every log line

Checklist

  • Tests added and passing
  • Backward compatible (additive only — no API changes)
  • New() → NewWithConfig(ctx, nil) path also enriched (delegates)
  • NewForTesting intentionally bypassed (test isolation)

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