perf(lint): isolate golangci-lint cache and lock per worktree

[Erik Osterman (Cloud Posse) (osterman)]

what

• Point TMPDIR and GOLANGCI_LINT_CACHE at repo-local dirs in scripts/run-custom-golangci-lint.sh so each worktree gets its own golangci-lint lock and cache (GOCACHE stays shared for warm typecheck data); opt out with ATMOS_LINT_SHARED_CACHE=1.
• Skip rebuilding the custom-gcl binary in atmos lint custom-gcl when it is already up to date (staleness guard mirroring lint lintroller/lint gomodcheck).
• Drop the redundant standalone lint lintroller pass from atmos lint changed (it already runs as a plugin inside custom-gcl).

why

• golangci-lint's single-instance lock is a fixed machine-global path (os.TempDir()/golangci-lint.lock), not inside GOLANGCI_LINT_CACHE, so parallel worktree lints (e.g. rebase storms after a merge) serialized on one lock and a run orphaned by a tool timeout froze every other worktree; relocating the lock via a per-worktree TMPDIR lets them run in parallel and contains an orphan to its own worktree.
• Rebuilding custom-gcl (clone + compile) on every lint changed was the single biggest per-run cost during a rebase storm when the binary is identical across worktrees.
• Verified empirically: an isolated-TMPDIR lint ran at ~94% CPU in parallel with another holding the global lock, with its lock file under .golangci-tmp/.

references

• Contributor tooling only (dev lint flow + pre-commit hook); no user-visible change to the Atmos binary — labeled no-release.

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Dependency Review

✅ No vulnerabilities or license issues found.

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📥 Commits

Reviewing files that changed from the base of the PR and between b271f89 and 3b6aaba.

📒 Files selected for processing (1)

• .gitignore

✅ Files skipped from review due to trivial changes (1)

• .gitignore

---

📝 Walkthrough

Walkthrough

The PR removes a redundant lint step, makes custom-gcl rebuild only when inputs are newer than the binary, and updates golangci-lint execution to use worktree-local cache and temp directories unless shared caching is enabled.

Changes

Lint pipeline updates

Layer / File(s)	Summary
Lint step ordering and conditional custom-gcl rebuild .atmos.d/lint.yaml	Removes the separate lint lintroller step after build deps, and changes custom-gcl to rebuild only when the binary is missing or stale relative to .custom-gcl.yml or tools/lintroller Go sources.
Per-worktree cache and lock isolation scripts/run-custom-golangci-lint.sh, .gitignore	Sets GOLANGCI_LINT_CACHE and TMPDIR to worktree-local directories unless ATMOS_LINT_SHARED_CACHE=1, creates the temp directory, and adds .golangci-tmp/ ignore entries with updated cache comments.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant lint_changed as lint changed
  participant run_custom_golangci_lint as run-custom-golangci-lint.sh
  participant filesystem as worktree filesystem

  lint_changed->>run_custom_golangci_lint: invoke lint
  run_custom_golangci_lint->>run_custom_golangci_lint: check ATMOS_LINT_SHARED_CACHE
  run_custom_golangci_lint->>filesystem: set GOLANGCI_LINT_CACHE to .golangci-cache
  run_custom_golangci_lint->>filesystem: set TMPDIR to .golangci-tmp
  run_custom_golangci_lint->>filesystem: create .golangci-tmp directory
  run_custom_golangci_lint->>lint_changed: run golangci-lint with isolated cache and lock paths

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Possibly related PRs

• cloudposse/atmos#1636: Both PRs touch the custom-gcl build/run flow in the lint pipeline.
• cloudposse/atmos#1666: Both PRs modify custom-gcl build behavior and isolate cache/build execution.
• cloudposse/atmos#2677: Both PRs touch .atmos.d/lint.yaml and the custom-gcl lint path.

Suggested reviewers: aknysh

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: isolating golangci-lint cache and lock behavior per worktree for lint performance.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch osterman/optimize-custom-gcl-caching

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.18%. Comparing base (b248714) to head (2cec399).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2701   +/-   ##
=======================================
  Coverage   81.18%   81.18%           
=======================================
  Files        1630     1630           
  Lines      154206   154206           
=======================================
+ Hits       125186   125193    +7     
+ Misses      22101    22093    -8     
- Partials     6919     6920    +1     

Flag	Coverage Δ
unittests	81.18% <ø> (+<0.01%)	⬆️

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[mergify]

💥 This pull request now has conflicts. Could you fix it Erik Osterman (Cloud Posse) (@osterman)? 🙏

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These changes were released in v1.223.0-rc.7.