Serialize Mops test dependency installs - #461
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May 21, 2026 11:16
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We need to update mops to be safe calling |
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## Why Two `mops` processes installing into the same project (editor watcher, [vscode-motoko's fixture installer](caffeinelabs/vscode-motoko#461), CI matrix sharing a global cache) race on cache writes and leave zero-byte / truncated files in `.mops/`. Symptom downstream: missing completions, hover, type-check errors. v2.13.2's concurrent-invocations fix covered `check`/`build`/`check-stable` scratch dirs, not the install cache path. Two race windows: - **Global cache** (`install-mops-dep.ts`): `Promise.all(mkdir + writeFile)` writes directly into `cacheDir` while `isDepCached = fs.existsSync(cacheDir)` — peer sees "cached" mid-write and copies a half-populated tree. - **Local `.mops/<pkg>`** (`syncLocalCache`): two concurrent installs both miss `existsSync(dest)` and interleave writes via `ncp`. GitHub installs were strictly worse — `mkdirSync(cacheDir)` ran *before* the download, so peers saw an empty dir as cached. The shared `.mops/_tmp/` zip dir was also clobbered by concurrent github installs. ## What Cache writes stage into a sibling `.staging-*` dir (`mkdtemp`, same filesystem) and **atomically `rename` onto the canonical path**. Race-loser catches `ENOTEMPTY` / `EEXIST` / `EPERM` (only when `dest` exists, to avoid masking real Windows AV / permission errors), drops its staging, and observes a complete cache. Applies to mops registry installs, github installs, local `.mops/` sync, and the github zip download dir. Stale staging is swept on the next install with a 1h mtime cutoff. ## Test plan - [x] New test: 5 parallel `mops install` runs against an isolated `XDG_CACHE_HOME` produce no zero-byte files and no `.staging-*` leftovers (cold-cache path actually exercised). - [x] Existing `parallel builds of the same canister both succeed` still passes. - [x] Full CLI test suite: 104 passed. - [x] `npm run check` + `npm run lint` clean. Refs LANG-1310, caffeinelabs/vscode-motoko#461. --------- Co-authored-by: Cursor <cursoragent@cursor.com>
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Prevents release/update CI from corrupting shared Mops package installs while preparing test fixtures. The Motoko update workflow can now install fixture dependencies deterministically before running the completion and hover test suites.
Before this, fixture installs ran concurrently and could leave zero-byte package files in
.mops, causing later language-server tests to fail unpredictably with missing completions or hover data.Validation:
npm install "motoko@^4.6.0" --min-release-age=0 && npm run compile && npm testpasses with 24 suites / 276 tests.Slack Thread