electron/.yarn

Vendored Yarn release

This directory holds the Yarn release used by this repo (yarnPath in .yarnrc.yml). The release file is checked in so every contributor and CI job runs the exact same Yarn, and so we can carry small local patches when needed.

releases/yarn-4.12.0.cjs currently carries one such patch, described below. If you bump the Yarn version, read the Upgrading Yarn section first.

Patch: use JsZipImpl for the node-modules link step

What changed

Two call sites in releases/yarn-4.12.0.cjs are modified so the node-modules linker (and the pnpm-loose linker) construct their read-only ZipOpenFS with customZipImplementation: ST — Yarn's pure-JS JsZipImpl — instead of falling through to the default WASM-backed LibZipImpl:

new $f({maxOpenFiles:80,readOnlyArchives:!0})
  → new $f({maxOpenFiles:80,readOnlyArchives:!0,customZipImplementation:ST})

A comment block at the top of the .cjs file marks the file as patched and points back here.

Why

On the linux-arm CI test shards we run a 32-bit arm32v7 container. During yarn install's Link step, Yarn opens up to 80 cache zips concurrently. With LibZipImpl, each open zip is readFileSync'd into a Node Buffer and copied again into the WASM linear memory, and every file read does a WASM _malloc(size) for the entry. The WASM heap has to grow as a single contiguous region of the 32-bit address space; once enough zips are resident, the _malloc for a large entry — most often typescript/lib/typescript.js (~9 MB inside a ~22 MB zip) — fails.

Yarn's cross-FS copyFilePromise swallows the underlying error and re-throws a generic one, so CI shows:

YN0001: While persisting .../typescript-patch-...zip/node_modules/typescript/
  EINVAL: invalid argument, copyfile '/node_modules/typescript/lib/typescript.js' -> '...'

The unmasked form (occasionally seen on pdfjs-dist) is the WASM-heap failure string Couldn't allocate enough memory. This started failing ~1-in-3 linux-arm / test shards at Install Dependencies on 2026-04-13, after #50692 grew the cache enough to push the 32-bit process over the edge nondeterministically — e.g. run 24739817558.

JsZipImpl avoids the problem entirely: it opens the zip by file descriptor, reads only the central directory into memory, and readSyncs individual entries into ordinary Node Buffers — no WASM heap involved. It is read-only and path-based, which is exactly how the linker uses these archives.

There is no .yarnrc.yml setting or environment variable to select the zip implementation (verified against the bundle), so editing the vendored release is the only way to switch it short of re-implementing the linker in a plugin.

Upstream references: yarnpkg/berry#3972, yarnpkg/berry#6722, yarnpkg/berry#6550.

Upgrading Yarn

When bumping releases/yarn-*.cjs:

1. Check whether upstream now defaults readOnlyArchives opens to JsZipImpl, or exposes a config knob for the zip implementation. If so, drop this patch.
2. Otherwise, re-apply: search the new bundle for maxOpenFiles:80,readOnlyArchives:!0 (the surrounding minified identifiers will differ) and add ,customZipImplementation:<JsZipImpl symbol> — that symbol is whatever the new bundle exports as JsZipImpl from @yarnpkg/libzip.
3. Re-add the header comment pointing back to this README.
4. Verify with rm -rf node_modules spec/node_modules && node script/yarn.js install --immutable --mode=skip-build and confirm node_modules/typescript/lib/typescript.js is byte-identical to an unpatched install.