perf(webpack-cli): hold cached argument metadata via WeakRef

claude · claude · commit 10cdeeb087a6 · 2026-05-26T19:10:32.000Z
The per-schema argument metadata cached for option parsing is large (~1MB for webpack, ~1.85MB including dev-server) but is only needed while setting up a command. Storing it via WeakRef lets the GC reclaim it once setup completes, which matters for long-running serve/watch sessions. A cache miss simply rebuilds it; in practice V8 keeps the target alive across the short setup window, so the dedup within a run (only one schema walk) is preserved. https://claude.ai/code/session_01PEtzv6Xqv2yXQaQsZaeoSF
diff --git a/.changeset/fast-pumas-cache.md b/.changeset/fast-pumas-cache.md
@@ -2,4 +2,4 @@
 "webpack-cli": patch
 ---
 
-Cache CLI argument metadata built from the webpack/dev-server schema and apply CLI options using the cached name-keyed map directly, avoiding a redundant schema walk and the rebuild of a large options array and lookup map on every run. Default-config discovery now reads each candidate directory once instead of probing every `<name><ext>` combination with a separate `fs.access` call (up to ~100 sequential syscalls when no config file exists). Colors are also created lazily, so commands that don't need webpack (such as `version` and `info`) no longer load it. This reduces per-invocation CPU work, syscalls, and memory allocations.
+Cache CLI argument metadata built from the webpack/dev-server schema and apply CLI options using the cached name-keyed map directly, avoiding a redundant schema walk and the rebuild of a large options array and lookup map on every run. Default-config discovery now reads each candidate directory once instead of probing every `<name><ext>` combination with a separate `fs.access` call (up to ~100 sequential syscalls when no config file exists). Colors are also created lazily, so commands that don't need webpack (such as `version` and `info`) no longer load it. The cached argument metadata (~1MB per schema) is held via `WeakRef` so the garbage collector can reclaim it once command setup is done, which matters for long-running `serve`/`watch`. This reduces per-invocation CPU work, syscalls, and memory usage.
diff --git a/packages/webpack-cli/src/webpack-cli.ts b/packages/webpack-cli/src/webpack-cli.ts
@@ -923,10 +923,13 @@ class WebpackCLI {
 
   // Building arguments from the webpack/dev-server schema walks a large JSON
   // schema and is repeated within a single run (e.g. once per command and again
-  // in `loadConfig`). Cache the result per webpack module and schema.
+  // in `loadConfig`). Cache the result per webpack module and schema. The values
+  // are large (~1MB each) and only needed while setting up a command, so they are
+  // held via `WeakRef` to let the GC reclaim them afterwards (important for
+  // long-running `serve`/`watch`); a miss simply rebuilds them.
   #argumentsCache = new WeakMap<
     object,
-    Map<Schema, ReturnType<(typeof webpack)["cli"]["getArguments"]>>
+    Map<Schema, WeakRef<ReturnType<(typeof webpack)["cli"]["getArguments"]>>>
   >();
 
   #getArguments(webpackMod: typeof webpack, schema: Schema) {
@@ -937,11 +940,11 @@ class WebpackCLI {
       this.#argumentsCache.set(webpackMod, perModuleCache);
     }
 
-    let args = perModuleCache.get(schema);
+    let args = perModuleCache.get(schema)?.deref();
 
     if (!args) {
       args = webpackMod.cli.getArguments(schema);
-      perModuleCache.set(schema, args);
+      perModuleCache.set(schema, new WeakRef(args));
     }
 
     return args;
