Bump WebKit (oven-sh/WebKit#567 preview): idle JSC worker threads release their mimalloc heap

scripts/build/deps/webkit.ts

@@ -3,7 +3,7 @@
  * for local mode. Override via `--webkit-version=<hash>` to test a branch.
  * From https://github.com/oven-sh/WebKit releases.
  */
-export const WEBKIT_VERSION = "2e2aa2290fac856d6f451ceacb58f7f5b44dd057";
+export const WEBKIT_VERSION = "autobuild-preview-pr-567-e62d118e";
 
 /**
  * WebKit (JavaScriptCore) — the JS engine.

test/js/bun/wasm/compile-rss.test.ts

@@ -0,0 +1,34 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, isASAN, isDebug } from "harness";
+import path from "node:path";
+
+// Unfixed, the 8 idle wasm compiler threads keep 17 to 25 MB of freed compile temporaries until
+// they exit after 10 s. Fixed, they release it about 100 ms after the last compile and RSS returns
+// to where it started.
+const idleTargetMiB = 10;
+
+// Debug and ASAN builds link a JavaScriptCore that does not allocate through mimalloc, so the
+// per-thread retention this test checks for does not exist there.
+test.skipIf(isDebug || isASAN)(
+  "WebAssembly.compile does not retain memory in idle compiler threads (#41438)",
+  async () => {
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), path.join(import.meta.dir, "compile-rss-fixture.mjs"), String(idleTargetMiB)],
+      env: {
+        ...bunEnv,
+        // The retained amount scales with the compiler thread count. Pin it so the test does not
+        // depend on the core count of the machine.
+        BUN_JSC_numberOfWasmCompilerThreads: "8",
+      },
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toBe("");
+    const result = JSON.parse(stdout.trim().split("\n").at(-1)!);
+    // The compiles have to grow RSS well past the target first, or the check below means nothing.
+    expect(result.peakDeltaMiB).toBeGreaterThan(idleTargetMiB * 2);
+    expect(result.idleDeltaMiB).toBeLessThan(idleTargetMiB);
+    expect(exitCode).toBe(0);
+  },
+);