tools(bench): rebootstrap (#12281)

Enable deno devs to bench/profile/test JS code changes without doing a full --release rebuild.

Incremental release builds take ~4mn on M1s, often more on other machines ...

1 files changed, 25 insertions, 0 deletions

diff --git a/tools/bench/rebootstrap.js b/tools/bench/rebootstrap.js
new file mode 100644
index 000000000..b85276ef3
--- /dev/null
+++ b/tools/bench/rebootstrap.js
@@ -0,0 +1,25 @@
+import { dirname, fromFileUrl, join } from "https://deno.land/std/path/mod.ts";
+import { expandGlobSync } from "https://deno.land/std/fs/mod.ts";
+
+const ROOT_DIR = join(dirname(fromFileUrl(import.meta.url)), "..", "..");
+
+export function rebootstrap(exts) {
+  [
+    "core/00_primordials.js",
+    ...exts.map((e) => `ext/${e}/*.js`),
+  ]
+    .map((pattern) => join(ROOT_DIR, pattern))
+    .map((pattern) => [...expandGlobSync(pattern)])
+    .flat()
+    .map((entry) => entry.path)
+    .forEach((file) => {
+      Deno.core.evalContext(Deno.readTextFileSync(file), file);
+    });
+  const bootstrap = globalThis.__bootstrap;
+  delete globalThis.__bootstrap;
+  // Patch dispatchEvent so we don't crash when MainWorker exits via:
+  // `window.dispatchEvent(new Event('unload'))`
+  // which fails since symbols are mangled during rebootstrap
+  globalThis.dispatchEvent = () => {};
+  return bootstrap;
+}