stats.toJson() blocking HMR in onDevCompileDone

[ms-jb]

Hi all, I am trying to track compilation time across my engineering team. When I include stats.toJson() in the onDevCompileDone lifecycle function, HMR is delayed until the promise resolves. I can see the recompile happen immediately.

const rsBuild = await createRsBuild();
rsBuild.onDevCompileDone(({ stats }) => {
  console.log(`Compile done in ${stats?.toJson({})?.time}ms`);
});
const rsBuildServer = await rsBuild.createDevServer();
rsBuildServer.listen()

I'm on "@rsbuild/core": "1.3.11" and I've tried offloading the function to a separate worker thread, using process.nextTick, setTimeout 0, etc. but nothing has helped. I can simulate this same behavior with a promise as well. Any other things I could try here? Thank you!

[ms-jb]

Resolved by creating a custom plugin and setting timestamps with onBeforeEnvironmentCompile/onAfterEnvironmentCompile.

const analyticsPlugin = (): RsbuildPlugin => ({
  name: 'AnalyticsPlugin',
  setup(api) {
    let compileStart: number;
    api.onBeforeEnvironmentCompile(() => {
      compileStart = Date.now();
    });
    api.onAfterEnvironmentCompile(({ isFirstCompile }) => {
      const durationMs = Date.now() - compileStart;
    });
  },
});

[chenjiahan]

Large stats objects can introduce significant Rust-JS communication overhead.

Usually we recommend getting the timing like this:

const statsJson = stats.toJson({
  all: false,
  timings: true,
});

[ms-jb]

That did the trick. Thank you!