Add build info watcher to the hardhat node task

[galargh]

This is a follow-up task to #5615

It is about adding a build info (from artifact) watcher functionality. The idea is to watch for build info changes and adding compilation info to EDR when they happen.

We'll be able to work on this once EDR is ready to receive build info from us.

Below, you'll find a draft of the implementation.

Implementation:

import fsPromises from "node:fs/promises";

export interface WatcherEvent {
  eventType: "change" | "rename";
  filename: string | null;
}

export type WatcherEventHandler = (event: WatcherEvent) => Promise<void>;

export class Watcher {
  readonly #abortController: AbortController;
  readonly #eventLoop: Promise<void>;

  constructor(path: string, eventHandler: WatcherEventHandler) {
    this.#abortController = new AbortController();

    const events = fsPromises.watch(path, {
      recursive: true,
      signal: this.#abortController.signal,
    });

    this.#eventLoop = new Promise(async () => {
      for await (const event of events) {
        await eventHandler(event);
      }
    });
  }

  public close(): Promise<void> {
    this.#abortController.abort();
    return this.#eventLoop;
  }
}

Usage:

import type { WatcherEvent } from "./watcher.js";
import type { BuildInfo } from "../../../types/artifacts.js";

import path from "node:path";

import { exists, readJsonFile } from "@ignored/hardhat-vnext-utils/fs";

import { BUILD_INFO_DIR_NAME } from "../artifacts/artifacts-manager.js";

import { Watcher } from "./watcher.js";

...

  const watcher = new Watcher(
    path.join(hre.config.paths.artifacts, BUILD_INFO_DIR_NAME),
    async ({ eventType, filename }: WatcherEvent) => {
      log(`Detected ${eventType} in ${filename}`);

      if (
        filename === null ||
        filename.endsWith(".output.json") ||
        !(await exists(filename))
      ) {
        return;
      }

      const filenameOutput = filename.replace(".json", ".output.json");
      if (await exists(filenameOutput)) {
        return;
      }

      const buildInfo: BuildInfo = await readJsonFile(filename);
      const buildInfoOutput = await readJsonFile(filenameOutput);

      try {
        await provider.request({
          method: "hardhat_addCompilationResult",
          params: [buildInfo.solcVersion, buildInfo.input, buildInfoOutput],
        });
      } catch (error) {
        log(error);
      }
    },
  );
  
  ...
  
  await watcher.close();
  
...