fix: backport tapPromise fix to v30.0.0 (last Vue 2 version) — webpack-dev-server hangs on watchRun

[yoyo837]

Description

Version 30.0.0 is the last version that supports Vue 2, but it has a bug where tapAsync with an async callback never calls the completion callback, causing webpack-dev-server to hang at "wait until bundle finished".

This issue was already fixed in PR #907 for the main branch by changing tapAsync to tapPromise, but since there is no branch backup for v30.0.0, the fix cannot be backported via a PR.

The Fix

In src/core/unplugin.ts, the following change is needed:

- compiler.hooks.watchRun.tapAsync(PLUGIN_NAME, async () => {
+ compiler.hooks.watchRun.tapPromise(PLUGIN_NAME, async () => {

Full context from the main branch fix:

// src/core/unplugin.ts
 webpack(compiler) {
   let watcher: Watching
   let fileDepQueue: { path: string, type: 'unlink' | 'add' }[] = []
-  compiler.hooks.watchRun.tapAsync(PLUGIN_NAME, async () => {
+  compiler.hooks.watchRun.tapPromise(PLUGIN_NAME, async () => {
     // ensure watcher is ready(supported since webpack@5.0.0-rc.1)
     if (!watcher && compiler.watching) {
       watcher = compiler.watching

Steps to Reproduce

1. Use unplugin-vue-components@30.0.0 with webpack-dev-server
2. Start dev server
3. Make a file change to trigger a rebuild
4. webpack-dev-server hangs with "wait until bundle finished"

Expected Behavior

The dev server should rebuild and reload normally.

Why an Issue instead of a PR

Version 30.0.0 does not have a corresponding branch in the repository, so a direct PR cannot be created against it. I'm hoping the maintainers can either:

1. Create a v30 branch and I can submit a PR against it, or
2. Apply this one-line fix and publish a 30.0.1 patch release

Linked Issues/PRs

• fix: use tapPromise instead of tapAsync for webpack watchRun hook #907 (the main branch fix)
• chore: update chokidar (#890) #891 (original issue)

[yoyo837]

@antfu Could you take a look at this?