Changes of projects in monorepo won't cause other projects rebuild in watch mode #880

Reproduction link or steps

• Assume there're project A, B and C; B and C imports declarations from A, and C will bundle A.
• With the config like this

export default defineConfig([
    { entry: 'src/from/a' },
    { entry: 'src/from/b' },
    { entry: 'src/from/c', deps: { onlyAllowBundle: false } },
])

• Build it in watch mode
• Edit project A, adding new exports or changing impl.

What is expected?

When adding new exports (changing dts), B and C should rebuild.
When changing impl (modifying function impl), C should rebuild.

What is actually happening?

Only A get rebuild, while B and C don't.

Any additional comments?

Using multiple calls to build in API mode does achieve part of the goal. In that case, editing A would causing B and C rebuilding as if A is missing (dist of A is cleaned). At least tsdown in this case knows that B and C depends on A.

https://github.com/neko-para/maa-support-extension/blob/276debb176cfeb06a729ed5b7c052d236ca02862/scripts/utils.mjs

/**
 *
 * @param {string[]} folders
 */
export async function watchChain(folders) {
  while (folders.length > 0) {
    const folder = folders.shift()
    console.log('watch', folder)

    const { promise, resolve } = Promise.withResolvers()
    build({
      config: path.resolve(import.meta.dirname, '..', folder, 'tsdown.config.mts'),
      watch: true,
      onSuccess: resolve
    })
    await promise
  }
}