bug: copy no longer treat `to` as full path of target or should mark as breaking

[nekomeowww]

Reproduction link or steps

https://stackblitz.com/edit/github-q5kq15gz?file=tsdown.config.ts

import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['src/index.ts'],
  external: ['./index.css'],
  copy: [
    { from: 'src/index.css', to: 'dist/index.css' },
  ],
  unbundle: true,
})

What is expected?

Copying files from src/index.css to dist/index.css

What is actually happening?

Copying files from src/index.css to dist/index.css/index.css

Any additional comments?

Workaround:

import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['src/index.ts'],
  external: ['./index.css'],
  copy: [
--    { from: 'src/index.css', to: 'dist/index.css' },
++    { from: 'src/index.css', to: 'dist' },
  ],
  unbundle: true,
})

[nekomeowww]

Possibly related to #634

[sxzz]

It's a breaking change.

[hi-ogawa]

Shouldn't this be released as v0.18?

[sxzz]

In v0.17.3, we unintentionally introduced a breaking change. At this point, whether we fix it or not, the breaking change has already been inevitably introduced.

[sxzz]

I will deprecate these two versions and release a minor soon