cli --external flag does not work as tsdown

[jantimon]

Reproduction link or steps

Migrated from tsup with npx tsdown migrate - worked well but I ran into one issue:

tsup --external react
ESM dist/context.mjs 603.00 B

vs

tsdown --external react
ℹ dist/context.mjs 13.53 kB │ gzip: 4.03 kB

Locally I fixed it with --external '/react/':
ℹ dist/context.mjs 0.79 kB │ gzip: 0.43 kB

Unfortunately that workaround with /react/ breaks my github pipeline as it hangs until timeout
maybe because react is part of the repository name?

jantimon/react-swc-suspense-tracker#4

Finally I fixed it with --external '/^react/':
ℹ dist/context.mjs 0.79 kB │ gzip: 0.43 kB

What is expected?

tsdown --external react should do the same as tsup --external react

What is actually happening?

tsup --external react added a lot of additional code to my dist file

Any additional comments?

No response

[sxzz]

This is indeed a minor difference between tsdown and tsup, and we should make sure to highlight it in the migration documentation.