Options for bundle#generate() are incorrectly passed

[Comandeer]

• Rollup Version: 1.26.4
• Operating System (or Browser): macOS 10.15.1
• Node Version: 12.6.0

How Do We Reproduce?

I've prepared repo with minimal reproduction: https://github.com/Comandeer/bugs-reports/tree/rollup-output-options

To reproduce the problem, clone the repo and run:

npm i && npm start

Expected Behavior

Rollup correctly creates bundle and display info about it.

Actual Behavior

Error is thrown:

Error: You must specify "output.format", which can be one of "amd", "cjs", "system", "esm", "iife" or "umd".

It seems that bundle#generate() does not get options.output options. Passing same object to rollup#rollup() and bundle#generate() works correctly in 1.26.3, it stopped working in 1.26.4 (probably due to https://github.com/rollup/rollup/pull/3217/files#diff-c5fd8e65630bd641bf07130346ee8778R438 ).

[lukastaegert]

Sorry about that. Fix at #3223. To my defence, this is a completely undocumented and untested feature from before my time, and also a somewhat dirty one as it only works if there is a single output and there was obviously no validation.