[BUG] Cannot destructure property 'output'

[resynth1943]

Describe the bug

When using the CLI, I have encountered the following runtime error.

deno run --unstable --allow-read --allow-write --allow-env --allow-net https://deno.land/x/denopack@0.10.0/cli.ts --config ./bundle.config.ts

error: Uncaught (in promise) TypeError: Cannot destructure property 'output' of 'opts' as it is undefined.
  const { output: _outputOpts, ...rollupOpts } = opts;
                  ^
    at mergeOptions (options.ts:64:19)
    at runBundler (runBundler.ts:30:53)

To Reproduce
Steps to reproduce the behavior:

1. Run the above command.
2. Error! 👻

Expected behavior

I expected it to work. 😛

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Fedora 33
• Deno version: see below.

deno 1.5.4 (bc79d55, release, x86_64-unknown-linux-gnu)
v8 8.8.278.2
typescript 4.0.5

• denopack version: 0.10.0

Checklist

• I am using Deno version 1.2.0 or higher

[resynth1943]

EDIT: I see the error. My Rollup configuration file is actually empty.

The error seems to occur here:

denopack/cli/options.ts

Line 64 in 2d491bb

const { output: _outputOpts, ...rollupOpts } = opts;

A possible solution would be to check if opts isn't undefined without destructuring it~~, but I'm unsure as to why it wouldn't be defined (especially when it's pointed at a valid configuration file)~~.

So mergeOptions is called here:

denopack/cli/runBundler.ts

Line 30 in dfe1060

const [rollupOpts, outputOpts, outputDir] = await mergeOptions(

It seems like you aren't checking the value of the import([...]) call before destructuring it. One possible solution would be to throw if a --config value has been provided, and one of the following apply:

• the path doesn't exist
• the exported value isn't correct

Would you like me to submit a PR?

[resynth1943]

P.S. nice code-base, keep it up! Love seeing clean code in the wild. ❤️