Support building debug versions of packages.

[itsybitesyspider]

I had a personal need to generate a debug version of a package in my project and quickly implemented a --debug flag. It may require some bikesheddish discussion:

(1) --debug is the opposite of the flag used by cargo (--release). Usage is more obvious if the wasm-pack flag is identical to the already-familiary cargo flag, however switching to --release also changes the default behavior of wasm-pack.

(2) There's a --debug flag in wasm-bindgen that we might also hook into.

(3) Not sure if this is within the scope of wasm-pack.

[ashleygwilliams]

hi @clanehin - thanks for filing this! i'm not opposed to a feature like this- though i am curious to learn more about the use case you had to generate a debug version of a package- would you mind sharing?

[itsybitesyspider]

Sure. Easiest just to tell the story. I was working on an electron app structured as a lerna monorepo. I decided that some of the modules were good candidates to experimentally port to rust, which I did, partly because wasm-pack was so easy to use.

Inevitably, one of the components had a bug, and I wrote some assertions to catch the problem early. The assertions are useful and I want to keep them in the program, but they change the big-O runtime of the program rather dramatically, so it seemed to make sense to put them behind cfg(debug_assertions).

Of course, those assertions only fire in --debug. At that point, adding the debug flag to wasm-pack was easy, and I've been wanting to contribute more anyway, so I did, and here we are. :)

I can budget some time to follow up with additional changes, if you think the project will benefit from them. Not sure what direction you want go, though.

[ashleygwilliams]

@clanehin thanks so much for sharing! i think i realy dig this and am gonna try to sneak it into today's release... :D