Would like a way to pass arguments to cargo, before "build"

[ijackson]

Motivation

I would like to be able to pass global options to cargo. In particular, I use --locked and --offline quite heavily. --locked is useful to avoid unwanted updates. --offline is important if I'm in a poor (or expensive) network environment.

💡 Feature description

Currently, -- introduces options to cargo build. It's not so easy to shoehorn an additional free-form list of arguments. I suggest we take a leaf from compiler drivers like gcc, and introduce a repeatable option that adds one additional cargo argument.

💻 Basic example

So, you could say something like

   wasm-pack --cargo-opt=--locked --cargo-opt=--verbose --cargo-opt=--color=never build

If your cargo is actually rustup pretending to be cargo (so normally you can say cargo +nightly build) and you encounter #629, you could say

  wasm-pack --cargo-opt=+nightly build

Alternatives

The only plausible alternative for a user like me right now, without some change to wasm-pack, is to live with the unwanted lockfile updates, or to put a stunt wrapper for cargo on the PATH. Or to abandon wasm-pack and go to wasm-bindgen-cli.

As for the proposed command line syntax for wasm-pack, I think --cargo-opt=... is probably the best but I'm happy to implement whatever syntax you prefer. If you are looking for prior art, gcc has -Wl,--some-linker-option, but that's not very readable. -C... would be a possibility but steals a single-letter option.

I'm sure the value ought to be the whole thing passed to cargo, not just the part after --. Anything else would be really very confusing.

Another possibilty would be to do something more complicated, perhaps with --- meaning something special, but it doesn't seem desirable for wasm-pack's command line parsing to be funky and exciting. It should be straightforward, and rather unusual use cases like mine definitely don't need super-brief syntax.