Use Cargo to install rust deps into //third_party/rust_crates

[ry]

Currently we are using gclient to mange rust deps:
https://github.com/ry/deno/blob/ad4f335847daffcc5556008aebebaf2d1eecac67/gclient_config.py#L42-L65
These get installed by tools/build_third_party.py
https://github.com/ry/deno/blob/ad4f335847daffcc5556008aebebaf2d1eecac67/tools/build_third_party.py#L30
This task would instead call cargo install to put that source code into //third_party/rust_crates.

I still want to define the build and linking manually in //build_extra/rust/BUILD.gn:
https://github.com/ry/deno/blob/master/build_extra/rust/BUILD.gn#L24-L57
This task is only about how to fetch the source code. Deno does not aim to build like a normal rust package at this point. "cargo build" in the root project directory will fail - that's ok.

Part of this task will be creating a Cargo.toml file for the project. There are only two third party deps so far: "url" and "libc".

[robbym]

I was under the assumption that cargo install was strictly for downloading and installing binary packages instead of libraries (mentioned here rust-lang/cargo#2552). Although I get the idea of what you want.

[robbym]

cargo fetch seems to be the one. Will investigate.
Have also been referenced https://github.com/alexcrichton/cargo-vendor

Edit: cargo fetch and the info on it seems to be outdated.

[robbym]

This functionality doesn't seem to exist in one place, one tool more specifically.
There is an open issue that addresses it though.
rust-lang/cargo#1861

[robbym]

The third-party cargo subcommand cargo clone does the right thing: https://github.com/JanLikar/cargo-clone, but its command line arguments only.

[f-a-a]

Following from the discussions in #370:

• Manually parsing Cargo.toml and maintaining the program within deno is a no-go (introducing unnecessary complexity)
• Most sensible approach is to introduce a cargo subcommand to achieve:

cargo download-deps --download_path=third_party/rust_crates/ --config=./Cargo.toml

and call it in ./tools/build_third_party.py. (@robbym created a POC)

[ry]

Fixed in d93bd4b