racer-rust-src-path defaults to rustup source directory

[ghost]

Fixes issue #54. Works for both old and new versions of racer.

[coveralls]

Coverage remained the same at 66.106% when pulling c843e09 on jonves:master into 485b827 on racer-rust:master.

[coveralls]

Coverage remained the same at 66.106% when pulling c843e09 on jonves:master into 485b827 on racer-rust:master.

[Wilfred]

Thanks for your contribution! This is definitely a worthwhile improvement.

This code currently assumes that rustc is on path, which leads to:

ELISP> (concat (shell-command-to-string "rustc --print sysroot") "/lib/rustlib/src/rust/src")
"zsh:1: command not found: rustc\n/lib/rustlib/src/rust/src"

I suggest we use (executable-find "rustc") to confirm that rustc is on path first.

In the spirit of not breaking people's setups, I think we should still fall back to "/usr/local/src/rust/src". Users might be depending on that.

[coveralls]

Coverage remained the same at 66.106% when pulling 4952491 on jonves:master into 485b827 on racer-rust:master.

[coveralls]

Coverage remained the same at 66.106% when pulling 4952491 on jonves:master into 485b827 on racer-rust:master.

[ghost]

Updated pull request.

racer-rust-src-path will now verify that rustc is in path, and if so, will check if the rust source has been installed via rustup. If present, use it, otherwise fall back to "/usr/local/src/rust/src" as default.

I think this would allow users of rustup to safely ignore racer-rust-src-path, while remaining backwards compatible with current users.

[Wilfred]

Thanks! :)