Check if rustc exists before building a Rust project type

[ObsidianMinor]

Fixes #487

[EverlastingBugstopper]

looks good! thanks for adding this 😄

[EverlastingBugstopper]

use wrangler::terminal::styles;

let rust_url = styles::url("https://www.rust-lang.org/tools/install");

Suggested change

	.map_err(|e| failure::format_err!("'rustc' not found: {}", e))?;
	.map_err(|e| failure::format_err!("'rustc' not found, installation documentation can be found here: {}, rust_url))?;

[EverlastingBugstopper]

lets point the devs in the right direction for installation here just so it's easy for them to find.

[ObsidianMinor]

It might be good to still print the error message. Maybe:

                .map_err(|e| failure::format_err!(
"'rustc' not found: {}. Installation documentation can be found here: {}",
e, styles::url("https://www.rust-lang.org/tools/install")))?;

[EverlastingBugstopper]

what does the error message look like when it's printed out there? can you give an example?

[ObsidianMinor]

I believe it'd look something like:
'rustc' not found: cannot find binary path. Installation documentation can be found here: https://www.rust-lang.org/tools/install

Where "cannot find binary path" would be any of the messages from which::Error

#[derive(thiserror::Error, Copy, Clone, Eq, PartialEq, Debug)]
pub enum Error {
    #[error("bad absolute path")]
    BadAbsolutePath,
    #[error("bad relative path")]
    BadRelativePath,
    #[error("cannot find binary path")]
    CannotFindBinaryPath,
    #[error("cannot get current directory")]
    CannotGetCurrentDir,
    #[error("cannot canonicalize path")]
    CannotCanonicalize,
}

[EverlastingBugstopper]

👍 sounds good to me

[EverlastingBugstopper]

thanks :)