Syntax check rust with -Zno-trans instead of -Zparse-only

[faern]

Only parsing missed a lot of errors. This PR changes so more steps of the compile is executed and more errors are found. The solution required some extra code to detect if we are in a standalone rs file or inside a crate since that affected if I could use crate rustc -Zno-trans or rustc -Zno-trans

Fixes #67

[rust-highfive]

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[chris-morgan]

With anything like this I’m concerned about performance. Even no-trans can take many seconds for larger crates, where parse-only of the current file is universally fast.

[faern]

You are right, this is a problem. On the other hand the linting really need to get better IMO. Do you know if there is any way to run this in the background that will not block the editor?

[somini]

I'm sorry if I'm intruding, but this interests me, as syntax-only linting is pretty poor as @faern said.
I think the best course of action is making the fast behaviour the default, and having this as an option. You can then use syntastic in passive mode for rust files, meaning it will only run on SyntasticCheck. That should diminish the performance problems.

[faern]

@somini Not intruding at all. You could continue on this PR if you would like to. I don't have any time to continue on this as I'm not using vim for Rust any longer.

[ticki]

Any update on this?

[faern]

Nope. I don't use vim any longer so I won't contribute to this. Could close the PR, but not sure if anyone else wanted to continue.

[somini]

I'm tracking this on #76, so you can close this.

[ghost]

@faern what do you use instead? curious if I would be interested to make the same change :)