Add cargo as a checker for syntastic

[innerand]

Add let g:syntastic_rust_checkers = ['cargo'] to vimrc and syntastic uses cargo check for syntax checking.

[arrufat]

I just want to say that I have been using this for some months now without any issue. I hope it gets accepted

[ghost]

Does this work correctly inside a workspace? (note: that #76 does not, for it finds the subproject Cargo.toml only, instead of workspace's Cargo.toml which is ../ relative to subproject, thus vim/syntastic won't know how to find the files reported in the errors since they are relative to workspace dir, not subproject(aka package?) dir)

[ghost]

Looks like the file that this PR adds, already exists in the repo: https://github.com/rust-lang/rust.vim/blob/master/syntax_checkers/rust/cargo.vim
and it seems to do the same thing? although there are differences:

--- thisPR/cargo.vim	2018-01-05 04:16:42.279586031 +0100
+++ repo/cargo.vim	2018-01-02 22:00:32.568566104 +0100
@@ -1,47 +1,47 @@
 " Vim syntastic plugin
 " Language:     Rust
-" Maintainer:   Innerand  <innerand@nxa.at>
-"
-" Adapted version of the rustc plugin by Andrew Gallant
+" Maintainer:   Julien Levesy <jlevesy@gmail.com>
 "
 " See for details on how to add an external Syntastic checker:
 " https://github.com/scrooloose/syntastic/wiki/Syntax-Checker-Guide#external
-"
 
 if exists("g:loaded_syntastic_rust_cargo_checker")
     finish
 endif
+
 let g:loaded_syntastic_rust_cargo_checker = 1
 
+" Force syntastic to call cargo without a specific file name
+let g:syntastic_rust_cargo_fname = ""
+
 let s:save_cpo = &cpo
 set cpo&vim
 
+function! SyntaxCheckers_rust_cargo_IsAvailable() dict
+  return executable(self.getExec()) &&
+    \ syntastic#util#versionIsAtLeast(self.getVersion(), [0, 16, 0])
+endfunction
+
 function! SyntaxCheckers_rust_cargo_GetLocList() dict
-    let makeprg = self.makeprgBuild({
-             \ 'args': 'check',
-             \ 'fname': '' })
+    let makeprg = self.makeprgBuild({ "args": "check" })
 
-    " Old errorformat (before nightly 2016/08/10)
+    " Ignored patterns, and blank lines
     let errorformat  =
-        \ '%E%f:%l:%c: %\d%#:%\d%# %.%\{-}error:%.%\{-} %m,'   .
-        \ '%W%f:%l:%c: %\d%#:%\d%# %.%\{-}warning:%.%\{-} %m,' .
-        \ '%C%f:%l %m'
-
-    " New errorformat (after nightly 2016/08/10)
-    let errorformat  .=
-        \ ',' .
         \ '%-G,' .
         \ '%-Gerror: aborting %.%#,' .
-        \ '%-Gerror: Could not compile %.%#,' .
+        \ '%-Gerror: Could not compile %.%#,'
+
+    " Meaningful lines (errors, notes, warnings, contextual information)
+    let errorformat .=
         \ '%Eerror: %m,' .
         \ '%Eerror[E%n]: %m,' .
-        \ '%-Gwarning: the option `Z` is unstable %.%#,' .
         \ '%Wwarning: %m,' .
         \ '%Inote: %m,' .
         \ '%C %#--> %f:%l:%c'
 
     return SyntasticMake({
         \ 'makeprg': makeprg,
+        \ 'cwd': expand('%:p:h'),
         \ 'errorformat': errorformat })
 endfunction
 

[innerand]

This PR is from 03/17, that file was added by a PR from 12/16 merged in 08/17.
#132
I should have checked open PRs before implementing.

[ghost]

well, from what I tested, neither handle the case when cwd is src, like PR #76 does :)
ie. they assume I always do vim src/main.rs instead of cd src; vim main.rs and thus in the latter case, no errors will be shown in vim.

No matter though, I patched cargo, for my own use, to always pass absolute filenames to rustc, thus rustc-reported errors are always full paths, thus not needing any cwd changes for vim to show errors even in case of workspaces.