Set proper current directory for quickfix with 'cargo' compiler

The buffer-local current directory of the quickfix window should
match the location of the Cargo.toml file.

Fixes rust-lang#230.

Author: da-x

autoload/cargo/quickfix.vim

@@ -0,0 +1,26 @@
+function! cargo#quickfix#CmdPre() abort
+    if &filetype ==# 'rust' && get(b:, 'current_compiler', '') ==# 'cargo'
+        " Preserve the current directory, and 'lcd' to the nearest Cargo file.
+        let b:rust_compiler_cargo_qf_has_lcd = haslocaldir()
+        let b:rust_compiler_cargo_qf_prev_cd = getcwd()
+        let b:rust_compiler_cargo_qf_prev_cd_saved = 1
+        let l:nearest = fnamemodify(cargo#nearestRootCargo(0), ':h')
+        execute 'lchdir! '.l:nearest
+    else
+        let b:rust_compiler_cargo_qf_prev_cd_saved = 0
+    endif
+endfunction
+
+function! cargo#quickfix#CmdPost() abort
+    if b:rust_compiler_cargo_qf_prev_cd_saved
+        " Restore the current directory.
+        if b:rust_compiler_cargo_qf_has_lcd
+            execute 'lchdir! '.b:rust_compiler_cargo_qf_prev_cd
+        else
+            execute 'chdir! '.b:rust_compiler_cargo_qf_prev_cd
+        endif
+        let b:rust_compiler_cargo_qf_prev_cd_saved = 0
+    endif
+endfunction
+
+" vim: set et sw=4 sts=4 ts=8:

compiler/cargo.vim

@@ -23,6 +23,12 @@ else
     CompilerSet makeprg=cargo\ $*
 endif
 
+augroup RustCargoQuickFixHooks
+    autocmd!
+    autocmd QuickFixCmdPre make call cargo#quickfix#CmdPre()
+    autocmd QuickFixCmdPost make call cargo#quickfix#CmdPost()
+augroup END
+
 " Ignore general cargo progress messages
 CompilerSet errorformat+=
             \%-G%\\s%#Downloading%.%#,