Rust Cargo linter: Improve workspace support (#1679)

* Rust Cargo linter: Improve workspace support

When using Cargo workspaces [1], there is a 'Cargo.toml' directory in a
top level directory, listing all the crates in the project. If we are
currently editing one of the crates, 'cargo build' should execute in
that directory for that crate's separate `Cargo.toml`, otherwise Cargo
may spend more time possibly rebuilding the entire workspace, and maybe
failing on one of the other crates, instead of succeeding on the current.

[1] https://doc.rust-lang.org/book/second-edition/ch14-03-cargo-workspaces.html

ale_linters/rust/cargo.vim

@@ -6,6 +6,7 @@ call ale#Set('rust_cargo_use_check', 1)
 call ale#Set('rust_cargo_check_all_targets', 0)
 call ale#Set('rust_cargo_check_examples', 0)
 call ale#Set('rust_cargo_check_tests', 0)
+call ale#Set('rust_cargo_avoid_whole_workspace', 1)
 call ale#Set('rust_cargo_default_feature_behavior', 'default')
 call ale#Set('rust_cargo_include_features', '')
 
@@ -45,6 +46,18 @@ function! ale_linters#rust#cargo#GetCommand(buffer, version_output) abort
         let l:include_features = ' --features ' . ale#Escape(l:include_features)
     endif
 
+    let l:avoid_whole_workspace = ale#Var(a:buffer, 'rust_cargo_avoid_whole_workspace')
+    let l:nearest_cargo_prefix = ''
+
+    if l:avoid_whole_workspace
+        let l:nearest_cargo = ale#path#FindNearestFile(a:buffer, 'Cargo.toml')
+        let l:nearest_cargo_dir = fnamemodify(l:nearest_cargo, ':h')
+
+        if l:nearest_cargo_dir isnot# '.'
+            let l:nearest_cargo_prefix = 'cd '. ale#Escape(l:nearest_cargo_dir) .' && '
+        endif
+    endif
+
     let l:default_feature_behavior = ale#Var(a:buffer, 'rust_cargo_default_feature_behavior')
     if l:default_feature_behavior is# 'all'
         let l:include_features = ''
@@ -55,7 +68,7 @@ function! ale_linters#rust#cargo#GetCommand(buffer, version_output) abort
         let l:default_feature = ''
     endif
 
-    return 'cargo '
+    return l:nearest_cargo_prefix . 'cargo '
     \   . (l:use_check ? 'check' : 'build')
     \   . (l:use_all_targets ? ' --all-targets' : '')
     \   . (l:use_examples ? ' --examples' : '')

doc/ale-rust.txt

@@ -108,6 +108,15 @@ g:ale_rust_cargo_include_features           *g:ale_rust_cargo_include_features*
   When defined, ALE will set the `--features` option when invoking `cargo` to
   perform the lint check. See |g:ale_rust_cargo_default_feature_behavior|.
 
+g:ale_rust_cargo_avoid_whole_workspace *g:ale_rust_cargo_avoid_whole_workspace*
+                                       *b:ale_rust_cargo_avoid_whole_workspace*
+  Type: |Number|
+  Default: `1`
+
+  When set to 1, and ALE is used to edit a crate that is part of a Cargo
+  workspace, avoid building the entire entire workspace by invoking
+  `cargo` directly in the crate's directory. Otherwise, behave as usual.
+
 
 ===============================================================================
 rls                                                              *ale-rust-rls*

test/command_callback/test_cargo_command_callbacks.vader

@@ -5,6 +5,7 @@ Before:
   Save g:ale_rust_cargo_check_examples
   Save g:ale_rust_cargo_default_feature_behavior
   Save g:ale_rust_cargo_include_features
+  Save g:ale_rust_cargo_avoid_whole_workspace
 
   unlet! g:ale_rust_cargo_use_check
   unlet! g:ale_rust_cargo_check_all_targets
@@ -12,6 +13,7 @@ Before:
   unlet! g:ale_rust_cargo_check_examples
   unlet! g:ale_rust_cargo_default_feature_behavior
   unlet! g:ale_rust_cargo_include_features
+  unlet! g:ale_rust_cargo_avoid_whole_workspace
 
   runtime ale_linters/rust/cargo.vim
   call ale#test#SetDirectory('/testplugin/test/command_callback')
@@ -198,3 +200,24 @@ Execute(--all-features should be used when g:ale_rust_cargo_default_feature_beha
   \ ale_linters#rust#cargo#GetCommand(bufnr(''), [
   \   'cargo 0.22.0 (3423351a5 2017-10-06)',
   \ ])
+
+Execute(When a crate belongs to a workspace we chdir into the crate.):
+  call ale#test#SetFilename('cargo_workspace_paths/subpath/test.rs')
+
+  if ale#Has('win32')
+    let test_cdprefix = "C:\\testplugin\\test\\command_callback\\cargo_workspace_paths\\subpath"
+  else
+    let test_cdprefix = "'/testplugin/test/command_callback/cargo_workspace_paths/subpath'"
+  endif
+                    
+  AssertEqual
+  \ "cd ".test_cdprefix." && cargo build --frozen --message-format=json -q",
+  \ ale_linters#rust#cargo#GetCommand(bufnr(''), [])
+
+Execute(When a crate belongs to a workspace we chdir into the crate, unless we disabled it):
+  let g:ale_rust_cargo_avoid_whole_workspace = 0
+  call ale#test#SetFilename('cargo_workspace_paths/subpath/test.rs')
+
+  AssertEqual
+  \ "cargo build --frozen --message-format=json -q",
+  \ ale_linters#rust#cargo#GetCommand(bufnr(''), [])