Add support for `cargo clippy` (#2001)

* Add support for `cargo clippy`
* Add tests for cargo-clippy support
* Add an example to doc for how to configure ale_rust_cargo_use_clippy

ale_linters/rust/cargo.vim

@@ -9,6 +9,8 @@ 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', '')
+call ale#Set('rust_cargo_use_clippy', 0)
+call ale#Set('rust_cargo_clippy_options', '')
 
 function! ale_linters#rust#cargo#GetCargoExecutable(bufnr) abort
     if ale#path#FindNearestFile(a:bufnr, 'Cargo.toml') isnot# ''
@@ -70,14 +72,23 @@ function! ale_linters#rust#cargo#GetCommand(buffer, version_output) abort
         let l:default_feature = ''
     endif
 
+    let l:subcommand = l:use_check ? 'check' : 'build'
+    let l:clippy_options = ''
+
+    if ale#Var(a:buffer, 'rust_cargo_use_clippy')
+        let l:subcommand = 'clippy'
+        let l:clippy_options = ' ' . ale#Var(a:buffer, 'rust_cargo_clippy_options')
+    endif
+
     return l:nearest_cargo_prefix . 'cargo '
-    \   . (l:use_check ? 'check' : 'build')
+    \   . l:subcommand
     \   . (l:use_all_targets ? ' --all-targets' : '')
     \   . (l:use_examples ? ' --examples' : '')
     \   . (l:use_tests ? ' --tests' : '')
     \   . ' --frozen --message-format=json -q'
     \   . l:default_feature
     \   . l:include_features
+    \   . l:clippy_options
 endfunction
 
 call ale#linter#Define('rust', {

doc/ale-rust.txt

@@ -109,6 +109,7 @@ 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|
@@ -119,6 +120,36 @@ g:ale_rust_cargo_avoid_whole_workspace *g:ale_rust_cargo_avoid_whole_workspace*
   in the crate's directory. Otherwise, behave as usual.
 
 
+g:ale_rust_cargo_use_clippy
+                                                  *g:ale_rust_cargo_use_clippy*
+                                                  *b:ale_rust_cargo_use_clippy*
+  Type: |Number|
+  Default: `0`
+
+  When set to 1, `cargo clippy` will be used instead of `cargo check` or
+  `cargo build` as linter.
+  For details of `cargo clippy`, please visit the following link:
+
+  https://github.com/rust-lang-nursery/rust-clippy
+
+  Since `cargo clippy` is optional toolchain, it's safer to check whether
+  `cargo-clippy` is executable as follows:
+>
+    let g:ale_rust_cargo_use_clippy = executable('cargo-clippy')
+<
+
+g:ale_rust_cargo_clippy_options
+                                              *g:ale_rust_cargo_clippy_options*
+                                              *b:ale_rust_cargo_clippy_options*
+
+  Type: |String|
+  Default: `''`
+
+  When `cargo clippy` is used, this value will be added to a command line to run
+  it. This variable is useful when you want to add some extra options which
+  only `cargo clippy` supports (e.g. `--deny`).
+
+
 ===============================================================================
 rls                                                              *ale-rust-rls*
 

test/command_callback/test_cargo_command_callbacks.vader

@@ -128,3 +128,27 @@ Execute(When a crate belongs to a workspace we chdir into the crate, unless we d
   \ 'cargo --version',
   \ 'cargo check --frozen --message-format=json -q',
   \]
+
+Execute(When ale_rust_cargo_use_clippy is set, cargo-clippy is used as linter):
+  let b:ale_rust_cargo_use_clippy = 1
+  AssertLinter '', [
+  \ 'cargo --version',
+  \ 'cargo clippy --frozen --message-format=json -q ',
+  \]
+
+Execute(When ale_rust_cargo_clippy_options is set, cargo-clippy appends it to commandline):
+  let b:ale_rust_cargo_use_clippy = 1
+  let b:ale_rust_cargo_clippy_options = '-- -D warnings'
+  AssertLinter '', [
+  \ 'cargo --version',
+  \ 'cargo clippy --frozen --message-format=json -q -- -D warnings',
+  \]
+
+Execute(cargo-check does not refer ale_rust_cargo_clippy_options):
+  let b:ale_rust_cargo_use_clippy = 0
+  let b:ale_rust_cargo_use_check = 1
+  let b:ale_rust_cargo_clippy_options = '-- -D warnings'
+  AssertLinter '', [
+  \ 'cargo --version',
+  \ 'cargo check --frozen --message-format=json -q',
+  \]