Implement statix Linter and Fixer (#3969)

* Add Statix for Linting

Add `statix check` as a linter. Provides a simple set of definition
tests additionally. Variable names specify "check" to allow for later
addition of `statix fix` as a formatter once stream support is added.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fixup Supported Tools List

I didn't realise there were two separate lists of tools, so add statix
to the other list. Also, remembered "S" comes after "R", and so
re-ordered it.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fix statix Test File

I refactored the variables for statix to allow for writing a fixer
later, and forgot to update them in the test, so update them now. Also
remove a stray "i", add missing space before checks

Signed-off-by: David Houston <houstdav000@gmail.com>

* Update Output Stream for v0.4.0

statix v0.4.0 provides a breaking change of output stream from stderr to
stdout.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Add statix fix Fixer

Implement statix fix as a fixer for simple Nix antipatterns.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fix statix Fixer Tests

Fix the statix fixer tests by removing the unnecessary
'read_temporary_file' value from the command, since it simply uses the
default value.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Add statix Handler Test

Add a test for the statix handler per @hsanson's request.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Fix to run only on stdin for linting

Signed-off-by: David Houston <houstdav000@gmail.com>

doc/ale-nix.txt

@@ -7,24 +7,24 @@ nixfmt                                                         *ale-nix-nixfmt*
 
 g:ale_nix_nixfmt_executable                       *g:ale_nix_nixfmt_executable*
                                                   *b:ale_nix_nixfmt_executable*
-  Type: String
-  Default: 'nixfmt'
+  Type: |String|
+  Default: `'nixfmt'`
 
   This variable sets the executable used for nixfmt.
 
 g:ale_nix_nixfmt_options                             *g:ale_nix_nixfmt_options*
                                                      *b:ale_nix_nixfmt_options*
-  Type: String
-  Default: ''
+  Type: |String|
+  Default: `''`
 
   This variable can be set to pass additional options to the nixfmt fixer.
 
 
 ===============================================================================
-nixpkgs-fmt                                                 *ale-nix-nixpkgs-fmt*
+nixpkgs-fmt                                               *ale-nix-nixpkgs-fmt*
 
-g:ale_nix_nixpkgsfmt_executable                *g:ale_nix_nixpkgsfmt_executable*
-                                               *b:ale_nix_nixpkgsfmt_executable*
+g:ale_nix_nixpkgsfmt_executable               *g:ale_nix_nixpkgsfmt_executable*
+                                              *b:ale_nix_nixpkgsfmt_executable*
   Type: |String|
   Default: `'nixpkgs-fmt'`
 
@@ -35,7 +35,44 @@ g:ale_nix_nixpkgsfmt_options                     *g:ale_nix_nixpkgsfmt_options*
   Type: |String|
   Default: `''`
 
-  This variable can be set to pass additional options to the nixpkgs-fmt fixer.
+  This variable can be set to pass additional options to the nixpkgs-fmt
+  fixer.
+
+
+===============================================================================
+statix                                                         *ale-nix-statix*
+
+g:ale_nix_statix_check_executable           *g:ale_nix_statix_check_executable*
+                                            *b:ale_nix_statix_check_executable*
+  Type: |String|
+  Default: `'statix'`
+
+  This variable sets the executable used for statix when running it as a
+  linter.
+
+g:ale_nix_statix_check_options                 *g:ale_nix_statix_check_options*
+                                               *b:ale_nix_statix_check_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be used to pass additional options to statix when running
+  it as a linter.
+
+g:ale_nix_statix_fix_executable                *g:ale_nix_fix_check_executable*
+                                               *b:ale_nix_fix_check_executable*
+  Type: |String|
+  Default: `'statix'`
+
+  This variable sets the executable used for statix when running it as a
+  fixer.
+
+g:ale_nix_statix_fix_options                     *g:ale_nix_statix_fix_options*
+                                                 *b:ale_nix_statix_fix_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be used to pass additional options to statix when running
+  it as a fixer.
 
 
 ===============================================================================

doc/ale-supported-languages-and-tools.txt

@@ -340,6 +340,7 @@ Notes:
   * `nixfmt`
   * `nixpkgs-fmt`
   * `rnix-lsp`
+  * `statix`
 * nroff
   * `alex`!!
   * `proselint`

doc/ale.txt

@@ -2879,6 +2879,7 @@ documented in additional help files.
   nix.....................................|ale-nix-options|
     nixfmt................................|ale-nix-nixfmt|
     nixpkgs-fmt...........................|ale-nix-nixpkgs-fmt|
+    statix................................|ale-nix-statix|
   nroff...................................|ale-nroff-options|
     write-good............................|ale-nroff-write-good|
   objc....................................|ale-objc-options|