Improve pyrex cython linter.

Like many other linters, use variables for the executable and options
used by the linter.
By default, the linter now report every warnings as errors with
`--warning-errors`.
Also add include directory and set working directory to file directory.

ale_linters/pyrex/cython.vim

@@ -1,10 +1,27 @@
-" Author: w0rp <devw0rp@gmail.com>
+" Author: w0rp <devw0rp@gmail.com>,
+" Nicolas Pauss <https://github.com/nicopauss>
 " Description: cython syntax checking for cython files.
 
+call ale#Set('pyrex_cython_executable', 'cython')
+call ale#Set('pyrex_cython_options', '--warning-extra --warning-errors')
+
+function! ale_linters#pyrex#cython#GetExecutable(buffer) abort
+    return ale#Var(a:buffer, 'pyrex_cython_executable')
+endfunction
+
+function! ale_linters#pyrex#cython#GetCommand(buffer) abort
+    let l:local_dir = ale#Escape(fnamemodify(bufname(a:buffer), ':p:h'))
+
+    return ale#Escape(ale_linters#pyrex#cython#GetExecutable(a:buffer))
+    \   . ' --working ' . l:local_dir . ' --include-dir ' . l:local_dir
+    \   . ' ' . ale#Var(a:buffer, 'pyrex_cython_options')
+    \   . ' --output-file ' . g:ale#util#nul_file . ' %t'
+endfunction
+
 call ale#linter#Define('pyrex', {
 \   'name': 'cython',
 \   'output_stream': 'stderr',
-\   'executable': 'cython',
+\   'executable_callback': 'ale_linters#pyrex#cython#GetExecutable',
-\   'command': 'cython --warning-extra -o ' . g:ale#util#nul_file . ' %t',
+\   'command_callback': 'ale_linters#pyrex#cython#GetCommand',
 \   'callback': 'ale#handlers#unix#HandleAsError',
 \})

doc/ale-pyrex.txt

@@ -0,0 +1,25 @@
+===============================================================================
+ALE Pyrex (Cython) Integration                              *ale-pyrex-options*
+
+
+===============================================================================
+cython                                                       *ale-pyrex-cython*
+
+g:ale_pyrex_cython_executable                   *g:ale_pyrex_cython_executable*
+                                                *b:ale_pyrex_cython_executable*
+  Type: |String|
+  Default: `'cython'`
+
+  This variable can be changed to use a different executable for cython.
+
+
+g:ale_pyrex_cython_options                         *g:ale_pyrex_cython_options*
+                                                   *b:ale_pyrex_cython_options*
+  Type: |String|
+  Default: `'--warning-extra --warning-errors'`
+
+  This variable can be changed to modify flags given to cython.
+
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -185,6 +185,8 @@ CONTENTS                                                         *ale-contents*
       puglint.............................|ale-pug-puglint|
     puppet................................|ale-puppet-options|
       puppetlint..........................|ale-puppet-puppetlint|
+    pyrex (cython)........................|ale-pyrex-options|
+      cython..............................|ale-pyrex-cython|
     python................................|ale-python-options|
       autopep8............................|ale-python-autopep8|
       black...............................|ale-python-black|