Fix #518 Fix handling of spaces in filenames for various linters

autoload/ale/path.vim

@@ -55,3 +55,30 @@ endfunction
 function! ale#path#BufferCdString(buffer) abort
     return ale#path#CdString(fnamemodify(bufname(a:buffer), ':p:h'))
 endfunction
+
+" Return 1 if a path is an absolute path.
+function! ale#path#IsAbsolute(filename) abort
+    return match(a:filename, '^\v/|^[a-zA-Z]:\\') == 0
+endfunction
+
+" Given a directory and a filename, resolve the path, which may be relative
+" or absolute, and get an absolute path to the file, following symlinks.
+function! ale#path#Resolve(directory, filename) abort
+    return resolve(
+    \   ale#path#IsAbsolute(a:filename)
+    \       ? a:filename
+    \       : a:directory . '/' . a:filename
+    \)
+endfunction
+
+" Given a buffer number and a relative or absolute path, return 1 if the
+" two paths represent the same file on disk.
+function! ale#path#IsBufferPath(buffer, filename) abort
+    let l:buffer_filename = expand('#' . a:buffer . ':p')
+    let l:resolved_filename = ale#path#Resolve(
+    \   fnamemodify(l:buffer_filename, ':h'),
+    \   a:filename
+    \)
+
+    return resolve(l:buffer_filename) == l:resolved_filename
+endfunction