#333 Add the List needed for the lint_file option, and option itself. Neither do anything meaningful yet

autoload/ale/engine.vim

@@ -28,6 +28,8 @@ function! ale#engine#InitBufferInfo(buffer) abort
     if !has_key(g:ale_buffer_info, a:buffer)
         " job_list will hold the list of jobs
         " loclist holds the loclist items after all jobs have completed.
+        " lint_file_loclist holds items from the last run including linters
+        "   which use the lint_file option.
         " new_loclist holds loclist items while jobs are being run.
         " temporary_file_list holds temporary files to be cleaned up
         " temporary_directory_list holds temporary directories to be cleaned up
@@ -35,6 +37,7 @@ function! ale#engine#InitBufferInfo(buffer) abort
         let g:ale_buffer_info[a:buffer] = {
         \   'job_list': [],
         \   'loclist': [],
+        \   'lint_file_loclist': [],
         \   'new_loclist': [],
         \   'temporary_file_list': [],
         \   'temporary_directory_list': [],

autoload/ale/linter.vim

@@ -142,13 +142,25 @@ function! ale#linter#PreProcess(linter) abort
         throw "`output_stream` must be 'stdout', 'stderr', or 'both'"
     endif
 
+    " An option indicating that this linter should only be run against the
+    " file on disk.
+    let l:obj.lint_file = get(a:linter, 'lint_file', 0)
+
+    if !s:IsBoolean(l:obj.lint_file)
+        throw '`lint_file` must be `0` or `1`'
+    endif
+
     " An option indicating that the buffer should be read.
-    let l:obj.read_buffer = get(a:linter, 'read_buffer', 1)
+    let l:obj.read_buffer = get(a:linter, 'read_buffer', !l:obj.lint_file)
 
     if !s:IsBoolean(l:obj.read_buffer)
         throw '`read_buffer` must be `0` or `1`'
     endif
 
+    if l:obj.lint_file && l:obj.read_buffer
+        throw 'Only one of `lint_file` or `read_buffer` can be `1`'
+    endif
+
     return l:obj
 endfunction