Fix and enable python-black flycheck checker

emacs.el

@@ -2030,12 +2030,25 @@ initializing."
 
 (require 'flycheck)
 
-'(flycheck-define-checker python-black
+(flycheck-define-checker python-black
+  "A Python style checker."
+  :command ("python3"
+            "-m" "black"
+            (config-file "--config" flycheck-black)
+            "--check" source)
+  :error-parser my-flycheck-parse-any-error
+  :enabled (lambda ()
+             (or (not (flycheck-python-needs-module-p 'python-black))
+                 (flycheck-python-find-module 'python-black "black")))
+  :verify (lambda (_) (flycheck-python-verify-module 'python-black "black"))
+  :modes python-mode)
+
+'(flycheck-define-checker python-black-diff
    "A Python style checker."
    :command ("python3"
              "-m" "black"
              (config-file "--config" flycheck-black)
-             "--check" source)
+             "--diff" source)
    :error-parser my-flycheck-parse-unified-diff
    :enabled (lambda ()
               (or (not (flycheck-python-needs-module-p 'python-black))
@@ -2050,8 +2063,19 @@ initializing."
              'python-black)
 
 (defun my-flycheck-parse-any-error (output checker buffer)
-  "Flycheck parser to check if OUTPUT is not empty."
-  ())
+  "Flycheck parser to check if reformat is required."
+  (with-temp-buffer
+    (insert output)
+    (goto-char (point-min))
+    (when (re-search-forward "^would reformat .*$" nil t)
+      (list (flycheck-error-new-at
+             (point-min)
+             nil
+             'error
+             ;;(format "Black: %s" (match-string 0))
+             "Black: would reformat buffer"
+             :buffer buffer
+             :checker checker)))))
 
 (defun my-flycheck-parse-unified-diff (output checker buffer)
   "Flycheck parser to parse diff output."