Better handle slow completion functions.

This change sets a very long timeout for custom completion, as
completion functions can take an arbitrarily long time to run.

Bash commands that are not custom completions still have the current,
short timeout, to better deal with unresponsive bash processes.

Additionally, the completion table function now caches any error, to
avoid failed calls being retried when next time the function is called.

Author: szermatt

bash-completion.el

@@ -187,6 +187,15 @@ ignored."
   :type '(float)
   :group 'bash-completion)
 
+(defcustom bash-completion-command-timeout 30
+  "Number of seconds to wait for an answer from programmable
+completion functions.
+
+Programmable completion functions might take an arbitrary long
+time to run, so this should be long."
+  :type '(float)
+  :group 'bash-completion)
+
 (defcustom bash-completion-message-delay 0.4
   "Time to wait before displaying a message while waiting for results.
 
@@ -851,8 +860,13 @@ COMP_CWORD) and calls compgen.
 
 The result is a list of candidates, which might be empty."
   (let* ((buffer (bash-completion--get-buffer process))
+         (cmd-timeout (if (eq 'custom (bash-completion--type comp))
+                          bash-completion-command-timeout
+                        bash-completion-process-timeout))
          (completion-status))
-    (setq completion-status (bash-completion-send (bash-completion-generate-line comp) process))
+    (setq completion-status (bash-completion-send
+                             (bash-completion-generate-line comp)
+                             process cmd-timeout))
     (when (eq 124 completion-status)
       ;; Special 'retry-completion' exit status, typically returned by
       ;; functions bound by complete -D. Presumably, the function has
@@ -861,7 +875,9 @@ The result is a list of candidates, which might be empty."
       (bash-completion-send "complete -p" process)
       (process-put process 'complete-p (bash-completion-build-alist buffer))
       (bash-completion--customize comp process 'nodefault)
-      (setq completion-status (bash-completion-send (bash-completion-generate-line comp) process)))
+      (setq completion-status (bash-completion-send
+                               (bash-completion-generate-line comp)
+                               process cmd-timeout)))
     (when (eq 0 completion-status)
       (bash-completion-extract-candidates comp buffer))))
 
@@ -1541,7 +1557,8 @@ The result is a function that works like one built by
 `completion-table-with-cache' with the difference that the
 completions, built by `bash-completion-comm' are not filtered
 using the current Emacs completion style."
-  (let ((last-result)
+  (let ((last-result nil)
+        (last-error nil)
         (calling-buffer (current-buffer))
         (dir default-directory)
         (use-separate-process bash-completion-use-separate-processes)
@@ -1550,13 +1567,18 @@ using the current Emacs completion style."
       (if (or (eq (car-safe action) 'boundaries)
               (eq action 'metadata))
           nil
+        (when last-error (signal (car last-error) (cdr last-error)))
         (let ((result
                (or last-result
                    (let ((bash-completion-use-separate-processes use-separate-process)
                          (bash-completion-nospace nospace)
                          (default-directory dir))
                      (with-current-buffer calling-buffer
-                       (bash-completion-comm comp process))))))
+                       (condition-case err
+                           (bash-completion-comm comp process)
+                         (error
+                          (setq last-error err)
+                          (signal (car err) (cdr err)))))))))
           (setq last-result result)
           (let ((filtered-result (if predicate (mapcar predicate result) result))
                 (completion-ignore-case (process-get process 'completion-ignore-case)))