From 3f27a63fe5be884464a6a68407e0b6990186c4a6 Mon Sep 17 00:00:00 2001
From: Augusto Stoffel <arstoffel@gmail.com>
Date: Fri, 10 Sep 2021 20:44:10 +0200
Subject: [PATCH] Implement caching for 'python-shell-completion-at-point'

* lisp/progmodes/python.el (python-shell-completion-at-point): cache
results, since computing them involves talking with the inferior
process and, potentially, network communications
(python-shell--capf-cache): new variable, for cache
(python-shell-completion-get-completions,
python-shell-completion-native-get-completions): 'import' argument is
not needed anymore.
(python-shell-completion-native-setup,
python-shell-completion-native-try): pass the setup code
synchronously, to avoid printing a message in the shell.
---
 lisp/progmodes/python.el | 59 ++++++++++++++++++++--------------------
 1 file changed, 30 insertions(+), 29 deletions(-)

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 2eef52de0c..e71a8102df 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -3577,13 +3577,12 @@ python-shell-completion-native-try
          python-shell-completion-native-try-output-timeout))
     (python-shell-completion-native-get-completions
      (get-buffer-process (current-buffer))
-     nil "_")))
+     "_")))
 
 (defun python-shell-completion-native-setup ()
   "Try to setup native completion, return non-nil on success."
-  (let ((process (python-shell-get-process)))
-    (with-current-buffer (process-buffer process)
-      (python-shell-send-string "
+  (let* ((process (python-shell-get-process))
+         (output (python-shell-send-string-no-output "
 def __PYTHON_EL_native_completion_setup():
     try:
         import readline
@@ -3693,14 +3692,10 @@ python-shell-completion-native-setup
         print ('python.el: native completion setup failed, %s: %s'
                % sys.exc_info()[:2])
 
-__PYTHON_EL_native_completion_setup()" process)
-      (when (and
-             (python-shell-accept-process-output
-              process python-shell-completion-native-try-output-timeout)
-             (save-excursion
-               (re-search-backward
-                (regexp-quote "python.el: native completion setup loaded") nil t 1)))
-        (python-shell-completion-native-try)))))
+__PYTHON_EL_native_completion_setup()" process)))
+    (when (string-match-p "python\\.el: native completion setup loaded"
+                          output)
+      (python-shell-completion-native-try))))
 
 (defun python-shell-completion-native-turn-off (&optional msg)
   "Turn off shell native completions.
@@ -3760,13 +3755,10 @@ python-shell-completion-native-toggle
       (python-shell-completion-native-turn-on msg))
     python-shell-completion-native-enable))
 
-(defun python-shell-completion-native-get-completions (process import input)
-  "Get completions using native readline for PROCESS.
-When IMPORT is non-nil takes precedence over INPUT for
-completion."
+(defun python-shell-completion-native-get-completions (process input)
+  "Get completions of INPUT using native readline for PROCESS."
   (with-current-buffer (process-buffer process)
-    (let* ((input (or import input))
-           (original-filter-fn (process-filter process))
+    (let* ((original-filter-fn (process-filter process))
            (redirect-buffer (get-buffer-create
                              python-shell-completion-native-redirect-buffer))
            (trigger "\t")
@@ -3818,11 +3810,8 @@ python-shell-completion-native-get-completions
                  :test #'string=))))
         (set-process-filter process original-filter-fn)))))
 
-(defun python-shell-completion-get-completions (process import input)
-  "Do completion at point using PROCESS for IMPORT or INPUT.
-When IMPORT is non-nil takes precedence over INPUT for
-completion."
-  (setq input (or import input))
+(defun python-shell-completion-get-completions (process input)
+  "Get completions of INPUT using PROCESS."
   (with-current-buffer (process-buffer process)
     (let ((completions
            (python-util-strip-string
@@ -3836,6 +3825,9 @@ python-shell-completion-get-completions
         (split-string completions
                       "^'\\|^\"\\|;\\|'$\\|\"$" t)))))
 
+(defvar-local python-shell--capf-cache nil
+  "Variable to store cached completions and invalidation keys.")
+
 (defun python-shell-completion-at-point (&optional process)
   "Function for `completion-at-point-functions' in `inferior-python-mode'.
 Optional argument PROCESS forces completions to be retrieved
@@ -3889,12 +3881,21 @@ python-shell-completion-at-point
                        ;; it during a multiline statement (Bug#28051).
                        #'ignore
                      #'python-shell-completion-get-completions))
-                  (t #'python-shell-completion-native-get-completions)))))
-    (list start end
-          (completion-table-dynamic
-           (apply-partially
-            completion-fn
-            process import-statement)))))
+                  (t #'python-shell-completion-native-get-completions))))
+         (prev-prompt (car python-shell--capf-cache))
+         (re (or (cadr python-shell--capf-cache) regexp-unmatchable))
+         (prefix (buffer-substring-no-properties start end)))
+    ;; To invalidate the cache, we check if the prompt position or the
+    ;; completion prefix changed.
+    (unless (and (equal prev-prompt (car prompt-boundaries))
+                 (string-match re prefix))
+      (setq python-shell--capf-cache
+            `(,(car prompt-boundaries)
+              ,(if (string-empty-p prefix)
+                   regexp-unmatchable
+                 (concat "\\`" (regexp-quote prefix) "\\(?:\\sw\\|\\s_\\)*\\'"))
+              ,@(funcall completion-fn process (or import-statement prefix)))))
+    (list start end (cddr python-shell--capf-cache))))
 
 (define-obsolete-function-alias
   'python-shell-completion-complete-at-point
-- 
2.31.1