Subject: [PATCH] Allow limiting the size of *Completions*

From: Spencer Baugh <[email-masked]>
Date: Wed, 27 Nov 2024 15:25:19 -0500

Tags: patch

>From profiling, the main bottleneck in completion over large
completion sets is display-completion-list, when there are many
available candidates.  For example, in my large monorepo, when
completing over the 589196 files or the 73897 branches, even with the
candidates narrowed down by typing some prefix to complete, TAB (when
it shows *Completions*) or ? is slow, mostly in
display-completion-list.

By adding completions-list-max with a very large default, performance
is greatly improved in these situations without impacting the normal
case of completion on reasonably sized sets.

Limiting the work done by display-completion-list is also important
for packages which auto-update *Completions* inside while-no-input:
since display-completion-list doesn't do anything which reads input,
while-no-input won't interrupt it.  Such packages can instead just
bind completions-list-max to a smaller value.

* lisp/minibuffer.el (display-completion-list): Add FULL-COUNT
argument.
(completions-list-max): Add.
(minibuffer-completion-help): Truncate completions based on
completions-list-max.

In GNU Emacs 29.2.50 (build 9, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2024-11-20 built on
 igm-qws-u22796a
Repository revision: 28dc0b6f9987e0def7dff4deaa23aa60f021d2a7
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Rocky Linux 8.10 (Green Obsidian)

Configured using:
 'configure --with-x-toolkit=lucid --without-gpm --without-gconf
 --without-selinux --without-imagemagick --with-modules --with-gif=no
 --with-tree-sitter --with-native-compilation=aot
 PKG_CONFIG_PATH=/usr/local/home/garnish/libtree-sitter/0.22.6-1/lib/pkgconfig/'

>From 808b1a6d01fcd2d2cc03324aa9826b3160047653 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <[email-masked]>
Date: Thu, 14 Nov 2024 17:14:10 -0500
Subject: [PATCH] Allow limiting the size of *Completions*

>From profiling, the main bottleneck in completion over large
completion sets is display-completion-list, when there are many
available candidates.  For example, in my large monorepo, when
completing over the 589196 files or the 73897 branches, even with the
candidates narrowed down by typing some prefix to complete, TAB (when
it shows *Completions*) or ? is slow, mostly in
display-completion-list.

By adding completions-list-max with a very large default, performance
is greatly improved in these situations without impacting the normal
case of completion on reasonably sized sets.

Limiting the work done by display-completion-list is also important
for packages which auto-update *Completions* inside while-no-input:
since display-completion-list doesn't do anything which reads input,
while-no-input won't interrupt it.  Such packages can instead just
bind completions-list-max to a smaller value.

* lisp/minibuffer.el (display-completion-list): Add FULL-COUNT
argument.
(completions-list-max): Add.
(minibuffer-completion-help): Truncate completions based on
completions-list-max.
---
 lisp/minibuffer.el | 38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 5d11064d900..8078e1603ae 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -2354,7 +2354,7 @@ completion-hilit-commonality
         completions)
        base-size))))
 
-(defun display-completion-list (completions &optional common-substring group-fun)
+(defun display-completion-list (completions &optional common-substring group-fun full-count)
   "Display the list of completions, COMPLETIONS, using `standard-output'.
 Each element may be just a symbol or string
 or may be a list of two strings to be printed as if concatenated.
@@ -2366,7 +2366,9 @@ display-completion-list
 At the end, this runs the normal hook `completion-setup-hook'.
 It can find the completion buffer in `standard-output'.
 GROUP-FUN is a `group-function' used for grouping the completion
-candidates."
+candidates.
+If FULL-COUNT is non-nil, it's used as the total number of
+completions."
   (declare (advertised-calling-convention (completions) "24.4"))
   (if common-substring
       (setq completions (completion-hilit-commonality
@@ -2379,17 +2381,24 @@ display-completion-list
 	(let ((standard-output (current-buffer))
 	      (completion-setup-hook nil))
           (with-suppressed-warnings ((callargs display-completion-list))
-	    (display-completion-list completions common-substring group-fun)))
+	    (display-completion-list completions common-substring group-fun full-count)))
 	(princ (buffer-string)))
 
     (with-current-buffer standard-output
       (goto-char (point-max))
       (if completions-header-format
-          (insert (format completions-header-format (length completions)))
+          (insert (format completions-header-format (or full-count (length completions))))
         (unless completion-show-help
           ;; Ensure beginning-of-buffer isn't a completion.
           (insert (propertize "\n" 'face '(:height 0)))))
-      (completion--insert-strings completions group-fun)))
+      (completion--insert-strings completions group-fun)
+      (when (and full-count (/= full-count (length completions)))
+        (newline)
+        (insert (propertize
+                 (format "Displaying %s of %s possible completions.\n"
+                         (length completions) full-count)
+                 'face
+                 'shadow)))))
 
   (run-hooks 'completion-setup-hook)
   nil)
@@ -2455,6 +2464,15 @@ completions--fit-window-to-buffer
         (resize-temp-buffer-window win))
     (fit-window-to-buffer win completions-max-height)))
 
+(defcustom completions-list-max 10000
+  "Maximum number of completions for `minibuffer-completion-help' to list.
+
+After the completions are sorted, any beyond this amount are
+discarded and a message about truncation is inserted.  This can
+improve performance when displaying large numbers of completions."
+  :type 'number
+  :version "31.1")
+
 (defcustom completion-auto-deselect t
   "If non-nil, deselect current completion candidate when you type in minibuffer.
 
@@ -2554,7 +2572,8 @@ minibuffer-completion-help
              ;; window, mark it as softly-dedicated, so bury-buffer in
              ;; minibuffer-hide-completions will know whether to
              ;; delete the window or not.
-             (display-buffer-mark-dedicated 'soft))
+             (display-buffer-mark-dedicated 'soft)
+             full-count)
         (with-current-buffer-window
           "*Completions*"
           ;; This is a copy of `display-buffer-fallback-action'
@@ -2610,6 +2629,11 @@ minibuffer-completion-help
                                  (_ completions-group-sort))
                                completions)))
 
+                      (when completions-list-max
+                        (setq full-count (length completions))
+                        (when (< completions-list-max full-count)
+                          (setq completions (take completions-list-max completions))))
+
                       (cond
                        (aff-fun
                         (setq completions
@@ -2661,7 +2685,7 @@ minibuffer-completion-help
                                                      (if (eq (car bounds) (length result))
                                                          'exact 'finished))))))
 
-                      (display-completion-list completions nil group-fun)
+                      (display-completion-list completions nil group-fun full-count)
                       (when current-candidate-and-offset
                         (with-current-buffer standard-output
                           (when-let* ((match (text-property-search-forward
-- 
2.39.3