bug#74561: [PATCH] Allow limiting the size of *Completions*

[Spencer Baugh]

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/'

0001-Allow-limiting-the-size-of-Completions.patch
Description: Text Data