WIP: Use `buffer-line-statistics'

2 files changed, 53 insertions, 16 deletions

diff --git a/etc/NEWS b/etc/NEWS
index fb4e8a03c4f..3f390b97712 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2235,9 +2235,17 @@ defines an additional key to exit mode like 'isearch-exit' ('RET').
 ** So Long
 
 ---
+*** New 'so-long-predicate' function 'so-long-statistics-excessive-p'
+efficiently detects the presence of a long line anywhere in the buffer
+using 'buffer-line-statistics' (see above).  This is now the default
+predicate (replacing 'so-long-detected-long-line-p').
+
+---
 *** 'so-long-threshold' and 'so-long-max-lines' have been raised to
 10000 characters and 500 lines respectively, to reduce the likelihood
-of false-positives when 'global-so-long-mode' is enabled.
+of false-positives when 'global-so-long-mode' is enabled.  The latter
+value is now only used by the old predicate, as the new predicate
+knows the longest line in the entire buffer.
 
 ---
 *** 'so-long-target-modes' now includes 'fundamental-mode' by default,
diff --git a/lisp/so-long.el b/lisp/so-long.el
index 79d0d347f80..833c4b45295 100644
--- a/lisp/so-long.el
+++ b/lisp/so-long.el
@@ -128,9 +128,9 @@
 ;; Use M-x customize-group RET so-long RET
 ;; (or M-x so-long-customize RET)
 ;;
-;; The user options `so-long-target-modes', `so-long-threshold', and
-;; `so-long-max-lines' determine whether action will be taken automatically when
-;; visiting a file, and `so-long-action' determines what will be done.
+;; The user options `so-long-target-modes' and `so-long-threshold' determine
+;; whether action will be taken automatically when visiting a file, and
+;; `so-long-action' determines what will be done.
 
 ;; * Actions and menus
 ;; -------------------
@@ -306,8 +306,9 @@
 ;; the criteria for calling `so-long' in any given mode (plus its derivatives)
 ;; by setting buffer-local values for the variables in question.  This includes
 ;; `so-long-predicate' itself, as well as any variables used by the predicate
-;; when determining the result.  By default this means `so-long-max-lines',
-;; `so-long-skip-leading-comments', and `so-long-threshold'.  E.g.:
+;; when determining the result.  By default this means `so-long-threshold' and
+;; possibly also `so-long-max-lines' and `so-long-skip-leading-comments' (these
+;; latter two are not used by default starting from Emacs 28.1).  E.g.:
 ;;
 ;;   (add-hook 'js-mode-hook 'my-js-mode-hook)
 ;;
@@ -409,7 +410,9 @@
 
 ;; * Change Log:
 ;;
-;; 1.1   - Increase `so-long-threshold' from 250 to 10,000.
+;; 1.1   - Utilise `buffer-line-statistics' in Emacs 28+, with the new
+;;         `so-long-predicate' function `so-long-statistics-excessive-p'.
+;;       - Increase `so-long-threshold' from 250 to 10,000.
 ;;       - Increase `so-long-max-lines' from 5 to 500.
 ;;       - Include `fundamental-mode' in `so-long-target-modes'.
 ;;       - New user option `so-long-mode-preserved-minor-modes'.
@@ -472,8 +475,10 @@
 
 (defconst so-long--latest-version "1.1")
 
+(declare-function buffer-line-statistics "fns.c" t t) ;; Emacs 28+
 (declare-function longlines-mode "longlines")
 (defvar longlines-mode)
+
 (defvar so-long-enabled nil
   ;; This was initially a renaming of the old `so-long-mode-enabled' and
   ;; documented as "Set to nil to prevent `so-long' from being triggered
@@ -516,7 +521,8 @@
 (defcustom so-long-threshold 10000
   "Maximum line length permitted before invoking `so-long-function'.
 
-See `so-long-detected-long-line-p' for details."
+This is the only variable used to determine the presence of long lines if
+the `so-long-predicate' function is `so-long-statistics-excessive-p'."
   :type 'integer
   :package-version '(so-long . "1.1"))
 
@@ -591,7 +597,9 @@ the mentioned options might interfere with some intended processing."
                 (function :tag "Custom function"))
   :package-version '(so-long . "1.0"))
 
-(defcustom so-long-predicate 'so-long-detected-long-line-p
+(defcustom so-long-predicate (if (fboundp 'buffer-line-statistics)
+                                 'so-long-statistics-excessive-p
+                               'so-long-detected-long-line-p)
   "Function, called after `set-auto-mode' to decide whether action is needed.
 
 Only called if the major mode is a member of `so-long-target-modes'.
@@ -599,10 +607,12 @@ Only called if the major mode is a member of `so-long-target-modes'.
 The specified function will be called with no arguments.  If it returns non-nil
 then `so-long' will be invoked.
 
-Defaults to `so-long-detected-long-line-p'."
-  :type '(radio (const so-long-detected-long-line-p)
+Defaults to `so-long-statistics-excessive-p' starting from Emacs 28, or
+`so-long-detected-long-line-p' in earlier versions."
+  :type '(radio (const so-long-statistics-excessive-p)
+                (const so-long-detected-long-line-p)
                 (function :tag "Custom function"))
-  :package-version '(so-long . "1.0"))
+  :package-version '(so-long . "1.1"))
 
 ;; Silence byte-compiler warning.  `so-long-action-alist' is defined below
 ;; as a user option; but the definition sequence required for its setter
@@ -1149,12 +1159,23 @@ serves the same purpose.")
 ;; We change automatically to faster code
 ;; And then I won't feel so mad
 
+(defun so-long-statistics-excessive-p ()
+  "Non-nil if the buffer contains a line longer than `so-long-threshold' bytes.
+
+This uses `buffer-line-statistics' (available from Emacs 28.1) to establish the
+longest line in the buffer (counted in bytes rather than characters).
+
+This is the default value of `so-long-predicate' in Emacs versions >= 28.1.
+\(In earlier versions `so-long-detected-long-line-p' is used by default.)"
+  (> (cadr (buffer-line-statistics))
+     so-long-threshold))
+
 (defun so-long-detected-long-line-p ()
   "Determine whether the current buffer contains long lines.
 
 Following any initial comments and blank lines, the next N lines of the buffer
-will be tested for excessive length (where \"excessive\" means above
-`so-long-threshold', and N is `so-long-max-lines').
+will be tested for excessive length (where \"excessive\" means greater than
+`so-long-threshold' characters, and N is `so-long-max-lines').
 
 Returns non-nil if any such excessive-length line is detected.
 
@@ -1162,7 +1183,9 @@ If `so-long-skip-leading-comments' is nil then the N lines will be counted
 starting from the first line of the buffer.  In this instance you will likely
 want to increase `so-long-max-lines' to allow for possible comments.
 
-This is the default value of `so-long-predicate'."
+This is the default `so-long-predicate' function in Emacs versions < 28.1.
+\(Starting from 28.1, the default and recommended predicate function is
+`so-long-statistics-excessive-p', which is faster and sees the entire buffer.)"
   (let ((count 0) start)
     (save-excursion
       (goto-char (point-min))
@@ -2000,7 +2023,13 @@ If it appears in `%s', you should remove it."
     (makunbound 'so-long-mode-enabled))
   ;; Update to version 1.1 from earlier versions:
   (when (version< so-long-version "1.1")
-    (add-to-list 'so-long-target-modes 'fundamental-mode))
+    (add-to-list 'so-long-target-modes 'fundamental-mode)
+    (let ((saved (eval (car (get 'so-long-predicate 'saved-value))))
+          (standard (eval (car (get 'so-long-predicate 'standard-value)))))
+      (when (and (eq standard 'so-long-statistics-excessive-p)
+                 (or (not saved)
+                     (eq saved 'so-long-detected-long-line-p)))
+        (setq so-long-predicate standard))))
   ;; Update to version 1.N:
   ;; (when (version< so-long-version "1.N") ...)
   ;;