bug#51809: 29.0.50; [PATCH] Support for outline default state in Diff buffers

[Matthias Meulien]

Updated patch that takes Juri comments into account.

>From 4a9f53e73dcbcd77df339bca012ee72aec343f18 Mon Sep 17 00:00:00 2001
From: Matthias Meulien <orontee@gmail.com>
Date: Sat, 13 Nov 2021 12:08:58 +0100
Subject: [PATCH] Support for outline default state in Diff buffers

* lisp/outline.el (outline-map-sublevel-overlay):
* lisp/vc/diff-mode.el (diff-outline-default-state): Variable that
defines an outline state.
(diff-outline-apply-default-state)
(diff--outline-set-file-heading-visibility): Apply outline state
defined in `diff-outline-default-state'.
---
 lisp/outline.el      |  40 ++++++++++++++
 lisp/vc/diff-mode.el | 128 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 166 insertions(+), 2 deletions(-)

diff --git a/lisp/outline.el b/lisp/outline.el
index cefb811703..77de31f785 100644
--- a/lisp/outline.el
+++ b/lisp/outline.el
@@ -1100,6 +1100,46 @@ outline-hide-sublevels
 
 (define-obsolete-function-alias 'hide-sublevels #'outline-hide-sublevels 
"25.1")
 
+(defun outline-map-sublevel-overlay (level fun)
+  "Hide everything and call FUN on the LEVEL sublevels of headers .
+
+When FUN is called, point is at the beginning of the heading, the
+match data is set appropriately, and FUN receives one argument,
+the outline overlay for the heading entry.
+
+This also unhides the top heading-less body, if any."
+  (if (< level 1)
+      (error "Must keep at least one level of headers"))
+  (save-excursion
+    (let* (outline-view-change-hook
+           (beg (progn
+                  (goto-char (point-min))
+                  ;; Skip the prelude, if any.
+                  (unless (outline-on-heading-p t) (outline-next-heading))
+                  (point)))
+           (end (progn
+                  (goto-char (point-max))
+                  ;; Keep empty last line, if available.
+                  (if (bolp) (1- (point)) (point)))))
+      (if (< end beg)
+         (setq beg (prog1 end (setq end beg))))
+      ;; First hide everything.
+      (outline-hide-sublevels level)
+      ;; Then unhide the top level headers.
+      (outline-map-region
+       (lambda ()
+        (when (= (funcall outline-level) level)
+           (goto-char (match-end 0))
+           (let ((overlays (overlays-at (point))))
+             (while overlays
+              (let ((overlay (car overlays)))
+                 (when (eq (overlay-get overlay 'invisible) 'outline)
+                   (goto-char (match-beginning 0))
+                   (funcall fun overlay))
+                 (setq overlays (cdr overlays)))))))
+       beg end)))
+  (run-hooks 'outline-view-change-hook))
+
 (defun outline-hide-other ()
   "Hide everything except current body and parent and top-level headings.
 This also unhides the top heading-less body, if any."
diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index e68aa2257d..9617e6ceee 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -50,6 +50,7 @@
 ;;
 ;; - in diff-apply-hunk, strip context in replace-match to better
 ;;   preserve markers and spacing.
+;;
 ;; - Handle `diff -b' output in context->unified.
 
 ;;; Code:
@@ -62,6 +63,18 @@
 (defvar vc-find-revision-no-save)
 (defvar add-log-buffer-file-name-function)
 
+(eval-when-compile (require 'outline))
+(defvar outline-minor-mode)
+(declare-function outline-minor-mode "outline" (&optional args))
+(declare-function outline-hide-entry "outline")
+(declare-function outline-show-branches "outline")
+(declare-function outline-show-subtree "outline" (&optional event))
+
+(eval-when-compile (require 'so-long))
+(autoload 'so-long-detected-long-line-p "so-long")
+(defvar so-long-skip-leading-comments)
+(defvar so-long-threshold)
+(defvar so-long-max-lines)
 
 (defgroup diff-mode ()
   "Major mode for viewing/editing diffs."
@@ -147,6 +160,61 @@ diff-font-lock-syntax
                  (const :tag "Highlight syntax" t)
                  (const :tag "Allow hunk-based fallback" hunk-also)))
 
+(defcustom diff-outline-default-state nil
+  "If non-nil, some files or hunk are outlined.
+Outlining is performed by Outline minor mode.
+
+If equal to `outline-hunks', only file and hunk headings are
+visibles.
+
+If equal to a lambda function or function name, this function is
+expected to toggle file or hunks visibility, and will be called
+after the mode is enabled.
+
+If equal to a list of symbols, hunk headings will be outlined
+depending on the conditions defined for each symbol:
+
+- If `line-count-threshold', when hunks under a given file
+  heading cover more than `diff-outline-line-count-threshold'
+  lines, they are outlined;
+
+- If `file-heading-regexp', file headings which match the regexp
+  `diff-outline-file-heading-regexp' are outlined;
+
+- If `long-line-threshold', when a hunk under a given file
+  heading have a line with more than
+  `diff-outline-long-line-threshold' characters, all hunks for
+  that file heading are outlined."
+  :version "29.1"
+  :type '(choice (const :tag "Don't outline " nil)
+                 (const :tag "Outline hunks" outline-hunks)
+                 (set :tag "Outline some files"
+                      (const
+                       :tag "Outline files with long hunks"
+                       line-count-threshold)
+                      (const
+                       :tag "Outline files by name"
+                       file-heading-regexp)
+                      (const
+                       :tag "Outline files whose hunks involve long lines"
+                       long-line-threshold))
+                 (function :tag "Custom function")))
+
+(defcustom diff-outline-line-count-threshold 50
+  "Minimal number of lines of hunks for a file to be outlined."
+  :version "29.1"
+  :type '(natnum :tag "Number of lines"))
+
+(defcustom diff-outline-file-heading-regexp "ChangeLog\\|package-lock\\.json"
+  "Regexp to match file headings to be outlined."
+  :version "29.1"
+  :type '(regexp :tag "Files to outline"))
+
+(defcustom diff-outline-long-line-threshold 1000
+  "Minimal number of characters in a line for a file to be outlined."
+  :version "29.1"
+  :type '(natnum :tag "Number of lines"))
+
 (defvar diff-vc-backend nil
   "The VC backend that created the current Diff buffer, if any.")
 
@@ -1578,7 +1646,8 @@ diff-setup-whitespace
 
 (defun diff-setup-buffer-type ()
   "Try to guess the `diff-buffer-type' from content of current Diff mode 
buffer.
-`outline-regexp' is updated accordingly."
+`outline-regexp' is updated accordingly and outline default state
+applied."
   (save-excursion
     (goto-char (point-min))
     (setq-local diff-buffer-type
@@ -1589,7 +1658,8 @@ diff-setup-buffer-type
     (setq diff-outline-regexp
           (concat "\\(^diff --git.*\n\\|" diff-hunk-header-re "\\)"))
     (setq-local outline-level #'diff--outline-level))
-  (setq-local outline-regexp diff-outline-regexp))
+  (setq-local outline-regexp diff-outline-regexp)
+  (diff-outline-apply-default-state))
 
 (defun diff-delete-if-empty ()
   ;; An empty diff file means there's no more diffs to integrate, so we
@@ -2143,6 +2213,60 @@ diff-refresh-hunk
       (delete-file file1)
       (delete-file file2))))
 
+(defun diff-outline-apply-default-state ()
+  "Apply the outline state defined by `diff-outline-default-state'.
+
+When `diff-outline-default-state' is non-nil, Outline minor mode
+is enabled."
+  (interactive)
+  (when diff-outline-default-state
+    (when (not outline-minor-mode)
+      (outline-minor-mode))
+    (cond
+     ((eq diff-outline-default-state 'outline-hunks)
+      (outline-hide-body))
+     ((listp diff-outline-default-state)
+      (outline-map-sublevel-overlay
+       1 #'diff--outline-set-file-heading-visibility))
+     ((when (functionp diff-outline-default-state)
+        (funcall diff-outline-default-state))))))
+
+(defun diff--outline-set-file-heading-visibility (overlay)
+  (cond
+   ;; hide entry when file heading match
+   ;; `diff-outline-file-heading-regexp'
+   ((and
+     (memq 'file-heading-regexp
+           diff-outline-default-state)
+     (string-match-p
+      diff-outline-file-heading-regexp
+      (match-string 0)))
+    (outline-hide-entry))
+   ;; show only branches when line count > threshold
+   ((and
+     (memq 'line-count-threshold
+           diff-outline-default-state)
+     (let ((line-count (count-lines
+                        (overlay-end overlay)
+                        (overlay-start overlay))))
+       (< diff-outline-line-count-threshold line-count)))
+    (outline-show-branches))
+   ;; show only branches when a long line is detected
+   ((and
+     (memq 'long-line-threshold
+           diff-outline-default-state)
+     (save-restriction
+       (narrow-to-region (overlay-start overlay)
+                         (overlay-end overlay))
+       (let ((so-long-skip-leading-comments nil)
+             (so-long-threshold
+              diff-outline-long-line-threshold)
+             (so-long-max-lines nil))
+         (so-long-detected-long-line-p))))
+    (outline-show-branches))
+   ;; otherwise show subtree
+   (t (outline-show-subtree))))
+
 ;;; Fine change highlighting.
 
 (defface diff-refine-changed
-- 
2.30.2

-- 
Matthias