feat(emacs): Configure Ediff

- Restore window configuration on quit.
- Very simple, half-broken helper for resolving Syncthing conflicts.
  - Doesn't automatically delete the conflict file after resolve. }:\

users/crumb/programs/emacs/init.el

@@ -51,6 +51,7 @@
 (require 'syd-completion)
 (require 'syd-custom)
 (require 'syd-display-startup-time)
+(require 'syd-ediff)
 (require 'syd-editing)
 (require 'syd-eshell)
 (require 'syd-evil)
@@ -60,6 +61,6 @@
 (require 'syd-projects)
 (require 'syd-scratch)
 (require 'syd-smartparens)
-(require 'syd-tramp)
 (require 'syd-tooling)
+(require 'syd-tramp)
 (require 'syd-ui)

users/crumb/programs/emacs/lib/syd-file.el

@@ -94,4 +94,45 @@ If FORCE-P, delete without confirmation."
  :desc "Open current file as root.  See `doom/sudo-this-file'."
  :interactive t)
 
+(defun syd--make-syncthing-merge-finalise-hook (file-name conflict-file-name)
+  (lambda ()
+    (let ((merge-result-file (read-file-name
+                              (format "Write merge to (default: %s):"
+                                      file-name)
+                              nil file-name))
+          (delete-conflict-p (yes-or-no-p (format "Delete conflict file? (%s)"
+                                                  conflict-file-name)))))
+    (when merge-result-file
+      (with-current-buffer ediff-buffer-C
+        (set-visited-file-name merge-result-file)
+        (save-buffer))
+      (kill-buffer ediff-buffer-C))
+    (when delete-conflict-p
+      (kill-buffer (find-buffer-visiting conflict-file-name))
+      (delete-file conflict-file-name))))
+
+(defun syd--read-syncthing-conflict-file (&optional directory)
+  (let ((conflict-files (directory-files-recursively
+                         (or directory default-directory)
+                         (rx ".sync-conflict-"))))
+    (completing-read "Conflict file: " conflict-files nil t)))
+
+(defun syd--syncthing-conflict-file-base-name (conflict-file)
+  (replace-regexp-in-string (rx ".sync-conflict-" (* (not ?.)))
+                            ""
+                            conflict-file))
+
+(defun syd-resolve-syncthing-conflict (conflict-file)
+  (interactive (list (syd--read-syncthing-conflict-file)))
+  (require 'ediff)
+  (let* ((base-file (syd--syncthing-conflict-file-base-name conflict-file))
+         (ediff-after-quit-hook-internal
+          ;; Override Ediff's "save and quit" hook with our own.
+          (cons (syd--make-syncthing-merge-finalise-hook base-file conflict-file)
+                (remq #'ediff-write-merge-buffer-and-maybe-kill
+                      (ensure-list ediff-quit-merge-hook)))))
+    (ediff-merge-files
+     base-file
+     conflict-file)))
+
 (provide 'syd-file)

users/crumb/programs/emacs/modules/syd-ediff.el

@@ -0,0 +1,19 @@
+;;; syd-ediff.el -*- lexical-binding: t; -*-
+
+(require 'syd-prelude)
+
+(with-eval-after-load 'ediff
+  (setq ediff-diff-options "-w" ; Ignore whitespace
+        ediff-window-setup-function #'ediff-setup-windows-plain)
+  (defvar syd--ediff-saved-wconf nil)
+
+  ;; Restore window config after quitting Ediff.
+  (syd-add-hook 'ediff-before-setup-hook
+    (defun syd--ediff-save-wconf-h ()
+      (setq syd--ediff-saved-wconf (current-window-configuration))))
+  (syd-add-hook '(ediff-quit-hook ediff-suspend-hook)
+    (defun syd--ediff-restore-wconf-h ()
+      (when (window-configuration-p syd--ediff-saved-wconf)
+        (set-window-configuration syd--ediff-saved-wconf)))))
+
+(provide 'syd-ediff)