feat(vc-gutter): add +diff-hl backend

This adds an alternative backend to the :ui vc-gutter module, enabled
with the +diff-hl flag. In the future, I intend for diff-hl to replace
git-gutter, as it is slightly faster and depends on more native
functionality (vc.el), but it's still a little buggy. It will remain
opt-in until those issues are sorted out.

modules/config/default/+emacs-bindings.el

@@ -349,11 +349,11 @@
        :desc "Kill link to remote"         "y"   #'+vc/browse-at-remote-kill
        :desc "Kill link to homepage"       "Y"   #'+vc/browse-at-remote-kill-homepage
        (:when (featurep! :ui vc-gutter)
-        :desc "Git revert hunk"            "r"   #'git-gutter:revert-hunk
-        :desc "Git stage hunk"             "s"   #'git-gutter:stage-hunk
+        :desc "Git revert hunk"            "r"   #'+vc-gutter/revert-hunk
+        :desc "Git stage hunk"             "s"   #'+vc-gutter/stage-hunk
         :desc "Git time machine"           "t"   #'git-timemachine-toggle
-        :desc "Jump to next hunk"          "n"   #'git-gutter:next-hunk
-        :desc "Jump to previous hunk"      "p"   #'git-gutter:previous-hunk)
+        :desc "Jump to next hunk"          "n"   #'+vc-gutter/next-hunk
+        :desc "Jump to previous hunk"      "p"   #'+vc-gutter/previous-hunk)
        (:when (featurep! :tools magit)
         :desc "Magit dispatch"             "/"   #'magit-dispatch
         :desc "Magit file dispatch"        "."   #'magit-file-dispatch

modules/config/default/+evil-bindings.el

@@ -452,11 +452,11 @@
        (:when (featurep! :ui vc-gutter)
         (:when (featurep! :ui hydra)
          :desc "VCGutter"                "."   #'+vc/gutter-hydra/body)
-        :desc "Revert hunk"               "r"   #'git-gutter:revert-hunk
-        :desc "Git stage hunk"            "s"   #'git-gutter:stage-hunk
+        :desc "Revert hunk at point"      "r"   #'+vc-gutter/revert-hunk
+        :desc "stage hunk at point"       "s"   #'+vc-gutter/stage-hunk
         :desc "Git time machine"          "t"   #'git-timemachine-toggle
-        :desc "Jump to next hunk"         "]"   #'git-gutter:next-hunk
-        :desc "Jump to previous hunk"     "["   #'git-gutter:previous-hunk)
+        :desc "Jump to next hunk"         "]"   #'+vc-gutter/next-hunk
+        :desc "Jump to previous hunk"     "["   #'+vc-gutter/previous-hunk)
        (:when (featurep! :tools magit)
         :desc "Magit dispatch"            "/"   #'magit-dispatch
         :desc "Magit file dispatch"       "."   #'magit-file-dispatch

modules/editor/evil/config.el

@@ -445,8 +445,8 @@ directives. By default, this only recognizes C directives.")
        :m "]x"   #'+web:encode-html-entities
        :m "[x"   #'+web:decode-html-entities)
       (:when (featurep! :ui vc-gutter)
-       :m "]d"   #'git-gutter:next-hunk
-       :m "[d"   #'git-gutter:previous-hunk)
+       :m "]d"   #'+vc-gutter/next-hunk
+       :m "[d"   #'+vc-gutter/previous-hunk)
       (:when (featurep! :ui hl-todo)
        :m "]t"   #'hl-todo-next
        :m "[t"   #'hl-todo-previous)

modules/emacs/dired/config.el

@@ -72,11 +72,12 @@ Fixes #3939: unsortable dired entries on Windows."
 
 
 (use-package! diff-hl
-  :hook (dired-mode . diff-hl-dired-mode-unless-remote)
-  :hook (magit-post-refresh . diff-hl-magit-post-refresh)
-  :config
-  ;; use margin instead of fringe
-  (diff-hl-margin-mode))
+  :when (featurep! :ui vc-gutter)
+  :hook (dired-mode-hook . diff-hl-margin-local-mode)
+  :init
+  (unless (featurep! :ui vc-gutter +diff-hl)
+    (add-hook 'dired-mode-hook #'diff-hl-dired-mode-unless-remote)
+    (add-hook 'magit-post-refresh-hook #'diff-hl-magit-post-refresh)))
 
 
 (use-package! ranger

modules/ui/vc-gutter/README.org

@@ -13,6 +13,10 @@ Supports Git, Svn, Hg, and Bzr.
 [[doom-contrib-maintainer:][Become a maintainer?]]
 
 ** Module flags
+- +diff-hl ::
+  Use [[doom-package:][diff-hl]] instead of git-gutter to power the VC gutter. It is a little
+  faster, but is slightly more prone to visual glitching. [[doom-package:][diff-hl]] is intended to
+  replace git-gutter at some point in the future.
 - +pretty ::
   Apply some stylistic defaults to the fringe, enabling thin bars in the fringe.
   This look takes after the modern look of git-gutter in VSCode and Sublime
@@ -22,7 +26,8 @@ Supports Git, Svn, Hg, and Bzr.
   diff-hl's faces (like modus-themes does).
 
 ** Packages
-- [[doom-package:][git-gutter-fringe]]
+- [[doom-package:][git-gutter-fringe]] unless [[doom-module:][+diff-hl]]
+- [[doom-package:][diff-hl]] if [[doom-module:][+diff-hl]]
 
 ** TODO Hacks
 #+begin_quote

modules/ui/vc-gutter/autoload.el

@@ -1,34 +0,0 @@
-;;; ui/vc-gutter/autoload.el -*- lexical-binding: t; -*-
-;;;###if (featurep! :ui hydra)
-
-;;;###autoload (autoload '+vc/gutter-hydra/body "ui/vc-gutter/autoload" nil t)
-(defhydra +vc/gutter-hydra
-  (:body-pre (git-gutter-mode 1) :hint nil)
-  "
-                                               [git gutter]
-   Movement  Hunk Actions     Misc.         +%-4s(car (git-gutter:statistic))/ -%-4s(cdr (git-gutter:statistic))
-  ╭──────────────────────────────────┴────────────────╯
-     ^_g_^       [_s_] stage        [_R_] set start Rev
-     ^_k_^       [_r_] revert
-     ^↑ ^      [_m_] mark
-     ^↓ ^      [_p_] popup             ╭─────────────────────
-     ^_j_^                             │[_q_] quit
-     ^_G_^                             │[_Q_] Quit and disable"
-  ("j" (progn (git-gutter:next-hunk 1) (recenter)))
-  ("k" (progn (git-gutter:previous-hunk 1) (recenter)))
-  ("g" (progn (goto-char (point-min)) (git-gutter:next-hunk 1)))
-  ("G" (progn (goto-char (point-min)) (git-gutter:previous-hunk 1)))
-  ("s" git-gutter:stage-hunk)
-  ("r" git-gutter:revert-hunk)
-  ("m" git-gutter:mark-hunk)
-  ("p" git-gutter:popup-hunk)
-  ("R" git-gutter:set-start-revision)
-  ("q"
-   (when (get-buffer git-gutter:popup-buffer)
-     (kill-buffer (get-buffer git-gutter:popup-buffer)))
-   :color blue)
-  ("Q"
-   (progn (git-gutter-mode -1)
-          (when (get-buffer git-gutter:popup-buffer)
-            (kill-buffer (get-buffer git-gutter:popup-buffer))))
-   :color blue))

modules/ui/vc-gutter/autoload/diff-hl.el

@@ -0,0 +1,11 @@
+;;; ui/vc-gutter/autoload/diff-hl.el -*- lexical-binding: t; -*-
+;;;###if (featurep! +diff-hl)
+
+;;;###autoload
+(defalias '+vc-gutter/stage-hunk #'diff-hl-stage-current-hunk)
+;;;###autoload
+(defalias '+vc-gutter/revert-hunk #'diff-hl-revert-hunk)
+;;;###autoload
+(defalias '+vc-gutter/next-hunk #'diff-hl-next-hunk)
+;;;###autoload
+(defalias '+vc-gutter/previous-hunk #'diff-hl-previous-hunk)

modules/ui/vc-gutter/autoload/git-gutter.el

@@ -0,0 +1,11 @@
+;;; ui/vc-gutter/autoload/vc-gutter.el -*- lexical-binding: t; -*-
+;;;###if (not (featurep! +diff-hl))
+
+;;;###autoload
+(defalias '+vc-gutter/stage-hunk #'git-gutter:stage-hunk)
+;;;###autoload
+(defalias '+vc-gutter/revert-hunk #'git-gutter:revert-hunk)
+;;;###autoload
+(defalias '+vc-gutter/next-hunk #'git-gutter:next-hunk)
+;;;###autoload
+(defalias '+vc-gutter/previous-hunk #'git-gutter:previous-hunk)

modules/ui/vc-gutter/config.el

@@ -1,20 +1,12 @@
 ;;; ui/vc-gutter/config.el -*- lexical-binding: t; -*-
 
+;; TODO Implement me
 (defvar +vc-gutter-in-margin nil
   "If non-nil, use the margin for diffs instead of the fringe.")
 
 (defvar +vc-gutter-in-remote-files nil
   "If non-nil, enable the vc gutter in remote files (e.g. open through TRAMP).")
 
-(defvar +vc-gutter-diff-unsaved-buffer nil
-  "If non-nil, `diff-hl-flydiff-mode' will be activated. This allows on-the-fly
-diffing, even for unsaved buffers.")
-
-(defvar +vc-gutter-default-style t
-  "If non-nil, enable the default look of the vc gutter.
-This means subtle thin bitmaps on the left, an arrow bitmap for flycheck, and
-flycheck indicators moved to the right fringe.")
-
 
 ;;
 ;;; Default styles
@@ -31,13 +23,29 @@ flycheck indicators moved to the right fringe.")
   ;; to shrink the fringe and sacrifice precious space for other fringe
   ;; indicators (like flycheck or flyspell).
   ;; TODO Extract these into a package with faces that themes can target.
-  (after! git-gutter-fringe
-    (define-fringe-bitmap 'git-gutter-fr:added [224]
-      nil nil '(center repeated))
-    (define-fringe-bitmap 'git-gutter-fr:modified [224]
-      nil nil '(center repeated))
-    (define-fringe-bitmap 'git-gutter-fr:deleted [128 192 224 240]
-      nil nil 'bottom))
+  (if (not (featurep! +diff-hl))
+      (after! git-gutter-fringe
+        (define-fringe-bitmap 'git-gutter-fr:added [224]
+          nil nil '(center repeated))
+        (define-fringe-bitmap 'git-gutter-fr:modified [224]
+          nil nil '(center repeated))
+        (define-fringe-bitmap 'git-gutter-fr:deleted [128 192 224 240]
+          nil nil 'bottom))
+    (defadvice! +vc-gutter-define-thin-bitmaps-a (&rest args)
+      :override #'diff-hl-define-bitmaps
+      (set-face-background 'diff-hl-insert nil)
+      (set-face-background 'diff-hl-delete nil)
+      (set-face-background 'diff-hl-change nil)
+      (define-fringe-bitmap 'diff-hl-bmp-middle [224] nil nil '(center repeated))
+      (define-fringe-bitmap 'diff-hl-bmp-delete [240 224 192 128] nil nil 'top))
+    (defun +vc-gutter-type-face-fn (type _pos)
+      (intern (format "diff-hl-%s" type)))
+    (defun +vc-gutter-type-at-pos-fn (type _pos)
+      (if (eq type 'delete)
+          'diff-hl-bmp-delete
+        'diff-hl-bmp-middle))
+    (setq diff-hl-fringe-bmp-function #'+vc-gutter-type-at-pos-fn
+          diff-hl-draw-borders nil))
 
   ;; FIX: To minimize overlap between flycheck indicators and git-gutter/diff-hl
   ;; indicators in the left fringe.
@@ -50,9 +58,10 @@ flycheck indicators moved to the right fringe.")
 
 
 ;;
-;;; Packages
+;;; git-gutter
 
 (use-package! git-gutter
+  :unless (featurep! +diff-hl)
   :commands git-gutter:revert-hunk git-gutter:stage-hunk
   :init
   (add-hook! 'find-file-hook
@@ -129,26 +138,69 @@ is deferred until the file is saved. Respects `git-gutter:disabled-modes'."
                     :from-end is-reverse)))
 
 
-;; subtle diff indicators in the fringe
-(after! git-gutter-fringe
-  (when +vc-gutter-default-style
-    ;; standardize default fringe width
-    (if (fboundp 'fringe-mode) (fringe-mode '4))
+;;
+;;; diff-hl
 
-    ;; places the git gutter outside the margins.
-    (setq-default fringes-outside-margins t)
-    ;; thin fringe bitmaps
-    (define-fringe-bitmap 'git-gutter-fr:added [224]
-      nil nil '(center repeated))
-    (define-fringe-bitmap 'git-gutter-fr:modified [224]
-      nil nil '(center repeated))
-    (define-fringe-bitmap 'git-gutter-fr:deleted [128 192 224 240]
-      nil nil 'bottom)))
+(use-package! diff-hl
+  :when (featurep! +diff-hl)
+  :hook (doom-first-file . global-diff-hl-mode)
+  :hook (diff-hl-mode . diff-hl-flydiff-mode)
+  :config
+  (set-popup-rule! "^\\*diff-hl" :select nil :size '+popup-shrink-to-fit)
 
-(after! flycheck
-  (when +vc-gutter-default-style
-    ;; let diff have left fringe, flycheck can have right fringe
-    (setq flycheck-indication-mode 'right-fringe)
-    ;; A non-descript, left-pointing arrow
-    (define-fringe-bitmap 'flycheck-fringe-bitmap-double-arrow
-      [16 48 112 240 112 48 16] nil nil 'center)))
+  ;; PERF: reduce load on remote
+  (defvaralias 'diff-hl-disable-on-remote '+vc-gutter-in-remote-files)
+  ;; PERF: A slightly faster algorithm for diffing.
+  (setq vc-git-diff-switches '("--histogram"))
+  ;; PERF: Slightly more conservative delay before updating the diff
+  (setq diff-hl-flydiff-delay 0.5)  ; default: 0.3
+
+  ;; UX: get realtime feedback in diffs after staging/unstaging hunks.
+  (setq diff-hl-show-staged-changes nil)
+
+  ;; UX: Update diffs when it makes sense too, without being too slow
+  (when (featurep! :editor evil)
+    (map! :after diff-hl-show-hunk
+          :map diff-hl-show-hunk-map
+          :n "p" #'diff-hl-show-hunk-previous
+          :n "n" #'diff-hl-show-hunk-next
+          :n "c" #'diff-hl-show-hunk-copy-original-text
+          :n "r" #'diff-hl-show-hunk-revert-hunk
+          :n "[" #'diff-hl-show-hunk-previous
+          :n "]" #'diff-hl-show-hunk-next
+          :n "{" #'diff-hl-show-hunk-previous
+          :n "}" #'diff-hl-show-hunk-next
+          :n "S" #'diff-hl-show-hunk-stage-hunk))
+  ;; UX: Refresh git-gutter on ESC or refocusing the Emacs frame.
+  (add-hook! '(doom-escape-hook doom-switch-window-hook) :append
+    (defun +vc-gutter-update-h (&rest _)
+      "Return nil to prevent shadowing other `doom-escape-hook' hooks."
+      (ignore (or inhibit-redisplay
+                  (and (or (bound-and-true-p diff-hl-mode)
+                           (bound-and-true-p diff-hl-dir-mode))
+                       (diff-hl-update-once))))))
+  ;; UX: Update diff-hl when magit alters git state.
+  (when (featurep! :tools magit)
+    (add-hook 'magit-pre-refresh-hook  #'diff-hl-magit-pre-refresh)
+    (add-hook 'magit-post-refresh-hook #'diff-hl-magit-post-refresh)
+    (add-hook 'magit-post-stage-hook   #'+vc-gutter-update-h)
+    (add-hook 'magit-post-unstage-hook #'+vc-gutter-update-h))
+
+  ;; UX: Don't delete the current hunk's indicators while we're editing
+  (add-hook! 'diff-hl-flydiff-mode-hook
+    (defun +vc-gutter-init-flydiff-mode-h ()
+      (if diff-hl-flydiff-mode
+          (progn
+            (advice-remove #'diff-hl-overlay-modified #'ignore)
+            (when (featurep! :editor evil)
+              (add-hook 'evil-insert-state-exit-hook #'diff-hl-flydiff-update)))
+        (remove-hook 'evil-insert-state-exit-hook #'diff-hl-flydiff-update))))
+
+  ;; FIX: Reverting a hunk causes the cursor to be moved to an unexpected place,
+  ;; often far from the target hunk.
+  (defadvice! +vc-gutter--save-excursion-a (fn &rest args)
+    "Suppresses unexpected cursor movement by `diff-hl-revert-hunk'."
+    :around #'diff-hl-revert-hunk
+    (let ((pt (point)))
+      (prog1 (apply fn args)
+        (goto-char pt)))))

modules/ui/vc-gutter/packages.el

@@ -1,4 +1,6 @@
 ;; -*- no-byte-compile: t; -*-
 ;;; ui/vc-gutter/packages.el
 
-(package! git-gutter-fringe :pin "648cb5b57faec55711803cdc9434e55a733c3eba")
+(if (featurep! +diff-hl)
+    (package! diff-hl :pin "dabb7be6283488abd8d232ea8ce590d502713ed8")
+  (package! git-gutter-fringe :pin "648cb5b57faec55711803cdc9434e55a733c3eba"))