From a16c40d493c470c9d62e79224b00731ae4354c54 Mon Sep 17 00:00:00 2001
From: Henrik Lissner <henrik@lissner.net>
Date: Wed, 5 Aug 2020 21:13:42 -0400
Subject: [PATCH] tools/magit: split sub-windows to the side

When a log or diff buffer is opened from the magit status buffer, it
would display them in a random window (or split, if none were
available). This changes forces it to predictably open to the right of
the magit status window (using the next window over, if available).
---
 modules/tools/magit/autoload.el | 24 +++++++++++++++++++++++-
 modules/tools/magit/config.el   |  8 ++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/modules/tools/magit/autoload.el b/modules/tools/magit/autoload.el
index 03682c185..e23b88829 100644
--- a/modules/tools/magit/autoload.el
+++ b/modules/tools/magit/autoload.el
@@ -53,7 +53,29 @@
                                magit-diff-mode
                                magit-stash-mode
                                magit-status-mode))))
-              '(display-buffer-same-window))))))
+              '(display-buffer-same-window))
+
+             ('(+magit--display-buffer-in-direction))))))
+
+(defun +magit--display-buffer-in-direction (buffer alist)
+  "`display-buffer-alist' handler that opens BUFFER in a direction.
+
+This differs from `display-buffer-in-direction' in one way: it will try to use a
+window that already exists in that direction. It will split otherwise."
+  (let ((direction (or (alist-get 'direction alist)
+                       +magit-open-windows-in-direction)))
+    (if-let (window (window-in-direction direction))
+        (select-window window)
+      (if-let (window (window-in-direction
+                       (pcase direction
+                         (`right 'left)
+                         (`left 'right)
+                         ((or `up `above) 'down)
+                         ((or `down `below) 'up))))
+          (select-window window)
+        (split-window-horizontally)))
+    (switch-to-buffer buffer)
+    (selected-window)))
 
 
 ;;
diff --git a/modules/tools/magit/config.el b/modules/tools/magit/config.el
index 1ff772114..d5eb0ecba 100644
--- a/modules/tools/magit/config.el
+++ b/modules/tools/magit/config.el
@@ -1,5 +1,13 @@
 ;;; tools/magit/config.el -*- lexical-binding: t; -*-
 
+(defvar +magit-open-windows-in-direction 'right
+  "What direction to open new windows from the status buffer.
+For example, diffs and log buffers. Accepts `left', `right', `up', and `down'.")
+
+
+;;
+;;; Packages
+
 (use-package! magit
   :commands magit-file-delete
   :defer-incrementally (dash f s with-editor git-commit package eieio lv transient)