feat(slack): open rooms in another window, never the selected one

slack-buffer-function defaulted to switch-to-buffer-other-window, which gives no real guarantee about placement: with three or more panes it picks a least-recently-used window, and it offers nothing that keeps Slack out of the window point is in. So opening a room in a split could land it wherever, including over the buffer I was working in.

I set slack-buffer-function to cj/slack--display-buffer, a pop-to-buffer call with inhibit-same-window and a reuse / use-some-window / pop-up-window action list. In a split it reuses one of the other windows and leaves the selected window alone; with a lone window it splits. Tests cover both the split-placement case and the selected-window-preserved invariant.

1 files changed, 48 insertions, 0 deletions

diff --git a/tests/test-slack-config-display.el b/tests/test-slack-config-display.el
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+++ b/tests/test-slack-config-display.el
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+;;; test-slack-config-display.el --- Slack buffer placement -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; cj/slack--display-buffer is wired as `slack-buffer-function' so opening a
+;; Slack room or thread shows it in another window and never replaces the
+;; selected window's buffer.  These exercise the placement directly with plain
+;; buffers (no live Slack), using a side-by-side split so the window math is
+;; reliable under `emacs --batch'.
+
+;;; Code:
+
+(require 'ert)
+(require 'slack-config)
+
+(ert-deftest test-slack-config-display-buffer-uses-other-window-when-split ()
+  "Normal: with a split, the buffer lands in a non-selected window."
+  (let ((a (get-buffer-create "*slack-disp-a*"))
+        (b (get-buffer-create "*slack-disp-b*")))
+    (unwind-protect
+        (save-window-excursion
+          (delete-other-windows)
+          (set-window-buffer (selected-window) a)
+          (let ((win-a (selected-window)))
+            (split-window win-a nil t)   ;; side-by-side, batch-friendly
+            (cj/slack--display-buffer b)
+            (let ((win-b (get-buffer-window b)))
+              (should win-b)
+              (should-not (eq win-b win-a)))))
+      (ignore-errors (kill-buffer a))
+      (ignore-errors (kill-buffer b)))))
+
+(ert-deftest test-slack-config-display-buffer-keeps-selected-window ()
+  "Boundary: displaying does not replace the selected window's buffer."
+  (let ((a (get-buffer-create "*slack-disp-a*"))
+        (b (get-buffer-create "*slack-disp-b*")))
+    (unwind-protect
+        (save-window-excursion
+          (delete-other-windows)
+          (set-window-buffer (selected-window) a)
+          (let ((win-a (selected-window)))
+            (split-window win-a nil t)
+            (cj/slack--display-buffer b)
+            (should (eq (window-buffer win-a) a))))
+      (ignore-errors (kill-buffer a))
+      (ignore-errors (kill-buffer b)))))
+
+(provide 'test-slack-config-display)
+;;; test-slack-config-display.el ends here