Keep point and scroll steady in the eca-workspaces dashboard

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Bugfix: the `eca-workspaces` dashboard was impossible to navigate while a chat ran, since the live refresh (once a second) scrolled the view and could throw point to the top. Rendering erases the buffer, which collapses every window start marker, so a window shorter than the content recentered on each refresh; point resting on a line with no entity, the footer, fell back to the buffer start. Each window now keeps its scroll position, and point on the footer stays on it.
 - The `stop`, `Steering:` and `Queued:` lines of a running prompt now show right below its progress status, above the `@` context line, instead of splitting that line from the prompt field (#322).
 - Show the `@cursor` context with `eca-chat-context-cursor-unsaved-face` (inheriting `warning`) while its buffer has unsaved changes, since ECA only sees the file on disk (#291).
 - Image mentions show inline as thumbnails: screenshots pasted in the prompt, image files added as context and images mentioned in sent messages. `RET` toggles them back to text. Customize with `eca-chat-image-show-thumbnails` and `eca-chat-image-thumbnail-size`.

eca-workspaces.el

@@ -248,13 +248,35 @@ whitespace."
             (forward-line 1)))
         found))))
 
-(defun eca-workspaces--restore-point (entity column)
-  "Move point to ENTITY line at COLUMN, falling back to buffer start."
-  (if-let* ((position (eca-workspaces--find-entity entity)))
-      (progn
-        (goto-char position)
-        (move-to-column (or column 0)))
-    (goto-char (point-min))))
+(defun eca-workspaces--line-position (line)
+  "Return the position where LINE starts, clamped to the buffer."
+  (save-excursion
+    (goto-char (point-min))
+    (forward-line (1- line))
+    (point)))
+
+(defun eca-workspaces--point-state (position)
+  "Return the (ENTITY COLUMN LINE) state that finds POSITION again."
+  (save-excursion
+    (goto-char position)
+    (list (eca-workspaces--entity-at position)
+          (current-column)
+          (line-number-at-pos position))))
+
+(defun eca-workspaces--point-position (state)
+  "Return where STATE points to in the freshly rendered buffer.
+STATE comes from `eca-workspaces--point-state'.  A line without an
+entity, the footer one, is found back by its line number, so point
+resting there survives a render too.  A row whose entity is gone
+falls back to buffer start."
+  (-let* (((entity column line) state)
+          (position (and entity (eca-workspaces--find-entity entity))))
+    (if (and entity (not position))
+        (point-min)
+      (save-excursion
+        (goto-char (or position (eca-workspaces--line-position line)))
+        (move-to-column (or column 0))
+        (point)))))
 
 (defun eca-workspaces--footer ()
   "Return the dashboard footer hint line."
@@ -268,20 +290,19 @@ whitespace."
           "\n"))
 
 (defun eca-workspaces--window-state (window)
-  "Return (WINDOW ENTITY COLUMN) for WINDOW's current point."
-  (let ((position (window-point window)))
-    (list window
-          (eca-workspaces--entity-at position)
-          (save-excursion
-            (goto-char position)
-            (current-column)))))
+  "Return (WINDOW POINT-STATE START-LINE) of WINDOW.
+START-LINE is the line WINDOW starts at: `erase-buffer' collapses
+the window start marker, so a window shorter than the content
+scrolls back and recenters on every refresh without it."
+  (list window
+        (eca-workspaces--point-state (window-point window))
+        (line-number-at-pos (window-start window))))
 
 (defun eca-workspaces--render ()
   "Render the dashboard into the current buffer.
-Preserves point, per-window points and fold state across renders."
+Preserves point, per-window points and scroll, and fold state."
   (let* ((inhibit-read-only t)
-         (point-entity (eca-workspaces--entity-at (point)))
-         (point-column (current-column))
+         (point-state (eca-workspaces--point-state (point)))
          (window-states (-map #'eca-workspaces--window-state
                               (get-buffer-window-list nil nil t))))
     (erase-buffer)
@@ -297,15 +318,14 @@ Preserves point, per-window points and fold state across renders."
             (dolist (chat-buffer (eca-chat-buffers session))
               (insert (eca-workspaces--chat-line session chat-buffer)))))))
     (insert (eca-workspaces--footer))
-    (eca-workspaces--restore-point point-entity point-column)
+    (goto-char (eca-workspaces--point-position point-state))
     (dolist (state window-states)
-      (-let [(window entity column) state]
-        (when-let* ((position (eca-workspaces--find-entity entity)))
-          (set-window-point window
-                            (save-excursion
-                              (goto-char position)
-                              (move-to-column (or column 0))
-                              (point))))))))
+      (-let [(window window-point-state start-line) state]
+        (set-window-point window
+                          (eca-workspaces--point-position window-point-state))
+        (set-window-start window
+                          (eca-workspaces--line-position start-line)
+                          t)))))
 
 (defun eca-workspaces--any-chat-running-p ()
   "Return non-nil when any chat of any session is loading."

test/eca-workspaces-test.el

@@ -316,6 +316,39 @@ CHATS is a list of chat buffers ordered oldest-first."
           (expect (eca-workspaces--chat-id-at-point) :to-equal chat-id)
           (expect (current-column) :to-equal column)))))
 
+  (it "keeps point on a line without an entity, like the footer"
+    (eca-workspaces-test--make-session
+     1 "/tmp/proj"
+     (list (eca-workspaces-test--make-chat :title "Chat A")))
+    (with-current-buffer (eca-workspaces-test--render)
+      (eca-workspaces-test--goto "type ?")
+      (let ((line (line-number-at-pos)))
+        (expect (eca-workspaces--entity-at (point)) :to-be nil)
+        (eca-workspaces--render)
+        (expect (line-number-at-pos) :to-equal line))))
+
+  (it "keeps the point and scroll of each window across re-renders"
+    (let ((chat-c (eca-workspaces-test--make-chat :title "Chat C")))
+      (eca-workspaces-test--make-session
+       1 "/tmp/proj"
+       (list (eca-workspaces-test--make-chat :title "Chat A")
+             (eca-workspaces-test--make-chat :title "Chat B")
+             chat-c))
+      (let ((buffer (eca-workspaces-test--render)))
+        (save-window-excursion
+          (set-window-buffer (selected-window) buffer)
+          (with-current-buffer buffer
+            (let ((window (get-buffer-window buffer))
+                  (chat-id (buffer-local-value 'eca-chat--id chat-c)))
+              ;; A window scrolled past the first chat, point on the last one.
+              (set-window-start window (eca-workspaces--line-position 3) t)
+              (eca-workspaces-test--goto "Chat C")
+              (set-window-point window (point))
+              (eca-workspaces--render)
+              (expect (line-number-at-pos (window-start window)) :to-equal 3)
+              (expect (eca-workspaces--entity-at (window-point window))
+                      :to-equal (cons 1 chat-id))))))))
+
   (it "falls back to buffer start when the entity is gone"
     (let ((chat (eca-workspaces-test--make-chat :title "Chat A")))
       (eca-workspaces-test--make-session 1 "/tmp/proj" (list chat))