fix(ui-config): use the writeable cursor color in a live vterm

`vterm-mode' sets `buffer-read-only', so `cj/set-cursor-color-according-to-mode' painted the cursor with the read-only color (orange) whenever point was in a vterm. That includes the live terminal, not just `vterm-copy-mode'. But a live terminal takes input: keystrokes go to the process, not the buffer. So a live vterm now reports `unmodified' instead. `vterm-copy-mode' still reports `read-only': there it really is a read-only Emacs buffer the user navigates, and the orange cursor is the right signal.

I pulled the state cond out of `cj/set-cursor-color-according-to-mode' into `cj/--buffer-cursor-state' so it's unit-testable without a real frame or `set-cursor-color'.

2 files changed, 116 insertions, 6 deletions

diff --git a/modules/ui-config.el b/modules/ui-config.el
index 775aefb2..f9fddb0d 100644
--- a/modules/ui-config.el
+++ b/modules/ui-config.el
@@ -96,17 +96,34 @@ When `cj/enable-transparency' is nil, reset alpha to fully opaque."
 (defvar cj/-cursor-last-buffer nil
   "Last buffer name where cursor color was applied.")
 
+(defun cj/--buffer-cursor-state ()
+  "Return the buffer-state symbol used to choose the cursor color.
+
+One of `read-only', `overwrite', `modified', or `unmodified' — keys
+of `cj/buffer-status-colors'.
+
+A live vterm buffer (in `vterm-mode' but NOT `vterm-copy-mode')
+reports `unmodified' even though `vterm-mode' sets `buffer-read-only':
+keystrokes there go to the terminal process, so from the user's side
+the buffer is writeable, and the read-only (orange) cursor would be
+misleading.  `vterm-copy-mode' is the exception — there the buffer
+really is a read-only Emacs buffer the user navigates, so it falls
+through to `read-only' and keeps the orange cursor."
+  (cond
+   ((and (eq major-mode 'vterm-mode)
+		 (not (bound-and-true-p vterm-copy-mode)))
+	'unmodified)
+   (buffer-read-only       'read-only)
+   (overwrite-mode         'overwrite)
+   ((buffer-modified-p)    'modified)
+   (t                      'unmodified)))
+
 (defun cj/set-cursor-color-according-to-mode ()
   "Change cursor color according to buffer state (modified, read-only, overwrite).
 Only updates for real user buffers, not internal/temporary buffers."
   ;; Only update cursor for real buffers (not internal ones like *temp*, *Echo Area*, etc.)
   (unless (string-prefix-p " " (buffer-name))  ; Internal buffers start with space
-	(let* ((state (cond
-				   (buffer-read-only       'read-only)
-				   (overwrite-mode         'overwrite)
-				   ((buffer-modified-p)    'modified)
-				   (t                      'unmodified)))
-		   (color (alist-get state cj/buffer-status-colors)))
+	(let ((color (alist-get (cj/--buffer-cursor-state) cj/buffer-status-colors)))
 	  ;; Only skip if BOTH color AND buffer are the same (optimization)
 	  ;; This allows color to update when buffer state changes
 	  (unless (and (string= color cj/-cursor-last-color)
diff --git a/tests/test-ui-config--buffer-cursor-state.el b/tests/test-ui-config--buffer-cursor-state.el
new file mode 100644
index 00000000..add0d030
--- /dev/null
+++ b/tests/test-ui-config--buffer-cursor-state.el
@@ -0,0 +1,93 @@
+;;; test-ui-config--buffer-cursor-state.el --- Tests for cursor-state classification -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; `cj/--buffer-cursor-state' picks the buffer-state symbol that
+;; `cj/set-cursor-color-according-to-mode' maps to a cursor color via
+;; `cj/buffer-status-colors'.  The subtle case: a live vterm buffer is
+;; technically `buffer-read-only' (the `vterm-mode' body sets it) but the
+;; user can type into it -- keystrokes go to the terminal process -- so it
+;; must report a writeable state, not `read-only'.  `vterm-copy-mode' is
+;; the exception: there the buffer really is a read-only Emacs buffer the
+;; user navigates, so `read-only' (the orange cursor) is correct and kept.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(add-to-list 'load-path (expand-file-name "tests" user-emacs-directory))
+(setq load-prefer-newer t)
+(defvar vterm-copy-mode nil)
+(require 'ui-config)
+(require 'testutil-vterm-buffers)
+
+(ert-deftest test-ui-config-buffer-cursor-state-readwrite-unmodified ()
+  "Normal: a clean writeable buffer reports `unmodified'."
+  (with-temp-buffer
+    (set-buffer-modified-p nil)
+    (should (eq (cj/--buffer-cursor-state) 'unmodified))))
+
+(ert-deftest test-ui-config-buffer-cursor-state-readwrite-modified ()
+  "Normal: a writeable buffer with unsaved changes reports `modified'."
+  (with-temp-buffer
+    (insert "x")
+    (should (eq (cj/--buffer-cursor-state) 'modified))))
+
+(ert-deftest test-ui-config-buffer-cursor-state-read-only ()
+  "Normal: a plain read-only buffer reports `read-only'."
+  (with-temp-buffer
+    (setq buffer-read-only t)
+    (should (eq (cj/--buffer-cursor-state) 'read-only))))
+
+(ert-deftest test-ui-config-buffer-cursor-state-overwrite ()
+  "Boundary: `overwrite-mode' wins over the modified/unmodified split."
+  (with-temp-buffer
+    (insert "x")
+    (overwrite-mode 1)
+    (should (eq (cj/--buffer-cursor-state) 'overwrite))))
+
+(ert-deftest test-ui-config-buffer-cursor-state-live-vterm-is-writeable ()
+  "Boundary: a live vterm buffer is `buffer-read-only' but reports a
+writeable state -- the user types into the terminal process there, so the
+read-only (orange) cursor would be misleading."
+  (let ((buf (cj/test--make-fake-vterm-buffer "*test-vterm-cursor-state*")))
+    (unwind-protect
+        (with-current-buffer buf
+          (setq buffer-read-only t)            ; `vterm-mode' does this
+          (setq-local vterm-copy-mode nil)
+          (should-not (eq (cj/--buffer-cursor-state) 'read-only)))
+      (when (buffer-live-p buf) (kill-buffer buf)))))
+
+(ert-deftest test-ui-config-buffer-cursor-state-vterm-copy-mode-is-read-only ()
+  "Boundary: in `vterm-copy-mode' the vterm buffer is a read-only Emacs
+buffer the user navigates, so `read-only' (orange) is kept."
+  (let ((buf (cj/test--make-fake-vterm-buffer "*test-vterm-cursor-state-copy*")))
+    (unwind-protect
+        (with-current-buffer buf
+          (setq buffer-read-only t)
+          (setq-local vterm-copy-mode t)
+          (should (eq (cj/--buffer-cursor-state) 'read-only)))
+      (when (buffer-live-p buf) (kill-buffer buf)))))
+
+(ert-deftest test-ui-config-set-cursor-color-live-vterm-not-orange ()
+  "Normal: in a live vterm the cursor-color hook picks a writeable color,
+not the read-only orange -- even though the vterm buffer is read-only."
+  (let ((buf (cj/test--make-fake-vterm-buffer "*test-vterm-cursor-color*"))
+        (applied 'unset))
+    (unwind-protect
+        (with-current-buffer buf
+          (setq buffer-read-only t)
+          (setq-local vterm-copy-mode nil)
+          (let ((cj/-cursor-last-color nil)
+                (cj/-cursor-last-buffer nil))
+            (cl-letf (((symbol-function 'set-cursor-color)
+                       (lambda (c) (setq applied c))))
+              (cj/set-cursor-color-according-to-mode)))
+          (should (stringp applied))
+          (should-not (equal applied
+                             (alist-get 'read-only cj/buffer-status-colors))))
+      (when (buffer-live-p buf) (kill-buffer buf)))))
+
+(provide 'test-ui-config--buffer-cursor-state)
+;;; test-ui-config--buffer-cursor-state.el ends here