fix: Allow adjusting terminal window of TRAMP processes.

Before this change, the terminal window of TRAMP processes was never
adjusted, which resulted in badly-sized output.

This change resets the adjust-window-size-function set to ignore by
TRAMP to its default function and tests its effect in a remote shell.

mistty-term.el

@@ -577,7 +577,12 @@ This function returns the newly-created buffer."
       (setq-local term-height height)
       (setq-local term-command-function #'mistty--term-command-hook)
       (mistty-term--exec program args)
-      (set-process-window-size (get-buffer-process term-buffer) height width)
+      (let ((proc (get-buffer-process term-buffer)))
+        ;; TRAMP sets adjust-window-size-function to #'ignore, which
+        ;; prevents normal terminal resizing from working. This turns
+        ;; it on again.
+        (process-put proc 'adjust-window-size-function nil)
+        (set-process-window-size proc height width))
       (setq-local term-raw-map local-map)
       (term-char-mode)
       (advice-add 'move-to-column :around #'mistty--around-move-to-column)

mistty.el

@@ -2741,6 +2741,7 @@ only spaces with ==\'mistty-skip t between them."
                             window-adjust-process-window-size-function))
            (size (funcall adjust-func mistty-proc
                           (get-buffer-window-list mistty-work-buffer nil t))))
+      (mistty-log "set-process-window-size %s" size)
       (when size
         (let ((width (- (car size) left-margin-width))
               (height (cdr size)))

test/mistty-tramp-test.el

@@ -137,3 +137,23 @@
       (mistty--send-string mistty-proc "printf '\\032//home\\nok\\n'")
       (should (equal "ok" (mistty-send-and-capture-command-output)))
       (should (equal (concat sg-prefix "/home/") default-directory)))))
+
+(ert-deftest mistty-tramp-test-window-size ()
+  (let* ((sg-prefix (mistty-test-sg-prefix))
+         (home (file-name-directory "/"))
+         (default-directory (concat sg-prefix home)))
+    (mistty-with-test-buffer (:selected t)
+      (let ((win (selected-window))
+            cols-before cols-after)
+        (mistty-send-text "tput cols")
+        (setq cols-before (string-to-number (mistty-send-and-capture-command-output)))
+
+        (split-window-horizontally nil win)
+        (mistty--window-size-change win)
+
+        ;; This makes sure the terminal is told about the window size
+        ;; change.
+        (mistty-send-text "tput cols")
+        (setq cols-after (string-to-number (mistty-send-and-capture-command-output)))
+        (should-not (equal cols-before cols-after))
+        (should (< cols-after cols-before))))))