Add a test.

regress/image-feature-redraw.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+
+# Terminal replies which change no features must not replay our images.
+# A reply which adds a feature must still cause a redraw.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export TERM
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+python3 -B - "$TEST_TMUX" <<'PY'
+import os
+import sys
+from image_test import image_test, sixel, check_image
+
+with image_test(sys.argv[1]) as test:
+    client = test.attach()
+    test.emit(sixel(8, 16, [(100, 0, 0)], [0] * (8 * 16)))
+    assert len(client.images()) == 1
+    client.clear()
+    # The primary DA was answered during attach. This secondary DA adds
+    # nothing, but still calls tty_update_features().
+    os.write(client.fd, b'\033[>0;1;0c')
+    client.read(0.5)
+    assert not client.images(), 'unchanged features replayed the image'
+    features = test.run('display-message', '-p', '#{client_termfeatures}')
+    assert 'sync' not in features.split(','), features
+    os.write(client.fd, b'\033[?2026;1$y')
+    test.wait(lambda: 'sync' in test.run('display-message', '-p',
+        '#{client_termfeatures}').split(','))
+    client.read(0.2)
+    assert len(client.images()) == 1, 'new terminal feature did not redraw'
+    check_image(client.images()[0], 8, 16, [(255, 0, 0)] * (8 * 16))
+PY