tui/input.c: add support for mouse release events in urxvt (#8309)

Some terminals don't report which buttons are involved in some mouse
events. For example, the urxvt protocol
(http://www.huge-man-linux.net/man7/urxvt.html section "Mouse
reporting") does not report which button has been released.
In this case libtermkey reports button 0
(http://www.leonerd.org.uk/code/libtermkey/doc/termkey_interpret_mouse.3.html)

Up to now, forward_mouse_event did not handle button==0.
On press events there is not much we can do, and we keep the
current behavior which is dropping the event. But on drag-and-release
events we can compensate by remembering the last button pressed.

fixes #3182 for urxvt
fixes #5400

1 files changed, 13 insertions, 2 deletions

diff --git a/src/nvim/tui/input.c b/src/nvim/tui/input.c
index b04a6ce4f9..0362820687 100644
--- a/src/nvim/tui/input.c
+++ b/src/nvim/tui/input.c
@@ -170,11 +170,21 @@ static void forward_mouse_event(TermInput *input, TermKeyKey *key)
   char buf[64];
   size_t len = 0;
   int button, row, col;
+  static int last_pressed_button = 0;
   TermKeyMouseEvent ev;
   termkey_interpret_mouse(input->tk, key, &ev, &button, &row, &col);
 
-  if (ev != TERMKEY_MOUSE_PRESS && ev != TERMKEY_MOUSE_DRAG
-      && ev != TERMKEY_MOUSE_RELEASE) {
+  if ((ev == TERMKEY_MOUSE_RELEASE || ev == TERMKEY_MOUSE_DRAG)
+      && button == 0) {
+    // Some terminals (like urxvt) don't report which button was released.
+    // libtermkey reports button 0 in this case.
+    // For drag and release, we can reasonably infer the button to be the last
+    // pressed one.
+    button = last_pressed_button;
+  }
+
+  if (button == 0 || (ev != TERMKEY_MOUSE_PRESS && ev != TERMKEY_MOUSE_DRAG
+                      && ev != TERMKEY_MOUSE_RELEASE)) {
     return;
   }
 
@@ -210,6 +220,7 @@ static void forward_mouse_event(TermInput *input, TermKeyKey *key)
                                 "ScrollWheelDown");
       } else {
         len += (size_t)snprintf(buf + len, sizeof(buf) - len, "Mouse");
+        last_pressed_button = button;
       }
       break;
     case TERMKEY_MOUSE_DRAG: