View: fix/simplify logic in applyPending()

In particular, this fixes a crash that can happen if a client is made
non-fullscreen and then, while that transaction is ongoing, made
fullscreen again.

 river/View.zig         | 37 ++++++++++++++-----------------------
 river/XdgToplevel.zig  |  6 ++++--
 river/XwaylandView.zig |  6 ++++--
 3 files changed, 22 insertions(+), 27 deletions(-)

diff --git a/river/View.zig b/river/View.zig
index dd6a87d..d88c536 100644
--- a/river/View.zig
+++ b/river/View.zig
@@ -171,26 +171,16 @@ pub fn destroy(self: *Self) void {
 
 /// Handle changes to pending state and start a transaction to apply them
 pub fn applyPending(self: *Self) void {
-    var arrange_output = false;
-
-    if (self.current.tags != self.pending.tags) arrange_output = true;
-
-    // If switching from float -> layout or layout -> float arrange the output
-    // to get assigned a new size or fill the hole in the layout left behind.
-    if (self.current.float != self.pending.float) {
-        assert(!self.pending.fullscreen); // float state modifed while in fullscreen
-        arrange_output = true;
+    if (self.current.float and !self.pending.float) {
+        // If switching from float to non-float, save the dimensions.
+        self.float_box = self.current.box;
+    } else if (!self.current.float and self.pending.float) {
+        // If switching from non-float to float, apply the saved float dimensions.
+        self.pending.box = self.float_box;
     }
 
-    // If switching from float to non-float, save the dimensions.
-    if (self.current.float and !self.pending.float) self.float_box = self.current.box;
-
-    // If switching from non-float to float, apply the saved float dimensions.
-    if (!self.current.float and self.pending.float) self.pending.box = self.float_box;
-
-    // If switching to fullscreen, set the dimensions to the full area of the output
-    // Since no other views will be visible, we can skip arranging the output.
     if (!self.current.fullscreen and self.pending.fullscreen) {
+        // If switching to fullscreen, set the dimensions to the full area of the output
         self.setFullscreen(true);
         self.post_fullscreen_box = self.current.box;
         const dimensions = self.output.getEffectiveResolution();
@@ -200,16 +190,17 @@ pub fn applyPending(self: *Self) void {
             .width = dimensions.width,
             .height = dimensions.height,
         };
-    }
-
-    if (self.current.fullscreen and !self.pending.fullscreen) {
+    } else if (self.current.fullscreen and !self.pending.fullscreen) {
         self.setFullscreen(false);
         self.pending.box = self.post_fullscreen_box;
-        // If switching from fullscreen to layout, we need to arrange the output.
-        if (!self.pending.float) arrange_output = true;
     }
 
-    if (arrange_output) self.output.arrangeViews();
+    // We always need to arrange the output, as there could already be a
+    // transaction in progress. If we were able to check against the state
+    // that was pending when that transaction was started, we could in some
+    // cases avoid the arrangeViews() call here, but we don't store that
+    // information and it's simpler to always arrange anyways.
+    self.output.arrangeViews();
 
     server.root.startTransaction();
 }
diff --git a/river/XdgToplevel.zig b/river/XdgToplevel.zig
index 37b2a2b..6a56b70 100644
--- a/river/XdgToplevel.zig
+++ b/river/XdgToplevel.zig
@@ -329,8 +329,10 @@ fn handleRequestFullscreen(
     event: *wlr.XdgToplevel.event.SetFullscreen,
 ) void {
     const self = @fieldParentPtr(Self, "request_fullscreen", listener);
-    self.view.pending.fullscreen = event.fullscreen;
-    self.view.applyPending();
+    if (self.view.pending.fullscreen != event.fullscreen) {
+        self.view.pending.fullscreen = event.fullscreen;
+        self.view.applyPending();
+    }
 }
 
 /// Called when the client asks to be moved via the cursor, for example when the
diff --git a/river/XwaylandView.zig b/river/XwaylandView.zig
index 99c11d0..4d7e9f5 100644
--- a/river/XwaylandView.zig
+++ b/river/XwaylandView.zig
@@ -273,8 +273,10 @@ fn handleSetClass(listener: *wl.Listener(*wlr.XwaylandSurface), _: *wlr.Xwayland
 
 fn handleRequestFullscreen(listener: *wl.Listener(*wlr.XwaylandSurface), xwayland_surface: *wlr.XwaylandSurface) void {
     const self = @fieldParentPtr(Self, "request_fullscreen", listener);
-    self.view.pending.fullscreen = xwayland_surface.fullscreen;
-    self.view.applyPending();
+    if (self.view.pending.fullscreen != xwayland_surface.fullscreen) {
+        self.view.pending.fullscreen = xwayland_surface.fullscreen;
+        self.view.applyPending();
+    }
 }
 
 /// Some X11 clients will minimize themselves regardless of how we respond.