Fix two crashes

One was where WM was assuming that a seat existed during first manage,
but that's not always true, so we have to check that before running the
initialization code. I also split that off into its own function like in
Window.

The other crash was when trying to calculate the layout with the
output's width and/or height equal to zero, it would crash subtracting
the border width.

I discovered both of these when try to restart beansprout without
restarting River.

src/Output.zig

@@ -576,8 +576,11 @@ pub fn manage(output: *Output) void {
         }
     }
 
-    // Calculate layout before managing windows
+    // Calculate layout before managing windows, but only if output dimensions are initialized
-    output.calculateLayout();
+    if (output.usable_geometry.width > 0 and output.usable_geometry.height > 0) {
+        output.calculateLayout();
+    }
+
     var it = output.windows.iterator(.forward);
     while (it.next()) |window| {
         window.manage();
@@ -612,6 +615,8 @@ pub fn render(output: *Output) void {
 /// - Single window: maximized
 /// - Multiple windows: stack (45% left, vertically tiled), primary (55% right)
 fn calculateLayout(output: *Output) void {
+    // Shouldn't be called if height/width are not positive
+    assert(output.geometry.width > 0 and output.geometry.height > 0);
     // Get a list of active windows
     var active_list: DoublyLinkedList = .{};
     var active_count: u31 = 0;
@@ -714,8 +719,14 @@ fn calculateLayout(output: *Output) void {
         }
 
         // Make space for borders
-        window.pending_manage.dimensions.?.height -= 2 * border_width;
+        if (window.pending_manage.dimensions.?.height > 2 * border_width and
-        window.pending_manage.dimensions.?.width -= 2 * border_width;
+            window.pending_manage.dimensions.?.width > 2 * border_width)
+        {
+            window.pending_manage.dimensions.?.height -= 2 * border_width;
+            window.pending_manage.dimensions.?.width -= 2 * border_width;
+        } else {
+            log.warn("Can't add borders to some window; {s}'s dimensions are too small.", .{output.name orelse "some output"});
+        }
         window.pending_render.position.?.x += border_width;
         window.pending_render.position.?.y += border_width;
     }

src/WindowManager.zig

@@ -72,7 +72,63 @@ pub fn prevOutput(wm: *WindowManager, current: *Output) ?*Output {
     return @fieldParentPtr("link", prev_link);
 }
 
-fn manage_start(wm: *WindowManager) void {
+fn initialize(wm: *WindowManager) void {
+    if (wm.context.initialized) return;
+
+    // We need a seat to intitialize this stuff, so let's just not do it right now.
+    // The WM can run fine without it, though, it won't be fully usuable.
+    const seat = wm.seats.first() orelse return;
+    const river_seat_v1 = seat.river_seat_v1;
+
+    const context = wm.context;
+    context.initialized = true;
+
+    // Tag bindings
+    for (context.config.tag_binds.items) |tag_bind| {
+        comptime var i: u8 = 1;
+        comptime var buffer: [1]u8 = undefined;
+        inline while (i <= 9) : (i += 1) {
+            const tags: u32 = 1 << (i - 1);
+            buffer[0] = i + '0';
+            const command: XkbBindings.Command = switch (tag_bind.command) {
+                .set_output_tags => .{ .set_output_tags = tags },
+                .set_window_tags => .{ .set_window_tags = tags },
+                .toggle_output_tags => .{ .toggle_output_tags = tags },
+                .toggle_window_tags => .{ .toggle_window_tags = tags },
+                else => unreachable,
+            };
+            context.xkb_bindings.addBinding(river_seat_v1, @field(xkbcommon.Keysym, &buffer), tag_bind.modifiers, command);
+        }
+    }
+    // Rest of the keybinds
+    for (context.config.keybinds.keys(), context.config.keybinds.values()) |key, command| {
+        context.xkb_bindings.addBinding(river_seat_v1, key.keysym, key.modifiers, command);
+    }
+
+    // Pointer bindings
+    for (context.config.pointer_binds.items) |pointer_bind| {
+        const binding = river_seat_v1.getPointerBinding(pointer_bind.button, pointer_bind.modifiers) catch {
+            log.err("Failed to create pointer binding", .{});
+            continue;
+        };
+
+        switch (pointer_bind.action) {
+            .move_window => {
+                if (seat.move_pointer_binding) |old| old.destroy();
+                binding.setListener(*Seat, Seat.movePointerBindingListener, seat);
+                seat.move_pointer_binding = binding;
+            },
+            .resize_window => {
+                if (seat.resize_pointer_binding) |old| old.destroy();
+                binding.setListener(*Seat, Seat.resizePointerBindingListener, seat);
+                seat.resize_pointer_binding = binding;
+            },
+        }
+        binding.enable();
+    }
+}
+
+fn manage(wm: *WindowManager) void {
     const river_window_manager_v1 = wm.river_window_manager_v1;
     const context = wm.context;
 
@@ -82,54 +138,7 @@ fn manage_start(wm: *WindowManager) void {
     if (!context.initialized) {
         // This code runs during initial startup and after config reloads.
         @branchHint(.cold);
-        context.initialized = true;
+        wm.initialize();
-
-        const seat = wm.seats.first() orelse @panic("Failed to get seat");
-        const river_seat_v1 = seat.river_seat_v1;
-
-        // Tag bindings
-        for (context.config.tag_binds.items) |tag_bind| {
-            comptime var i: u8 = 1;
-            comptime var buffer: [1]u8 = undefined;
-            inline while (i <= 9) : (i += 1) {
-                const tags: u32 = 1 << (i - 1);
-                buffer[0] = i + '0';
-                const command: XkbBindings.Command = switch (tag_bind.command) {
-                    .set_output_tags => .{ .set_output_tags = tags },
-                    .set_window_tags => .{ .set_window_tags = tags },
-                    .toggle_output_tags => .{ .toggle_output_tags = tags },
-                    .toggle_window_tags => .{ .toggle_window_tags = tags },
-                    else => unreachable,
-                };
-                context.xkb_bindings.addBinding(river_seat_v1, @field(xkbcommon.Keysym, &buffer), tag_bind.modifiers, command);
-            }
-        }
-        // Rest of the keybinds
-        for (context.config.keybinds.keys(), context.config.keybinds.values()) |key, command| {
-            context.xkb_bindings.addBinding(river_seat_v1, key.keysym, key.modifiers, command);
-        }
-
-        // Pointer bindings
-        for (context.config.pointer_binds.items) |pointer_bind| {
-            const binding = river_seat_v1.getPointerBinding(pointer_bind.button, pointer_bind.modifiers) catch {
-                log.err("Failed to create pointer binding", .{});
-                continue;
-            };
-
-            switch (pointer_bind.action) {
-                .move_window => {
-                    if (seat.move_pointer_binding) |old| old.destroy();
-                    binding.setListener(*Seat, Seat.movePointerBindingListener, seat);
-                    seat.move_pointer_binding = binding;
-                },
-                .resize_window => {
-                    if (seat.resize_pointer_binding) |old| old.destroy();
-                    binding.setListener(*Seat, Seat.resizePointerBindingListener, seat);
-                    seat.resize_pointer_binding = binding;
-                },
-            }
-            binding.enable();
-        }
     }
 
     {
@@ -147,7 +156,7 @@ fn manage_start(wm: *WindowManager) void {
     river_window_manager_v1.manageFinish();
 }
 
-fn render_start(wm: *WindowManager) void {
+fn render(wm: *WindowManager) void {
     const river_window_manager_v1 = wm.river_window_manager_v1;
     {
         var it = wm.seats.iterator(.forward);
@@ -171,8 +180,8 @@ fn windowManagerV1Listener(window_manager_v1: *river.WindowManagerV1, event: riv
         .unavailable => {
             fatal("Window manager unavailable (some other wm instance is running). Exiting", .{});
         },
-        .manage_start => wm.manage_start(),
+        .manage_start => wm.manage(),
-        .render_start => wm.render_start(),
+        .render_start => wm.render(),
         .output => |ev| {
             const output = Output.create(context, ev.id) catch @panic("Out of memory");
             wm.outputs.append(output);