layer-shell: error on 0 dimension without anchors

The protocol requires clients to set opposing anchors when requesting
a width or height of 0.

The goal of this patch is not to break clients that rely on this
behavior but to improve the consistency of the layer shell ecosystem
through adherence to the protocol.

types/wlr_layer_shell_v1.c

@@ -307,6 +307,26 @@ static void layer_surface_role_commit(struct wlr_surface *wlr_surface) {
 		return;
 	}
 
+	const uint32_t horiz = ZWLR_LAYER_SURFACE_V1_ANCHOR_LEFT |
+		ZWLR_LAYER_SURFACE_V1_ANCHOR_RIGHT;
+	if (surface->client_pending.desired_width == 0 &&
+		(surface->client_pending.anchor & horiz) != horiz) {
+		wl_resource_post_error(surface->resource,
+			ZWLR_LAYER_SURFACE_V1_ERROR_INVALID_SIZE,
+			"width 0 requested without setting left and right anchors");
+		return;
+	}
+
+	const uint32_t vert = ZWLR_LAYER_SURFACE_V1_ANCHOR_TOP |
+		ZWLR_LAYER_SURFACE_V1_ANCHOR_BOTTOM;
+	if (surface->client_pending.desired_height == 0 &&
+		(surface->client_pending.anchor & vert) != vert) {
+		wl_resource_post_error(surface->resource,
+			ZWLR_LAYER_SURFACE_V1_ERROR_INVALID_SIZE,
+			"height 0 requested without setting top and bottom anchors");
+		return;
+	}
+
 	if (surface->closed) {
 		// Ignore commits after the compositor has closed it
 		return;