Add a mock backend for testing (including on other compositors)

Should help determine which issues are cosmic-comp bugs.

src/backend/mod.rs

@@ -0,0 +1,75 @@
+// Copyright 2023 System76 <info@system76.com>
+// SPDX-License-Identifier: GPL-3.0-only
+
+//! The backend of getting workspace/toplevel information and previews, and
+//! sending commands to change them.
+//!
+//! There are two backends: one that uses cosmic-comp protocols, and a mock
+//! backend for testing without any special protocols.
+
+use cosmic::{
+    cctk::wayland_client::protocol::wl_output, iced_sctk::subsurface_widget::SubsurfaceBuffer,
+};
+use std::collections::HashSet;
+
+// Wayland backend using cosmic-comp specific protocols
+#[cfg(not(feature = "mock-backend"))]
+mod wayland;
+#[cfg(not(feature = "mock-backend"))]
+pub use cosmic::cctk::{
+    cosmic_protocols::{
+        toplevel_info::v1::client::zcosmic_toplevel_handle_v1::ZcosmicToplevelHandleV1,
+        workspace::v1::client::zcosmic_workspace_handle_v1::ZcosmicWorkspaceHandleV1,
+    },
+    toplevel_info::ToplevelInfo,
+    workspace::Workspace,
+};
+#[cfg(not(feature = "mock-backend"))]
+pub use wayland::subscription;
+
+// Mock backend
+#[cfg(feature = "mock-backend")]
+mod mock;
+#[cfg(feature = "mock-backend")]
+pub use mock::{
+    subscription, ToplevelInfo, Workspace, ZcosmicToplevelHandleV1, ZcosmicWorkspaceHandleV1,
+};
+
+#[derive(Clone, Debug, Default)]
+pub struct CaptureFilter {
+    pub workspaces_on_outputs: Vec<wl_output::WlOutput>,
+    pub toplevels_on_workspaces: Vec<ZcosmicWorkspaceHandleV1>,
+}
+
+#[derive(Clone, Debug)]
+pub struct CaptureImage {
+    pub width: u32,
+    pub height: u32,
+    pub wl_buffer: SubsurfaceBuffer,
+    #[cfg(feature = "no-subsurfaces")]
+    pub image: cosmic::widget::image::Handle,
+}
+
+#[derive(Clone, Debug)]
+pub enum Event {
+    CmdSender(calloop::channel::Sender<Cmd>),
+    Workspaces(Vec<(HashSet<wl_output::WlOutput>, Workspace)>),
+    WorkspaceCapture(ZcosmicWorkspaceHandleV1, wl_output::WlOutput, CaptureImage),
+    NewToplevel(ZcosmicToplevelHandleV1, ToplevelInfo),
+    UpdateToplevel(ZcosmicToplevelHandleV1, ToplevelInfo),
+    CloseToplevel(ZcosmicToplevelHandleV1),
+    ToplevelCapture(ZcosmicToplevelHandleV1, CaptureImage),
+}
+
+#[derive(Debug)]
+pub enum Cmd {
+    CaptureFilter(CaptureFilter),
+    ActivateToplevel(ZcosmicToplevelHandleV1),
+    CloseToplevel(ZcosmicToplevelHandleV1),
+    MoveToplevelToWorkspace(
+        ZcosmicToplevelHandleV1,
+        ZcosmicWorkspaceHandleV1,
+        wl_output::WlOutput,
+    ),
+    ActivateWorkspace(ZcosmicWorkspaceHandleV1),
+}