feat: WindowRules Workspace Assignment

[karlskewes]

Related issues

• Part of: [Feature Request] Window Rules cosmic-epoch#847
• Closes: Make it possible to let auto started applications start on a specific workspace cosmic-epoch#1819
• Closes: [Feature Request] Assign application to workspace like i3wm cosmic-epoch#1395
• Closes: How to always launch certain apps on certain workspaces? cosmic-epoch#1129

Feature

Extend WindowRules enabling launching applications on specific workspaces instead of the current active workspace.

Requires: pop-os/cosmic-settings-daemon#137

How to use

Get Application ID and Title:

Deprecated but works, see: pop-os/cosmic-protocols#70 (comment)

$ nix-shell -p wayland pkg-config

[nix-shell:~/path/to/cosmic-protocols]$  cargo run --example toplevel-list
     Running `target/debug/examples/toplevel-list`
Toplevel ObjectId(zcosmic_toplevel_handle_v1@4278190080)
	Title: Some("cargo run --example toplevel-list")
	App ID: Some("kitty")
	States: [Activated]
	Outputs: []
	Workspaces: []
Toplevel ObjectId(zcosmic_toplevel_handle_v1@4278190082)
	Title: Some("Some webpage — Mozilla Firefox")
	App ID: Some("firefox")
	States: []
	Outputs: []
	Workspaces: []

Pin workspaces using UI or via file:

$ cat ~/.config/cosmic/com.system76.CosmicComp/v1/pinned_workspaces 
[
    (
        output: (
            name: "eDP-1",
            edid: None,
        ),
        tiling_enabled: true,
        id: Some("11f90a5"),
    ),
    (
        output: (
            name: "eDP-1",
            edid: None,
        ),
        tiling_enabled: true,
        id: Some("b382cb"),
    ),
]

Define Workspace Assignment configuration file with matching id's, regex supported:

$ cat ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/v1/workspace_assignment_custom
[
  (
    enabled: true,
    appid: "kitty",
    title: ".*",
    workspace_id: "11f90a5"
  ),
  (
    enabled: true,
    appid: "firefox",
    title: ".*",
    workspace_id: "b382cb"
  )
]

Disable the window rule by setting enabled: false.

Behaviours

1. Workspaces are NOT created if the assigned workspace ID doesn't exist. A warning will be logged and the window will be launched on the current active workspace as if the assignment didn't exist.
   For example, if workspaces a and b exist but the application config pins to c, then workspace c will NOT be added.
   2026-03-20T21:37:45.920671Z WARN cosmic_comp::shell: Assigned workspace id not found: foobar1
2. Active workspace does NOT change if the window is launched on a different workspace. For example, on workspace b, launch Firefox pinned to c, active workspace stays on b.
3. workspace_assignment_custom is auto-reloaded when the file changes however existing windows are not moved if the assigned workspace id was changed.
4. Declarative workspace_id's: Can define in pinned_workspaces. Doesn't reload but does load on login. Can use custom workspace_id String values, e.g: terminal, browser, work.
5. In practice, workspaces need to be pinned as workspace.id's are created with a random generator when using UI to pin.
   • there's no code for reloading this file (I could add if desired). Changes to the file take effect on next login.

   $ cat ~/.config/cosmic/com.system76.CosmicComp/v1/pinned_workspaces
   [
    (
        output: (
            name: "eDP-1",
            edid: None,
        ),
        tiling_enabled: true,
        id: Some("11f90a5"),
    ),
    (
        output: (
            name: "eDP-1",
            edid: None,
        ),
        tiling_enabled: true,
        id: Some("b382cb"),
    ),
   ]   

Testing

flake.nix -> nix develop

When rebased onto: #2219 and using pop-os/cosmic-settings-daemon#138

# enter dev environment
nix develop

v ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/v1/workspace_assignment_custom

COSMIC_COMP=winnit cargo run

# active workspace is the first pinned one
WAYLAND_DISPLAY=2 kitty & # launches on active
WAYLAND_DISPLAY=2 firefox & # launches on workspace in background (not active)
WAYLAND_DISPLAY=wayland-2 cosmic-ext-calculator # launches on active

flake.nix -> nix build

When rebased onto: #2219 and using pop-os/cosmic-settings-daemon#138

# build cosmic-comp
nix build

Can't run the resulting binary because of missing dependencies/version clashes.

NixOS package overlay

1. Patching the NixOS package source with fork and branch.
2. Build and install.
3. Use appropriate config file.
4. Launch applications and observe they are autostarted on workspaces other than the current active workspace.

UI Component

Whilst the configuration file support in this PR is sufficient for my use case, I saw mention of UI support for a similar feature in: #1292 (comment)

There will be UI to do this from cosmic-settings and the tiling applet eventually.

Could that be this? pop-os/cosmic-settings#438

Something I could pickup next perhaps. Or other window rules.

Note to reviewers

This is my first contribution to Cosmic and I may have misunderstood or completely missed project structure/styling or other conventions. Please let me know and I'll rework accordingly. Thank you!

• "workspace assignment" naming chosen based off i3wm:
  assign [class="<application_class>"] <workspace_number>
• separate file path/to/WindowRules/workspace_assignment_custom because it appears to be convention to have a file per feature, rather than a catch all ../WindowRules/window_rules with features: sticky, tiling exceptions, workspace assignment, etc
• left workspace_assignment_defaults free for implementation if required.

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[karlskewes]

Removed formatting commit, reduced Cargo changes and rebased.

[karlskewes]

1. Running this full time per: karlskewes/nixos@6d3a2d5
2. I use custom defined workspace names, terminal, chat, browser.
3. Corrected the PR description appid & title mixup in workspace_assignment_custom.

$ nix-shell -p wayland pkg-config

[nix-shell:~/src/github.com/karlskewes/cosmic-protocols]$ cargo run --example toplevel-list
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/examples/toplevel-list`
Toplevel ObjectId(zcosmic_toplevel_handle_v1@4278190080)
	Title: Some("cargo run --example toplevel-list")
	App ID: Some("kitty")
	States: [Activated]
	Outputs: []
	Workspaces: []
Toplevel ObjectId(zcosmic_toplevel_handle_v1@4278190081)
	Title: Some("feat: WindowRules Workspace Assignment by karlskewes · Pull Request #2214 · pop-os/cosmic-comp — Mozilla Firefox")
	App ID: Some("firefox")
	States: []
	Outputs: []
	Workspaces: []

[karlskewes]

When #2427 lands I will rework this to match on workspace names instead.

Assign to first matching workspace name (assuming duplicates could exist?).