feat(custom) Implement dropdown menu support for custom modules

[koshea]

Objective

Enable custom modules to show an inline dropdown picker for context-switching use cases (kubectl, gcloud, etc.) without requiring new Rust code per widget, pure config only.

Solution

Added three new config fields to CustomModuleDefinition:

• dropdown-list-command — shell command returning newline-separated options
• dropdown-select-command — shell command run on selection; the chosen item is passed via $WAYLE_SELECTED env var (not string interpolation) to avoid shell injection
• label-ellipsize — end (default), middle, or start; controls pango truncation mode for both the bar label and dropdown items

left-click = "dropdown" (bare, no colon) opens the module's own inline popover. A new ClickAction::InlineDropdown variant handles parsing; the registry dispatcher treats it as a no-op since the custom module handles it directly.

The dropdown picker (CustomDropdownPicker) follows the existing DevicePicker pattern: ListBox + FactoryVecDeque, single-click activation, checkmark on the active item (matched by exact trimmed text against the module's current output). The popover uses the standard .dropdown wrapper, autohide, position detection, and shadow styling.

A BarButtonInput::SetEllipsize message was added to allow modules to override the label truncation mode without changing BarButtonBehavior.

Additional robustness:

• Generation counter on dropdown loads discards stale results from rapid toggle cycles
• Non-interactive (no items) placeholder with disabled styling when the list command returns empty
• Selection triggers sequential execution: select command (awaited) → main command refresh → immediate label update
• Dropdown is cleaned up on definition change/removal

Example config:

[[modules.custom]]
id = "kube-context"
command = "kubectl config current-context"
interval-ms = 5000
format = "{{ output }}"
icon-name = "ld-layers-symbolic"
label-max-length = 24
label-ellipsize = "middle"
left-click = "dropdown"
dropdown-list-command = "kubectl config get-contexts -o name"
dropdown-select-command = 'kubectl config use-context "$WAYLE_SELECTED"'

Test Plan

• Add custom module with dropdown config → dropdown opens with items on click
• Select an item → select command runs, label refreshes immediately
• Active item shows checkmark and accent styling
• label-ellipsize = "middle" with label-max-length → bar label and dropdown items truncate in the middle
• No dropdown-list-command → left-click = "dropdown" is a no-op
• Command returns empty → (no items) placeholder shown, non-interactive
• Rapid toggle while loading → no stale results or duplicate popovers
• Hot-reload dropdown-list-command → dropdown recreated on next open
• Hot-reload label-ellipsize → takes effect immediately

[agrahamlincoln]

I really liked the idea here, and wanted a similar feature for a custom module that i "hacked" in a dropdown with wofi. I wrote up my own solution for this in #83 that i think is more idiomatic and scalable for other usecases and I considered your kubectl usecase as well to see if my solution would enable you as well. take a look! i'd love to collaborate with you on a solution that works well and is extensible for more/future wayle usecases.

[koshea]

I really liked the idea here, and wanted a similar feature for a custom module that i "hacked" in a dropdown with wofi. I wrote up my own solution for this in #83 that i think is more idiomatic and scalable for other usecases and I considered your kubectl usecase as well to see if my solution would enable you as well. take a look! i'd love to collaborate with you on a solution that works well and is extensible for more/future wayle usecases.

Hi @agrahamlincoln glad to hear I am not the only one who wanted this functionality. I don't have a strong case on whether these should be rolled up into the dropdown registry. They seemed less likely to be re-usable to me hence keeping in the module. Appreciate the other improvements you made and happy to collaborate to get one or the other version merged.