feat(plugins): Given an optional plugin, conditionally discard deps

[abeldekat]

Currently, when a plugin is marked with "enabled = false", lazy.nvim investigates the dependencies of that plugin,and disables them when appropriate.
Such behaviour is not implemented for a plugin marked with "optional = true".

Example

Consider a stock LazyVim installation with "extras/lang/python" added to "config/lazy.lua"
The resulting installation includes nvim-dap-python and its keys, but without nvim-dap installed.

Pressing <leader> d P c leads to an error.
The UI of which-key shows "prefix" as description for "d".

The cause

In "extras/lang/python", nvim-dap-python is a dependency of nvim-dap.
When "extras/dap/core" is not added to "config/lazy.lua", nvim-dap becomes completely optional and will not be installed.
Currently, the dependency of nvim-dap, nvim-dap-python, does get installed.

Note: This pattern applies to multiple configs in extras.

Is it a problem?

If the user wants to use "extras/lang/python" without "extras/dap/core", the following options are available:

• the user accepts a plugin he has no benefit of.
  The plugin will never load, unless the aforementioned keys are pressed, resulting in an error.
• the user explicitly disables nvim-dap-python
• the maintainer moves nvim-dap to its own python specific config.
  The user now needs to include both python configs for complete functionality.

Implementation

This is relatively straightforward, reusing the existing algorithm doing the disabling of explicitly disabled plugins.

• The user might see some unexpected plugins to be cleaned in the UI of lazy.nvim.
• Performance is not expected to degrade. I did not observe a decline.

References

• discussion dependency inheritance
• Optional keyword added

[folke]

Merged, thanks!

[abeldekat]

You are most welcome. Happy to contribute!