How can I know if a plugin is enabled in another plugin?

[Mister-Hope]

My basic question is, how can a plugin know if the plugin it want to use is enabled or not.

e.g.: my sitemap and seo plugin would both want git plugin to be enabled.

If I redeclare plugins to make sure they are enabled, I will get errors like

warning plugin @vuepress/plugin-git has been used multiple times, only the last one will take effect

And this can be awful when I am using:

git → reading-time→   theme
↓            ↓       ↗ ↑
  ↘   →  pageinfo      ↑
      ↘   →   seo  ↗  ↑
           ↘ sitemap  ↗
              ↘ feed↗



     ↗        →      ↘
palatte→ reading-time→   theme
↓            ↓       ↗ ↑
  ↘   →  pageinfo      ↑
      ↘   →   seo  ↗  ↑
           ↘ sitemap  ↗
              ↘ feed↗
           ↘copy-code↗
    ↘md-enhance↗
       ↘  pwa↗

(palette is my own plugin controling styles)

when I want them to be able to work standalone and in one theme

Common idea are:

• check in my plugin whether the plugin has already been declared or not and decide whether to enable it.

  This seems hard to implement

• Make a soft declare on depending on this plugin and wait for users to input options.

  In this way only theme and user config have full control of using and setting options for plugins, while plugins can only decalre the plugins they are depending and emit warnings if the plugin is not actually enabled. This is a huge breaking change

• Make a search squence, and then merge all the options if the plugin(do not support mutiple instance) is declared in mutiple plugins or theme and warned if some options are covered when merging.

  This don't have much affect to current code.

I hope one of them above can be achieved, or there is something which I can do to avoid the warning.

[meteorlxy]

You can use following snippet to detect if a plugin has already been used:

https://github.com/vuepress/vuepress-next/blob/5e96641b8d2dd947372222e0af2ea47729afbada/packages/%40vuepress/core/src/app/appUse.ts#L17-L32

---

TBH, supporting nested plugins does have this kind of tradeoff.

@shigma made vuepress-mergable in v1 to solve this problem (I think it wouldn't work in v2 now 😓 ).

[meteorlxy]

A plugin can print warning when some deps are missing.

I prefer not to add options if it is not necessary (the reason why clientDynamicModules was removed).

[Mister-Hope]

Actually no new options are need to add, just using the existing plugin option and make:

• Actual use plugin supporring mutiple
• Check and warn if the other plugin listed not in use.

[Mister-Hope]

I saw you remove the entire plugin config in the latest commit.

But I think supporting plugins to use mutiple plugin is good, I have common cases to use some 'tool-like' plugins in my other plugins e.g.: a palette system.

It's hard to make a mutiple plugin used in other plugins just like vue3's composition api.@meteorlxy Letting users configue them mutiple times will lead to a confused plugin config.

Check and warn if the other plugin listed not in use.

If you think above is unecessary, I still want you to rethink about this:

• can use plugin which supports mutiple

This has no side effects

[meteorlxy]

In fact, you can still use plugins via app.use() in your plugin.

But it will be an undocumented usage, because we should discourage plugin nesting.

[Mister-Hope]

Got it, thanks!😀