Hi,

(Sorry, it seems I've deleted the original message, and I'm not answering to 
the mail I should be answering to).

> On 30/07/2017 04:40, sash...@gmail.com wrote:
> > I'm writing a plugin and want it to depend on another plugin
> > installed. At the moment I just have a line
> > 
> > source <path to plugin>
> > 
> > in my plugin that pulls in that plugin. Is there a standard way of
> > doing this or do plugin authors just invent their own way? Could I
> > use Vundle here instead?


There is no standard way of proceeding. Also there are two sides to the 
question: 
1- making sure what we depend upon is installed;
2- making sure what we depend upon is defined.

Beside the actual answer will depend on what you are actually depending upon.

1- Regarding availability
a- Most people simply document the dependency(/ies), and it's up to the 
end-users to make sure every dependency is properly installed.
In all cases, I consider that **documenting is mandatory**.


b- Some will use git submodules to make this as simple as possible.
The only, and main disadvantage, as Lifepillar said, is that a plugin may be 
installed several times. An incorrectly written plugin may even duplicate 
events. We could also experience very tricky bugs when several versions of a 
same plugin are installed.

IMO, this is not a good solution.


c- A few of us are specifying the dependencies for the only two plugin managers 
that support dependencies. I even go further and advocate their use. 
Unfortunately, the popular plugin managers are the simple ones, which don't 
understand dependencies so far.

The only two plugin managers that support dependencies (and that I'm aware of 
at this moment) are:
- VAM: https://github.com/MarcWeber/vim-addon-manager (through vim-py)
- VimFlavor: https://github.com/kana/vim-flavor

Even if you're not using them, nor expect to ever use them, I highly recommend 
that you specify the dependencies of your plugin for these two plugin managers. 
IOW, you'll have to define an addon-info.json file and a VimFlavor file -- 
unfortunately they don't share a common syntax. :(

You'll find plenty examples in my plugins. See for instance: 
https://github.com/LucHermitte/lh-brackets


d- Vim 8 packages don't solve anything. We can still have multiple versions of 
a same plugin installed (which is clumsy and bad), and they are not able to 
automatically install the dependencies.

If there was a notion of "environment" like we have in Python or conda, or of 
"sandbox" like with Haskell or nix, then may be we could have multiple packages 
that contain different versions of a same plugin. So far and AFAIK, this is not 
the case. Hence my current stance.



2- Regarding "sourcing"

a- Before Vim7, we had to source plugins where global functions, mappings, 
abbreviations, command, etc. were defined.

A simple way was to check for something we need, and if it isn't detected as 
defined, then we explicitly source the dependency.

  if ! exists('*SomeGlobalFunction')
    runtime plugin/MyDependencyThatDefineSomeGlobalFunction.vim
    if ! exists('*SomeGlobalFunction')
      echoerr "WARNING: MyDependencyThatDefineSomeGlobalFunction isn't 
installed. MyFooBar plugin is disabled. Please see xxxx"
    endif
  endif

Or if you don't care about sourcing something that may have already been 
sourced, you could simply type:

  runtime plugin/MyDependencyThatDefineSomeGlobalFunction.vim
  if ! exists('*SomeGlobalFunction')
    echoerr "WARNING: MyDependencyThatDefineSomeGlobalFunction isn't installed. 
MyFooBar plugin is disabled. Please see xxxx"
  endif

You could also check the plugin version in case it stores its version number in 
its `g:loaded_MyDependencyThatDefineSomeGlobalFunction` header-gate variable. 
This has been described in another answer.


(In case of definitions done in filetype plugins, what we had to do was a 
little bit trickier)


b- Now, we are past Vim 7. Vim 7 has introduced autoload plugins and their 
autoloaded functions.
Modern plugins will use autoload plugin files to store their functions. Most of 
the time this is just to speedup the starting time. Sometimes, this is because 
some of us are aware this is the best way to define libraries.

This time instead of checking whether a particular symbol is defined in order 
to source on the fly, we simply call the autoloaded functions. Given their 
name, foo#bar#func(), Vim will know that if the function doesn't exist then it 
must execute `:runtime foo/bar.vim`. If the function still doesn't exist, Vim 
will issue an error message.
Sometimes, you'll see a few issues from the users, of your plugin, that have 
skipped the installation procedure you have described in your plugin 
documentation.


Of course if you're not trying to execute a function defined in an autoload 
plugin file, you're back to square 2.a-.

Regards,
-- 
Luc Hermitte

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