Vim9script Function Scope: Plugin Dev Guide

by Henrik Larsen 44 views

Hey guys! Today, we're diving deep into the fascinating world of Vim9script function scopes. If you're building Vim9 plugins, understanding how function scopes work is absolutely crucial for creating robust and maintainable code. We'll explore the different scopes, how they affect function visibility, and tackle a common issue that plugin developers often encounter.

The Question: Function Scope Woes in Vim9 Plugins

Let's start with the core issue. Imagine you're developing a plugin called MyPlugin, and you've organized your code in the standard Vim plugin directory structure. You have a main function defined in plugin/MyPlugin.vim that gets invoked from after/plugin/MyPlugin.vim. So far, so good. But what happens when you try to call this function from other parts of your plugin or even from your vimrc? You might find yourself scratching your head, wondering why Vim can't seem to find your function. This is where understanding function scope becomes paramount.

Decoding the Function Scope Puzzle

In Vim9script, the scope of a function determines where it can be called from. Think of it like this: a function's scope is its neighborhood. If you're not in the neighborhood, you can't knock on its door! There are a few key scopes to be aware of in Vim9script:

  • Script Scope: Functions defined at the top level of a Vim script (outside of any other function or block) have script scope. They're like the friendly neighbors on your street – they're visible within the entire script they're defined in. However, they're not directly accessible from outside the script unless you explicitly make them so.
  • Function Scope: Functions defined inside another function have function scope. They're like a secret recipe passed down within a family – only the members of that family (i.e., the enclosing function and any functions defined within it) can access them.
  • Global Scope: Functions defined with the g: prefix have global scope. They're like the town crier – they can be called from anywhere in Vim, including your vimrc, other plugins, and even the command line. This is the broadest scope, but it's important to use it judiciously to avoid naming conflicts.

The Plugin Structure and Scope Implications

Now, let's relate these scopes to our plugin example. The plugin/MyPlugin.vim file is a Vim script, so functions defined at the top level within it will have script scope. This means they're visible within MyPlugin.vim itself. When after/plugin/MyPlugin.vim sources plugin/MyPlugin.vim, it effectively executes the script, making those script-scoped functions available within the context of after/plugin/MyPlugin.vim as well. This is why the initial invocation from after/plugin/MyPlugin.vim works.

However, the key point is that these functions are not automatically available globally. If you try to call them from your vimrc or another plugin, Vim won't be able to find them because they're confined to the script scope of plugin/MyPlugin.vim. This is the core of the problem our plugin developer is facing.

The Solution: Making Functions Accessible

So, how do we make our functions accessible from outside the script they're defined in? There are a couple of ways to tackle this, and the best approach depends on your specific needs and design goals.

Option 1: Global Scope with g:

The simplest solution is to define your function with the g: prefix, explicitly making it global. For example: