The upcoming PhpStorm 8 features built-in WordPress support, as explained in this support document. However what’s the best way to set up your WordPress install in order to write plugins? Here’s my personal answer — feel free to suggest alternatives in the comments section.
When working on a WordPress plugin, you don’t want functions, classes, variables, etc. from other plugins to leak into your current plugin through auto-complete or other types of automation. For this reason, I suggest avoiding opening a whole WordPress checkout with all of your plugins inside of it using PhpStorm. At the same time, you don’t want to have a separate copy of WordPress for each plugin that you work on. This is redundant and makes keeping WordPress up to date harder.
So instead do a single checkout of WordPress to its own folder and then define
WP_PLUGIN_URL, as described on the Codex, so that your plugins folder will live outside of your WordPress folder. This way you can open and index the WordPress folder without getting all of your plugins along with it.
Now create a new project for each individual plugin. When doing so, you’ll want to add the WordPress folder as an include path in PhpStorm, as described in their documentation.
All of this will result in only your individual plugin’s folder showing up in PhpStorm but with WordPress showing up under the “External Libraries” list. This one WordPress install can be used in your browser to test all of your plugins but the plugin codes won’t overlap.