Requires Unity 2019.2 or later
Add vim to the Unity's External Tools section in Preferences so all your files open in gvim.
Double click files to open them, just like built-in Visual Studio support.
Several options are available:
Win: Edit > Preferences > External Tools Mac: Unity > Preferences > External Tools
Tested with Unity 2019.4.3 on multiple platforms:
Add this line to your Packages/manifest.json:
"com.github.idbrii.unity-vimeditor": "https://github.com/idbrii/unity-vimeditor.git#latest-release",
Win: Edit > Preferences > External Tools Mac: Unity > Preferences > External Tools
Then select "Vim (gvim.exe)" from the "External Script Editor" dropdown. "(gvim.exe)" will vary based on your vim setup -- if you have the .bat files installed, you can choose them.