Do not generate json file at runtime

[KAction]

This only works with local user installations, it does not work with
proper package managers.

[humitos]

Hi! Thanks for opening this PR. Can you explain a little more what's the issue and how your PR solves it? I'm not sure to understand it just from reading the changes. Thanks!

[KAction]

Sure. Without this patch function for generating json is called when building documentation of something else, something that depends on sphinx-version-warning (in my case I was building documentation of sphinx-hoverxref). At this point installation location of sphinx-version-warning is already read-only.

Problem is following line: STATIC_PATH = os.path.join(os.path.dirname(__file__), '_static'). If file is located in build directory, that will write into build directory, which is fine. When this file is already installed, STATIC_PATH will resolve to root-owned path.

I am no expert of sphinx, so I can't tell you why this function is called during build of other package.

[humitos]

Can you tell me how to reproduce this locally so I can dig a little more to understand what's happening behind the scenes?

[KAction]

Alright, here is failed build log: https://gist.github.com/dc604d01c3c6ea33ae1a669a2a79953e
To get it locally, checkout this nixpkgs commit https://github.com/KAction/nixpkgs/tree/v1/bug/sphinx-version-warning
and try to build nix-build -A python3.pkgs.sphinx-hoverxref.

Sorry, I don't have any smaller reproducer (like with pip + chmod or something), although Nix installation is quite easy on top of any linux distribution: https://nixos.org/download.html