Undocumented minetest.get_gametime() returning nil at init time

[gd2shoe]

Minetest version

Minetest 5.7.0 (Windows)
Using Irrlicht 1.9.0mt10
Using LuaJIT 2.1.0-beta3
BUILD_TYPE=Release
RUN_IN_PLACE=1
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1
STATIC_SHAREDIR="."
STATIC_LOCALEDIR="locale"

Active renderer

No response

Irrlicht device

No response

Operating system and version

Windows 10

CPU model

AMD FX 6100

GPU model

No response

OpenGL version

No response

Summary

Very simply, I was experimenting to see if minetest.get_gametime() could be useful, and my code exploded. Turns out, it's returning nil. (or at the least, type(minetest.get_gametime())==nil.)

Discovered the issue when trying to subtract one timestamp from another. I wasn't aware of #10221. Still, subtracting one integer from another shouldn't cause problems.

Occurs in minetest_game, both stable-5 and main (if this makes any difference).

Steps to reproduce

assert(minetest.get_gametime(), 'get_gametime should be a number of seconds')

2023-10-11 02:48:38: ERROR[Main]: ModError: Failed to load and run script from C:\local\opt\minetest-5.7.0-win64\bin..\mods\sane_liquid\init.lua:
2023-10-11 02:48:38: ERROR[Main]: ...pt\minetest-5.7.0-win64\bin..\mods\sane_liquid\init.lua:159: get_gametime should be a number of seconds
2023-10-11 02:48:38: ERROR[Main]: stack traceback:
2023-10-11 02:48:38: ERROR[Main]: [C]: in function 'assert'
2023-10-11 02:48:38: ERROR[Main]: ...pt\minetest-5.7.0-win64\bin..\mods\sane_liquid\init.lua:159: in main chunk

[sfan5]

Works fine for me, make sure you're not calling it before during init time of the mods.

[gd2shoe]

That explains it. This is a documentation issue.
(and arguably, a missing feature)

I was looking to use it in an ABM for interval monitoring, but I was initializing the mod timestamp during init. I confirm that it does work in the ABM and on_step so long as I'm not subtracting the timestamp I got during init.

Conceptually speaking, it makes sense for get_gametime() to be available during init. If someone is desperate, and knows to look for it, they can always pull it out of world/env_meta.txt. But I don't think they should have to. A mock function during init might be appreciated by some. I still can't use it because of #10221, which I think is a bigger issue.

That brings up a broader question though: Are there other functions that are not available during init, but where the doc doesn't specify? get_gametime() is in the Environment access section. Should that section have a warning? (like Global callback registration functions does -- "Call these functions only at load time!")