exported float is rounded down

[jan-kapoli]

Tested versions

• Reproducible in: v4.4.1.stable.official [49a5bc7], v4.4.stable.custom_build [4c311cb]

System information

Godot v4.4.1.stable - Debian GNU/Linux 13 (trixie) 13 on Wayland - X11 display driver, Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce MX150 (nvidia) - Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz (8 threads)

Issue description

When setting an exported float variable to a small value via the editor it gets rounded down to 0.0. This happens even when the Default Float Step would allow for such small increments to be entered.

Steps to reproduce

1. Set the Default Float Step (Editor / Editor Settings... / Interface / Inspector / Default Float Step) to 0.000001 (that is 1×10^-6).
2. Attach a script to a Node.
3. Enter the following line: @export var f: float
4. Set the value of f to 0.000001 through the editor.
5. Observe how when hovering over it, it shows as 0.00000099999306. (What format is this? IEEE 754 32-bit and 64-bit formats store 0.0000009999999974752427078783512115478515625 and 0.000000999999999999999954748111825886258685613938723690807819366455078125 respectively)
6. Run the scene. The value of f can be checked via the following lines:
   print_debug(f) and print_debug(f == 0.0)
   They return 0.0 and true respectively.
   This is unexpected. I would expect 0.000001 or 0.00000099999306 and false respectively.

Additional steps to verify that it only happens to values set via the inspector:

1. Enter the following line var g: float = 0.000001.
2. Check the value of g via the following lines:
   print_debug(g) and print_debug(g == 0.0)
   They return "0.00001" and "false" respectively.

This shows that the rounding happens to values set through the inspector.

Minimal reproduction project (MRP)

Bug.zip

Note that when editing the file Node.tscn, the line f = 0.000001 is nowhere to be seen.

[Calinou]

Can you test 4.5.beta6? It should be fixed by #98750.

[jan-kapoli]

The issue is still reproducible in v4.5.beta6.official [d5ad055].

[jan-kapoli]

It's worse now in v4.5.beta7.official [4ebf67c]. Entering in 0.000001 (that is 1×10^-6) via the editor then pressing enter results in the editor displaying 0.000012. That is 12 times the entered value or one order of magnitude larger. Furthermore when running the scene the statement print_debug(f) prints 0.00001084202172. This is nowhere near to either of the previous values.
@Calinou sorry, but can we bump the severity of this issue? I feel this is quite a serious usability bug. Or should I report a new issue?

[Calinou]

cc @aaronfranke

This may be a regression from #109887.