Add a warning when taking the negative value of .abs() on a literal. (eg -1.abs())

[task-jp]

Bug Description

-1deg.abs() returns -1deg whereas Math.abs(-1deg) returns 1deg.

I expect -1deg.abs() equals 1deg.

Reproducible Code (if applicable)

export component AbsAngle inherits VerticalLayout {
    Text {
        text: -1deg.abs() / 1deg;  // => -1
    }
    Text {
        text: Math.abs(-1deg) / 1deg; // => 1
    }
}

Environment Details

• Slint Version:
• Platform/OS: Linux/X11
• Programming Language: .slint
• Backend/Renderer:

Product Impact

No response

[task-jp]

Is - applied to the result of 1deg.abs()?

[ogoffart]

Right, -1deg.abs() is the same as -(1deg.abs()).
This is the same precedence rules as in Rust, C++, and so on.

We can't change the precedence rules because then then things like -self.foo wouldn't work anymore because that would become (-self).foo

If anything we could detect this specific case and have a warning.

[tronical]

If anything we could detect this specific case and have a warning.

That might be an option, I agree. Otherwise I'd say that this isn't a bug.

[task-jp]

We may improve the documentation for that.

https://github.com/slint-ui/slint/blob/ee6f78fc8df32fc1cb07585792eb703782f76f49/docs/astro/src/content/docs/reference/global-functions/math.mdx says

T type
Many of the math functions can be used with any such as angle, duration, float, int, length, and percent. These are represented on this page as T.

General Math Functions

abs(T) -> T

Return the absolute value, where T is a numeric type.

Math.abs(-10); // returns 10
abs(-10); // returns 10
-10.abs(); // returns 10

This looks like I can write -10deg.abs().