Add const on some functions

[jaudiger]

Constify some functions, in order to use them in const context for other crates.

[nickelc]

If you move the Style::default() details into a private Style::const_default method then you can also constify Style::new() and Style::is_plain().

[sholderbach]

I know for nushell it doesn't matter as much as we are pretty aggressive in that regard but do we want to commit to a certain minimum supported Rust version? Then I am not fully up to speed how far we can go with constification without precluding certain users.

[jaudiger]

I can revert some const functions if needed. For example, to not enforce a specific rust version, I can remove the const keywords when the saturating functions are involved, and so on. What your thoughts on that?

I can suggest two approaches for now:

• imply const on easy functions that don’t rely on sub const functions from rust
• or just close this PR

[jaudiger]

At a certain point, my initial assumption was: most of the API exposed by this crate could be const. Since there is no a strong logic in there. And I was thinking that enforcing this trait could make sense for the end users. Anyway, you’re right about the no usage of a rust version as of today.

Just let me know, what would you prefer.

[nickelc]

I've tested the PR with cargo msrv and it bumps the MSRV from 1.56 to 1.61.

[sholderbach]

I've tested the PR with cargo msrv and it bumps the MSRV from 1.56 to 1.61.

Thanks for investigating that!

For the stuff I am doing both would be fine.

[jaudiger]

So, what's next @sholderbach? Should I enforce the usage of the Rust version in cargo.toml without doing any further modifications?

About your comment @nickelc, bevy did already that in their latest release (https://bevyengine.org/news/bevy-0-10/#const-bevy-ui-defaults). It could enable the usage of const in additional functions until Rust enables it inside the Default trait.

[jaudiger]

I just rebased this PR on main, and I added the field rust-version inside Cargo.toml.

[jaudiger]

@fdncred I don't know what is the current strategy regarding const functions. At least, the MSRV now announced is 1.62.1 with #30. There is no more blocker regarding adding those const keywords.

But I'm open to any discussion. I could reduce the set of APIs using const, or we can even close it if this is not the right time !

[sholderbach]

As we already bumped the MSRV for that default syntactic sugar we can go ahead with this constification.