Use a macro to create null-terminated C strings

[jdm]

When we write them by hand (eg. b"some string\0"), we invariably get them wrong in ways that are tricky to notice (#19915). We should use a macro like this instead:

macro_rules! c_str {
    ($str:expr) => {
        concat!($str, "\0").as_bytes()
    }
}

This would allow us to write code like (c_str!("PEParseDeclarationDeclExpected"), Action::Skip) instead of https://github.com/emilio/servo/blob/d82c54bd3033cc3277ebeb4854739bebe4e20f2f/ports/geckolib/error_reporter.rs#L237. We should be able to clean up all of the uses in that file.

No need to run any automated tests; if it builds with ./mach build-geckolib, then it's good enough for a pull request.

[highfive]

Hi! If you have any questions regarding this issue, feel free to make a comment here, or ask it in the #servo channel in IRC.

If you intend to work on this issue, then add @highfive: assign me to your comment, and I'll assign this to you. 😄

[thiagopnts]

@highfive: assign me

[highfive]

Hey @thiagopnts! Thanks for your interest in working on this issue. It's now assigned to you!

[KiChjang]

Shouldn't the to_geck_message fn really return a CStr instead in order to at least have some type checking in place?

[KiChjang]

We can also use from_bytes_with_nul for some stronger guarantees, but I don't think the overhead is worth it.

[jdm]

Returning a CStr does sound like an improvement. The macro could use CStr::from_bytes_with_nul_unchecked under the hood.

[upsuper]

Hmmm... I didn't notice this issue, and wrote a PR #19925 for fixing this...

[jdm]

@thiagopnts Given that the solution in #19925 is safer than what I propose here, we're going to go with that. Sorry for the duplication of effort!