[JuliaSyntax] Add type-asserts to the results of parse_brackets()

[JamesWrigley]

As discussed in JuliaLang/JuliaSyntax.jl#600 and JuliaLang/JuliaSyntax.jl#615. Tested manually on 1.12. Should finally for-realsies fix JuliaLang/JuliaSyntax.jl#600 🤞

[c42f]

Looks great, thanks!

[c42f]

Possibly neater?

Suggested change

	end::NamedTuple{(:needs_parameters, :is_paren_call, :is_block, :delim_flags), Tuple{Bool, Bool, Bool, RawFlags}}
	end
	opts::NamedTuple{(:needs_parameters, :is_paren_call, :is_block, :delim_flags), Tuple{Bool, Bool, Bool, RawFlags}}

[JamesWrigley]

I actually didn't realize that was possible 👀 Does a type-assert after the variable initialization have the same effect? I think I have a mild preference for the current version because that's clearer to me.

[topolarity]

Type-inference knows that opts is constrained by the type-assert everywhere "downstream" of this, so this should be effectively the same in practice yeah

(no opinion from me w.r.t. style)

[c42f]

yup what Cody said. To expand: type inference follows the data flow according to program control flow. Unlike in some languages, the type assert opts::T is not a global statement about the binding opts. It just asserts the type of the value bound to opts is T at that one point in the program and inference can follow the program dataflow from there.

Style-wise I think it makes slight sense to separate performance annotations from the rest of the code as they're not semantically relevant for humans reading the code. But that's nitpicking, I think this is fine and we can just merge it :)