RangeLimits variant naming

[dtolnay]

Here is syn's current RangeLimits enum:

syn/src/expr.rs

Lines 904 to 909 in 391c9c6

	pub enum RangeLimits {
	/// Inclusive at the beginning, exclusive at the end.
	HalfOpen(Token![..]),
	/// Inclusive at the beginning and end.
	Closed(Token![..=]),
	}

Rustc has the exact same thing: https://github.com/rust-lang/rust/blob/1.67.0/compiler/rustc_ast/src/ast.rs#L1323-L1328

pub enum RangeLimits {
    /// Inclusive at the beginning, exclusive at the end
    HalfOpen,
    /// Inclusive at the beginning and end
    Closed,
}

However it's ambiguous whether "half open" means "exclusive of upper bound" vs "bounded only on one side".

The opposite approach is taken by the current Rust Reference: https://doc.rust-lang.org/1.67.0/reference/patterns.html#range-patterns

RangePattern :
    InclusiveRangePattern | HalfOpenRangePattern

InclusiveRangePattern :
    RangePatternBound `..=` RangePatternBound

HalfOpenRangePattern :
    RangePatternBound `..` | `..=` RangePatternBound

Notice how it has a ..= pattern which it refers to as half open, even though ..= is never considered half open in syn or rustc.