chumsky/
span.rs

1//! Types and traits related to spans.
2//!
3//! *“We demand rigidly defined areas of doubt and uncertainty!”*
4//!
5//! You can use the [`Span`] trait to connect up chumsky to your compiler's knowledge of the input source.
6
7use core::ops::Range;
8
9/// A trait that describes a span over a particular range of inputs.
10///
11/// Spans typically consist of some context, such as the file they originated from, and a start/end offset. Spans are
12/// permitted to overlap one-another. The end offset must always be greater than or equal to the start offset.
13///
14/// Span is automatically implemented for [`Range<T>`] and [`(C, Range<T>)`].
15pub trait Span: Clone {
16    /// Extra context used in a span.
17    ///
18    /// This is usually some way to uniquely identity the source file that a span originated in such as the file's
19    /// path, URL, etc.
20    ///
21    /// NOTE: Span contexts have no inherent meaning to Chumsky and can be anything. For example, [`Range<usize>`]'s
22    /// implementation of [`Span`] simply uses [`()`] as its context.
23    type Context: Clone;
24
25    /// A type representing a span's start or end offset from the start of the input.
26    ///
27    /// Typically, [`usize`] is used.
28    ///
29    /// NOTE: Offsets have no inherently meaning to Chumsky and are not used to decide how to prioritise errors. This
30    /// means that it's perfectly fine for tokens to have non-continuous spans that bear no relation to their actual
31    /// location in the input stream. This is useful for languages with an AST-level macro system that need to
32    /// correctly point to symbols in the macro input when producing errors.
33    type Offset: Clone;
34
35    /// Create a new span given a context and an offset range.
36    fn new(context: Self::Context, range: Range<Self::Offset>) -> Self;
37
38    /// Return the span's context.
39    fn context(&self) -> Self::Context;
40
41    /// Return the start offset of the span.
42    fn start(&self) -> Self::Offset;
43
44    /// Return the end offset of the span.
45    fn end(&self) -> Self::Offset;
46}
47
48impl<T: Clone + Ord> Span for Range<T> {
49    type Context = ();
50    type Offset = T;
51
52    fn new((): Self::Context, range: Self) -> Self {
53        range
54    }
55    fn context(&self) -> Self::Context {}
56    fn start(&self) -> Self::Offset {
57        self.start.clone()
58    }
59    fn end(&self) -> Self::Offset {
60        self.end.clone()
61    }
62}
63
64impl<C: Clone, T: Clone> Span for (C, Range<T>) {
65    type Context = C;
66    type Offset = T;
67
68    fn new(context: Self::Context, range: Range<T>) -> Self {
69        (context, range)
70    }
71    fn context(&self) -> Self::Context {
72        self.0.clone()
73    }
74    fn start(&self) -> Self::Offset {
75        self.1.start.clone()
76    }
77    fn end(&self) -> Self::Offset {
78        self.1.end.clone()
79    }
80}
chumsky/span.rs

chumsky/
span.rs
