bhc-span

Source location tracking and span management for the Basel Haskell Compiler.

Overview

This crate provides types for tracking source locations throughout the compilation pipeline, enabling accurate error reporting and source mapping.

Key Types

Type	Description
`BytePos`	A byte offset into a source file
`Span`	A half-open byte range `[lo, hi)` representing a region of source code
`Spanned<T>`	A value with an associated span
`FileId`	Unique identifier for a source file
`FullSpan`	A span with an associated file ID for cross-file spans
`LineCol`	Line and column information (1-indexed)
`SourceFile`	Information about a source file including content and line offsets

Usage

use bhc_span::{Span, BytePos, SourceFile, FileId};

// Create a span from byte positions
let span = Span::new(BytePos::new(10), BytePos::new(20));
assert_eq!(span.len(), 10);

// Create a source file and look up line/column
let file = SourceFile::new(
    FileId::new(0),
    "example.hs".to_string(),
    "main = putStrLn \"Hello\"".to_string()
);

let loc = file.lookup_line_col(BytePos::new(7));
assert_eq!(loc.line, 1);
assert_eq!(loc.col, 8);

// Merge spans
let span1 = Span::from_raw(10, 20);
let span2 = Span::from_raw(15, 30);
let merged = span1.merge(span2);
assert_eq!(merged, Span::from_raw(10, 30));

Features

Zero-cost span representation (just two u32 values)
Efficient line/column lookup with precomputed line starts
Span merging and manipulation operations
Serialization support via serde

Design Notes

Spans use byte offsets rather than character offsets for efficiency
The DUMMY span ([0, 0)) is used for generated code or when location is irrelevant
Line and column numbers are 1-indexed to match editor conventions

Related Crates

bhc-diagnostics - Uses spans for error reporting
bhc-lexer - Attaches spans to tokens
bhc-parser - Attaches spans to AST nodes