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winnow/_tutorial/
chapter_8.rs

1//! # Chapter 8: Debugging
2//!
3//! When things inevitably go wrong, you can introspect the parsing state by running your test case
4//! with `--features winnow/debug`.
5//!
6//! For example, the trace output of an [escaped string parser][crate::_topic::language#escaped-strings]:
7//! ![Trace output from string example](https://raw.githubusercontent.com/winnow-rs/winnow/main/assets/trace.svg "Example output")
8//!
9//! You can extend your own parsers to show up by wrapping their body with
10//! [`trace`][crate::combinator::trace].  Going back to [`do_nothing_parser`][super::chapter_1].
11//! ```rust
12//! # use winnow::ModalResult;
13//! # use winnow::Parser;
14//! use winnow::combinator::trace;
15//!
16//! pub fn do_nothing_parser<'s>(input: &mut &'s str) -> ModalResult<&'s str> {
17//!     trace(
18//!         "do_nothing_parser",
19//!         |i: &mut _| Ok("")
20//!     ).parse_next(input)
21//! }
22//! #
23//! # fn main() {
24//! #     let mut input = "0x1a2b Hello";
25//! #
26//! #     let output = do_nothing_parser.parse_next(&mut input).unwrap();
27//! #     // Same as:
28//! #     // let output = do_nothing_parser(&mut input).unwrap();
29//! #
30//! #     assert_eq!(input, "0x1a2b Hello");
31//! #     assert_eq!(output, "");
32//! # }
33//! ```
34
35pub use super::chapter_7 as previous;
36pub use crate::_topic as next;
37pub use crate::_tutorial as table_of_contents;