The syntax crate contains those things concerned purely with syntax – that is, the AST ("abstract syntax tree"), parser, pretty-printer, lexer, macro expander, and utilities for traversing ASTs.

For more information about how these things work in rustc, see the rustc guide:

• Parsing
• Macro Expansion

lib.rs:

The Rust parser and macro expander.

Note

This API is completely unstable and subject to change.