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This is the home for the Rust Grammar Working Group. The goal of the working group is to satisfy RFC 1331 and produce a testable, canonical grammar for the Rust language. The primary audiences for the grammar are:

  • Rust RFC authors who wish to propose and communicate changes.
  • rustc and Rust tool developers who need an authoritative definition of the grammar.
  • To assist documentation efforts to communicate valid Rust syntax to users, and to facilitate the Rust language specification.

The grammar tools produced here are not intended to be used directly within rustc, or any other existing tools.

Meeting Schedule

Meetings take place on the #wg-grammar channel on Discord at 20:00 CET every other Wednesday. Feel free to drop by the Discord channel if you are interested!

Test Suite

This project includes a executable binary for exercising the grammar. Use cargo run to build and run it. Using --release is encouraged as it is many times faster. It supports several subcommands to point it at different files or directories to examine. For example, if you check out the submodule (explained below), you can run the tests with the following command:

cargo run --bin coverage --release -- dir external/rust/src

This repository includes a submodule to the main rust repo to use as a collection of Rust code to test against the grammar. The command git submodule update --init may be used to fetch it. However, it is not necessary and you may run the tool against any collection of Rust code at your disposal.

Snapshot tests

Additionaly, a number of snapshot tests are maintained in testdata. These files are named according to the convention of <production>.<test-name>.input, and the parse forest that they produce is tracked in src/bin/snapshots. The tests are run with:

cargo run --bin snapshots --release

Once a snapshot is present for a given production, that production is, to the best of the maintainers' ability, considered "complete" in terms of its structure.

Note, however, that this is a shallow and non-transitive property: if e.g. Expr is tested, the structural completeness extends only to Expr itself and not to OuterAttr nor ExprKind.

A test may also have the name <production>.<variant>.<test-name>.input, in which case only that variant should be considered tested and marked "complete" by that test case.

At all times we reserve the right to change parse forests that do not produce unique parse trees, and to disambiguate tested parse forests to a subset.



Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


Where the work of WG-grammar, aiming to provide a canonical grammar for Rust, resides







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