Google Git
Sign in
rust/rust-lang/reference/refs/heads/TC/non_exhaustive-same-crate
commit
d2faa486394799bf8947b168dec0b61b7c6d8c50
[log] [tgz]
author
Travis Cross <tc@traviscross.com>
Thu Feb 05 17:12:05 2026 +0000
committer
Travis Cross <tc@traviscross.com>
Thu Feb 05 17:22:49 2026 +0000
tree
397731bf73cbbdf9324e5e0e6ee5cd8a86297640
parent
addd0602c819b6526b9cc97653b0fadca395528c [diff]
Remove exception WRT same-crate `non_exhaustive` reads

When matching against a single-variant enum marked `non_exhaustive`
and defined in a different crate, we pretend that there might be
multiple variants and force a read of the discriminant.  In [Rust PR
150681], we decided to remove the same-crate exception.  Now matching
against a single-variant `non_exhaustive` enum in the same crate will
also cause a discriminant read.

Separately, prior to [Rust PR 150681], `rustc` was eliding the
discriminant read when an enum has only one *inhabited* variant.  This
contradicts what the Reference says in:

> r[type.closure.capture.precision.discriminants.uninhabited-variants]
>
> Even if all variants but the one being matched against are
> uninhabited, making the pattern [irrefutable][patterns.refutable],
> the discriminant is still read if it otherwise would be.

We decided with our lang FCP to confirm the behavior already encoded
in the Reference, so no change is needed there.

[Rust PR 150681]: https://github.com/rust-lang/rust/pull/150681
1 file changed
tree: 397731bf73cbbdf9324e5e0e6ee5cd8a86297640
  1. .cargo/
  2. .github/
  3. docs/
  4. src/
  5. theme/
  6. tools/
  7. .gitattributes
  8. .gitignore
  9. book.toml
  10. Cargo.lock
  11. Cargo.toml
  12. CONTRIBUTING.md
  13. LICENSE-APACHE
  14. LICENSE-MIT
  15. README.md
  16. reference.md
  17. rust-toolchain.toml
  18. rustfmt.toml
  19. STYLE.md
  20. triagebot.toml
README.md

The Rust Language Reference

This document is the primary reference for the Rust programming language.

Contributor docs

There are several pages for those working on the reference:

Building

To build the Reference, first clone the project:

git clone https://github.com/rust-lang/reference.git
cd reference

(Alternatively, if you don't want to use git, download a ZIP file of the project, extract it using your preferred tool, and rename the top-level directory to reference.)

Installing mdbook

The Reference is built using mdbook.

First, ensure that you have a recent copy of the nightly Rust compiler installed, as this is needed in order to run the tests:

rustup toolchain install nightly
rustup override set nightly

Now, ensure you have mdbook installed, as this is needed in order to build the Reference:

cargo install --locked mdbook

Running mdbook

mdbook provides a variety of different commands and options to help you work on the book:

  • mdbook build --open: Build the book and open it in a web browser.
  • mdbook serve --open: Launches a web server on localhost. It also automatically rebuilds the book whenever any file changes and automatically reloads your web browser.

The book contents are driven by a SUMMARY.md file, and every file must be linked there. See https://rust-lang.github.io/mdBook/ for its usage.

SPEC_RELATIVE

The SPEC_RELATIVE=0 environment variable makes links to the standard library go to https://doc.rust-lang.org/ instead of being relative, which is useful when viewing locally since you normally don't have a copy of the standard library.

SPEC_RELATIVE=0 mdbook serve --open

The published site at https://doc.rust-lang.org/reference/ (or local docs using rustup doc) does not set this, which means it will use relative links which supports offline viewing and links to the correct version (for example, links in https://doc.rust-lang.org/1.81.0/reference/ will stay within the 1.81.0 directory).

SPEC_DENY_WARNINGS

The SPEC_DENY_WARNINGS=1 environment variable will turn all warnings generated by mdbook-spec to errors. This is used in CI to ensure that there aren't any problems with the book content.

SPEC_RUST_ROOT

The SPEC_RUST_ROOT can be used to point to the directory of a checkout of https://github.com/rust-lang/rust. This is used by the test-linking feature so that it can find tests linked to reference rules. If this is not set, then the tests won't be linked.

Running tests

There are several different kinds of tests you can run (these are enforced on CI):

  • mdbook test: This will run the inline Rust codeblocks (internally it uses rustdoc to do this).
  • cargo xtask style-check: This will validate some style checks (see authoring guide).
  • cargo xtask linkcheck: This will validate that markdown links aren't broken.
  • cargo xtask test-all: Runs all tests.

How is this published?

The process for getting the reference content into a Rust release and on the website is:

  1. Changes are merged to this repository.
  2. Triagebot will automatically synchronize this repository to rust-lang/rust. This happens every other week. The reference is tracked in rust-lang/rust as a submodule.
  • This will open a PR on rust-lang/rust which needs to be merged, and that can take up to several days.
  1. At midnight UTC, whatever is on the default branch of rust-lang/rust will be a part of that nightly release, and will be published after a few hours to https://doc.rust-lang.org/nightly/reference/.
  2. Following Rust's release process, every 6 weeks, nightly will be promoted to beta (https://doc.rust-lang.org/beta/reference/), and then 6 weeks after that it will be promoted to stable (https://doc.rust-lang.org/stable/reference/).