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rust / rust-lang / reference / e0c96122040b9eb85590029fee04caefd7a72da2
commite0c96122040b9eb85590029fee04caefd7a72da2[log] [tgz]
authorTravis Cross <tc@traviscross.com>Tue Oct 14 01:00:27 2025 +0000
committerEric Huss <eric@huss.org>Thu Dec 18 19:55:45 2025 -0800
treecf0ceb3398ce93749b00c71dbcbb94871c6d6615
parenta2877af7316dd2b3344ce3440349587731e0eba0 [diff]
Revise `...discriminants.slice-patterns-*` rules

The section here stated:

> Matching against a slice pattern that needs to inspect the length of
> the scrutinee performs a read of the pointer value in order to fetch
> the length. The read will cause the closure to borrow the relevant
> place by `ImmBorrow`.

It then goes on to state exceptions for arrays matched against slice
patterns and slice patterns containing only a rest pattern.

In saying that the pointer value is read, this might suggest that the
pointer is captured.  Actually, though, it's the slice (the pointee)
that is captured.  Let's fix this.

Beyond that, as we saw in an earlier commit, it's better to not lean
on the reader to infer the "relevant place" or when the length needs
to be inspected.  Let's elaborate those details and state the full
rule in one go, upfront, and then state a separate guarantee that
matching an array against a slice pattern does not do a read.

We'll also fix a typo, add rule identifiers, and tighten up the
examples.
1 file changed
tree: cf0ceb3398ce93749b00c71dbcbb94871c6d6615
  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/).