A guide to how rustc works and how to contribute to it.
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Matthias Krüger dfb06b2176
Rollup merge of #138632 - clubby789:stabilize-cfg-boolean-lit, r=davidtwco,Urgau,traviscross
Stabilize `cfg_boolean_literals`

Closes #131204
`@rustbot` labels +T-lang +I-lang-nominated
This will end up conflicting with the test in #138293 so whichever doesn't land first will need updating

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# Stabilization Report

## General design

### What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized?

[RFC 3695](https://github.com/rust-lang/rfcs/pull/3695), none.

### What behavior are we committing to that has been controversial? Summarize the major arguments pro/con.

None

### Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those?

None

## Has a call-for-testing period been conducted? If so, what feedback was received?

Yes; only positive feedback was received.

## Implementation quality

### Summarize the major parts of the implementation and provide links into the code (or to PRs)

Implemented in [#131034](https://github.com/rust-lang/rust/pull/131034).

### Summarize existing test coverage of this feature

- [Basic usage, including `#[cfg()]`, `cfg!()` and `#[cfg_attr()]`](6d71251cf9/tests/ui/cfg/true-false.rs)
- [`--cfg=true/false` on the command line being accessible via `r#true/r#false`](6d71251cf9/tests/ui/cfg/raw-true-false.rs)
- [Interaction with the unstable `#[doc(cfg(..))]` feature](https://github.com/rust-lang/rust/tree/6d71251/tests/rustdoc-ui/cfg-boolean-literal.rs)
- [Denying `--check-cfg=cfg(true/false)`](https://github.com/rust-lang/rust/tree/6d71251/tests/ui/check-cfg/invalid-arguments.rs)
- Ensuring `--cfg false` on the command line doesn't change the meaning of `cfg(false)`: `tests/ui/cfg/cmdline-false.rs`
- Ensuring both `cfg(true)` and `cfg(false)` on the same item result in it being disabled: `tests/ui/cfg/both-true-false.rs`

### What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking?

The above mentioned issue; it should not block as it interacts with another unstable feature.

### What FIXMEs are still in the code for that feature and why is it ok to leave them there?

None

### Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization
- `@clubby789` (RFC)
- `@Urgau` (Implementation in rustc)

### Which tools need to be adjusted to support this feature. Has this work been done?

`rustdoc`'s  unstable`#[doc(cfg(..)]` has been updated to respect it. `cargo` has been updated with a forward compatibility lint to enable supporting it in cargo once stabilized.

## Type system and execution rules

### What updates are needed to the reference/specification? (link to PRs when they exist)

A few lines to be added to the reference for configuration predicates, specified in the RFC.
2025-04-17 06:25:15 +02:00
.github/workflows Set linkcheck in `ci.yml` 2025-03-19 17:25:07 +08:00
ci add rustfmt settings file 2025-03-30 00:31:44 +02:00
examples add rustfmt settings file 2025-03-30 00:31:44 +02:00
josh-sync Distinguish between "nothing to pull" and "pull error" in josh-sync 2025-01-30 16:48:39 +01:00
src Improve `borrowck_graphviz_*` documentation. 2025-04-16 08:57:15 +10:00
.editorconfig Set max line length in `.editorconfig` to 100 (#1788) 2023-09-05 23:24:59 +09:00
.gitattributes .gitattributes: Mark minified javascript as binary to filter greps 2022-10-07 18:34:51 +02:00
.gitignore add josh-sync build dir to gitignore (#2196) 2025-01-06 02:57:03 +08:00
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CNAME cname (#606) 2020-03-09 18:10:52 -03:00
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README.md Document `fetch.prunetags = true` gotcha during rustc-pull 2025-03-13 15:44:23 +08:00
book.toml Update book.toml fix the authors field 2025-04-04 08:34:08 +03:00
mermaid-init.js add mdbook-mermaid 2022-07-17 23:34:12 +02:00
mermaid.min.js add mdbook-mermaid 2022-07-17 23:34:12 +02:00
rust-version Preparing for merge from rustc 2025-04-07 04:06:33 +00:00
rustfmt.toml add rustfmt settings file 2025-03-30 00:31:44 +02:00
triagebot.toml Add CI workflow for performing rustc-pull 2025-01-11 17:50:07 +01:00

README.md

CI

This is a collaborative effort to build a guide that explains how rustc works. The aim of the guide is to help new contributors get oriented to rustc, as well as to help more experienced folks in figuring out some new part of the compiler that they haven't worked on before.

You can read the latest version of the guide here.

You may also find the rustdocs for the compiler itself useful. Note that these are not intended as a guide; it's recommended that you search for the docs you're looking for instead of reading them top to bottom.

For documentation on developing the standard library, see std-dev-guide.

Contributing to the guide

The guide is useful today, but it has a lot of work still to go.

If you'd like to help improve the guide, we'd love to have you! You can find plenty of issues on the issue tracker. Just post a comment on the issue you would like to work on to make sure that we don't accidentally duplicate work. If you think something is missing, please open an issue about it!

In general, if you don't know how the compiler works, that is not a problem! In that case, what we will do is to schedule a bit of time for you to talk with someone who does know the code, or who wants to pair with you and figure it out. Then you can work on writing up what you learned.

In general, when writing about a particular part of the compiler's code, we recommend that you link to the relevant parts of the rustc rustdocs.

Build Instructions

To build a local static HTML site, install mdbook with:

> cargo install mdbook mdbook-linkcheck2 mdbook-toc mdbook-mermaid

and execute the following command in the root of the repository:

> mdbook build --open

The build files are found in the book/html directory.

We use mdbook-linkcheck2 to validate URLs included in our documentation. Link checking is not run by default locally, though it is in CI. To enable it locally, set the environment variable ENABLE_LINKCHECK=1 like in the following example.

$ ENABLE_LINKCHECK=1 mdbook serve

Table of Contents

We use mdbook-toc to auto-generate TOCs for long sections. You can invoke the preprocessor by including the <!-- toc --> marker at the place where you want the TOC.

Synchronizing josh subtree with rustc

This repository is linked to rust-lang/rust as a josh subtree. You can use the following commands to synchronize the subtree in both directions.

You'll need to install josh-proxy locally via

cargo +stable install josh-proxy --git https://github.com/josh-project/josh --tag r24.10.04

Older versions of josh-proxy may not round trip commits losslessly so it is important to install this exact version.

Pull changes from rust-lang/rust into this repository

  1. Checkout a new branch that will be used to create a PR into rust-lang/rustc-dev-guide
  2. Run the pull command
    $ cargo run --manifest-path josh-sync/Cargo.toml rustc-pull
    
  3. Push the branch to your fork and create a PR into rustc-dev-guide

Push changes from this repository into rust-lang/rust

  1. Run the push command to create a branch named <branch-name> in a rustc fork under the <gh-username> account
    $ cargo run --manifest-path josh-sync/Cargo.toml rustc-push <branch-name> <gh-username>
    
  2. Create a PR from <branch-name> into rust-lang/rust

Minimal git config

For simplicity (ease of implementation purposes), the josh-sync script simply calls out to system git. This means that the git invocation may be influenced by global (or local) git configuration.

You may observe "Nothing to pull" even if you know rustc-pull has something to pull if your global git config sets fetch.prunetags = true (and possibly other configurations may cause unexpected outcomes).

To minimize the likelihood of this happening, you may wish to keep a separate minimal git config that only has [user] entries from global git config, then repoint system git to use the minimal git config instead. E.g.

$ GIT_CONFIG_GLOBAL=/path/to/minimal/gitconfig GIT_CONFIG_SYSTEM='' cargo +stable run --manifest-path josh-sync/Cargo.toml -- rustc-pull