A guide to how rustc works and how to contribute to it.
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bors 9f227ffb56 Auto merge of #139578 - ferrocene:pa-compiletest-edition, r=jieyouxu
Fix breakage when running compiletest with `--test-args=--edition=2015`

Compiletest has an `--edition` flag to change the default edition tests are run with. Unfortunately no test suite successfully executes when that flag is passed. If the edition is set to something greater than 2015 the breakage is expected, since the test suite currently supports only edition 2015 (Ferrous Systems will open an MCP about fixing that soonish). Surprisingly, the test suite is also broken if `--edition=2015` is passed to compiletest. This PR focuses on fixing the latter.

This PR fixes the two categories of failures happening when `--edition=2015` is passed:

* Some edition-specific tests set their edition through `//@ compile-flags` instead of `//@ edition`. Compiletest doesn't parse the compile flags, so it would see no `//@ edition` and add another `--edition` flag, leading to a rustc error.
* Compiletest would add the edition after `//@ compile-flags`, while some tests depend on flags passed to `//@ compile-flags` being the last flags in the rustc invocation.

Note that for the first category, I opted to manually go and replace all `//@ compile-flags` setting an edition with an explicit `//@ edition`. We could've changed compiletest to instead check whether an edition was set in `//@ compile-flags`, but I thought it was better to enforce a consistent way to set the edition in tests.

I also added the edition to the stamp, so that changing `--edition` results in tests being re-executed.

r? `@jieyouxu`
2025-04-11 10:53:45 +00:00
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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