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rustc
10th chunk of `src/git.md`
74c71d240f8ee462b390fa07810c3a5c65dbd9a3d2bf7c6d0000000100000854


### Moving large sections of code

Git and Github's default diff view for large moves *within* a file is quite poor; it will show each
line as deleted and each line as added, forcing you to compare each line yourself. Git has an option
to show moved lines in a different color:

```console
git log -p --color-moved=dimmed-zebra --color-moved-ws=allow-indentation-change
```

See [the docs for `--color-moved`](https://git-scm.com/docs/git-diff#Documentation/git-diff.txt---color-movedltmodegt) for more info.

### range-diff

See [the relevant section for PR authors](#git-range-diff). This can be useful for comparing code
that was force-pushed to make sure there are no unexpected changes.

### Ignoring changes to specific files

Many large files in the repo are autogenerated. To view a diff that ignores changes to those files,
you can use the following syntax (e.g. Cargo.lock):

```console
git log -p ':!Cargo.lock'
```

Arbitrary patterns are supported (e.g. `:!compiler/*`). Patterns use the same syntax as
`.gitignore`, with `:` prepended to indicate a pattern.

## Git submodules

**NOTE**: submodules are a nice thing to know about, but it *isn't* an absolute
prerequisite to contribute to `rustc`. If you are using Git for the first time,
you might want to get used to the main concepts of Git before reading this section.

The `rust-lang/rust` repository uses [Git submodules] as a way to use other
Rust projects from within the `rust` repo. Examples include Rust's fork of
`llvm-project`, `cargo`  and libraries like `stdarch` and `backtrace`.

Those projects are developed and maintained in an separate Git (and GitHub)
repository, and they have their own Git history/commits, issue tracker and PRs.
Submodules allow us to create some sort of embedded sub-repository inside the
`rust` repository and use them like they were directories in the `rust` repository.

Take `llvm-project` for example. `llvm-project` is maintained in the [`rust-lang/llvm-project`]
repository, but it is used in `rust-lang/rust` by the compiler for code generation and
Title: Working with Git Diff and Submodules
Summary
This section provides tips for dealing with large code movements in Git, including using `git log` with the `--color-moved` option to highlight moved lines. It also covers using `git range-diff` to compare code after force-pushes and ignoring changes to specific files, particularly autogenerated ones, using the `:!` pattern in `git log`. The section then introduces Git submodules, explaining their purpose in the rust-lang/rust repository for incorporating external Rust projects like llvm-project and cargo.