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miri is no longer a submodule but a subtree. #1488

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Oct 22, 2022
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miri is no longer a submodule but a subtree. #1488

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1f79697
miri is no longer a submodule but a subtree.
luqmana Oct 20, 2022
80c6b4a
Remove duplicate git submodule content.
luqmana Oct 21, 2022
96faf55
Remove date-check
luqmana Oct 21, 2022
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24 changes: 15 additions & 9 deletions src/contributing.md
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Expand Up @@ -183,6 +183,7 @@ As a developer to this repository, you don't have to treat the following externa
differently from other crates that are directly in this repo:

* [Clippy](https://github.com/rust-lang/rust-clippy)
* [Miri](https://github.com/rust-lang/miri)
* [rustfmt](https://github.com/rust-lang/rustfmt)
* [rust-analyzer](https://github.com/rust-lang/rust-analyzer)

Expand Down Expand Up @@ -257,20 +258,19 @@ some of them are optional (like [Miri]).
Usage of submodules is discussed more in the [Using Git
chapter](git.md#git-submodules).

Some of the submodules are allowed to be in a "broken" state where they either
don't build or their tests don't pass. These include [Miri] and the
documentation books like [The Rust Reference]. Maintainers of these projects
will be notified when the project is in a broken state, and they should fix
them as soon as possible. The current status is tracked on the [toolstate
website]. More information may be found on the Forge [Toolstate chapter].
Some of the submodules are allowed to be in a "broken" state where they
either don't build or their tests don't pass, e.g. the documentation books
like [The Rust Reference]. Maintainers of these projects will be notified
when the project is in a broken state, and they should fix them as soon
as possible. The current status is tracked on the [toolstate website].
More information may be found on the Forge [Toolstate chapter].

Breakage is not allowed in the beta and stable channels, and must be addressed
before the PR is merged. They are also not allowed to be broken on master in
the week leading up to the beta cut.

[git submodules]: https://git-scm.com/book/en/v2/Git-Tools-Submodules
[`.gitmodules`]: https://github.com/rust-lang/rust/blob/master/.gitmodules
[Miri]: https://github.com/rust-lang/miri
[The Rust Reference]: https://github.com/rust-lang/reference/
[toolstate website]: https://rust-lang-nursery.github.io/rust-toolstate/
[Toolstate chapter]: https://forge.rust-lang.org/infra/toolstate.html
Expand Down Expand Up @@ -309,8 +309,8 @@ Here are those same steps in detail:
from resetting to the original branch after you make your changes. If you
need to [update any submodules to their latest versions](#updating-submodules),
see the section of this file about that for more information.
2. (optional) Run `./x.py test src/tools/miri` (substituting the submodule
that broke for `miri`). Fix any errors in the submodule (and possibly others).
2. (optional) Run `./x.py test src/tools/cargo` (substituting the submodule
that broke for `cargo`). Fix any errors in the submodule (and possibly others).
3. (optional) Make commits for your changes and send them to upstream repositories as a PR.
4. (optional) Maintainers of these submodules will **not** merge the PR. The PR can't be
merged because CI will be broken. You'll want to write a message on the PR referencing
Expand All @@ -322,6 +322,12 @@ Here are those same steps in detail:

#### Updating submodules

(As of <!-- date-check --> Sept 2022 `miri` is no longer a submodule but a subtree. The following
instructions are still broadly correct for updating submodules in general. For a more specific
example you can also see the steps for [upgrading llvm][upgrading-llvm].)

[upgrading-llvm]: https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html
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These instructions are specific to updating `miri`, however they may apply
to the other submodules as well. Please help by improving these instructions
if you find any discrepancies or special cases that need to be addressed.
Expand Down
28 changes: 15 additions & 13 deletions src/git.md
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Expand Up @@ -148,8 +148,8 @@ Your branch is up to date with 'origin/master'.
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git restore <file>..." to discard changes in working directory)
modified: src/llvm-project (new commits)
modified: src/tools/cargo (new commits)
modified: src/tools/miri (new commits)

no changes added to commit (use "git add" and/or "git commit -a")
```
Expand All @@ -176,6 +176,8 @@ There is a workaround in [the issue][#77620-workaround].
[#77620]: https://github.com/rust-lang/rust/issues/77620
[#77620-workaround]: https://github.com/rust-lang/rust/issues/77620#issuecomment-705228229

(Note that as of <!-- date-check --> Sept 2022 `miri` is a subtree and not a submodule.)
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## Rebasing and Conflicts

When you edit your code locally, you are making changes to the version of
Expand Down Expand Up @@ -391,41 +393,41 @@ you might want to get used to the main concepts of Git before reading this secti

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` and many devtools such as `cargo` and `miri`.
`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 `miri` for example. `miri` is maintained in the [`rust-lang/miri`] repository,
but it is used in `rust-lang/rust` by the compiler for const evaluation. We bring it
in `rust` as a submodule, in the `src/tools/miri` folder.
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
optimization. We bring it in `rust` as a submodule, in the `src/llvm-project` folder.

The contents of submodules are ignored by Git: submodules are in some sense isolated
from the rest of the repository. However, if you try to `cd src/tools/miri` and then
from the rest of the repository. However, if you try to `cd src/llvm-project` and then
run `git status`:

```
HEAD detached at 3fafb835
HEAD detached at 9567f08afc943
nothing to commit, working tree clean
```

As far as git is concerned, you are no longer in the `rust` repo, but in the `miri` repo.
As far as git is concerned, you are no longer in the `rust` repo, but in the `llvm-project` repo.
You will notice that we are in "detached HEAD" state, i.e. not on a branch but on a
particular commit.

This is because, like any dependency, we want to be able to control which version to use.
Submodules allow us to do just that: every submodule is "pinned" to a certain
commit, which doesn't change unless modified manually. If you use `git checkout <commit>`
in the `miri` directory and go back to the `rust` directory, you can stage this
change like any other, e.g. by running `git add src/tools/miri`. (Note that if
in the `llvm-project` directory and go back to the `rust` directory, you can stage this
change like any other, e.g. by running `git add src/llvm-project`. (Note that if
you *don't* stage the change to commit, then you run the risk that running
`x.py` will just undo your change by switching back to the previous commit when
it automatically "updates" the submodules.)

This version selection is usually done by the maintainers of the project, and
looks like [this][miri-update].
looks like [this][llvm-update].

Git submodules take some time to get used to, so don't worry if it isn't perfectly
clear yet. You will rarely have to use them directly and, again, you don't need
Expand All @@ -434,5 +436,5 @@ exist and that they correspond to some sort of embedded subrepository dependency
that Git can nicely and fairly conveniently handle for us.

[Git submodules]: https://git-scm.com/book/en/v2/Git-Tools-Submodules
[`rust-lang/miri`]: https://github.com/rust-lang/miri
[miri-update]: https://github.com/rust-lang/rust/pull/77500/files
[`rust-lang/llvm-project`]: https://github.com/rust-lang/llvm-project
[llvm-update]: https://github.com/rust-lang/rust/pull/99464/files