2022-06-02 05:07:25 -05:00
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This crate is regularly synced with its mirror in the rustc repo at `compiler/rustc_smir`.
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We use `git subtree` for this to preserve commits and allow the rustc repo to
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edit these crates without having to touch this repo. This keeps the crates compiling
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while allowing us to independently work on them here. The effort of keeping them in
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sync is pushed entirely onto us, without affecting rustc workflows negatively.
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This may change in the future, but changes to policy should only be done via a
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compiler team MCP.
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## Instructions for working on this crate locally
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Since the crate is the same in the rustc repo and here, the dependencies on rustc_* crates
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will only either work here or there, but never in both places at the same time. Thus we use
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optional dependencies on the rustc_* crates, requiring local development to use
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```
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cargo build --no-default-features -Zavoid-dev-deps
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```
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in order to compile successfully.
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## Instructions for syncing
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### Updating this repository
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In the rustc repo, execute
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```
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git subtree push --prefix=compiler/rustc_smir url_to_your_fork_of_project_stable_mir some_feature_branch
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```
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and then open a PR of your `some_feature_branch` against https://github.com/rust-lang/project-stable-mir
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### Updating the rustc library
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First we need to bump our stack limit, as the rustc repo otherwise quickly hits that:
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```
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ulimit -s 60000
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```
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#### Maximum function recursion depth (1000) reached
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Then we need to disable `dash` as the default shell for sh scripts, as otherwise we run into a
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hard limit of a recursion depth of 1000:
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```
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sudo dpkg-reconfigure dash
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```
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and then select `No` to disable dash.
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#### Patching your `git worktree`
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The regular git worktree does not scale to repos of the size of the rustc repo.
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So download the `git-subtree.sh` from https://github.com/gitgitgadget/git/pull/493/files and run
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```
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sudo cp --backup /path/to/patched/git-subtree.sh /usr/lib/git-core/git-subtree
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sudo chmod --reference=/usr/lib/git-core/git-subtree~ /usr/lib/git-core/git-subtree
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sudo chown --reference=/usr/lib/git-core/git-subtree~ /usr/lib/git-core/git-subtree
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```
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#### Actually doing a sync
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In the rustc repo, execute
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```
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git subtree pull --prefix=compiler/rustc_smir https://github.com/rust-lang/project-stable-mir smir
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```
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Note: only ever sync to rustc from the project-stable-mir's `smir` branch. Do not sync with your own forks.
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Then open a PR against rustc just like a regular PR.
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2023-03-03 19:08:49 -06:00
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## Stable MIR Design
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The stable-mir will follow a similar approach to proc-macro2. It’s
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implementation will eventually be broken down into two main crates:
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- `stable_mir`: Public crate, to be published on crates.io, which will contain
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the stable data structure as well as proxy APIs to make calls to the
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compiler.
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- `rustc_smir`: The compiler crate that will translate from internal MIR to
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SMIR. This crate will also implement APIs that will be invoked by
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stable-mir to query the compiler for more information.
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This will help tools to communicate with the rust compiler via stable APIs. Tools will depend on
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`stable_mir` crate, which will invoke the compiler using APIs defined in `rustc_smir`. I.e.:
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```
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┌──────────────────────────────────┐ ┌──────────────────────────────────┐
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│ External Tool ┌──────────┐ │ │ ┌──────────┐ Rust Compiler │
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│ │ │ │ │ │ │ │
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│ │stable_mir| │ │ │rustc_smir│ │
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│ │ │ ├──────────►| │ │ │
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│ │ │ │◄──────────┤ │ │ │
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│ │ │ │ │ │ │ │
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│ │ │ │ │ │ │ │
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│ └──────────┘ │ │ └──────────┘ │
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└──────────────────────────────────┘ └──────────────────────────────────┘
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```
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More details can be found here:
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https://hackmd.io/XhnYHKKuR6-LChhobvlT-g?view
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For now, the code for these two crates are in separate modules of this crate.
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The modules have the same name for simplicity. We also have a third module,
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`rustc_internal` which will expose APIs and definitions that allow users to
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gather information from internal MIR constructs that haven't been exposed in
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the `stable_mir` module.
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