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Update architecture.md for mbe and proc-macro

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Edwin Cheng 2021-02-07 12:31:33 +08:00
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docs/dev/architecture.md
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@ -254,6 +254,17 @@ A single `rust-analyzer` process can serve many projects, so it is important tha
These crates implement macros as token tree -> token tree transforms.
They are independent from the rest of the code.
`tt` crate defined `TokenTree`, a single token or a delimited sequence of token trees.
`mbe` crate contains tools for transforming between syntax trees and token tree.
And it also handles the actual parsing and expansion of declarative macro (a-la "Macros By Example" or mbe).
For proc macros, we pass the token trees by loading the corresponding dynamic library (which built by `cargo`).
That's why the client (`proc_macro_api`) and server (`proc_macro_srv`) model are used to run proc-macro in separate process in background.
**Architecture Invariant:**
Bad proc macros may panic or segfault accidentally. So we run it in another process and recover it from fatal error.
And they may be non-deterministic which conflict how `salsa` works, so special attention is required.
### `crates/cfg`
This crate is responsible for parsing, evaluation and general definition of `cfg` attributes.