# Architecture This document describes the high-level architecture of rust-analyzer. If you want to familiarize yourself with the code base, you are just in the right place! See also the [guide](./guide.md), which walks through a particular snapshot of rust-analyzer code base. For syntax-trees specifically, there's a [video walk through](https://youtu.be/DGAuLWdCCAI) as well. ## The Big Picture ![](https://user-images.githubusercontent.com/1711539/50114578-e8a34280-0255-11e9-902c-7cfc70747966.png) On the highest level, rust-analyzer is a thing which accepts input source code from the client and produces a structured semantic model of the code. More specifically, input data consists of a set of test files (`(PathBuf, String)` pairs) and information about project structure, captured in the so called `CrateGraph`. The crate graph specifies which files are crate roots, which cfg flags are specified for each crate (TODO: actually implement this) and what dependencies exist between the crates. The analyzer keeps all this input data in memory and never does any IO. Because the input data is source code, which typically measures in tens of megabytes at most, keeping all input data in memory is OK. A "structured semantic model" is basically an object-oriented representation of modules, functions and types which appear in the source code. This representation is fully "resolved": all expressions have types, all references are bound to declarations, etc. The client can submit a small delta of input data (typically, a change to a single file) and get a fresh code model which accounts for changes. The underlying engine makes sure that model is computed lazily (on-demand) and can be quickly updated for small modifications. ## Code generation Some of the components of this repository are generated through automatic processes. These are outlined below: - `gen-syntax`: The kinds of tokens that are reused in several places, so a generator is used. We use tera templates to generate the files listed below, based on the grammar described in [grammar.ron]: - [ast/generated.rs][ast generated] in `ra_syntax` based on [ast/generated.tera.rs][ast source] - [syntax_kinds/generated.rs][syntax_kinds generated] in `ra_syntax` based on [syntax_kinds/generated.tera.rs][syntax_kinds source] [tera]: https://tera.netlify.com/ [grammar.ron]: ./crates/ra_syntax/src/grammar.ron [ast generated]: ./crates/ra_syntax/src/ast/generated.rs [ast source]: ./crates/ra_syntax/src/ast/generated.rs.tera [syntax_kinds generated]: ./crates/ra_syntax/src/syntax_kinds/generated.rs [syntax_kinds source]: ./crates/ra_syntax/src/syntax_kinds/generated.rs.tera ## Code Walk-Through ### `crates/ra_syntax` Rust syntax tree structure and parser. See [RFC](https://github.com/rust-lang/rfcs/pull/2256) for some design notes. - [rowan](https://github.com/rust-analyzer/rowan) library is used for constructing syntax trees. - `grammar` module is the actual parser. It is a hand-written recursive descent parser, which produces a sequence of events like "start node X", "finish not Y". It works similarly to [kotlin's parser](https://github.com/JetBrains/kotlin/blob/4d951de616b20feca92f3e9cc9679b2de9e65195/compiler/frontend/src/org/jetbrains/kotlin/parsing/KotlinParsing.java), which is a good source of inspiration for dealing with syntax errors and incomplete input. Original [libsyntax parser](https://github.com/rust-lang/rust/blob/6b99adeb11313197f409b4f7c4083c2ceca8a4fe/src/libsyntax/parse/parser.rs) is what we use for the definition of the Rust language. - `parser_api/parser_impl` bridges the tree-agnostic parser from `grammar` with `rowan` trees. This is the thing that turns a flat list of events into a tree (see `EventProcessor`) - `ast` provides a type safe API on top of the raw `rowan` tree. - `grammar.ron` RON description of the grammar, which is used to generate `syntax_kinds` and `ast` modules, using `cargo gen-syntax` command. - `algo`: generic tree algorithms, including `walk` for O(1) stack space tree traversal (this is cool) and `visit` for type-driven visiting the nodes (this is double plus cool, if you understand how `Visitor` works, you understand the design of syntax trees). Tests for ra_syntax are mostly data-driven: `tests/data/parser` contains a bunch of `.rs` (test vectors) and `.txt` files with corresponding syntax trees. During testing, we check `.rs` against `.txt`. If the `.txt` file is missing, it is created (this is how you update tests). Additionally, running `cargo gen-tests` will walk the grammar module and collect all `//test test_name` comments into files inside `tests/data` directory. See [#93](https://github.com/rust-analyzer/rust-analyzer/pull/93) for an example PR which fixes a bug in the grammar. ### `crates/ra_db` We use the [salsa](https://github.com/salsa-rs/salsa) crate for incremental and on-demand computation. Roughly, you can think of salsa as a key-value store, but it also can compute derived values using specified functions. The `ra_db` crate provides basic infrastructure for interacting with salsa. Crucially, it defines most of the "input" queries: facts supplied by the client of the analyzer. Reading the docs of the `ra_db::input` module should be useful: everything else is strictly derived from those inputs. ### `crates/ra_hir` HIR provides high-level "object oriented" access to Rust code. The principal difference between HIR and syntax trees is that HIR is bound to a particular crate instance. That is, it has cfg flags and features applied (in theory, in practice this is to be implemented). So, the relation between syntax and HIR is many-to-one. The `source_binder` module is responsible for guessing a HIR for a particular source position. Underneath, HIR works on top of salsa, using a `HirDatabase` trait. ### `crates/ra_ide_api` A stateful library for analyzing many Rust files as they change. `AnalysisHost` is a mutable entity (clojure's atom) which holds the current state, incorporates changes and hands out `Analysis` --- an immutable and consistent snapshot of the world state at a point in time, which actually powers analysis. One interesting aspect of analysis is its support for cancellation. When a change is applied to `AnalysisHost`, first all currently active snapshots are canceled. Only after all snapshots are dropped the change actually affects the database. APIs in this crate are IDE centric: they take text offsets as input and produce offsets and strings as output. This works on top of rich code model powered by `hir`. ### `crates/ra_ide_api_light` All IDE features which can be implemented if you only have access to a single file. `ra_ide_api_light` could be used to enhance editing of Rust code without the need to fiddle with build-systems, file synchronization and such. In a sense, `ra_ide_api_light` is just a bunch of pure functions which take a syntax tree as input. The tests for `ra_ide_api_light` are `#[cfg(test)] mod tests` unit-tests spread throughout its modules. ### `crates/ra_lsp_server` An LSP implementation which wraps `ra_ide_api` into a langauge server protocol. ### `crates/ra_vfs` Although `hir` and `ra_ide_api` don't do any IO, we need to be able to read files from disk at the end of the day. This is what `ra_vfs` does. It also manages overlays: "dirty" files in the editor, whose "true" contents is different from data on disk. ### `crates/gen_lsp_server` A language server scaffold, exposing a synchronous crossbeam-channel based API. This crate handles protocol handshaking and parsing messages, while you control the message dispatch loop yourself. Run with `RUST_LOG=sync_lsp_server=debug` to see all the messages. ### `crates/ra_cli` A CLI interface to rust-analyzer. ### `crate/tools` Custom Cargo tasks used to develop rust-analyzer: - `cargo gen-syntax` -- generate `ast` and `syntax_kinds` - `cargo gen-tests` -- collect inline tests from grammar - `cargo install-code` -- build and install VS Code extension and server ### `editors/code` VS Code plugin ## Common workflows To try out VS Code extensions, run `cargo install-code`. This installs both the `ra_lsp_server` binary and the VS Code extension. To install only the binary, use `cargo install-lsp` (shorthand for `cargo install --path crates/ra_lsp_server --force`) To see logs from the language server, set `RUST_LOG=info` env variable. To see all communication between the server and the client, use `RUST_LOG=gen_lsp_server=debug` (this will print quite a bit of stuff). There's `rust-analyzer: status` command which prints common high-level debug info. In particular, it prints info about memory usage of various data structures, and, if compiled with jemalloc support (`cargo jinstall-lsp` or `cargo install --path crates/ra_lsp_server --force --features jemalloc`), includes statistic about the heap. To run tests, just `cargo test`. To work on the VS Code extension, launch code inside `editors/code` and use `F5` to launch/debug. To automatically apply formatter and linter suggestions, use `npm run fix`.