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154 lines
3.9 KiB
Markdown
154 lines
3.9 KiB
Markdown
# SWC architecture
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This document gives a high level overview of SWC internals. You may find it useful if you want to contribute to SWC or if you are interested in the inner workings of SWC.
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## Macros
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<!-- TODO: fix link -->
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<!-- See [blog post about SWC macros](https://swc.rs/blog/2020/01/04/pmutil#macros-built-with-pmutil). -->
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SWC uses proc macro extensively to reduce work. Please see links below to know what each macro do.
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- [enum_kind][]
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- [string_enum][]
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- [ast_node][]
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And some adhoc-macros are used.
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- [parser_macros][]
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- [codegen_macros][]
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These macro breaks macro hygiene.
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## Structure
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### [`/crates/swc_atoms`](crates/swc_atoms)
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Handle string interning for the SWC project. The crate depends on [string_cache](https://github.com/servo/string-cache) from servo.
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### [`/crates/swc_common`](crates/swc_common)
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Contains code related to span, hygiene and error reporting.
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Also, it contains / re-exports codes for visitor pattern. `Visit<T>` is non-mutating visitor, while `Fold<T>` is a mutating visitor.
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### [`/crates/swc_ecma_ast`](crates/swc_ecma_ast)
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Contains AST nodes for javascript and typescript.
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### [`/crates/swc_ecma_codegen`](crates/swc_ecma_codegen)
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Converts javascript AST into javascript code.
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### [`/crates/swc_ecma_parser`](crates/swc_ecma_parser)
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Parses javascript and typescript
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### [`/crates/swc_ecma_transforms_base`](crates/swc_ecma_transforms_base)
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There are three core transforms named `resolver`, `hygiene`, `fixer`. Other transforms depend on them.
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#### [`/crates/swc_ecma_transforms_base/src/resolver`](crates/swc_ecma_transforms_base/src/resolver)
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This pass resolves and marks all identifiers in the file.
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e.g.
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```js
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let a = 1;
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{
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let a = 1;
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}
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```
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becomes
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```js
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let a#0 = 1;
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{
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let a#1 = 1;
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}
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```
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where the number after the hash (`#`) denotes the hygiene id. If two identifiers have the same symbol but different hygiene ids, they are considered different.
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#### [`/crates/swc_ecma_transforms_base/src/hygiene`](crates/swc_ecma_transforms_base/src/hygiene)
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The hygiene pass actually changes symbols of identifiers with the same symbol but different hygiene ids to different symbols.
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```js
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let a#0 = 1;
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{
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let a#1 = 2;
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}
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```
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becomes
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```js
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let a = 1;
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{
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let a1 = 2;
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}
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```
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#### [`/crates/swc_ecma_transforms_base/src/fixer`](crates/swc_ecma_transforms_base/src/fixer)
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Fixes broken AST. This allow us to simply fold types like `BinExpr` without caring about operator precedence.
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It means,
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```rust
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let v = BinExpr {
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left: "1 + 2",
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op: "*",
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right: "3",
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};
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```
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(other passes generate AST like this)
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is converted into
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```rust
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let v = BinExpr {
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left: "(1 + 2)",
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op: "*",
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right: "3",
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};
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```
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and printed as
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```js
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(1 + 2) * 3;
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```
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<!-- TODO: add correct references to files -->
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<!-- #### `/ecmascript/transforms/src/compat`
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Contains code related to converting new generation javascript code into code understood by old browsers.
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#### `/ecmascript/transforms/src/modules`
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Contains code related to transforming es6 modules to other modules.
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#### `/ecmascript/transforms/src/optimization`
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Contains code related to making code faster on runtime. Currently only a small set of optimizations is implemented. -->
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## Tests
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SWC uses the [official ecmascript conformance test suite called test262][test262] for testing.
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Parser tests ensure that the parsed results of `test262/pass` are identical with `test262/pass-explicit`.
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Codegen tests ensure that the generated code is equivalent to the golden fixture files located at [tests/references](crates/swc_ecma_codegen/tests).
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[enum_kind]: https://rustdoc.swc.rs/enum_kind/derive.Kind.html
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[string_enum]: https://rustdoc.swc.rs/string_enum/derive.StringEnum.html
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[ast_node]: https://rustdoc.swc.rs/ast_node/index.html
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[parser_macros]: https://rustdoc.swc.rs/swc_ecma_parser_macros/index.html
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[codegen_macros]: https://rustdoc.swc.rs/swc_ecma_codegen_macros/index.html
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[test262]: https://github.com/tc39/test262
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