docs(ast_macros): update docs

crates/oxc_ast_macros/src/lib.rs

@@ -3,74 +3,36 @@ use syn::{parse_macro_input, Item};
 
 mod ast;
 
-/// This attribute serves two purposes.
-/// First, it is a marker for `ast_tools`, to understand AST types.
-/// Secondly, it generates the following code:
+/// This attribute serves two purposes:
 ///
-/// * Prepend `#[repr(C)]` to structs.
-/// * Prepend `#[repr(C, u8)]` to fieldful enums e.g. `enum E { X: u32, Y: u8 }`.
-/// * Prepend `#[repr(u8)]` to unit (fieldless) enums e.g. `enum E { X, Y, Z, }`.
-/// * Prepend `#[derive(oxc_ast_macros::Ast)]` to all structs and enums.
-/// * Add assertions that traits used in `#[generate_derive(...)]` are in scope.
+/// Firstly, it is a marker for `oxc_ast_tools`, to understand that a type is part of the AST.
 ///
-/// It allows the usage of these helper attributes via deriving the `Ast` no-op derive macro:
+/// Secondly, it adds the following code around the type:
 ///
-/// # Generator Attributes
+/// ### `#[repr(C)]`
 ///
-/// ## `#[scope(...)]`
+/// `#[repr]` attribute is added to the type, to make the memory layout of the type predictable:
 ///
-/// This attribute can be used in 2 places:
+/// * Structs: `#[repr(C)]`. e.g. `#[repr(C)] struct S { x: X, y: Y }`
+/// * Fieldless enums: `#[repr(u8)]` e.g. `#[repr(u8)] enum E { X, Y, Z, }`.
+/// * Fieldful enums: `#[repr(C, u8)]` e.g. `#[repr(C, u8)] enum E { X(X), Y(Y) }`
 ///
-/// ### On `struct`s / `enum`s
-/// When this attribute comes before an AST type definition it accepts 3 optional arguments.
-/// 1. `flags(expr)`: It accepts an expression that would evaluate to `ScopeFlags`.
-///    It is used to annotate scope flags of the AST type.
-/// 2. `if(expr)`: It accepts an expression that would evaluate to `bool` used for conditional scope creation.
-/// 3. `strict_if(expr)`: It accepts an expression that would evaluate to `bool`.
-///    If this value is `true` the created scope would be `strict`.
+/// ### Derive `Ast` trait
 ///
-/// NOTE: All these expressions can use `self` to access the current node they are getting executed on
-/// via an immutable reference.
+/// `#[derive(oxc_ast_macros::Ast)]` is added to the type.
 ///
-/// ### On `struct` fields
-/// At this position this attribute can only have one shape: `#[scope(enter_before)]` / `#[scope(exit_before)]`.
-/// It marks where `Visit::enter_scope` and `Visit::exit_scope` events should be fired for this AST type.
+/// `Ast` derive macro is a no-op (see below) but allows custom attributes on AST types.
 ///
-/// ## `#[visit(args(arg = expr))]`
+/// See `derives` and `generators` directories in `tasks/ast_tools` for details of the various
+/// custom attributes, and how they're used.
 ///
-/// This attribute can only occur on `struct` fields, or `enum` variants.
-/// Accepts an argument name and an expression.
-/// `expr` is an expression that would evaluate to `ScopeFlags`.
-/// This argument can only be used at places where the AST type is `Function`.
+/// ### Trait assertions
 ///
-/// ## `#[span]`
+/// `oxc_ast_tools` generates code for trait impls where those traits are specified with
+/// `#[generate_derive(SomeTrait)]`. This is similar to `#[derive(SomeTrait)]`, but the code is
+/// generated ahead-of-time, rather than in a proc macro.
 ///
-/// This attribute can be used to hint to `ast_tools` which field should be used to obtain the span
-/// of this AST type.
-///
-/// ## `#[generate_derive(...)]`
-///
-/// This attribute has the same purpose as Rust's `#[derive(...)]` macro.
-/// It is used to derive traits for the types.
-/// However, instead of expanding the derive at compile-time, we generate the derived code at build time
-/// via `ast_tools` code generation.
-/// These derived implementations are output as `src/generated/derive_*.rs` in the crate the type is
-/// defined in.
-///
-/// ## `#[ts]`
-///
-/// Marks a struct field as only relevant for TypeScript ASTs.
-///
-/// # Derive Helper Attributes
-///
-/// These are helper attributes that are only meaningful when their respective trait is derived
-/// via `generate_derive`.
-///
-/// ## `#[clone_in(default)]`
-///
-/// This attribute is only used by `CloneIn` derive.
-/// `struct` fields marked with this attribute at cloning will use the `Default::default()` value
-/// instead of `CloneIn::clone_in` to initialize.
+/// Add assertions that traits used in `#[generate_derive(...)]` are in scope.
 #[proc_macro_attribute]
 pub fn ast(_args: TokenStream, input: TokenStream) -> TokenStream {
     let input = parse_macro_input!(input as Item);
@@ -83,7 +45,7 @@ pub fn ast(_args: TokenStream, input: TokenStream) -> TokenStream {
 /// Does not generate any code.
 /// Its only purpose is to allow the occurrence of helper attributes used in `tasks/ast_tools`.
 ///
-/// Read [`macro@ast`] for further details.
+/// See [`macro@ast`] for further details.
 #[proc_macro_derive(Ast, attributes(clone_in, estree, generate_derive, scope, span, ts, visit))]
 pub fn ast_derive(_input: TokenStream) -> TokenStream {
     TokenStream::new()