docs(ast, ast_macros, ast_tools): better documentation for Ast help…

…er attributes. (#4856)

crates/oxc_ast/src/ast/js.rs

@@ -1,6 +1,6 @@
-// NB: `#[span]`, `#[scope(...)]` and `#[visit(...)]` do NOT do anything to the code.
-// They are purely markers for codegen used in
-// `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// NB: `#[span]`, `#[scope(...)]`,`#[visit(...)]` and `#[generate_derive(...)]` do NOT do anything to the code.
+// They are purely markers for codegen used in `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// Read [`macro@oxc_ast_macros::ast`] for more information.
 
 // Silence erroneous warnings from Rust Analyser for `#[derive(Tsify)]`
 #![allow(non_snake_case)]

crates/oxc_ast/src/ast/jsx.rs

@@ -1,8 +1,8 @@
 //! [JSX](https://facebook.github.io/jsx)
 
-// NB: `#[span]`, `#[scope(...)]` and `#[visit(...)]` do NOT do anything to the code.
-// They are purely markers for codegen used in
-// `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// NB: `#[span]`, `#[scope(...)]`,`#[visit(...)]` and `#[generate_derive(...)]` do NOT do anything to the code.
+// They are purely markers for codegen used in `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// Read [`macro@oxc_ast_macros::ast`] for more information.
 
 // Silence erroneous warnings from Rust Analyser for `#[derive(Tsify)]`
 #![allow(non_snake_case)]

crates/oxc_ast/src/ast/literal.rs

@@ -1,8 +1,8 @@
 //! Literals
 
-// NB: `#[span]`, `#[scope(...)]` and `#[visit(...)]` do NOT do anything to the code.
-// They are purely markers for codegen used in
-// `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// NB: `#[span]`, `#[scope(...)]`,`#[visit(...)]` and `#[generate_derive(...)]` do NOT do anything to the code.
+// They are purely markers for codegen used in `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// Read [`macro@oxc_ast_macros::ast`] for more information.
 
 // Silence erroneous warnings from Rust Analyser for `#[derive(Tsify)]`
 #![allow(non_snake_case)]

crates/oxc_ast/src/ast/ts.rs

@@ -3,9 +3,9 @@
 //! [AST Spec](https://github.com/typescript-eslint/typescript-eslint/tree/main/packages/ast-spec)
 //! [Archived TypeScript spec](https://github.com/microsoft/TypeScript/blob/3c99d50da5a579d9fa92d02664b1b66d4ff55944/doc/spec-ARCHIVED.md)
 
-// NB: `#[span]`, `#[scope(...)]` and `#[visit(...)]` do NOT do anything to the code.
-// They are purely markers for codegen used in
-// `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// NB: `#[span]`, `#[scope(...)]`,`#[visit(...)]` and `#[generate_derive(...)]` do NOT do anything to the code.
+// They are purely markers for codegen used in `tasks/ast_tools` and `crates/oxc_traverse/scripts`. See docs in those crates.
+// Read [`macro@oxc_ast_macros::ast`] for more information.
 
 // Silence erroneous warnings from Rust Analyser for `#[derive(Tsify)]`
 #![allow(non_snake_case)]

crates/oxc_ast_macros/src/lib.rs

@@ -54,7 +54,7 @@ fn assert_generated_derives(attrs: &[syn::Attribute]) -> TokenStream2 {
     }
 
     // NOTE: At this level we don't care if a trait is derived multiple times, It is the
-    // responsibility of the codegen to raise errors for those.
+    // responsibility of the `ast_tools` to raise errors for those.
     let assertion =
         attrs.iter().filter(|attr| attr.path().is_ident("generate_derive")).flat_map(parse).map(
             |derive| {
@@ -70,14 +70,70 @@ fn assert_generated_derives(attrs: &[syn::Attribute]) -> TokenStream2 {
 }
 
 /// This attribute serves two purposes.
-/// First, it is a marker for our codegen to detect AST types.
+/// First, it is a marker for our `ast_tools` to detect AST types.
 /// Secondly, it generates the following code:
 ///
 /// * 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.
+///
+/// It also allows the usage of these helper attributes via deriving a "no-op" derive macro.
+///
+/// # Generator Attributes:
+///
+/// ## `#[scope(...)]`:
+///
+/// This attribute can be used in 2 places:
+/// ### On `struct`/`enum` items:
+/// 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`.
+///
+/// NOTE: All these expressions can use `self` to access the current node they are getting executed on via an immutable reference.
+///
+/// ### On `struct` fields:
+/// At this position this attribute can only have one shape: `#[scope(enter_before)]`.
+/// It marks where `Visit::enter_scope` events should be fired for this AST type.
+///
+/// ## `#[visit(...)]`:
+///
+/// This attribute can only occur on `struct` fields, Or `enum` attributes.
+/// It accepts 4 optional arguments.
+///     1. `as(ident)`: It accepts an identifier, our generators would treat the type of this field/variant as if they were called as the given identifier.
+///     2. `args(arg = expr)`: It accepts an argument name and an expression. Currently it only
+///        accepts one argument.
+///        a. `args(flags = expr)`: `expr` is an expression that would evaluate to `ScopeFlags`, This argument can only be used at places where the AST type is `Function`.
+///     3. `enter_before`: It marks where this AST type should fire `Visit::enter_node` events.
+///     4. `ignore`: It would ignore this field/variant in visits.
+///
+/// ## `#[span]`:
+///
+/// This attribute can be used to hint to the `ast_tools` which field should be used to obtain the span of this AST type.
+///
+/// ## `#[generate_derive(...)]`
+///
+/// This attribute has the same spirit as the `#[derive(...)]` macro, It is used to derive traits for the types.
+/// However, Instead of expanding the derive at compile-time, We do this process on PR submits via `ast_tools` code generation.
+/// These derived implementations would be output in the `crates/oxc_ast/src/generated` directory.
+///
+/// # 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.
+///
+/// # Mocked attributes:
+///
+/// These are just here to remove the need for boilerplate `#[cfg_attr(...)]`. If their actual trait is derived they would consume these, Otherwise, Our mock attributes will prevent compile errors.
+///
+/// 1. `serde`
+/// 2. `tsify`
 #[proc_macro_attribute]
 #[allow(clippy::missing_panics_doc)]
 pub fn ast(_args: TokenStream, input: TokenStream) -> TokenStream {
@@ -104,9 +160,10 @@ pub fn ast(_args: TokenStream, input: TokenStream) -> TokenStream {
 /// Dummy derive macro for a non-existent trait `Ast`.
 ///
 /// Does not generate any code.
-/// Only purpose is to allow using `#[scope]`, `#[visit]`, and other attrs in the AST node type defs.
-/// These "marker" attributes are used in codegen.
-#[proc_macro_derive(Ast, attributes(scope, visit, span, serde, tsify, generate_derive, clone_in))]
+/// The only purpose is to allow the occurrence of helper attributes used with the `tasks/ast_tools`.
+///
+/// Read [`macro@ast`] for further details.
+#[proc_macro_derive(Ast, attributes(scope, visit, span, generate_derive, clone_in, serde, tsify))]
 pub fn ast_derive(_item: TokenStream) -> TokenStream {
     TokenStream::new()
 }

tasks/ast_tools/src/markers.rs

@@ -66,13 +66,13 @@ pub struct ScopeMarkers {
     pub enter_before: bool,
 }
 
-/// A struct representing the `#[scope(...)]` attribute.
+/// A struct representing all the helper attributes that might be used with `#[generate_derive(...)]`
 #[derive(Debug, Default, Serialize)]
 pub struct DeriveAttributes {
     pub clone_in: CloneInAttribute,
 }
 
-/// A enum representing the value passed in `#[clone_in(...)]` derive attribute.
+/// A enum representing the value passed in `#[clone_in(...)]` derive helper attribute.
 #[derive(Debug, Default, Serialize)]
 pub enum CloneInAttribute {
     #[default]