fix(ast/estree): fix Function.this_param (#9913)

`Function.this_param` is included in `Function.params` as an `Identifier` with `name: "this"`

https://ast-explorer.dev/#eNolykEKwzAMRNGrmFm10F7AB+lKG2MU6uAoJlICwfjuUchiNu9PR0XEnI6keSvN8EFzsLPxA1/WWuT27D7tkq2sEqaX/YvG0Mfb53X12klCIHBe0o839R8hOtRkrEYgGRgXircmAw==

crates/oxc_ast/src/ast/js.rs

@@ -1658,7 +1658,7 @@ pub struct BindingRestElement<'a> {
     add_fields(expression = False),
     field_order(
         r#type, span, id, expression, generator, r#async, params, body,
-        declare, type_parameters, this_param, return_type,
+        declare, type_parameters, return_type,
     ),
 )]
 pub struct Function<'a> {
@@ -1695,10 +1695,12 @@ pub struct Function<'a> {
     /// });
     /// ```
     #[ts]
+    #[estree(skip)]
     pub this_param: Option<Box<'a, TSThisParameter<'a>>>,
     /// Function parameters.
     ///
     /// Does not include `this` parameters used by some TypeScript functions.
+    #[estree(via = FunctionFormalParameters)]
     pub params: Box<'a, FormalParameters<'a>>,
     /// The TypeScript return type annotation.
     #[ts]

crates/oxc_ast/src/ast/ts.rs

@@ -31,6 +31,10 @@ use super::{inherit_variants, js::*, literal::*};
 #[ast(visit)]
 #[derive(Debug)]
 #[generate_derive(CloneIn, GetSpan, GetSpanMut, ContentEq, ESTree)]
+#[estree(
+    rename = "Identifier",
+    add_fields(decorators = TsEmptyArray, optional = TsFalse, name = This)
+)]
 pub struct TSThisParameter<'a> {
     pub span: Span,
     #[estree(skip)]

crates/oxc_ast/src/generated/derive_estree.rs

@@ -1345,11 +1345,10 @@ impl ESTree for Function<'_> {
         state.serialize_field("expression", &crate::serialize::False(self));
         state.serialize_field("generator", &self.generator);
         state.serialize_field("async", &self.r#async);
-        state.serialize_field("params", &self.params);
+        state.serialize_field("params", &crate::serialize::FunctionFormalParameters(self));
         state.serialize_field("body", &self.body);
         state.serialize_ts_field("declare", &self.declare);
         state.serialize_ts_field("typeParameters", &self.type_parameters);
-        state.serialize_ts_field("thisParam", &self.this_param);
         state.serialize_ts_field("returnType", &self.return_type);
         state.end();
     }
@@ -2278,10 +2277,13 @@ impl ESTree for JSXText<'_> {
 impl ESTree for TSThisParameter<'_> {
     fn serialize<S: Serializer>(&self, serializer: S) {
         let mut state = serializer.serialize_struct();
-        state.serialize_field("type", &JsonSafeString("TSThisParameter"));
+        state.serialize_field("type", &JsonSafeString("Identifier"));
         state.serialize_field("start", &self.span.start);
         state.serialize_field("end", &self.span.end);
         state.serialize_field("typeAnnotation", &self.type_annotation);
+        state.serialize_field("name", &crate::serialize::This(self));
+        state.serialize_ts_field("decorators", &crate::serialize::TsEmptyArray(self));
+        state.serialize_ts_field("optional", &crate::serialize::TsFalse(self));
         state.end();
     }
 }

crates/oxc_ast/src/serialize.rs

@@ -150,6 +150,17 @@ impl<T> ESTree for Init<'_, T> {
     }
 }
 
+/// Serialized as `"this"`.
+#[ast_meta]
+#[estree(ts_type = "'this'", raw_deser = "'this'")]
+pub struct This<'b, T>(#[expect(dead_code)] pub &'b T);
+
+impl<T> ESTree for This<'_, T> {
+    fn serialize<S: Serializer>(&self, serializer: S) {
+        JsonSafeString("this").serialize(serializer);
+    }
+}
+
 #[ast_meta]
 #[estree(ts_type = "[]", raw_deser = "[]")]
 #[ts]
@@ -642,6 +653,42 @@ impl ESTree for ExpressionStatementDirective<'_, '_> {
     }
 }
 
+#[ast_meta]
+#[estree(
+    ts_type = "ParamPattern[]",
+    raw_deser = "
+        const params = DESER[Box<FormalParameters>](POS_OFFSET.params);
+        /* IF_TS */
+        const thisParam = DESER[Option<Box<TSThisParameter>>](POS_OFFSET.this_param)
+        if (thisParam !== null) {
+            params.unshift(thisParam);
+        }
+        /* END_IF_TS */
+        params
+    "
+)]
+pub struct FunctionFormalParameters<'a, 'b>(pub &'b Function<'a>);
+
+impl ESTree for FunctionFormalParameters<'_, '_> {
+    fn serialize<S: Serializer>(&self, serializer: S) {
+        let mut seq = serializer.serialize_sequence();
+
+        if let Some(this_param) = &self.0.this_param {
+            seq.serialize_ts_element(this_param);
+        }
+
+        for item in &self.0.params.items {
+            seq.serialize_element(item);
+        }
+
+        if let Some(rest) = &self.0.params.rest {
+            seq.serialize_element(&FormalParametersRest(rest));
+        }
+
+        seq.end();
+    }
+}
+
 // --------------------
 // Comments
 // --------------------

crates/oxc_estree/src/serialize/sequences.rs

@@ -4,6 +4,7 @@ use super::{Config, ESTree, ESTreeSerializer, Formatter, Serializer, SerializerP
 pub trait SequenceSerializer {
     /// Serialize sequence entry.
     fn serialize_element<T: ESTree + ?Sized>(&mut self, value: &T);
+    fn serialize_ts_element<T: ESTree + ?Sized>(&mut self, value: &T);
 
     /// Finish serializing sequence.
     fn end(self);
@@ -43,6 +44,12 @@ impl<C: Config, F: Formatter> SequenceSerializer for ESTreeSequenceSerializer<'_
         value.serialize(&mut *self.serializer);
     }
 
+    fn serialize_ts_element<T: ESTree + ?Sized>(&mut self, value: &T) {
+        if C::INCLUDE_TS_FIELDS {
+            self.serialize_element(value);
+        }
+    }
+
     /// Finish serializing sequence.
     fn end(mut self) {
         let (buffer, formatter) = self.serializer.buffer_and_formatter_mut();

napi/parser/deserialize-js.js

@@ -749,6 +749,7 @@ function deserializeBindingRestElement(pos) {
 }
 
 function deserializeFunction(pos) {
+  const params = deserializeBoxFormalParameters(pos + 72);
   return {
     type: deserializeFunctionType(pos + 8),
     start: deserializeU32(pos),
@@ -757,7 +758,7 @@ function deserializeFunction(pos) {
     expression: false,
     generator: deserializeBool(pos + 48),
     async: deserializeBool(pos + 49),
-    params: deserializeBoxFormalParameters(pos + 72),
+    params,
     body: deserializeOptionBoxFunctionBody(pos + 88),
   };
 }
@@ -1262,10 +1263,11 @@ function deserializeJSXText(pos) {
 
 function deserializeTSThisParameter(pos) {
   return {
-    type: 'TSThisParameter',
+    type: 'Identifier',
     start: deserializeU32(pos),
     end: deserializeU32(pos + 4),
     typeAnnotation: deserializeOptionBoxTSTypeAnnotation(pos + 16),
+    name: 'this',
   };
 }
 

napi/parser/deserialize-ts.js

@@ -768,6 +768,11 @@ function deserializeBindingRestElement(pos) {
 }
 
 function deserializeFunction(pos) {
+  const params = deserializeBoxFormalParameters(pos + 72);
+  const thisParam = deserializeOptionBoxTSThisParameter(pos + 64);
+  if (thisParam !== null) {
+    params.unshift(thisParam);
+  }
   return {
     type: deserializeFunctionType(pos + 8),
     start: deserializeU32(pos),
@@ -776,11 +781,10 @@ function deserializeFunction(pos) {
     expression: false,
     generator: deserializeBool(pos + 48),
     async: deserializeBool(pos + 49),
-    params: deserializeBoxFormalParameters(pos + 72),
+    params,
     body: deserializeOptionBoxFunctionBody(pos + 88),
     declare: deserializeBool(pos + 50),
     typeParameters: deserializeOptionBoxTSTypeParameterDeclaration(pos + 56),
-    thisParam: deserializeOptionBoxTSThisParameter(pos + 64),
     returnType: deserializeOptionBoxTSTypeAnnotation(pos + 80),
   };
 }
@@ -1326,10 +1330,13 @@ function deserializeJSXText(pos) {
 
 function deserializeTSThisParameter(pos) {
   return {
-    type: 'TSThisParameter',
+    type: 'Identifier',
     start: deserializeU32(pos),
     end: deserializeU32(pos + 4),
     typeAnnotation: deserializeOptionBoxTSTypeAnnotation(pos + 16),
+    name: 'this',
+    decorators: [],
+    optional: false,
   };
 }
 

npm/oxc-types/types.d.ts

@@ -553,7 +553,6 @@ export interface Function extends Span {
   body: FunctionBody | null;
   declare?: boolean;
   typeParameters?: TSTypeParameterDeclaration | null;
-  thisParam?: TSThisParameter | null;
   returnType?: TSTypeAnnotation | null;
 }
 
@@ -918,8 +917,11 @@ export interface JSXText extends Span {
 }
 
 export interface TSThisParameter extends Span {
-  type: 'TSThisParameter';
+  type: 'Identifier';
   typeAnnotation: TSTypeAnnotation | null;
+  name: 'this';
+  decorators?: [];
+  optional?: false;
 }
 
 export interface TSEnumDeclaration extends Span {