fix(transformer/arrow-functions): reaches unreachable when <this.foo> is inside an arrow function (#5356)

Fixes: https://github.com/oxc-project/oxc/issues/5353#issuecomment-2321792915

crates/oxc_transformer/src/es2015/arrow_functions.rs

@@ -137,22 +137,31 @@ impl<'a> Traverse<'a> for ArrowFunctions<'a> {
             return;
         }
 
-        let ident = match name {
-            JSXElementName::Identifier(ident) => ident,
-            JSXElementName::MemberExpression(member_expr) => {
-                member_expr.get_object_identifier_mut()
+        if let JSXElementName::Identifier(ident) = name {
+            if ident.name == "this" {
+                let mut new_ident = self.get_this_name(ctx).create_read_reference(ctx);
+                new_ident.span = ident.span;
+                *name = self.ctx.ast.jsx_element_name_from_identifier_reference(new_ident);
+            }
+        }
+    }
+
+    /// Change <this.foo></this.foo> to <_this.foo></_this.foo>, and mark it as found
+    fn enter_jsx_member_expression_object(
+        &mut self,
+        node: &mut JSXMemberExpressionObject<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        if !self.is_inside_arrow_function() {
+            return;
+        }
+
+        if let JSXMemberExpressionObject::IdentifierReference(ident) = node {
+            if ident.name == "this" {
+                let mut new_ident = self.get_this_name(ctx).create_read_reference(ctx);
+                new_ident.span = ident.span;
+                *node = ctx.ast.jsx_member_expression_object_from_identifier_reference(new_ident);
             }
-            JSXElementName::IdentifierReference(_) | JSXElementName::NamespacedName(_) => return,
-        };
-        if ident.name == "this" {
-            // We can't produce a proper identifier with a `ReferenceId` because `JSXIdentifier`
-            // lacks that field. https://github.com/oxc-project/oxc/issues/3528
-            // So generate a reference and just use its name.
-            // If JSX transform is enabled, that transform runs before this and will have converted
-            // this to a proper `ThisExpression`, and this visitor won't run.
-            // So only a problem if JSX transform is disabled.
-            let new_ident = self.get_this_name(ctx).create_read_reference(ctx);
-            ident.name = new_ident.name;
         }
     }
 

crates/oxc_transformer/src/es2015/mod.rs

@@ -57,6 +57,16 @@ impl<'a> Traverse<'a> for ES2015<'a> {
         }
     }
 
+    fn enter_jsx_member_expression_object(
+        &mut self,
+        node: &mut JSXMemberExpressionObject<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        if self.options.arrow_function.is_some() {
+            self.arrow_functions.enter_jsx_member_expression_object(node, ctx);
+        }
+    }
+
     fn enter_declaration(&mut self, decl: &mut Declaration<'a>, ctx: &mut TraverseCtx<'a>) {
         if self.options.arrow_function.is_some() {
             self.arrow_functions.enter_declaration(decl, ctx);

crates/oxc_transformer/src/lib.rs

@@ -240,6 +240,14 @@ impl<'a> Traverse<'a> for Transformer<'a> {
         self.x3_es2015.enter_jsx_element_name(elem, ctx);
     }
 
+    fn enter_jsx_member_expression_object(
+        &mut self,
+        node: &mut JSXMemberExpressionObject<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
+        self.x3_es2015.enter_jsx_member_expression_object(node, ctx);
+    }
+
     fn enter_method_definition(
         &mut self,
         def: &mut MethodDefinition<'a>,

tasks/transform_conformance/oxc.snap.md

@@ -1,10 +1,9 @@
 commit: 3bcfee23
 
-Passed: 10/38
+Passed: 10/39
 
 # All Passed:
 * babel-plugin-transform-optional-catch-binding
-* babel-plugin-transform-arrow-functions
 
 
 # babel-plugin-transform-nullish-coalescing-operator (0/1)
@@ -15,6 +14,14 @@ Passed: 10/38
 
 
 
+# babel-plugin-transform-arrow-functions (1/2)
+* with-this-member-expression/input.jsx
+  x Unresolved references mismatch:
+  | after transform: ["this"]
+  | rebuilt        : []
+
+
+
 # babel-plugin-transform-typescript (2/8)
 * class-property-definition/input.ts
   x Unresolved references mismatch:

tasks/transform_conformance/tests/babel-plugin-transform-arrow-functions/test/fixtures/with-this-member-expression/input.jsx

@@ -0,0 +1,3 @@
+() => {
+  <this.foo></this.foo>
+}

tasks/transform_conformance/tests/babel-plugin-transform-arrow-functions/test/fixtures/with-this-member-expression/output.js

@@ -0,0 +1,4 @@
+var _this = this;
+(function() {
+       <_this.foo></_this.foo>;
+});