fix(isolated-declarations): inferring an incorrect return type when t…

…here is an arrow function inside a function

crates/oxc_isolated_declarations/src/return_type.rs

@@ -1,7 +1,7 @@
 use oxc_ast::{
     ast::{
-        BindingIdentifier, Expression, Function, FunctionBody, ReturnStatement, TSType,
-        TSTypeAliasDeclaration, TSTypeName, TSTypeQueryExprName,
+        ArrowFunctionExpression, BindingIdentifier, Expression, Function, FunctionBody,
+        ReturnStatement, TSType, TSTypeAliasDeclaration, TSTypeName, TSTypeQueryExprName,
     },
     AstBuilder, Visit,
 };
@@ -138,6 +138,10 @@ impl<'a> Visit<'a> for FunctionReturnType<'a> {
         // We don't care about nested functions
     }
 
+    fn visit_arrow_expression(&mut self, _expr: &ArrowFunctionExpression<'a>) {
+        // We don't care about nested functions
+    }
+
     fn visit_return_statement(&mut self, stmt: &ReturnStatement<'a>) {
         self.return_statement_count += 1;
         if self.return_statement_count > 1 {

crates/oxc_isolated_declarations/tests/fixtures/infer_return_type.ts

@@ -7,14 +7,19 @@ function bar() {
   if (true) {
    return;
   }
-  return 1;
 }
 // inferred type is number | undefined
 
 function baz() {
  if (true) {
   return null;
  }
- return 1;
 }
-// We can't infer return type if there are multiple return statements with different types
+// We can't infer return type if there are multiple return statements with different types
+
+function qux() {
+  const a = (() => {
+    return 1;
+  })();
+ return `Hello, world!`;
+}

crates/oxc_isolated_declarations/tests/snapshots/infer_return_type.snap

@@ -5,17 +5,18 @@ input_file: crates/oxc_isolated_declarations/tests/fixtures/infer_return_type.ts
 ==================== .D.TS ====================
 
 declare function foo(): number;
-declare function bar(): ((number) | (undefined));
-declare function baz();
+declare function bar();
+declare function baz(): null;
+declare function qux(): string;
 
 
 ==================== Errors ====================
 
   x TS9007: Function must have an explicit return type annotation with
   | --isolatedDeclarations.
-    ,-[14:10]
- 13 | 
- 14 | function baz() {
-    :          ^^^
- 15 |  if (true) {
-    `----
+   ,-[6:10]
+ 5 | 
+ 6 | function bar() {
+   :          ^^^
+ 7 |   if (true) {
+   `----