fix(mangler): handle cases where a var is declared in a block scope

crates/oxc_mangler/src/lib.rs

@@ -232,13 +232,22 @@ impl Mangler {
             {
                 slots[symbol_id.index()] = assigned_slot;
 
+                let declared_scope_id =
+                    ast_nodes.get_node(symbol_table.get_declaration(*symbol_id)).scope_id();
+
                 // Calculate the scope ids that this symbol is alive in.
                 let lived_scope_ids = symbol_table
                     .get_resolved_references(*symbol_id)
                     .flat_map(|reference| {
                         let used_scope_id = ast_nodes.get_node(reference.node_id()).scope_id();
                         scope_tree.ancestors(used_scope_id).take_while(|s_id| *s_id != scope_id)
                     })
+                    // also include scopes that this symbol was declared (for cases like `function foo() { { var x; let y; } }`)
+                    .chain(
+                        scope_tree
+                            .ancestors(declared_scope_id)
+                            .take_while(|s_id| *s_id != scope_id),
+                    )
                     .chain(iter::once(scope_id));
 
                 // Since the slot is now assigned to this symbol, it is alive in all the scopes that this symbol is alive in.

crates/oxc_minifier/tests/mangler/mod.rs

@@ -40,6 +40,10 @@ fn mangler() {
         "function _() { var x; try { throw 0 } catch (e) { e } }", // e can shadow x
         "function _() { var x; try { throw 0 } catch (e) { var e } }", // e can shadow x (not implemented)
         "function _() { var x; try { throw 0 } catch { var e } }",     // e should not shadow x
+        "function _() { var x; var y; }", // x and y should have different names
+        "function _() { var x; let y; }", // x and y should have different names
+        "function _() { { var x; var y; } }", // x and y should have different names
+        "function _() { { var x; let y; } }", // x and y should have different names
     ];
     let top_level_cases = [
         "function foo(a) {a}",

crates/oxc_minifier/tests/mangler/snapshots/mangler.snap

@@ -153,6 +153,34 @@ function _() {
 	}
 }
 
+function _() { var x; var y; }
+function _() {
+	var a;
+	var b;
+}
+
+function _() { var x; let y; }
+function _() {
+	var a;
+	let b;
+}
+
+function _() { { var x; var y; } }
+function _() {
+	{
+		var a;
+		var b;
+	}
+}
+
+function _() { { var x; let y; } }
+function _() {
+	{
+		var a;
+		let b;
+	}
+}
+
 function foo(a) {a}
 function a(a) {
 	a;