fix(semantic): clear member write target for computed keys (#22302)

- clear `MemberWriteTarget` before visiting computed member keys
- add semantic snapshot coverage for computed keys versus computed objects

Fixes #22300

crates/oxc_semantic/src/builder.rs

@@ -2073,6 +2073,19 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
         self.current_reference_flags = ReferenceFlags::empty();
     }
 
+    fn visit_computed_member_expression(&mut self, it: &ComputedMemberExpression<'a>) {
+        let kind = AstKind::ComputedMemberExpression(self.alloc(it));
+        self.enter_node(kind);
+        self.visit_span(&it.span);
+        self.visit_expression(&it.object);
+        // The key expression is a read context, not part of the property write —
+        // strip MemberWriteTarget so it doesn't leak onto identifiers inside the key
+        // (e.g. `key` in `this[key] = 1`, where `this` doesn't consume the flag).
+        self.current_reference_flags -= ReferenceFlags::MemberWriteTarget;
+        self.visit_expression(&it.expression);
+        self.leave_node(kind);
+    }
+
     fn visit_simple_assignment_target(&mut self, it: &SimpleAssignmentTarget<'a>) {
         // Except that the read-write flags has been set in visit_assignment_expression
         // and visit_update_expression, this is always a write-only reference here.

crates/oxc_semantic/tests/fixtures/oxc/js/assignments/member-write-target.js

@@ -16,3 +16,14 @@ let c = {};
 let d = {};
 let e = {};
 (true ? d : e).foo = 1;
+
+// No MemberWriteTarget: computed property key
+let key;
+this[key] = 1;
+this[key] += 1;
+delete this[key];
+
+// MemberWriteTarget: computed object
+let f = {};
+f[key] = 1;
+f[key] += 1;

crates/oxc_semantic/tests/fixtures/oxc/js/assignments/member-write-target.snap

@@ -97,6 +97,71 @@ input_file: crates/oxc_semantic/tests/fixtures/oxc/js/assignments/member-write-t
             "scope_id": 0
           }
         ]
+      },
+      {
+        "flags": "SymbolFlags(BlockScopedVariable)",
+        "id": 5,
+        "name": "key",
+        "node": "VariableDeclarator(key)",
+        "references": [
+          {
+            "flags": "ReferenceFlags(Read)",
+            "id": 7,
+            "name": "key",
+            "node_id": 71,
+            "scope_id": 0
+          },
+          {
+            "flags": "ReferenceFlags(Read)",
+            "id": 8,
+            "name": "key",
+            "node_id": 77,
+            "scope_id": 0
+          },
+          {
+            "flags": "ReferenceFlags(Read)",
+            "id": 9,
+            "name": "key",
+            "node_id": 83,
+            "scope_id": 0
+          },
+          {
+            "flags": "ReferenceFlags(Read)",
+            "id": 11,
+            "name": "key",
+            "node_id": 92,
+            "scope_id": 0
+          },
+          {
+            "flags": "ReferenceFlags(Read)",
+            "id": 13,
+            "name": "key",
+            "node_id": 98,
+            "scope_id": 0
+          }
+        ]
+      },
+      {
+        "flags": "SymbolFlags(BlockScopedVariable)",
+        "id": 6,
+        "name": "f",
+        "node": "VariableDeclarator(f)",
+        "references": [
+          {
+            "flags": "ReferenceFlags(Read | MemberWriteTarget)",
+            "id": 10,
+            "name": "f",
+            "node_id": 91,
+            "scope_id": 0
+          },
+          {
+            "flags": "ReferenceFlags(Read | MemberWriteTarget)",
+            "id": 12,
+            "name": "f",
+            "node_id": 97,
+            "scope_id": 0
+          }
+        ]
       }
     ]
   }