sqlite: reject statement-less SQL in SQLTagStore

doc/api/sqlite.md

@@ -686,6 +686,9 @@ added: v22.5.0
 Compiles a SQL statement into a [prepared statement][]. This method is a wrapper
 around [`sqlite3_prepare_v2()`][].
 
+Throws an `ERR_INVALID_ARG_VALUE` error if `sql` contains no statement, such as
+an empty string or a lone comment.
+
 ### `database.createTagStore([maxSize])`
 
 <!-- YAML

src/node_sqlite.cc

@@ -1575,6 +1575,16 @@ void DatabaseSync::Prepare(const FunctionCallbackInfo<Value>& args) {
   int r = sqlite3_prepare_v2(db->connection_, *sql, -1, &s, nullptr);
 
   CHECK_ERROR_OR_THROW(env->isolate(), db, r, SQLITE_OK, void());
+
+  // sqlite3_prepare_v2() reports success without producing a statement when
+  // the input holds no SQL, such as a comment. Such a statement can never be
+  // stepped, and tracking it would leave a dangling pointer in statements_
+  // because its destructor treats a null statement as already finalized.
+  if (s == nullptr) {
+    THROW_ERR_INVALID_ARG_VALUE(env, "The SQL query contains no statement.");
+    return;
+  }
+
   BaseObjectPtr<StatementSync> stmt =
       StatementSync::Create(env, BaseObjectPtr<DatabaseSync>(db), s);
   db->statements_.insert(stmt.get());
@@ -3648,6 +3658,13 @@ BaseObjectPtr<StatementSync> SQLTagStore::PrepareStatement(
       return BaseObjectPtr<StatementSync>();
     }
 
+    // As in DatabaseSync::Prepare(), reject input that holds no SQL rather
+    // than caching a statement that can never be bound or stepped.
+    if (s == nullptr) {
+      THROW_ERR_INVALID_ARG_VALUE(env, "The SQL query contains no statement.");
+      return BaseObjectPtr<StatementSync>();
+    }
+
     BaseObjectPtr<StatementSync> stmt_obj = StatementSync::Create(
         env, BaseObjectPtr<DatabaseSync>(session->database_), s);
 

test/parallel/test-sqlite-database-sync.js

@@ -397,6 +397,32 @@ suite('DatabaseSync.prototype.prepare()', () => {
       message: /The "sql" argument must be a string/,
     });
   });
+
+  test('throws if sql contains no statement', (t) => {
+    using db = new DatabaseSync(nextDb());
+
+    for (const sql of ['', '   ', ';', '-- comment', '/* comment */']) {
+      t.assert.throws(() => {
+        db.prepare(sql);
+      }, {
+        code: 'ERR_INVALID_ARG_VALUE',
+        message: /contains no statement/,
+      });
+    }
+  });
+
+  test('prepares statements that contain comments', (t) => {
+    using db = new DatabaseSync(nextDb());
+    const queries = [
+      '-- lead\nSELECT 1 AS v',
+      'SELECT 1 AS v -- trail',
+      'SELECT /* mid */ 1 AS v',
+    ];
+
+    for (const sql of queries) {
+      t.assert.strictEqual(db.prepare(sql).get().v, 1);
+    }
+  });
 });
 
 suite('DatabaseSync.prototype.exec()', () => {

test/parallel/test-sqlite-template-tag.js

@@ -317,6 +317,29 @@ test('sql error messages are descriptive', () => {
   });
 });
 
+test('rejects SQL that contains no statement', () => {
+  const expectedError = {
+    code: 'ERR_INVALID_ARG_VALUE',
+    message: /contains no statement/,
+  };
+
+  for (const method of ['run', 'get', 'all', 'iterate']) {
+    assert.throws(() => {
+      // eslint-disable-next-line no-unused-expressions
+      sql[method]`-- comment`;
+    }, expectedError);
+
+    assert.throws(() => {
+      // eslint-disable-next-line no-unused-expressions
+      sql[method]``;
+    }, expectedError);
+  }
+
+  // A rejected statement must not be cached, so a later valid query with the
+  // same tag store still works.
+  assert.strictEqual(sql.run`INSERT INTO foo (text) VALUES (${'bob'})`.changes, 1);
+});
+
 test('a tag store keeps the database alive by itself', () => {
   const sql = new DatabaseSync(':memory:').createTagStore();