Twig and error messages - is this normal? - twig

Question

I've been testing Twig on localhost... the code here is the same as in this question but the query is different:
<?php
// include and register Twig auto-loader
include 'Twig/Autoloader.php';
Twig_Autoloader::register();
// attempt a connection
try {
$dbh = new PDO('mysql:dbname=world;host=localhost', 'root', 'mypass');
} catch (PDOException $e) {
echo "Error: Could not connect. " . $e->getMessage();
}
// set error mode
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
// attempt some queries
try {
// execute SELECT query
// store each row as an object
$sql = "SELECT manufacturer, model, modelinfo FROM automobiles WHERE id = '4' ";
$sth = $dbh->query($sql);
while ($row = $sth->fetchObject()) {
$data[] = $row;
}
// close connection, clean up
unset($dbh);
// define template directory location
$loader = new Twig_Loader_Filesystem('templates');
// initialize Twig environment
$twig = new Twig_Environment($loader);
// load template
$template = $twig->loadTemplate('cars.html');
// set template variables
// render template
echo $template->render(array (
'data' => $data
));
} catch (Exception $e) {
die ('ERROR: ' . $e->getMessage());
}
?>
I have 3 records; I decided to query a non-existent record to see what Twig's error handling was like, as I was comparing Twig vs Smarty - out of interest, and for a project.
This error message comes up:
Notice: Undefined variable: data in /Applications/MAMP/htdocs/mysite/twigtesting.php on line 42
Surely a notice saying 'Data not found' should happen or am I wrong here?
Undefined variable data refers to:
// set template variables
// render template
echo $template->render(array (
'data' => $data
));
Why is this happening? I'm new to Twig, and using the latest build from their site, f that's relevant.

Answer 1

You don't get a Twig error, because the error does not exists in the templates, but in the code that is generating these templates.
PHP is having issues to put the value of $data inside an array, because that variable does not exists.
If you want to see how twig handles errors, you need to access a non existing variable inside a template. For instance, putting {{ notExisting }} in your current template.
I can already say that Twig is handling errors by throwing parsing exceptions in PHP. All exceptions thrown by Twig are extending Twig_Error. To catch these, use a try { ... } catch (\Twig_Error $e) { ... } block.
Furthermore, Twig can throw 3 different types of Exceptions:
Twig_Error_Syntax is thrown when an error occurs when parsing a template (e.g. using malformed tags).
Twig_Error_Loader is thrown when Twig can't load a file. This can happen when using a render() method, or when you use some file features in Twig (e.g. {% extends ... %}).
Twig_Error_RunTime is thrown when an error occurs in runtime (e.g. an error inside extensions).