STAMP #3: How to Turn TWIG Helper Functions to Origin Object

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In the previous post, we looked at how to turn Messy TWIG PHP to something useful in general.

Today we'll look at how to change TWIG helper functions to their original object form.

Have you joined our "STAMP" series just in this post? We're trying to convert the TWIG file. In the TWIG template, we use the single variable meal, an App\Meal type object.

{{ meal.title }}

What do we want as an output? A PHP code that PHPStan can understand and analyze. All steps must happen automatically, without any manual effort, on a typical PHPStan run:

vendor/bin/phpstan

In the previous post, we managed to narrow the TWIG mess to a single proper method, doDisplay():

use Twig\Template;

/* templates/meal.twig */
class __TwigTemplate_8a9d1381e8329967... extends Template
{
    protected function doDisplay(array $context, array $blocks = [])
    {
        // line 1
        echo twig_escape_filter(
            $this->env,
            twig_get_attribute(
                $this->env,
                ($context["meal"] ?? null),
                "title",
                "any",
                false,
                false,
                false,
                1
            ),
            "html",
            null,
            true
        );
    }
}

Would it be enough to run PHPStan on an analyze App\Meal object? There is no single mention about App\Meal type, not even an object - we can see: functions, $this->env property, and some $context array.

Keep it Simple

This looks like a desperate situation in a new job when they tell you, "we have strict clean code standards".

Time to quit? Not so fast.


Let's get back to basics, our TWIG template:

{{ meal.title }}

Now forget everything we know about TWIG PHP and complex php-parser.

Back to the Facts

What are the known axioms we can work with?

namespace App;

final class Meal
{
    public function getTitle(): string
    {
        return 'Potato Salad and Schnitzel';
    }
}


Knowing only this, how could we write this code in pure PHP?

$meal->title

Probably not, there is no public property $title, so it would fail on undefined pubic property.


$meal->getTitle()

Better, but what does this method do? void. It does not show anything. How can we improve it?


echo $meal->getTitle()

Wow, almost like the original! But seeing only this line of code, the $meal could be just an empty string for PHPStan. What about that?


/** @var \App\Meal $meal */
echo $meal->getTitle()

Great! It would be better to define the type in parameter type of some function, but we don't see any function there. The important one is that PHPStan now sees an object of a specific type and method call of a specific name on it.

Stripping down twig_get_attribute()

It's important to know what one wants. Now we can modify the original echo statement in doDisplay() method. First, we can drop the twig_escape_filter() function call, which is TWIG internal, unrelated to our template code.

// line 1
-echo twig_escape_filter(
-    $this->env,
-    twig_get_attribute(
+echo twig_get_attribute(
         $this->env,
         ($context["meal"] ?? null),
         "title",
         "any",
          false,
          false,
          false,
          1
-    ),
+    );
-    "html",
-    null,
-    true
-);


We now have just the twig_get_attribute() function call:

// line 1
echo twig_get_attribute(
    $this->env,
    ($context["meal"] ?? null),
    "title",
    "any",
    false,
    false,
    false,
    1
);


Drop the Boolean and Repeated Values

Let's take it further. What does twig_get_attribute() probably do?

Now, we could drop always-present arguments unrelated to our original TWIG template:

 // line 1
 echo twig_get_attribute(
-    $this->env,
     ($context["meal"] ?? null),
     "title",
-    "any",
-    false,
-    false,
-    false,
-    1
 );

Still, Keep it Simple

What do we already know about our new code snippet?

// line 1
echo twig_get_attribute(
    ($context["meal"] ?? null),
    "title",
);


Let's apply this knowledge:

 // line 1
 echo twig_get_attribute(
-    ($context["meal"] ?? null),
+    /** @var \App\Meal $meal */
+    $meal,
-    "title",
+    "getTitle",
 );



What do we know about this code snippet?

// line 1
echo twig_get_attribute(
    /** @var \App\Meal $meal */
    $meal,
    "getTitle",
);


 // line 1
-echo twig_get_attribute(
-    /** @var \App\Meal $meal */
-    $meal,
-    "getTitle",
- );
+/** @var \App\Meal $meal */
+echo $meal->getTitle();


Great! It's a method call we've been waiting for:

/** @var \App\Meal $meal */
echo $meal->getTitle();

Now PHPStan can check the file and tell us if the getTitle method exists on App\Meal or not.

PHPStan now knows that $meal->getTitle() returns a string, and can report type errors:

10 * {{ meal.title }}

PHP Line vs. TWIG Line

You've probably noticed we kept // line 1 comment in every snippet. What is it for?

Every proper PHPStan error has:


Here we analyze a PHP file that is much bigger than the original TWIG file. Our 1 line in TWIG template was compiled to ~80 lines of PHP.

So why is the // line 1 important? The metadata from the native TWIG compiler tells us that code under this comment belongs to line X in the TWIG template.

Smart PHP => TWIG Line Mapping

How can we use line mapping? Let's say we change the method name in our template:

-{{ meal.title }}
+{{ meal.name }}

PHPStan then reports non-existing getName() method error. Without mapping, it would report line that does not even exist:

Error in /templates/meal.twig file on line 54:

With mapping, we get correct TWIG line:

Error in /templates/meal.twig file on line 1:


To Sum Up

All right, we have removed clutter from the compiled PHP template file and used NodeVisitor from php-parser to convert magical TWIG functions to explicit PHP code.

We're now ready use PHPStan for analysis:

vendor/bin/phpstan analyze /temp/twig/__TwigTemplate_8a9d1381e8329967...php


Or is there a better way to run all PHPStan rules on a single file? 🤔

You'll find the answer in the next post.


Happy coding!


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