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TwigStan is a static analyzer for Twig templates powered by PHPStan.

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This is very experimental

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This project requires a significant amount of my time and effort to develop. If you find it valuable, please consider sponsoring me to support its continued growth and give it a star! ⭐️ Your support is truly appreciated! 🙏

Introduction

TwigStan uses Twig to compile templates to PHP code. It then optimizes the compiled PHP code slightly, allowing PHPStan to analyze it better. It then reports any errors back to the original template and line number.

The process consists of the following steps:

Template Context Collecting

We use PHPStan to search the PHP codebase for places where a Twig template is rendered. We collect the context that is passed to the template.

Compilation

The TwigCompiler loads the template and converts it into a Twig AST (Abstract Syntax Tree). The AST is optimized by running several Twig NodeVisitors. The AST is then compiled into PHP using Twig's default compiler. The compiled PHP code is loaded and converted into a PHP AST. We inject the previously collected template context as PHPDocs into the template. On the PHP AST, we run various PHP NodeVisitors. The goal is no longer to render the template but to analyze it. This means we can remove elements that are not relevant to us. The PHP AST is then dumped back into PHP code and saved to disk as a compilation result.

In the next steps, we will use these PHP files.

Flattening

The next step is to flatten the Twig templates. Templates can extend other templates. The child template can choose to override blocks or not, and the parent template can also extend another template. Variables set in a parent template should be available in the child template.

The TwigFlattener processes all the compilation results. It reads the Twig metadata to identify the parent(s) and defined blocks. It takes the logic in the parent template (set variables, etc.) from the doDisplay method and copies it into the child template's doDisplay block.

The same is done for the block hierarchy. It understands which blocks are overridden. The child template will eventually have all blocks defined.

While flattening, the original filename and line numbers are preserved. This is important because later on, we want to trace errors back to their original location.

After the flattening process is finished, the PHP AST is again dumped to disk as a flattening result.

Block Context Collecting

Now that we have a flat template, we can analyze the context for every block.

We use PHPStan to run the BlockContextCollector. This collector gathers the context before rendering every block or parent block call.

Scope Injection

Now that we know the context before every block call in the template, we can inject this knowledge as PHPDocs into the flattened template.

Analysis

Every template is now flattened and has defined context types.

We ask PHPStan to run the analysis on these files.

While this analysis is running, we also collect {% include %} usage in the templates. Since we know the context at this point, we collect it.

If we found included templates, we will repeat the full analysis process for these templates. This means that we go back to the Compilation step.

The AnalysisResultFromJsonReader processes the results from PHPStan.

For every error in the flattened PHP code, it tries to find the original Twig file and line number. It filters out a few errors that are false positives. It also collapses errors that are already reported higher in the hierarchy. When an error is reported in a parent template, it should only be reported once, instead of every time it's flattened in a child template.

Installation

composer require --dev twigstan/twigstan:dev-main

Then run TwigStan and it will explain what to do next:

vendor/bin/twigstan

Usage

Make sure that you configure your phpPaths to point to the PHP codebase that renders the Twig templates.

This will make sure that TwigStan can collect the template context from the PHP codebase.

Use the dump_type tag to debug if types are properly resolved.

Marking templates abstract

When you have a template that is not rendered directly, but is used as a parent template, you can mark it as abstract.

The benfit of this is that it will not be analyzed as a standalone template, but only as part of the template hierarchy.

You can mark a template as abstract by adding a comment at the top of the file:

{# @twigstan-abstract #}

When you try to render an abstract template, TwigStan will report an error.

Debugging

You can dump the type of a variable by using:

{% dump_type variableName %}

If you want to dump the types for the whole context (everything that's available), you can do:

{% dump_type %}

Adding type hints

TwigStan supports the new {% types %} tag that was introduced in Twig 3.13.

If your types are not automatially resolved from where they are rendered, you manually type each and every variable like this:

{% types { variableName: 'type' } %}

Note

Keep in mind that TwigStan tries to resolve all these types automatically by collecting the context from the PHP codebase. Don't blindly start adding {% types %} tags. First investigate if TwigStan can resolve the types automatically.

The type can be a valid PHPDoc expression. For example:

{% types { name: 'string|null' } %}

Next to using multiple {% types %} tags, you can also define multiple types in a single line:

{% types {
    name: 'string',
    users: 'array<int, App\\User>',
} %}

If you want to indicate that a variable is optional, you can do it as follows:

{% types {
    isEnabled?: 'bool',
} %}

Note

Starting from Twig version 4 you no longer have to escape backslashes in fully qualified class names.

They use TwigStan

Credits & Inspiration

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TwigStan is a static analyzer for Twig templates powered by PHPStan

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