How to Upgrade Latte 2 Macro to Latte 3 Tag

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Latte 3 running on abstract syntax tree was released this week. Do you want to upgrade? First, check 5 steps to get ready.

Do you have any custom macros in your project? They're the biggest challenge of the Latte 3 upgrade. But don't worry, today we'll rewrite them together.

For Early Adopters

Note: this is an early way to upgrade macro to Latte 3 based on trial/error, and it might improve based on to-be-released documentation. Suppose you get stuck with your macro, ask in the dedicated topic on Nette Forum.


Latte macro is a Latte "shortcut" that unwraps to compiled PHP code of the cached template, and it is compiled once, re-used, and improves the performance. In Latte 3, they're called tags.

That's enough for theory. Now we check upgrade of actual code in Amateri.


A macro that inlines SVG files right to HTML code. From macro in Latte file...

{embeddedSvg "circle.svg"}
{embeddedSvg "circle.svg", "class" => "blue"}


...to compiled template PHP code:

echo '<svg width="10" height="10"><circle cx="4.5" cy="4.5" r="3.5"/></svg>';
echo '<svg width="10" height="10" class="blue"><circle cx="4.5" cy="4.5" r="3.5"/></svg>';

Before We Start...

We can upgrade the first macro to Latte 3 today, but in the case of 2nd, 3rd... or external dependency, it might take some time. We could stay in a traffic jam between both versions for a few weeks.


To support both Latte 2 macros and Latte 3 tags, use following trick:

if (version_compare(Latte\Engine::VERSION, '3', '<')) {
    // Latte 2
    $this->latte->onCompile[] = function { ... };
} else {
    // Latte 3
    $this->latte->addExtension(...);
}

1. From DI extension ot Latte Extension

Huh, what is this addExtension() method? Latte 3 uses its own extensions. No, it is not a usual aCompilerExtension as we know it.

What does it look like for our embeddedSvg macro, then?

namespace App\Latte;

use Latte\Extension;

final class EmbeddedSvgLatteExtension extends Extension
{
    // here we pass the configuration from config
    public function __construct(
        private string $baseDir
    ) {
    }
}


Then we replace the DI extension with the Latte extension in config.neon:

-extensions:
-    embeddedSvg: App\Latte\DI\EmbeddedSvgExtension
-
-embeddedSvg:
-    baseDir: %wwwDir%/images

+latte:
+    extensions:
+        - App\Latte\EmbeddedSvgLatteExtension(baseDir: %wwwDir%/images)


We've just added Latte 3 extension that loads itself and does nothing. Time to add the first node!

2. From Macro to an AST Node

Abstract syntax tree landed in Latte Three. What does it mean for macros? The macro set is gone, and we'll create our own node class instead. Let's call it EmbeddedSvgNode.

First, we register it in our newly created Latte extension in the getTags() method:

namespace App\Latte;

use Latte\Extension;
use Latte\Compiler\Tag;
use App\Latte\Node\EmbeddedSvgNode;

final class EmbeddedSvgLatteExtension extends Extension
{
    public function __construct(
        private string $baseDir
    ) {
    }

    public function getTags(): array
    {
        return [
            'embeddedSvg' => function (Tag $tag): EmbeddedSvgNode {
                return new EmbeddedSvgNode($tag, $this->baseDir);
            },
        ];
    }
}

How should we read this? Everytime we call {embeddedSvg ...} in Latte, the new EmbeddedSvgNode($tag, $this->baseDir) will be created on that place.

We can pass any arguments into its constructor. In our case:


3. From Macro::open() to the AST Node

In the old Latte 2 macro, we used an open() method that handles both input parsing and node printing:

use Latte\MacroNode;
use Latte\Macros\MacroSet;
use Latte\PhpWriter;

final class EmbeddedSvgMacro extends MacroSet
{
    // ...

    public function open(MacroNode $node, PhpWriter $writer): string
    {
        // here we get string of first argument, the file path
        $file = $node->tokenizer->fetchWord();
        if ($file === null) {
            throw new CompileException('Missing SVG file path.');
        }

        // don't forget to clean the quotes
        $svgFilepath = $this->baseDir . DIRECTORY_SEPARATOR . trim($file, '\'"');

        // get optional arguments
        $macroAttributes = $writer->formatArray();

        // print bellow
        // ...
    }

The EmbeddedSvgNode class splits these jobs into 2 separate methods:


How do we write input parsing of the macro above in the Latte 3 node?

use Latte\Compiler\Nodes\AreaNode;
use Latte\Compiler\Nodes\Php\Expression\ArrayNode;

// we chose AreaNode for parent, suitable for HTML nodes like <svg>
final class EmbeddedSvgNode extends AreaNode
{
    private ArrayNode $arguments;

    private string $svgFilepath;

    public function __construct(Tag $tag, string $baseDir)
    {
        // parse first argument
        $stringNode = $tag->parser->parseUnquotedStringOrExpression();
        if (! $stringNode instanceof StringNode) {
            // we need string node
            throw new InvalidArgumentException('File must be string value');
        }

        // fullpath to directory
        $this->svgFilepath = $baseDir . DIRECTORY_SEPARATOR . $stringNode->value;

        // parse optional arguments, after ","
        $tag->parser->stream->tryConsume(',');
        $this->arguments = $tag->parser->parseArguments();
    }
}


What has Changed in the Input?

Beautiful object API with IDE autocomplete and static validation!


Back to our macro node. Now we have 2 essential pieces ready:


The last step is to print them to compiled PHP code.


4. From $writer->write(...) To $node->print(...)

For the printing, we re-use the original macro. What should we print?

use Latte\MacroNode;
use Latte\Macros\MacroSet;
use Latte\PhpWriter;

final class EmbeddedSvgMacro extends MacroSet
{
    // ...

    public function open(MacroNode $node, PhpWriter $writer): string
    {
        // ...

        // contains ['width' => '10', 'height' => '10']
        $svgAttributes = $this->resolveSvgAttributes($svgFilepath);

        // contains <circle cx="4.5" cy="4.5" r="3.5"/>
        $innerSvgContent = $this->resolveSvgString($svgFilepath);

        return $writer->write('
            echo "<svg";
            foreach (%0.var + %1.raw as $key => $value) {
                echo " " . %escape($key) . "=\"" . %escape($value) . "\"";
         };
         echo ">" . %2.var . "</svg>";
         ',
            $svgAttributes,
            $macroAttributes,
            $innerSvgContent
        );
    }
}


It seems we have to:


How do we include it in EmbeddedSvgNode::print() method?

use Latte\Compiler\Nodes\AreaNode;
use Latte\Compiler\Nodes\TextNode;
use Latte\Compiler\PrintContext;

final class EmbeddedSvgNode extends AreaNode
{
    // ...

    public function print(PrintContext $context): string
    {
        // contains ['width' => '10', 'height' => '10']
        $svgAttributes = $this->resolveSvgAttributes($svgFilepath);

        // contains <circle cx="4.5" cy="4.5" r="3.5"/>
        $innerSvgContent = $this->resolveSvgString($svgFilepath);

        return $context->format(
            <<<'PHP_CONTENT'
echo '<svg';

foreach (%dump + %node as $key => $value) {
    echo ' ' . %escape($key) . "='" . %escape($value) . "'";
}

%node
echo '</svg>';
PHP_CONTENT,
            $svgAttributes,
            $this->arguments,
            new TextNode($innerSvgContent)
        );
    }


Tip: open this post in the 2nd tab and compare the old Latte 2 macro on the left side and the new Latte 3 node on the right side.


What has Changed in Printing?

-* foreach SVG attributes, in bare `array` format via `%0.var%` mask


-* + macro defined arguments in `string` format via `%1.raw` mask


-* print inner SVG `string` via `%2.var`


Proof over promise? Find an open-source version of this upgrade in this pull-request, including tests and detailed parsing SVG via XML.


Happy coding!


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