feature #28231 [VarExporter] a new component to serialize values to p…

…lain PHP code (nicolas-grekas)

This PR was merged into the 4.2-dev branch.

Discussion
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[VarExporter] a new component to serialize values to plain PHP code

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This PR proposes moving what is currently the `PhpMarshaller` class in the Cache component to a separate component.

This component would provide only one public static method:
`VarExporter::export($value, bool &$isStaticValue = null): string`.

This method returns `$value` serialized as plain PHP code. Running this code creates the same exact data structure that `$value` contained. This is exactly like `serialize()` and `unserialize()`, from which all semantics are preserved (`__sleep`, `__wakeup` and `Serializable`).

The reason to use this method *vs* `serialize()` or even igbinary is performance: thanks to OPcache, the resulting code is significantly faster and more memory efficient than using `unserialize()` or `igbinary_unserialize()`.

Unlike `var_export()`, this works on any serializable PHP value.

It also provides a few improvements over `var_export()`/`serialize()`:
- the output is PSR-2 compatible
- the output can be re-indented without messing up with any `\r` or `\n` in the data
- missing classes throw a `ReflectionException` instead of being unserialized to a `PHP_Incomplete_Class` object
- references involving `SplObjectStorage`, `ArrayObject` or `ArrayIterator` instances are preserved
- `Reflection*`, `IteratorIterator` and `RecursiveIteratorIterator` classes throw an exception when being serialized (their unserialized version is broken anyway, see  https://bugs.php.net/76737.)

Commits
-------

7831ad7 [VarExporter] a new component to serialize values to plain PHP code

.php_cs.dist

@@ -24,7 +24,6 @@ return PhpCsFixer\Config::create()
             ->exclude(array(
                 'Symfony/Bridge/ProxyManager/Tests/LazyProxy/PhpDumper/Fixtures',
                 // directories containing files with content that is autogenerated by `var_export`, which breaks CS in output code
-                'Symfony/Component/Cache/Tests/Marshaller/Fixtures',
                 'Symfony/Component/DependencyInjection/Tests/Fixtures',
                 'Symfony/Component/Routing/Tests/Fixtures/dumper',
                 // fixture templates
@@ -33,6 +32,7 @@ return PhpCsFixer\Config::create()
                 'Symfony/Bundle/FrameworkBundle/Tests/Templating/Helper/Resources/Custom',
                 // generated fixtures
                 'Symfony/Component/VarDumper/Tests/Fixtures',
+                'Symfony/Component/VarExporter/Tests/Fixtures',
                 // resource templates
                 'Symfony/Bundle/FrameworkBundle/Resources/views/Form',
                 // explicit trigger_error tests

composer.json

@@ -81,6 +81,7 @@
         "symfony/twig-bundle": "self.version",
         "symfony/validator": "self.version",
         "symfony/var-dumper": "self.version",
+        "symfony/var-exporter": "self.version",
         "symfony/web-link": "self.version",
         "symfony/web-profiler-bundle": "self.version",
         "symfony/web-server-bundle": "self.version",