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Fabien Potencier
415f4cc3ee
This PR was merged into the 3.x branch.
Discussion
----------
Compile Elvis operator into Elvis operator `?:`
When using ternary operator without "then" part, the "condition" part is evaluated twice, which is inconsistent with how PHP works.
The Twig template `A ?: B` is currently compiled as `A ? A : B` in PHP. This PR change it to `A ?: B`.
If `A` is a complex expression, it improves performance to only execute the expression once.
If `A` is has a side effect (like updating a variable), the expression being executed twice could result in a bug. ([example in PHP](https://3v4l.org/LWZLR))
Example with ``@WebProfiler`/Collector/form.html.twig` [line 9](https://github.com/symfony/symfony/blob/e6d1ed4edb5ae197ec7d25ddaf64cfa456229504/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/form.html.twig#L9) (see deep [diff](https://www.diffchecker.com/jOm3dE13/))
```twig
{{ collector.data.nb_errors ?: collector.data.forms|length }}
```
Previous compilation:
```php
echo twig_escape_filter($this->env, (((isset($context["error_count"]) || array_key_exists("error_count", $context) ? $context["error_count"] : (function () { throw new RuntimeError('Variable "error_count" does not exist.', 9, $this->source); })())) ? ((isset($context["error_count"]) || array_key_exists("error_count", $context) ? $context["error_count"] : (function () { throw new RuntimeError('Variable "error_count" does not exist.', 9, $this->source); })())) : (twig_get_attribute($this->env, $this->source, (isset($context["collector"]) || array_key_exists("collector", $context) ? $context["collector"] : (function () { throw new RuntimeError('Variable "collector" does not exist.', 9, $this->source); })()), "countDefines", [], "any", false, false, false, 9))), "html", null, true);
```
After this change:
```php
echo twig_escape_filter($this->env, ((isset($context["error_count"]) || array_key_exists("error_count", $context) ? $context["error_count"] : (function () { throw new RuntimeError('Variable "error_count" does not exist.', 9, $this->source); })()) ?: twig_get_attribute($this->env, $this->source, (isset($context["collector"]) || array_key_exists("collector", $context) ? $context["collector"] : (function () { throw new RuntimeError('Variable "collector" does not exist.', 9, $this->source); })()), "countDefines", [], "any", false, false, false, 9)), "html", null, true);
```
Commits
-------
fb0d7495 Compile Elvis operator with Elvis operator
Twig, the flexible, fast, and secure template language for PHP
==============================================================
Twig is a template language for PHP.
Twig uses a syntax similar to the Django and Jinja template languages which
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