feature #4735 Add the = assignment operator (fabpot)

This PR was merged into the 3.x branch.

Discussion
----------

Add the = assignment operator

Commits
-------

bfbbef05f2 Add the = assignment operator

CHANGELOG

@@ -1,5 +1,6 @@
 # 3.23.0 (2026-XX-XX)
 
+ * Add `=` assignment operator (allows to set variables in expression or to replace the short-form of the set tag)
  * Add `?.` null-safe operator
  * Add `===` and `!==` operators (equivalent to the `same as` and `not same as` tests)
 

doc/operators_precedence.rst

@@ -96,6 +96,8 @@
 +------------+------------------+---------+---------------+-------------------------------------------------------------------+
 |            | ``?``            | infix   | Left          | Conditional operator (a ? b : c)                                  |
 +------------+------------------+---------+---------------+-------------------------------------------------------------------+
+|            | ``=``            |         | Right         | Assignment operator                                               |
++------------+------------------+---------+---------------+-------------------------------------------------------------------+
 
 When a precedence will change in 4.0, the new precedence is indicated by the arrow ``=>``.
 
@@ -198,3 +200,5 @@ Here is the same table for Twig 4.0 with adjusted precedences:
 +------------+------------------+---------+---------------+-------------------------------------------------------------------+
 |            | ``?``            | infix   | Left          | Conditional operator (a ? b : c)                                  |
 +------------+------------------+---------+---------------+-------------------------------------------------------------------+
+|            | ``=``            |         | Right         | Assignment operator                                               |
++------------+------------------+---------+---------------+-------------------------------------------------------------------+

doc/tags/set.rst

@@ -27,6 +27,16 @@ The assigned value can be any valid :ref:`Twig expression
     {% set user = {'name': 'Fabien'} %}
     {% set name = 'Fabien' ~ ' ' ~ 'Potencier' %}
 
+.. tip::
+
+    To assign a value within an expression, use the :ref:`= operator
+    <assignment-operator>`:
+
+    .. code-block:: twig
+
+        {# use assignment within a larger expression #}
+        {{ (result = fetch_data()) ? result : 'default' }}
+
 Several variables can be assigned in one block:
 
 .. code-block:: twig

doc/templates.rst

@@ -131,8 +131,8 @@ The following variables are always available in templates:
 Setting Variables
 ~~~~~~~~~~~~~~~~~
 
-You can assign values to variables inside code blocks. Assignments use the
-:doc:`set<tags/set>` tag:
+You can assign values to variables inside code blocks using either the
+:doc:`set<tags/set>` tag or the :ref:`= operator <assignment-operator>`:
 
 .. code-block:: twig
 
@@ -140,6 +140,31 @@ You can assign values to variables inside code blocks. Assignments use the
     {% set numbers = [1, 2] %}
     {% set map = {'city': 'Paris'} %}
 
+    {# or #}
+
+    {% do name = 'Fabien' %}
+    {% do numbers = [1, 2] %}
+    {% do map = {'city': 'Paris'} %}
+
+For simple assignments, both are equivalent. However, the ``set`` tag provides
+additional features:
+
+* **Multi-target assignment**: Assign multiple variables at once:
+
+  .. code-block:: twig
+
+      {% set first, last = 'Fabien', 'Potencier' %}
+
+* **Block capture**: Capture chunks of template content into a variable:
+
+  .. code-block:: html+twig
+
+      {% set content %}
+          <div id="pagination">...</div>
+      {% endset %}
+
+See the :doc:`set<tags/set>` tag documentation for more details.
+
 Filters
 -------
 
@@ -994,6 +1019,29 @@ The following operators don't fit into any of the other categories:
     Support for expanding the arguments of a function call was introduced in
     Twig 3.15.
 
+.. _assignment-operator:
+
+* ``=``: The assignment operator assigns a value to a variable within an
+  expression:
+
+  .. code-block:: twig
+
+      {# assign #}
+      {% do b = 1 + 3 %}
+
+      {# assign and output the result #}
+      {{ b = 1 + 3 }}
+
+      {# assignments can be chained #}
+      {% do a = b = 'foo' %}
+
+      {# assignment can be used inside other expressions #}
+      {% do a = (b = 4) + 5 %}
+
+  .. versionadded:: 3.23
+
+      The ``=`` assignment operator was added in Twig 3.23.
+
 * ``=>``: The arrow operator allows the creation of functions. A function is
   made of arguments (use parentheses for multiple arguments) and an arrow
   (``=>``) followed by an expression to execute. The expression has access to

src/ExpressionParser/Infix/ArgumentsTrait.php

@@ -13,6 +13,7 @@ namespace Twig\ExpressionParser\Infix;
 
 use Twig\Error\SyntaxError;
 use Twig\Node\Expression\ArrayExpression;
+use Twig\Node\Expression\Binary\SetBinary;
 use Twig\Node\Expression\Unary\SpreadUnary;
 use Twig\Node\Expression\Variable\ContextVariable;
 use Twig\Node\Expression\Variable\LocalVariable;
@@ -58,7 +59,10 @@ trait ArgumentsTrait
             }
 
             $name = null;
-            if (($token = $stream->nextIf(Token::OPERATOR_TYPE, '=')) || ($token = $stream->nextIf(Token::PUNCTUATION_TYPE, ':'))) {
+            if ($value instanceof SetBinary) {
+                $name = $value->getNode('left')->getAttribute('name');
+                $value = $value->getNode('right');
+            } elseif (($token = $stream->nextIf(Token::OPERATOR_TYPE, '=')) || ($token = $stream->nextIf(Token::PUNCTUATION_TYPE, ':'))) {
                 if (!$value instanceof ContextVariable) {
                     throw new SyntaxError(\sprintf('A parameter name must be a string, "%s" given.', $value::class), $token->getLine(), $stream->getSourceContext());
                 }

src/ExpressionParser/Infix/AssignmentExpressionParser.php

@@ -0,0 +1,55 @@
+<?php
+
+/*
+ * This file is part of Twig.
+ *
+ * (c) Fabien Potencier
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Twig\ExpressionParser\Infix;
+
+use Twig\Error\SyntaxError;
+use Twig\ExpressionParser\InfixAssociativity;
+use Twig\Node\Expression\AbstractExpression;
+use Twig\Node\Expression\Binary\AbstractBinary;
+use Twig\Node\Expression\Binary\SetBinary;
+use Twig\Node\Expression\Variable\ContextVariable;
+use Twig\Parser;
+use Twig\Token;
+
+/**
+ * @internal
+ */
+class AssignmentExpressionParser extends BinaryOperatorExpressionParser
+{
+    public function __construct(
+        string $name,
+    ) {
+        parent::__construct(SetBinary::class, $name, 0, InfixAssociativity::Right);
+    }
+
+    /**
+     * @return AbstractBinary
+     */
+    public function parse(Parser $parser, AbstractExpression $left, Token $token): AbstractExpression
+    {
+        if (!$left instanceof ContextVariable) {
+            throw new SyntaxError(\sprintf('Cannot assign to "%s", only variables can be assigned.', $left::class), $token->getLine(), $parser->getStream()->getSourceContext());
+        }
+        $right = $parser->parseExpression(InfixAssociativity::Left === $this->getAssociativity() ? $this->getPrecedence() + 1 : $this->getPrecedence());
+        $right = match ($this->getName()) {
+            '=' => $right,
+            default => throw new \LogicException(\sprintf('Unknown operator: %s.', $this->getName())),
+        };
+
+        return new SetBinary($left, $right, $token->getLine());
+    }
+
+    public function getDescription(): string
+    {
+        return 'Assignment operator';
+    }
+}

src/Extension/CoreExtension.php

@@ -17,6 +17,7 @@ use Twig\Error\LoaderError;
 use Twig\Error\RuntimeError;
 use Twig\Error\SyntaxError;
 use Twig\ExpressionParser\Infix\ArrowExpressionParser;
+use Twig\ExpressionParser\Infix\AssignmentExpressionParser;
 use Twig\ExpressionParser\Infix\BinaryOperatorExpressionParser;
 use Twig\ExpressionParser\Infix\ConditionalTernaryExpressionParser;
 use Twig\ExpressionParser\Infix\DotExpressionParser;
@@ -377,6 +378,9 @@ final class CoreExtension extends AbstractExtension
             // ternary operator
             new ConditionalTernaryExpressionParser(),
 
+            // assignment operator
+            new AssignmentExpressionParser('='),
+
             // Twig callables
             new IsExpressionParser(),
             new IsNotExpressionParser(),

src/Lexer.php

@@ -525,7 +525,7 @@ class Lexer
 
     private function getOperatorRegex(): string
     {
-        $expressionParsers = ['='];
+        $expressionParsers = [];
         foreach ($this->env->getExpressionParsers() as $expressionParser) {
             $expressionParsers = array_merge($expressionParsers, [$expressionParser->getName()], $expressionParser->getAliases());
         }

src/Node/Expression/Binary/SetBinary.php

@@ -0,0 +1,44 @@
+<?php
+
+/*
+ * This file is part of Twig.
+ *
+ * (c) Fabien Potencier
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Twig\Node\Expression\Binary;
+
+use Twig\Compiler;
+use Twig\Node\Expression\AbstractExpression;
+use Twig\Node\Expression\Variable\AssignContextVariable;
+use Twig\Node\Expression\Variable\ContextVariable;
+use Twig\Node\Node;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class SetBinary extends AbstractBinary
+{
+    /**
+     * @param ContextVariable    $left
+     * @param AbstractExpression $right
+     */
+    public function __construct(Node $left, Node $right, int $lineno)
+    {
+        $name = $left->getAttribute('name');
+        if (!\is_string($name)) {
+            throw new \LogicException('The "name" attribute must be a string.');
+        }
+        $left = new AssignContextVariable($name, $left->getTemplateLine());
+
+        parent::__construct($left, $right, $lineno);
+    }
+
+    public function operator(Compiler $compiler): Compiler
+    {
+        return $compiler->raw('=');
+    }
+}

tests/ExpressionParserTest.php

@@ -735,6 +735,13 @@ class ExpressionParserTest extends TestCase
 
         // ?? stronger than ()
         // yield '?? vs ()' => ['{{ (1 ?? "a") }}', '{{ ((1 ?? "a")) }}', eval("return 1;")];
+
+        // = stronger than anything else
+        yield '= same as literal' => ['{% do c = "a" %}{{ c }}', '{% do c = ("a") %}{{ c }}', eval("return 'a';")];
+        yield '= stronger than .' => ['{% do c = a.b %}{{ c }}', '{% do c = (a.b) %}{{ c }}', eval("\$a = ['b' => 1]; return \$a['b'];"), $context];
+        yield '= stronger than math' => ['{% do a = 1 + 3 %}{{ a }}', '{% do a = (1 + 3) %}{{ a }}', eval('$a = 1 + 3; return $a;')];
+        yield '= stronger than logical' => ['{% do a = false or true %}{{ a }}', '{% do a = (false or true) %}{{ a }}', eval('$a = false || true; return $a;')];
+        yield '= stronger than ternary' => ['{% do c = 4 ? 0 : -1 %}{{ c }}', '{% do c = (4 ? 0 : -1) %}{{ c }}', eval('return 4 ? 0 : -1;')];
     }
 }
 

tests/Fixtures/exceptions/syntax_error_in_reused_template.test

@@ -4,7 +4,7 @@ Exception for syntax error in reused template
 {% use 'foo.twig' %}
 --TEMPLATE(foo.twig)--
 {% block bar %}
-    {% do node.data = 5 %}
+    {% do node.data 5 %}
 {% endblock %}
 --EXCEPTION--
-Twig\Error\SyntaxError: Unexpected token "operator" of value "=" ("end of statement block" expected) in "foo.twig" at line 3.
+Twig\Error\SyntaxError: Unexpected token "number" of value "5" ("end of statement block" expected) in "foo.twig" at line 3.

tests/Fixtures/expressions/set.test

@@ -0,0 +1,20 @@
+--TEST--
+Twig supports the "=" operator (assignment)
+--TEMPLATE--
+{# stores #}
+{% do b = 1 + 3 %}{{ b }}
+{# stores and displays #}
+{{ b = 1 + 3 }}{{ b }}
+{# stores and returns #}
+{% do (c = 4) ? 0 : -1 %}{{ c }}
+{# = can be chained #}
+{% do c = d = "a" %}{{ c }}{{ d }}
+{% do a = (b = 4) + 5 %}{{ a }}{{ b }}
+--DATA--
+return []
+--EXPECT--
+4
+44
+4
+aa
+94