Support short-circuiting in null-safe operator chains

doc/templates.rst

@@ -894,7 +894,8 @@ The following operators don't fit into any of the other categories:
       {{ user.name }}
 
   The null-safe operator (``?.``) works like the dot operator but returns
-  ``null`` instead of throwing an exception when the left operand is ``null``:
+  ``null`` instead of throwing an exception when the left operand is ``null``.
+  If the operand is part of a chain, the rest of the chain is skipped:
 
   .. code-block:: twig
 
@@ -904,6 +905,9 @@ The following operators don't fit into any of the other categories:
       {{ user?.address?.city }}
       {# can be chained for safe navigation through potentially null values #}
 
+      {{ user?.address.city }}
+      {# returns null if user is null, the rest of the chain is skipped (address.city is not evaluated) #}
+
   .. versionadded:: 3.23
 
       The null-safe operator was added in Twig 3.23.

src/Node/Expression/GetAttrExpression.php

@@ -36,7 +36,7 @@ class GetAttrExpression extends AbstractExpression implements SupportDefinedTest
             trigger_deprecation('twig/twig', '3.15', \sprintf('Not passing a "%s" instance as the "arguments" argument of the "%s" constructor is deprecated ("%s" given).', ArrayExpression::class, static::class, $arguments::class));
         }
 
-        parent::__construct($nodes, ['type' => $type, 'ignore_strict_check' => false, 'optimizable' => !$nullSafe, 'null_safe' => $nullSafe], $lineno);
+        parent::__construct($nodes, ['type' => $type, 'ignore_strict_check' => false, 'optimizable' => !$nullSafe, 'null_safe' => $nullSafe, 'is_short_circuited' => false, 'var_name' => null], $lineno);
     }
 
     public function enableDefinedTest(): void
@@ -50,7 +50,6 @@ class GetAttrExpression extends AbstractExpression implements SupportDefinedTest
         $env = $compiler->getEnvironment();
         $arrayAccessSandbox = false;
         $nullSafe = $this->getAttribute('null_safe');
-        $objectVar = null;
 
         // optimize array calls
         if (
@@ -99,18 +98,32 @@ class GetAttrExpression extends AbstractExpression implements SupportDefinedTest
             $this->getNode('node')->setAttribute('ignore_strict_check', true);
         }
 
-        if ($nullSafe) {
-            $objectVar = '$'.$compiler->getVarName();
+        if (null === $nullSafeNode = $nullSafe ? $this : null) {
+            $node = $this->getNode('node');
+            while ($node instanceof self) {
+                if ($node->getAttribute('null_safe')) {
+                    $nullSafeNode = $node;
+                    break;
+                }
+                $node = $node->getNode('node');
+            }
+        }
+
+        $isShortCircuited = false;
+        if (null !== $nullSafeNode && !$nullSafeNode->isShortCircuited()) {
             $compiler
-                ->raw('((null === ('.$objectVar.' = ')
-                ->subcompile($this->getNode('node'))
+                ->raw('((null === ('.$nullSafeNode->getVarName($compiler).' = ')
+                ->subcompile($nullSafeNode->getNode('node'))
                 ->raw(')) ? null : ');
+
+            $nullSafeNode->markAsShortCircuited();
+            $isShortCircuited = true;
         }
 
         $compiler->raw('CoreExtension::getAttribute($this->env, $this->source, ');
 
         if ($nullSafe) {
-            $compiler->raw($objectVar);
+            $compiler->raw($this->getVarName($compiler));
         } else {
             $compiler->subcompile($this->getNode('node'));
         }
@@ -139,7 +152,7 @@ class GetAttrExpression extends AbstractExpression implements SupportDefinedTest
             $compiler->raw(')');
         }
 
-        if ($nullSafe) {
+        if ($isShortCircuited) {
             $compiler->raw(')');
         }
     }
@@ -153,4 +166,23 @@ class GetAttrExpression extends AbstractExpression implements SupportDefinedTest
             $this->changeIgnoreStrictCheck($node->getNode('node'));
         }
     }
+
+    private function markAsShortCircuited(): void
+    {
+        $this->setAttribute('is_short_circuited', true);
+    }
+
+    private function isShortCircuited(): bool
+    {
+        return $this->getAttribute('is_short_circuited');
+    }
+
+    private function getVarName(Compiler $compiler): string
+    {
+        if (null === $this->getAttribute('var_name')) {
+            $this->setAttribute('var_name', $compiler->getVarName());
+        }
+
+        return '$'.$this->getAttribute('var_name');
+    }
 }

tests/ExpressionParserTest.php

@@ -25,6 +25,7 @@ use Symfony\Bridge\PhpUnit\ExpectDeprecationTrait;
 use Twig\Attribute\FirstClassTwigCallableReady;
 use Twig\Compiler;
 use Twig\Environment;
+use Twig\Error\RuntimeError;
 use Twig\Error\SyntaxError;
 use Twig\ExpressionParser\Prefix\UnaryOperatorExpressionParser;
 use Twig\Extension\AbstractExtension;
@@ -350,6 +351,49 @@ class ExpressionParserTest extends TestCase
                 ['foo' => (object) ['bar' => false]],
                 '',
             ],
+            // short-circuiting
+            [
+                '{{ foo?.bar.baz }}',
+                ['foo' => null],
+                '',
+            ],
+            [
+                '{{ foo?.bar.baz?.qux.corge }}',
+                ['foo' => null],
+                '',
+            ],
+            [
+                '{{ foo?.bar.baz?.qux.corge }}',
+                ['foo' => (object) ['bar' => (object) ['baz' => null]]],
+                '',
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider getTestForInvalidNullSafeOperatorShortCircuiting
+     */
+    public function testInvalidNullSafeOperatorShortCircuiting(string $template, array $data, string $expectedMessage)
+    {
+        $env = new Environment(new ArrayLoader(['template' => $template]), ['strict_variables' => true]);
+
+        $this->expectException(RuntimeError::class);
+        $this->expectExceptionMessage($expectedMessage);
+
+        $env->render('template', $data);
+    }
+
+    public static function getTestForInvalidNullSafeOperatorShortCircuiting()
+    {
+        yield [
+            '{{ foo?.bar.baz }}',
+            ['foo' => (object) ['bar' => null]],
+            'Impossible to access an attribute ("baz") on a null variable in "template" at line 1.',
+        ];
+        yield [
+            '{{ foo?.bar.baz?.qux.corge }}',
+            ['foo' => (object) ['bar' => (object) ['baz' => (object) ['qux' => null]]]],
+            'Impossible to access an attribute ("corge") on a null variable in "template" at line 1.',
         ];
     }
 

tests/Node/Expression/GetAttrTest.php

@@ -51,6 +51,9 @@ class GetAttrTest extends NodeTestCase
 
         $expr = new ContextVariable('foo', 1);
         $attr = new ConstantExpression('bar', 1);
+        $attr2 = new ConstantExpression('baz', 1);
+        $attr3 = new ConstantExpression('qux', 1);
+        $attr4 = new ConstantExpression('corge', 1);
         $args = new ArrayExpression([], 1);
 
         $node = new GetAttrExpression($expr, $attr, $args, Template::ANY_CALL, 1);
@@ -59,6 +62,16 @@ class GetAttrTest extends NodeTestCase
         $node = new GetAttrExpression($expr, $attr, $args, Template::ANY_CALL, 1, true);
         $tests[] = [$node, '((null === ($_v%s = // line 1'."\n".'($context["foo"] ?? null))) ? null : '.self::createAttributeGetter().'$_v%s, "bar", [], "any", false, false, false, 1))', null, true];
 
+        $node = new GetAttrExpression($expr, $attr, $args, Template::ANY_CALL, 1, true);
+        $node = new GetAttrExpression($node, $attr2, $args, Template::METHOD_CALL, 1);
+        $tests[] = [$node, '((null === ($_v%s = // line 1'."\n".'($context["foo"] ?? null))) ? null : '.self::createAttributeGetter().self::createAttributeGetter().'$_v%s, "bar", [], "any", false, false, false, 1), "baz", [], "method", false, false, false, 1))', null, true];
+
+        $node = new GetAttrExpression($expr, $attr, $args, Template::ANY_CALL, 1, true);
+        $node = new GetAttrExpression($node, $attr2, $args, Template::ANY_CALL, 1);
+        $node = new GetAttrExpression($node, $attr3, $args, Template::METHOD_CALL, 1, true);
+        $node = new GetAttrExpression($node, $attr4, $args, Template::ANY_CALL, 1);
+        $tests[] = [$node, '((null === ($_v0 = ((null === ($_v1 = // line 1'."\n".'($context["foo"] ?? null))) ? null : '.self::createAttributeGetter().self::createAttributeGetter().'$_v1, "bar", [], "any", false, false, false, 1), "baz", [], "any", false, false, false, 1)))) ? null : '.self::createAttributeGetter().self::createAttributeGetter().'$_v0, "qux", [], "method", false, false, false, 1), "corge", [], "any", false, false, false, 1))', null];
+
         $node = new GetAttrExpression($expr, $attr, $args, Template::ARRAY_CALL, 1);
         $tests[] = [$node, '(($_v%s = // line 1'."\n".
             '($context["foo"] ?? null)) && is_array($_v%s) || $_v%s instanceof ArrayAccess ? ($_v%s["bar"] ?? null) : null)', null, true, ];