Add support for recursive loops

CHANGELOG

@@ -1,5 +1,6 @@
 # 4.0.0 (2024-XX-XX)
 
+ * Add support for recursive loops (via `loop.recurse()`)
  * Add `loop.changed`, `loop.previous`, `loop.next`, and `loop.cycle` variables
  * Make `loop.last` always available (even for non-countable iterators)
  * Change the compilation of `for` loops to throw an exception when a `loop.*` variable is not defined

doc/tags/for.rst

@@ -110,6 +110,24 @@ replacement block by using ``else``:
         {% endfor %}
     </ul>
 
+Recursive Loops
+---------------
+
+To use loops recursively, pass the iterable you want to recurse to the
+``loop()`` function; the following example shows how to use it for a recursive
+sitemap:
+
+.. code-block:: html+twig
+
+    <ul class="sitemap">
+    {%- for item in sitemap %}
+        <li>{{ item.title }}
+        {%- if item.children -%}
+            <ul class="submenu">{{ loop(item.children) }}</ul>
+        {%- endif %}</li>
+    {%- endfor %}
+    </ul>
+
 The ``loop`` Object
 -------------------
 
@@ -132,6 +150,8 @@ Variable              Description
 ``loop.parent``       The parent context
 ``loop.previous``     The value from the previous iteration (``null`` for the first iteration)
 ``loop.next``         The value from the next iteration (``null`` for the last iteration)
+``loop.depth``        Deep level of a recursive loop (1 indexed)
+``loop.depth0``       Deep level of a recursive loop (0 indexed)
 ===================== ========================================================================
 
 .. note::
@@ -175,6 +195,7 @@ Function              Description
 ===================== ========================================================================
 ``loop.cycle()``      Cycle over a sequence of values
 ``loop.changed()``    True if previously called with a different value or if not called yet
+``loop()``            Allows to iterate over a nested sequence/mapping
 ===================== ========================================================================
 
 Use ``loop.cycle()`` to cycle among a list of values:

src/Extension/CoreExtension.php

@@ -56,6 +56,7 @@ use Twig\Node\Expression\Test\SameasTest;
 use Twig\Node\Expression\Unary\NegUnary;
 use Twig\Node\Expression\Unary\NotUnary;
 use Twig\Node\Expression\Unary\PosUnary;
+use Twig\NodeVisitor\ForNodeVisitor;
 use Twig\NodeVisitor\MacroAutoImportNodeVisitor;
 use Twig\Source;
 use Twig\Template;
@@ -268,7 +269,10 @@ final class CoreExtension extends AbstractExtension
 
     public function getNodeVisitors(): array
     {
-        return [new MacroAutoImportNodeVisitor()];
+        return [
+            new MacroAutoImportNodeVisitor(),
+            new ForNodeVisitor(),
+        ];
     }
 
     public function getOperators(): array

src/Node/ForNode.php

@@ -38,17 +38,21 @@ class ForNode extends Node
     public function compile(Compiler $compiler): void
     {
         $iteratorVar = $compiler->getVarName();
+        $functionVar = $compiler->getVarName();
 
         $compiler
             ->addDebugInfo($this)
-            ->write("\$context['_parent'] = \$context;\n")
             ->write("\$$iteratorVar = new \Twig\Runtime\LoopIterator(")
             ->subcompile($this->getNode('seq'))
             ->raw(");\n")
+            ->write("\$$functionVar = function (\$$iteratorVar, &\$context, \$blocks, &\$$functionVar, \$depth) {\n")
+            ->indent()
+            ->write("\$macros = \$this->macros;\n")
+            ->write("\$context['_parent'] = \$context;\n")
         ;
 
         if ($this->getAttribute('with_loop')) {
-            $compiler->write("\$context['loop'] = new \Twig\Runtime\LoopContext(\$$iteratorVar, \$context['_parent']);\n");
+            $compiler->write("\$context['loop'] = new \Twig\Runtime\LoopContext(\$$iteratorVar, \$context['_parent'], \$blocks, \$$functionVar, \$depth);\n");
         }
 
         $compiler
@@ -80,5 +84,13 @@ class ForNode extends Node
 
         // keep the values set in the inner context for variables defined in the outer context
         $compiler->write("\$context = array_intersect_key(\$context, \$_parent) + \$_parent;\n");
+
+        $compiler
+            ->write("return; yield;\n")
+            ->outdent()
+            ->write("};\n")
+            ->write("\Closure::bind(\$$functionVar, \$this, self::class);\n")
+            ->write("yield from \$$functionVar(\$$iteratorVar, \$context, \$blocks, \$$functionVar, 0);\n")
+        ;
     }
 }

src/NodeVisitor/ForNodeVisitor.php

@@ -0,0 +1,74 @@
+<?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\NodeVisitor;
+
+use Twig\Environment;
+use Twig\Node\Expression\ConstantExpression;
+use Twig\Node\Expression\GetAttrExpression;
+use Twig\Node\Expression\NameExpression;
+use Twig\Node\ForNode;
+use Twig\Node\Node;
+use Twig\Node\PrintNode;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ *
+ * @internal
+ */
+final class ForNodeVisitor implements NodeVisitorInterface
+{
+    private int $loops = 0;
+
+    public function enterNode(Node $node, Environment $env): Node
+    {
+        if ($node instanceof ForNode) {
+            ++$this->loops;
+
+            return $node;
+        } elseif (!$this->loops) {
+            // we are outside a loop
+            return $node;
+        }
+
+        if (!$node instanceof PrintNode) {
+            return $node;
+        }
+
+        // We look for exactly {{ loop.recurse(...) }}
+        $exprNode = $node->getNode('expr');
+        if (
+            $exprNode instanceof GetAttrExpression
+            && $exprNode->getNode('node') instanceof NameExpression
+            && 'loop' === $exprNode->getNode('node')->getAttribute('name')
+            && $exprNode->getNode('attribute') instanceof ConstantExpression
+            && 'recurse' === $exprNode->getNode('attribute')->getAttribute('value')
+        ) {
+            $exprNode->setAttribute('is_generator', true);
+        }
+
+        return $node;
+    }
+
+    public function leaveNode(Node $node, Environment $env): ?Node
+    {
+        if ($node instanceof ForNode) {
+            --$this->loops;
+        }
+
+        return $node;
+    }
+
+    public function getPriority(): int
+    {
+        return 0;
+    }
+}

src/Runtime/LoopContext.php

@@ -25,6 +25,9 @@ final class LoopContext
     public function __construct(
         private LoopIterator $loop,
         private $parent,
+        private $blocks,
+        private $recurseFunc,
+        private $depth,
     ) {
     }
 
@@ -99,4 +102,19 @@ final class LoopContext
 
         return $values[$this->getIndex0() % count($values)];
     }
+
+    public function recurse($iterator): \Generator
+    {
+        yield from ($this->recurseFunc)(new LoopIterator($iterator), $this->parent, $this->blocks, $this->recurseFunc, $this->depth + 1);
+    }
+
+    public function getDepth0(): int
+    {
+        return $this->depth;
+    }
+
+    public function getDepth(): int
+    {
+        return $this->depth + 1;
+    }
 }

tests/Fixtures/functions/include/with_context.test

@@ -10,7 +10,7 @@
 --DATA--
 return ['foo' => 'bar']
 --EXPECT--
-foo,global,_parent,
+foo,global,
-global,_parent,
+global,
-foo,global,foo1,_parent,
+foo,global,foo1,
-foo1,global,_parent,
+foo1,global,

tests/Fixtures/tags/include/only.test

@@ -12,9 +12,9 @@
 --DATA--
 return ['vars1' => ['foo1' => 'bar'], 'vars2' => new ArrayObject(['foo2' => 'bar'])]
 --EXPECT--
-vars1,vars2,global,_parent,
+vars1,vars2,global,
-global,_parent,
+global,
-vars1,vars2,global,foo1,_parent,
+vars1,vars2,global,foo1,
-foo1,global,_parent,
+foo1,global,
-vars1,vars2,global,foo2,_parent,
+vars1,vars2,global,foo2,
-foo2,global,_parent,
+foo2,global,

tests/Node/ForTest.php

@@ -56,14 +56,20 @@ class ForTest extends NodeTestCase
 
         $tests[] = [$node, <<<EOF
 // line 1
-\$context['_parent'] = \$context;
 \$__internal_compile_0 = new \Twig\Runtime\LoopIterator({$this->getVariableGetter('items')});
-foreach (\$__internal_compile_0 as \$context["key"] => \$context["item"]) {
+\$__internal_compile_1 = function (\$__internal_compile_0, &\$context, \$blocks, &\$__internal_compile_1, \$depth) {
-    yield {$this->getVariableGetter('foo')};
+    \$macros = \$this->macros;
-}
+    \$context['_parent'] = \$context;
-\$_parent = \$context['_parent'];
+    foreach (\$__internal_compile_0 as \$context["key"] => \$context["item"]) {
-unset(\$context['key'], \$context['item'], \$context['_parent'], \$context['loop']);
+        yield {$this->getVariableGetter('foo')};
-\$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    }
+    \$_parent = \$context['_parent'];
+    unset(\$context['key'], \$context['item'], \$context['_parent'], \$context['loop']);
+    \$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    return; yield;
+};
+\Closure::bind(\$__internal_compile_1, \$this, self::class);
+yield from \$__internal_compile_1(\$__internal_compile_0, \$context, \$blocks, \$__internal_compile_1, 0);
 EOF
         ];
 
@@ -77,15 +83,21 @@ EOF
 
         $tests[] = [$node, <<<EOF
 // line 1
-\$context['_parent'] = \$context;
 \$__internal_compile_0 = new \Twig\Runtime\LoopIterator({$this->getVariableGetter('values')});
-\$context['loop'] = new \Twig\Runtime\LoopContext(\$__internal_compile_0, \$context['_parent']);
+\$__internal_compile_1 = function (\$__internal_compile_0, &\$context, \$blocks, &\$__internal_compile_1, \$depth) {
-foreach (\$__internal_compile_0 as \$context["k"] => \$context["v"]) {
+    \$macros = \$this->macros;
-    yield {$this->getVariableGetter('foo')};
+    \$context['_parent'] = \$context;
-}
+    \$context['loop'] = new \Twig\Runtime\LoopContext(\$__internal_compile_0, \$context['_parent'], \$blocks, \$__internal_compile_1, \$depth);
-\$_parent = \$context['_parent'];
+    foreach (\$__internal_compile_0 as \$context["k"] => \$context["v"]) {
-unset(\$context['k'], \$context['v'], \$context['_parent'], \$context['loop']);
+        yield {$this->getVariableGetter('foo')};
-\$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    }
+    \$_parent = \$context['_parent'];
+    unset(\$context['k'], \$context['v'], \$context['_parent'], \$context['loop']);
+    \$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    return; yield;
+};
+\Closure::bind(\$__internal_compile_1, \$this, self::class);
+yield from \$__internal_compile_1(\$__internal_compile_0, \$context, \$blocks, \$__internal_compile_1, 0);
 EOF
         ];
 
@@ -99,15 +111,21 @@ EOF
 
         $tests[] = [$node, <<<EOF
 // line 1
-\$context['_parent'] = \$context;
 \$__internal_compile_0 = new \Twig\Runtime\LoopIterator({$this->getVariableGetter('values')});
-\$context['loop'] = new \Twig\Runtime\LoopContext(\$__internal_compile_0, \$context['_parent']);
+\$__internal_compile_1 = function (\$__internal_compile_0, &\$context, \$blocks, &\$__internal_compile_1, \$depth) {
-foreach (\$__internal_compile_0 as \$context["k"] => \$context["v"]) {
+    \$macros = \$this->macros;
-    yield {$this->getVariableGetter('foo')};
+    \$context['_parent'] = \$context;
-}
+    \$context['loop'] = new \Twig\Runtime\LoopContext(\$__internal_compile_0, \$context['_parent'], \$blocks, \$__internal_compile_1, \$depth);
-\$_parent = \$context['_parent'];
+    foreach (\$__internal_compile_0 as \$context["k"] => \$context["v"]) {
-unset(\$context['k'], \$context['v'], \$context['_parent'], \$context['loop']);
+        yield {$this->getVariableGetter('foo')};
-\$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    }
+    \$_parent = \$context['_parent'];
+    unset(\$context['k'], \$context['v'], \$context['_parent'], \$context['loop']);
+    \$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    return; yield;
+};
+\Closure::bind(\$__internal_compile_1, \$this, self::class);
+yield from \$__internal_compile_1(\$__internal_compile_0, \$context, \$blocks, \$__internal_compile_1, 0);
 EOF
         ];
 
@@ -121,18 +139,24 @@ EOF
 
         $tests[] = [$node, <<<EOF
 // line 1
-\$context['_parent'] = \$context;
 \$__internal_compile_0 = new \Twig\Runtime\LoopIterator({$this->getVariableGetter('values')});
-\$context['loop'] = new \Twig\Runtime\LoopContext(\$__internal_compile_0, \$context['_parent']);
+\$__internal_compile_1 = function (\$__internal_compile_0, &\$context, \$blocks, &\$__internal_compile_1, \$depth) {
-foreach (\$__internal_compile_0 as \$context["k"] => \$context["v"]) {
+    \$macros = \$this->macros;
-    yield {$this->getVariableGetter('foo')};
+    \$context['_parent'] = \$context;
-}
+    \$context['loop'] = new \Twig\Runtime\LoopContext(\$__internal_compile_0, \$context['_parent'], \$blocks, \$__internal_compile_1, \$depth);
-if (0 === \$__internal_compile_0->getIndex0()) {
+    foreach (\$__internal_compile_0 as \$context["k"] => \$context["v"]) {
-    yield {$this->getVariableGetter('foo')};
+        yield {$this->getVariableGetter('foo')};
-}
+    }
-\$_parent = \$context['_parent'];
+    if (0 === \$__internal_compile_0->getIndex0()) {
-unset(\$context['k'], \$context['v'], \$context['_parent'], \$context['loop']);
+        yield {$this->getVariableGetter('foo')};
-\$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    }
+    \$_parent = \$context['_parent'];
+    unset(\$context['k'], \$context['v'], \$context['_parent'], \$context['loop']);
+    \$context = array_intersect_key(\$context, \$_parent) + \$_parent;
+    return; yield;
+};
+\Closure::bind(\$__internal_compile_1, \$this, self::class);
+yield from \$__internal_compile_1(\$__internal_compile_0, \$context, \$blocks, \$__internal_compile_1, 0);
 EOF
         ];