Make loop.last always available

CHANGELOG

@@ -1,5 +1,6 @@
 # 4.0.0 (2024-XX-XX)
 
+ * 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
  * Make `Environment::getGlobals()` private
  * Drop support for PHP < 8.2

doc/tags/for.rst

@@ -77,8 +77,8 @@ Variable              Description
 .. note::
 
     When the underlying PHP iterator is not countable, the ``loop.length``,
-    ``loop.revindex``, ``loop.revindex0``, and ``loop.last`` variables are not
-    available and a ``RuntimeException`` is thrown if you try to use them.
+    ``loop.revindex``, and ``loop.revindex0`` variables are not available and a
+    ``RuntimeException`` is thrown if you try to use them.
 
 The ``else`` Clause
 -------------------

src/Runtime/Loop.php

@@ -25,6 +25,7 @@ final class Loop implements \Iterator
     private \Iterator $seq;
     private int $index0;
     private int $length;
+    private bool $peek = false;
 
     public function __construct($seq)
     {
@@ -44,7 +45,11 @@ final class Loop implements \Iterator
 
     public function next(): void
     {
-        $this->seq->next();
+        if ($this->peek) {
+            $this->peek = false;
+        } else {
+            $this->seq->next();
+        }
         ++$this->index0;
     }
 
@@ -81,4 +86,14 @@ final class Loop implements \Iterator
 
         return $this->length = count($this->seq);
     }
+
+    public function isLast(): bool
+    {
+        if (!$this->peek) {
+            $this->seq->next();
+            $this->peek = true;
+        }
+
+        return !$this->seq->valid();
+    }
 }

src/Runtime/LoopContext.php

@@ -61,6 +61,6 @@ final class LoopContext
 
     public function isLast(): bool
     {
-        return 0 === $this->loop->getLength('last') - $this->getIndex();
+        return $this->loop->isLast();
     }
 }

tests/Fixtures/tags/for/generator.test

@@ -2,11 +2,11 @@
 "for" tag supports Generators
 --TEMPLATE--
 {% for item in items %}
-{{ item }}
+{{ item }} {{ loop.last ? 'LAST' : '-' }}
 {% endfor %}
 --DATA--
 return ['items' => (function () { yield 'a'; yield 'b'; yield 'c'; })()]
 --EXPECT--
-a
-b
-c
+a -
+b -
+c LAST