SequentialArray: Proberly handle Generators that have begun already

Author: PhrozenByte

src/Constraint/SequentialArray.php

@@ -20,6 +20,7 @@
 namespace PhrozenByte\PHPUnitArrayAsserts\Constraint;
 
 use EmptyIterator;
+use Exception;
 use Generator;
 use Iterator;
 use IteratorAggregate;
@@ -175,10 +176,13 @@ protected function matches($other): bool
      * FALSE otherwise.
      *
      * Please note that this method will fully traverse a Traversable object.
-     * If an Iterator is given, this method will try to restore the object's
-     * pointer to its previous state. This will silently fail for instances of
-     * NoRewindIterator. Generators will be fully exhausted by this method. The
-     * behaviour for Iterators with non-unique keys is undefined.
+     * It expects Traversables to be rewindable. For NoRewindIterator instances
+     * it assumes that the iterator is still in its initial state. Generators
+     * will be fully exhausted; if the iterator has begun already, the object
+     * is considered invalid. If an Iterator is given, this method will try to
+     * restore the object's pointer to its previous state. This will silently
+     * fail for NoRewindIterator instances. The behaviour for Iterators with
+     * non-unique keys is undefined.
      *
      * The second item of the result array holds an integer representing the
      * number of items given. The integer will be ≥ 0 for any traversable data,
@@ -227,6 +231,14 @@ protected function inspectData($other): array
                 $other = $other->getIterator();
             }
 
+            if ($other instanceof Generator) {
+                try {
+                    $other->rewind();
+                } catch (Exception $e) {
+                    return [ false, -1, false ];
+                }
+            }
+
             $restorePointer = null;
             if ($other instanceof Iterator) {
                 if (!($other instanceof Generator) && !($other instanceof NoRewindIterator)) {

tests/Unit/Constraint/SequentialArrayTest.php

@@ -230,6 +230,29 @@ public function __construct()
         $this->assertSame(4, $other->current());
     }
 
+    public function testGeneratorWithIntermediatePointer(): void
+    {
+        $expectedException = ExpectationFailedException::class;
+        $expectedExceptionMessage = 'Failed asserting that %s is a sequential array.';
+
+        $itemConstraint = new SequentialArray();
+        $other = (function () {
+            for ($i = 1; $i <= 10; $i++) {
+                yield $i;
+            }
+        })();
+
+        // move pointer after item #2
+        $other->next();
+        $other->next();
+
+        $this->assertCallableThrows(
+            $this->callableProxy([ $itemConstraint, 'evaluate' ], $other),
+            $expectedException,
+            sprintf($expectedExceptionMessage, (new Exporter())->export($other))
+        );
+    }
+
     /**
      * @dataProvider dataProviderCountable
      *