General: Introduce a polyfill for `is_iterable()` function added in PHP 7.1.

Props jrf, schlessera, desrosj.
See #43619.

git-svn-id: https://develop.svn.wordpress.org/trunk@43036 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/compat.php

@@ -511,7 +511,7 @@ if ( ! function_exists( 'is_countable' ) ) {
 	 * Polyfill for is_countable() function added in PHP 7.3.
 	 *
 	 * Verify that the content of a variable is an array or an object
-	 * implementing Countable.
+	 * implementing the Countable interface.
 	 *
 	 * @since 4.9.6
 	 *
@@ -523,3 +523,21 @@ if ( ! function_exists( 'is_countable' ) ) {
 		return ( is_array( $var ) || $var instanceof Countable );
 	}
 }
+
+if ( ! function_exists( 'is_iterable' ) ) {
+	/**
+	 * Polyfill for is_iterable() function added in PHP 7.1.
+	 *
+	 * Verify that the content of a variable is an array or an object
+	 * implementing the Traversable interface.
+	 *
+	 * @since 4.9.6
+	 *
+	 * @param mixed $var The value to check.
+	 *
+	 * @return bool True if `$var` is iterable, false otherwise.
+	 */
+	function is_iterable( $var ) {
+		return ( is_array( $var ) || $var instanceof Traversable );
+	}
+}

tests/phpunit/tests/compat.php

@@ -230,6 +230,47 @@ EOT;
 			array( (object) array( 'foo', 'bar', 'baz' ), false ),
 		);
 	}
+
+	/**
+	 * @ticket 43619
+	 */
+	function test_is_iterable_availability() {
+		$this->assertTrue( function_exists( 'is_iterable' ) );
+	}
+
+	/**
+	 * Test is_iterable() polyfill.
+	 *
+	 * @ticket 43619
+	 *
+	 * @dataProvider iterable_variable_test_data
+	 */
+	function test_is_iterable_functionality( $variable, $is_iterable ) {
+		$this->assertEquals( is_iterable( $variable ), $is_iterable );
+	}
+
+	/**
+	 * Data provider for test_is_iterable_functionality().
+	 *
+	 * @ticket 43619
+	 *
+	 * @return array {
+	 *     @type array {
+	 *         @type mixed $variable    Variable to check.
+	 *         @type bool  $is_iterable The expected return value of PHP 7.1 is_iterable() function.
+	 *     }
+	 * }
+	 */
+	public function iterable_variable_test_data() {
+		return array(
+			array( array(), true ),
+			array( array( 1, 2, 3 ), true ),
+			array( new ArrayIterator( array( 1, 2, 3 ) ), true ),
+			array( 1, false ),
+			array( 3.14, false ),
+			array( new stdClass(), false ),
+		);
+	}
 }
 
 /* used in test_mb_substr_phpcore */