Date/Time: Return false from wp_date() when the timestamp cannot be parsed.

`wp_date()` only checked the timestamp with `is_numeric()`, which accepts
values that `date_create( '@' . $timestamp )` rejects, such as `'1e3'`, `1e20`,
`' 5'`, and `'.5'`. For those, `date_create()` returned false and the following
`setTimezone()` call caused a fatal error. Now false is returned, as documented
for invalid timestamp input and as already done for non-numeric input.

This also resolves the PHPStan `method.nonObject` errors on every use of
`$datetime` in the function.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: westonruter

src/wp-includes/functions.php

@@ -258,6 +258,11 @@ function wp_date( $format, $timestamp = null, $timezone = null ) {
 	}
 
 	$datetime = date_create( '@' . $timestamp );
+
+	if ( false === $datetime ) {
+		return false;
+	}
+
 	$datetime->setTimezone( $timezone );
 
 	if ( empty( $wp_locale->month ) || empty( $wp_locale->weekday ) ) {

tests/phpunit/tests/date/wpDate.php

@@ -34,6 +34,32 @@ public function test_should_return_false_on_invalid_timestamp() {
 		$this->assertFalse( wp_date( DATE_RFC3339, 'invalid' ) );
 	}
 
+	/**
+	 * Tests that a numeric timestamp which {@see date_create()} cannot parse returns false.
+	 *
+	 * @dataProvider data_should_return_false_on_unparsable_numeric_timestamp
+	 *
+	 * @param int|float|string $timestamp Numeric timestamp.
+	 */
+	public function test_should_return_false_on_unparsable_numeric_timestamp( $timestamp ): void {
+		$this->assertTrue( is_numeric( $timestamp ), 'Expected the timestamp to pass the is_numeric() check.' );
+		$this->assertFalse( wp_date( DATE_RFC3339, $timestamp ) ); // @phpstan-ignore argument.type (Intentionally invalid input.)
+	}
+
+	/**
+	 * Data provider for {@see self::test_should_return_false_on_unparsable_numeric_timestamp()}.
+	 *
+	 * @return array<non-falsy-string, array{ 0: int|float|string }>
+	 */
+	public static function data_should_return_false_on_unparsable_numeric_timestamp(): array {
+		return array(
+			'exponent notation'  => array( '1e3' ),
+			'out-of-range float' => array( 1e20 ),
+			'leading whitespace' => array( ' 5' ),
+			'leading decimal'    => array( '.5' ),
+		);
+	}
+
 	/**
 	 * @ticket 48319
 	 */