From 06dc5e170fb2683b25937a6e0c0c740dd8fe8128 Mon Sep 17 00:00:00 2001
From: Tonya Mork <hellofromtonya@git.wordpress.org>
Date: Thu, 11 Nov 2021 16:27:44 +0000
Subject: [PATCH] Template: Fix "undefined index: 00" when archive month query
 is empty in `wp_title()`.

When `m` query_tag has a valid year, i.e. `?m=2021`, and there are posts for that year, `substr()` returns a `false` on PHP 5.6 and an empty string on PHP 7.0+. Passing either of those values to `$wp_locale->get_month()` results in a PHP notice on PHP 5.6 to PHP 7.4 and a PHP Warning on PHP 8.0+.

Why? The `$month` lookup table has zeroized keys from '01' to '12'. A empty value is passed to `zeroise()` returns `'00'` which is directly passed as a key in the month property. That key does not exist.

While `$wp_locale->get_month()` would benefit from guarding/validation, this fix ensures a falsey value is not passed as a month.

Tests are added including a test that fails with this fix not applied.

Follow-up to [801], [35294], [35624].

Props antpb, audrasjb, costdev, davidmosterd, drewapicture, herregroen, hellofromTonya, michelwppi, sergeybiryukov.
Fixes #31521.

git-svn-id: https://develop.svn.wordpress.org/trunk@52136 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/general-template.php    |  6 ++-
 tests/phpunit/tests/general/wpTitle.php | 62 +++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 tests/phpunit/tests/general/wpTitle.php

diff --git a/src/wp-includes/general-template.php b/src/wp-includes/general-template.php
index 4a9835a478..1b743eddba 100644
--- a/src/wp-includes/general-template.php
+++ b/src/wp-includes/general-template.php
@@ -1376,9 +1376,11 @@ function wp_title( $sep = '&raquo;', $display = true, $seplocation = '' ) {
 	// If there's a month.
 	if ( is_archive() && ! empty( $m ) ) {
 		$my_year  = substr( $m, 0, 4 );
-		$my_month = $wp_locale->get_month( substr( $m, 4, 2 ) );
+		$my_month = substr( $m, 4, 2 );
 		$my_day   = (int) substr( $m, 6, 2 );
-		$title    = $my_year . ( $my_month ? $t_sep . $my_month : '' ) . ( $my_day ? $t_sep . $my_day : '' );
+		$title    = $my_year .
+			( $my_month ? $t_sep . $wp_locale->get_month( $my_month ) : '' ) .
+			( $my_day ? $t_sep . $my_day : '' );
 	}
 
 	// If there's a year.
diff --git a/tests/phpunit/tests/general/wpTitle.php b/tests/phpunit/tests/general/wpTitle.php
new file mode 100644
index 0000000000..272441a968
--- /dev/null
+++ b/tests/phpunit/tests/general/wpTitle.php
@@ -0,0 +1,62 @@
+<?php
+
+/**
+ * @group general
+ * @group template
+ * @covers ::wp_title
+ */
+class Tests_General_WpTitle extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 31521
+	 *
+	 * @dataProvider data_wp_title_archive
+	 */
+	public function test_wp_title_archive( $query, $expected ) {
+		self::factory()->post->create(
+			array(
+				'post_status' => 'publish',
+				'post_title'  => 'Test Post',
+				'post_type'   => 'post',
+				'post_date'   => '2021-11-01 18:52:17',
+			)
+		);
+		$this->go_to( '?m=' . $query );
+
+		$this->assertSame( $expected, wp_title( '&raquo;', false ) );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array
+	 */
+	public function data_wp_title_archive() {
+		return array(
+			'year with posts'                => array(
+				'query'    => '2021',
+				'expected' => ' &raquo; 2021',
+			),
+			'year without posts'             => array(
+				'query'    => '1910',
+				'expected' => ' &raquo; Page not found',
+			),
+			'year and month with posts'      => array(
+				'query'    => '202111',
+				'expected' => ' &raquo; 2021 &raquo; November',
+			),
+			'year and month without posts'   => array(
+				'query'    => '202101',
+				'expected' => ' &raquo; Page not found',
+			),
+			'year, month, day with posts'    => array(
+				'query'    => '20211101',
+				'expected' => ' &raquo; 2021 &raquo; November &raquo; 1',
+			),
+			'year, month, day without posts' => array(
+				'query'    => '20210101',
+				'expected' => ' &raquo; Page not found',
+			),
+		);
+	}
+}