From 851a0018ed2e11721a9d2867f85d9f80e9f33cc3 Mon Sep 17 00:00:00 2001
From: Gary Pendergast <pento@git.wordpress.org>
Date: Thu, 8 Sep 2016 23:53:25 +0000
Subject: [PATCH] Database: Fall back to `utf8` when `utf8mb4` isn't supported.

Sometimes, `DB_CHARSET` will be set to `utf8mb4`, even if the current setup doesn't support `utf8mb4`. After [38442], this can cause significant character set failures, causing the connection to fall back to `latin1`.

Instead of doing this, we now check that the connection supports `utf8mb4` before trying to use it, and fall back to `utf8` when we need to.

Merge of [38580] to the 4.6 branch.
Fixes #37982.



git-svn-id: https://develop.svn.wordpress.org/branches/4.6@38581 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/wp-db.php  |  5 +++++
 tests/phpunit/tests/db.php | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index 8ebee4c40e..8057bcc04e 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -779,6 +779,11 @@ class wpdb {
 			$charset = 'utf8mb4';
 		}
 
+		if ( 'utf8mb4' === $charset && ! $this->has_cap( 'utf8mb4' ) ) {
+			$charset = 'utf8';
+			$collate = str_replace( 'utf8mb4_', 'utf8_', $collate );
+		}
+
 		if ( 'utf8mb4' === $charset ) {
 			// _general_ is outdated, so we can upgrade it to _unicode_, instead.
 			if ( ! $collate || 'utf8_general_ci' === $collate ) {
diff --git a/tests/phpunit/tests/db.php b/tests/phpunit/tests/db.php
index a876869346..d67926e9fc 100644
--- a/tests/phpunit/tests/db.php
+++ b/tests/phpunit/tests/db.php
@@ -1029,4 +1029,23 @@ class Tests_DB extends WP_UnitTestCase {
 
 		$this->assertSame( 'utf8mb4_swedish_ci', $result['collate'] );
 	}
+
+	/**
+	 * @ticket 37982
+	 */
+	function test_charset_switched_to_utf8() {
+		global $wpdb;
+
+		if ( $wpdb->has_cap( 'utf8mb4' ) ) {
+			$this->markTestSkipped( 'This test requires utf8mb4 to not be supported.' );
+		}
+
+		$charset = 'utf8mb4';
+		$collate = 'utf8mb4_general_ci';
+
+		$result = $wpdb->determine_charset( $charset, $collate );
+
+		$this->assertSame( 'utf8', $result['charset'] );
+		$this->assertSame( 'utf8_general_ci', $result['collate'] );
+	}
 }