From 2b2f9e229d2772d680393c1e7d7e4a41dae5b114 Mon Sep 17 00:00:00 2001
From: Brad Jorsch <bjorsch@wikimedia.org>
Date: Wed, 29 Nov 2017 15:42:27 -0500
Subject: [PATCH] Database: Fix degenerate parenthesized joins

The SQL standard supports parenthesized joins like

    a JOIN (b JOIN c ON (...)) ON (...)

But it doesn't support parenthesizing a single table name, i.e. a
one-table "join", like

    a JOIN (b) ON (...)

Detect the degenerate single-table case and omit the parentheses.

Bug: T181674
Change-Id: I82cacd80465092aa67ff19bdcfd6682001bf12ab
---
 includes/libs/rdbms/database/Database.php        | 16 +++++++++++++---
 .../libs/rdbms/database/DatabaseTest.php         |  7 +++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/includes/libs/rdbms/database/Database.php b/includes/libs/rdbms/database/Database.php
index e04566eb49..b9367791c7 100644
--- a/includes/libs/rdbms/database/Database.php
+++ b/includes/libs/rdbms/database/Database.php
@@ -2019,9 +2019,19 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 
 			if ( is_array( $table ) ) {
 				// A parenthesized group
-				$joinedTable = '('
-					. $this->tableNamesWithIndexClauseOrJOIN( $table, $use_index, $ignore_index, $join_conds )
-					. ')';
+				if ( count( $table ) > 1 ) {
+					$joinedTable = '('
+						. $this->tableNamesWithIndexClauseOrJOIN( $table, $use_index, $ignore_index, $join_conds )
+						. ')';
+				} else {
+					// Degenerate case
+					$innerTable = reset( $table );
+					$innerAlias = key( $table );
+					$joinedTable = $this->tableNameWithAlias(
+						$innerTable,
+						is_string( $innerAlias ) ? $innerAlias : $innerTable
+					);
+				}
 			} else {
 				$joinedTable = $this->tableNameWithAlias( $table, $alias );
 			}
diff --git a/tests/phpunit/includes/libs/rdbms/database/DatabaseTest.php b/tests/phpunit/includes/libs/rdbms/database/DatabaseTest.php
index ee7ad2f2a2..7933f19f49 100644
--- a/tests/phpunit/includes/libs/rdbms/database/DatabaseTest.php
+++ b/tests/phpunit/includes/libs/rdbms/database/DatabaseTest.php
@@ -120,6 +120,13 @@ class DatabaseTest extends PHPUnit_Framework_TestCase {
 				],
 				'table1 LEFT JOIN (table2 JOIN table3 ON ((t2_id = t3_id))) ON ((t1_id = t2_id))'
 			],
+			'join with degenerate parenthesized group' => [
+				[ 'table1', 'n' => [ 't2' => 'table2' ] ],
+				[
+					'n' => [ 'LEFT JOIN', 't1_id = t2_id' ],
+				],
+				'table1 LEFT JOIN table2 t2 ON ((t1_id = t2_id))'
+			],
 		];
 	}
 
-- 
2.20.1