Fix length of index names for a create table statement (#133)

Fixes: #124 

This PR introduces some changes to how we determine the name of an
index. SQLite requires that each index is uniquely named across the
database (not just the table). This causes issues when multiple tables
have the same key names when importing from MySQL. To avoid these
issues, the index name is prefixed with the table name when it is
created. This however results in the indexes having names that are too
long for MySQL so when we run `show create table` the create statements
have these prefixed keys that are too long.

To solve this, we keep adding the table name as a prefix but we remove
it when we generate the create statement. Furthermore, we ensure that
the table name itself has no double underscores in it so we can be sure
that we can split on `__` safely. The result is that each create table
statement will have the original index name and prevents it from being
too long.

Author: jeroenpf

tests/WP_SQLite_Translator_Tests.php

@@ -283,8 +283,8 @@ public function testShowCreateTable1() {
 	`option_name` varchar(255) DEFAULT '',
 	`option_value` text NOT NULL DEFAULT '',
 	PRIMARY KEY (`ID`),
-	KEY `_tmp_table__composite` (`option_name`, `option_value`),
-	UNIQUE KEY `_tmp_table__option_name` (`option_name`)
+	KEY `composite` (`option_name`, `option_value`),
+	UNIQUE KEY `option_name` (`option_name`)
 );",
 			$results[0]->{'Create Table'}
 		);
@@ -312,8 +312,8 @@ public function testShowCreateTableQuoted() {
 	`option_name` varchar(255) DEFAULT '',
 	`option_value` text NOT NULL DEFAULT '',
 	PRIMARY KEY (`ID`),
-	KEY `_tmp_table__composite` (`option_name`, `option_value`),
-	UNIQUE KEY `_tmp_table__option_name` (`option_name`)
+	KEY `composite` (`option_name`, `option_value`),
+	UNIQUE KEY `option_name` (`option_name`)
 );",
 			$results[0]->{'Create Table'}
 		);
@@ -365,12 +365,32 @@ public function testShowCreateTableWithAlterAndCreateIndex() {
 	`option_name` smallint NOT NULL DEFAULT 14,
 	`option_value` text NOT NULL DEFAULT \'\',
 	PRIMARY KEY (`ID`),
-	KEY `_tmp_table__option_name` (`option_name`)
+	KEY `option_name` (`option_name`)
 );',
 			$results[0]->{'Create Table'}
 		);
 	}
 
+	public function testCreateTablseWithIdenticalIndexNames() {
+		$this->assertQuery(
+			"CREATE TABLE _tmp_table_a (
+					ID BIGINT PRIMARY KEY AUTO_INCREMENT NOT NULL,
+					option_name VARCHAR(255) default '',
+					option_value TEXT NOT NULL,
+					KEY `option_name` (`option_name`)
+				);"
+		);
+
+		$this->assertQuery(
+			"CREATE TABLE _tmp_table_b (
+					ID BIGINT PRIMARY KEY AUTO_INCREMENT NOT NULL,
+					option_name VARCHAR(255) default '',
+					option_value TEXT NOT NULL,
+					KEY `option_name` (`option_name`)
+				);"
+		);
+	}
+
 	public function testShowCreateTableWithPrimaryKeyColumnsReverseOrdered() {
 		$this->assertQuery(
 			'CREATE TABLE `_tmp_table` (

wp-includes/sqlite/class-wp-sqlite-translator.php

@@ -900,8 +900,7 @@ private function execute_create_table() {
 			if ( 'UNIQUE INDEX' === $index_type ) {
 				$unique = 'UNIQUE ';
 			}
-			$index_name = "{$table->name}__{$constraint->name}";
-
+			$index_name = $this->generate_index_name( $table->name, $constraint->name );
 			$this->execute_sqlite_query(
 				"CREATE $unique INDEX \"$index_name\" ON \"{$table->name}\" (\"" . implode( '", "', $constraint->columns ) . '")'
 			);
@@ -3086,7 +3085,7 @@ private function execute_alter() {
 			} elseif ( 'ADD' === $op_type && $is_index_op ) {
 				$key_name          = $this->rewriter->consume()->value;
 				$sqlite_index_type = $this->mysql_index_type_to_sqlite_type( $mysql_index_type );
-				$sqlite_index_name = "{$this->table_name}__$key_name";
+				$sqlite_index_name = $this->generate_index_name( $this->table_name, $key_name );
 				$this->rewriter->replace_all(
 					array(
 						new WP_SQLite_Token( 'CREATE', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
@@ -3570,7 +3569,12 @@ private function get_key_definitions( $table_name, $columns ) {
 
 			$key_definition[] = 'KEY';
 
-			$key_definition[] = sprintf( '`%s`', $key['index']['name'] );
+			// Remove the prefix from the index name if there is any. We use __ as a separator.
+			$index_name = strstr( $key['index']['name'], '__' )
+				? explode( '__', $key['index']['name'] )[1]
+				: $key['index']['name'];
+
+			$key_definition[] = sprintf( '`%s`', $index_name );
 
 			$cols = array_map(
 				function ( $column ) {
@@ -4199,4 +4203,18 @@ public function rollback() {
 		}
 		return $this->last_exec_returned;
 	}
+
+	/**
+	 * Create an index name consisting of table name and original index name.
+	 * This is to avoid duplicate index names in SQLite.
+	 *
+	 * @param $table
+	 * @param $original_index_name
+	 *
+	 * @return string
+	 */
+	private function generate_index_name( $table, $original_index_name ) {
+		// Strip the occurrences of 2 or more consecutive underscores to allow easier splitting on __ later.
+		return preg_replace( '/_{2,}/', '_', $table ) . '__' . $original_index_name;
+	}
 }