Fix datetime field with empty default (#166)

Fixes
#165

I propose to fix an issue where dumping the datetime field that has
empty value results with producing incorrect MySQL.

Author: JanJakes

tests/WP_SQLite_Translator_Tests.php

@@ -290,6 +290,47 @@ public function testShowCreateTable1() {
 		);
 	}
 
+	public function testShowCreateTableWithEmptyDatetimeDefault() {
+		$this->assertQuery(
+			"CREATE TABLE _tmp_table (
+				ID BIGINT PRIMARY KEY AUTO_INCREMENT,
+				timestamp1 datetime NOT NULL,
+				timestamp2 date NOT NULL,
+				timestamp3 time NOT NULL,
+				timestamp4 timestamp NOT NULL,
+				timestamp5 year NOT NULL,
+				notempty1 datetime DEFAULT '1999-12-12 12:12:12',
+				notempty2 date DEFAULT '1999-12-12',
+				notempty3 time DEFAULT '12:12:12',
+				notempty4 year DEFAULT '2024',
+				notempty5 timestamp DEFAULT '1734539165',
+			);"
+		);
+
+		$this->assertQuery(
+			'SHOW CREATE TABLE _tmp_table;'
+		);
+		$results = $this->engine->get_query_results();
+
+		$this->assertEquals(
+			"CREATE TABLE `_tmp_table` (
+	`ID` bigint AUTO_INCREMENT,
+	`timestamp1` datetime NOT NULL,
+	`timestamp2` date NOT NULL,
+	`timestamp3` time NOT NULL,
+	`timestamp4` timestamp NOT NULL,
+	`timestamp5` year NOT NULL,
+	`notempty1` datetime DEFAULT '1999-12-12 12:12:12',
+	`notempty2` date DEFAULT '1999-12-12',
+	`notempty3` time DEFAULT '12:12:12',
+	`notempty4` year DEFAULT '2024',
+	`notempty5` timestamp DEFAULT '1734539165',
+	PRIMARY KEY (`ID`)
+);",
+			$results[0]->{'Create Table'}
+		);
+	}
+
 	public function testShowCreateTableQuoted() {
 		$this->assertQuery(
 			"CREATE TABLE _tmp_table (

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

@@ -3693,16 +3693,17 @@ protected function get_column_definitions( $table_name, $columns ) {
 		$auto_increment_column = $this->get_autoincrement_column( $table_name );
 		$column_definitions    = array();
 		foreach ( $columns as $column ) {
+			$mysql_type   = $this->get_cached_mysql_data_type( $table_name, $column->name );
 			$is_auto_incr = $auto_increment_column && strtolower( $auto_increment_column ) === strtolower( $column->name );
 			$definition   = array();
 			$definition[] = '`' . $column->name . '`';
-			$definition[] = $this->get_cached_mysql_data_type( $table_name, $column->name ) ?? $column->name;
+			$definition[] = $mysql_type ?? $column->name;
 
 			if ( '1' === $column->notnull ) {
 				$definition[] = 'NOT NULL';
 			}
 
-			if ( null !== $column->dflt_value && '' !== $column->dflt_value && ! $is_auto_incr ) {
+			if ( $this->column_has_default( $column, $mysql_type ) && ! $is_auto_incr ) {
 				$definition[] = 'DEFAULT ' . $column->dflt_value;
 			}
 
@@ -3858,6 +3859,33 @@ function ( $row ) use ( $name_map ) {
 		);
 	}
 
+	/**
+	 * Checks if column should define the default.
+	 *
+	 * @param stdClass $column The table column
+	 * @param string $mysql_type The MySQL data type
+	 *
+	 * @return boolean If column should have a default definition.
+	 */
+	private function column_has_default( $column, $mysql_type ) {
+		if ( null === $column->dflt_value ) {
+			return false;
+		}
+
+		if ( '' === $column->dflt_value ) {
+			return false;
+		}
+
+		if (
+			in_array( strtolower( $mysql_type ), array( 'datetime', 'date', 'time', 'timestamp', 'year' ), true ) &&
+			"''" === $column->dflt_value
+		) {
+			return false;
+		}
+
+		return true;
+	}
+
 	/**
 	 * Consumes data types from the query.
 	 *