Translate MySQL CONVERT() expressions to SQLite

SQLite doesn't support the CONVERT() function. Translate its two forms:
- CONVERT(expr, type) is equivalent to CAST(expr AS type).
- CONVERT(expr USING charset) is a character set conversion that is
  a no-op in SQLite, as all text is stored as UTF-8.

Fixes #344

Author: JanJakes

.github/workflows/wp-tests-phpunit-run.js

@@ -58,9 +58,6 @@ const expectedFailures = [
 	'Tests_DB_Charset::test_strip_invalid_text with data set #32',
 	'Tests_DB_Charset::test_strip_invalid_text with data set #33',
 	'Tests_DB_Charset::test_strip_invalid_text with data set #34',
-	'Tests_DB_Charset::test_strip_invalid_text with data set #35',
-	'Tests_DB_Charset::test_strip_invalid_text with data set #36',
-	'Tests_DB_Charset::test_strip_invalid_text with data set #37',
 	'Tests_DB_Charset::test_strip_invalid_text with data set #39',
 	'Tests_DB_Charset::test_strip_invalid_text with data set #40',
 	'Tests_DB_Charset::test_strip_invalid_text with data set #41',

packages/mysql-on-sqlite/src/sqlite/class-wp-pdo-mysql-on-sqlite.php

@@ -4221,6 +4221,27 @@ private function translate_simple_expr_body( WP_Parser_Node $node ): string {
 			);
 		}
 
+		/**
+		 * Translate MySQL CONVERT() expression.
+		 *
+		 * MySQL supports two forms of CONVERT():
+		 *   1. CONVERT(expr, type):         Equivalent to CAST(expr AS type).
+		 *   2. CONVERT(expr USING charset): Converts the character set.
+		 */
+		if ( null !== $token && WP_MySQL_Lexer::CONVERT_SYMBOL === $token->id ) {
+			$expr      = $this->translate( $node->get_first_child_node( 'expr' ) );
+			$cast_type = $node->get_first_child_node( 'castType' );
+
+			if ( null !== $cast_type ) {
+				// CONVERT(expr, type): Translate to cast expression.
+				return sprintf( 'CAST(%s AS %s)', $expr, $this->translate( $cast_type ) );
+			} else {
+				// CONVERT(expr USING charset): Keep "expr" as is (no SQLite support).
+				// TODO: Consider rejecting UTF-8-incompatible charasets.
+				return $expr;
+			}
+		}
+
 		return $this->translate_sequence( $node->get_children() );
 	}
 

packages/mysql-on-sqlite/tests/WP_SQLite_Driver_Tests.php

@@ -9986,6 +9986,89 @@ public function testCastExpression(): void {
 		);
 	}
 
+	public function testConvertExpression(): void {
+		// CONVERT(expr, type) should behave like CAST(expr AS type).
+		$result = $this->assertQuery(
+			"SELECT
+				CONVERT('abc', BINARY) AS expr_1,
+				CONVERT('abc', CHAR) AS expr_2,
+				CONVERT('-10', SIGNED) AS expr_3,
+				CONVERT('-10', UNSIGNED) AS expr_4,
+				CONVERT('123.456', DECIMAL) AS expr_5,
+				CONVERT('2025-10-05', DATE) AS expr_6
+			"
+		);
+
+		$this->assertEquals(
+			array(
+				(object) array(
+					'expr_1' => 'abc',
+					'expr_2' => 'abc',
+					'expr_3' => '-10',
+					'expr_4' => '-10',
+					'expr_5' => '123.456',
+					'expr_6' => '2025-10-05',
+				),
+			),
+			$result
+		);
+	}
+
+	public function testConvertUsingExpression(): void {
+		// CONVERT(expr USING charset) converts character set.
+		// In SQLite, all text is UTF-8 — the conversion is a no-op.
+		$result = $this->assertQuery(
+			"SELECT
+				CONVERT('Customer' USING utf8mb4) AS expr_1,
+				CONVERT('test' USING utf8) AS expr_2,
+				CONVERT('data' USING latin1) AS expr_3
+			"
+		);
+
+		$this->assertEquals(
+			array(
+				(object) array(
+					'expr_1' => 'Customer',
+					'expr_2' => 'test',
+					'expr_3' => 'data',
+				),
+			),
+			$result
+		);
+	}
+
+	public function testConvertUsingWithCollate(): void {
+		$result = $this->assertQuery(
+			"SELECT CONVERT('Customer' USING utf8mb4) COLLATE utf8mb4_bin AS val"
+		);
+
+		$this->assertEquals(
+			array(
+				(object) array( 'val' => 'Customer' ),
+			),
+			$result
+		);
+	}
+
+	public function testConvertWithColumnReferences(): void {
+		$this->assertQuery( 'CREATE TABLE t (val VARCHAR(255), num VARCHAR(255))' );
+		$this->assertQuery( "INSERT INTO t (val, num) VALUES ('hello', '-42')" );
+
+		$result = $this->assertQuery(
+			'SELECT CONVERT(val, BINARY) AS v1, CONVERT(val USING utf8mb4) AS v2
+			FROM t WHERE CONVERT(num, SIGNED) < 0 ORDER BY CONVERT(val USING utf8mb4)'
+		);
+		$this->assertEquals(
+			array(
+				(object) array(
+					'v1' => 'hello',
+					'v2' => 'hello',
+				),
+			),
+			$result
+		);
+	}
+
 	public function testInsertWithoutInto(): void {
 		$this->assertQuery( 'CREATE TABLE t (id INT PRIMARY KEY, name VARCHAR(255))' );
 

packages/mysql-on-sqlite/tests/WP_SQLite_Driver_Translation_Tests.php

@@ -101,6 +101,41 @@ public function testSelect(): void {
 		);
 	}
 
+	public function testConvert(): void {
+		// CONVERT(expr, type) → CAST(expr AS type)
+		$this->assertQuery(
+			"SELECT CAST('abc' AS BLOB) AS `CONVERT('abc', BINARY)`",
+			"SELECT CONVERT('abc', BINARY)"
+		);
+
+		$this->assertQuery(
+			"SELECT CAST('abc' AS TEXT) AS `CONVERT('abc', CHAR)`",
+			"SELECT CONVERT('abc', CHAR)"
+		);
+
+		$this->assertQuery(
+			"SELECT CAST('-10' AS INTEGER) AS `CONVERT('-10', SIGNED)`",
+			"SELECT CONVERT('-10', SIGNED)"
+		);
+
+		// CONVERT(expr USING charset) → expr
+		$this->assertQuery(
+			"SELECT 'Customer' AS `Customer`",
+			"SELECT CONVERT('Customer' USING utf8mb4)"
+		);
+
+		$this->assertQuery(
+			"SELECT 'test' AS `test`",
+			"SELECT CONVERT('test' USING utf8)"
+		);
+
+		// CONVERT(expr USING charset) COLLATE collation → expr COLLATE collation
+		$this->assertQuery(
+			"SELECT 'Customer' COLLATE `utf8mb4_bin` AS `CONVERT('Customer' USING utf8mb4) COLLATE utf8mb4_bin`",
+			"SELECT CONVERT('Customer' USING utf8mb4) COLLATE utf8mb4_bin"
+		);
+	}
+
 	public function testInsert(): void {
 		$this->driver->query( 'CREATE TABLE t (c INT, c1 INT, c2 INT)' );
 		$this->driver->query( 'CREATE TABLE t1 (c1 INT, c2 INT)' );