Fix INSERT ... SELECT ... edge case in non-strict mode (#285)

In MySQL non-STRICT mode, when inserting from a `SELECT` query:

When a column is declared as `NOT NULL`, inserting a `NULL` value saves
an IMPLICIT DEFAULT value instead. This behavior only applies to the
`INSERT ... SELECT` syntax (not `VALUES` or `SET`).

In other words:
```sql
CREATE TABLE t (value INT NOT NULL);

-- Strict mode:
INSERT INTO t VALUES (NULL); -- error
INSERT INTO t SET value = NULL; -- error
INSERT INTO t SELECT NULL; -- error
INSERT INTO t VALUES ((SELECT NULL)); -- error

-- Non-strict mode:
INSERT INTO t VALUES (NULL); -- error
INSERT INTO t SET value = NULL; -- error
INSERT INTO t SELECT NULL; -- OK, saves 0 (the implicit default for integer)
INSERT INTO t VALUES ((SELECT NULL)); -- error
```

This fixes some failures in the activation of the top 100 plugins.

Author: adamziel

tests/WP_SQLite_Driver_Tests.php

@@ -10539,6 +10539,42 @@ public function testCastValuesOnInsertInNonStrictMode(): void {
 		$this->assertQuery( 'DROP TABLE t' );
 	}
 
+	public function testCastNotNullValuesOnInsert(): void {
+		$this->assertQuery( 'CREATE TABLE t (value INT NOT NULL)' );
+
+		// Strict mode:
+		$this->assertQueryError( 'INSERT INTO t VALUES (NULL)', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+		$this->assertQueryError( 'INSERT INTO t SET value = NULL', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+		$this->assertQueryError( 'INSERT INTO t SELECT NULL', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+		$this->assertQueryError( 'INSERT INTO t VALUES ((SELECT NULL))', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+
+		// Non-strict mode:
+		$this->assertQuery( "SET SESSION sql_mode = ''" );
+		$this->assertQueryError( 'INSERT INTO t VALUES (NULL)', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+		$this->assertQueryError( 'INSERT INTO t SET value = NULL', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+		$this->assertQuery( 'INSERT INTO t SELECT NULL' );
+		$this->assertSame( '0', $this->assertQuery( 'SELECT * FROM t' )[0]->value );
+		$this->assertQueryError( 'INSERT INTO t VALUES ((SELECT NULL))', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+	}
+
+	public function testCastNotNullValuesOnUpdate(): void {
+		$this->assertQuery( 'CREATE TABLE t (value INT NOT NULL)' );
+		$this->assertQuery( 'INSERT INTO t VALUES (1)' );
+
+		// Strict mode:
+		$this->assertQueryError( 'UPDATE t SET value = NULL', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+		$this->assertQueryError( 'UPDATE t SET value = (SELECT NULL)', 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: t.value' );
+
+		// Non-strict mode:
+		$this->assertQuery( "SET SESSION sql_mode = ''" );
+		$this->assertQuery( 'UPDATE t SET value = NULL' );
+		$this->assertSame( '0', $this->assertQuery( 'SELECT * FROM t' )[0]->value );
+
+		$this->assertQuery( 'UPDATE t SET value = (SELECT NULL)' );
+		$this->assertSame( '0', $this->assertQuery( 'SELECT * FROM t' )[0]->value );
+		$this->assertQuery( 'DROP TABLE t' );
+	}
+
 	public function testCastValuesOnDuplicateKeyUpdate(): void {
 		$this->assertQuery( 'CREATE TABLE t (value TEXT UNIQUE)' );
 		$this->assertQuery( "INSERT INTO t VALUES ('test')" );

wp-includes/sqlite-ast/class-wp-sqlite-driver.php

@@ -4594,7 +4594,23 @@ function ( $column ) use ( $is_strict_mode, $insert_map ) {
 				// When a column value is included, we need to apply type casting.
 				$position   = array_search( $column['COLUMN_NAME'], $insert_list, true );
 				$identifier = $this->quote_sqlite_identifier( $select_list[ $position ] );
-				$fragment  .= $this->cast_value_for_saving( $column['DATA_TYPE'], $identifier );
+				$value      = $this->cast_value_for_saving( $column['DATA_TYPE'], $identifier );
+
+				/*
+				 * In MySQL non-STRICT mode, when inserting from a SELECT query:
+				 *
+				 * When a column is declared as NOT NULL, inserting a NULL value
+				 * saves an IMPLICIT DEFAULT value instead. This behavior only
+				 * applies to the INSERT ... SELECT syntax (not VALUES or SET).
+				 */
+				$is_insert_from_select = 'insertQueryExpression' === $node->rule_name;
+				if ( ! $is_strict_mode && $is_insert_from_select && 'NO' === $column['IS_NULLABLE'] ) {
+					$implicit_default = self::DATA_TYPE_IMPLICIT_DEFAULT_MAP[ $column['DATA_TYPE'] ] ?? null;
+					if ( null !== $implicit_default ) {
+						$value = sprintf( 'COALESCE(%s, %s)', $value, $this->connection->quote( $implicit_default ) );
+					}
+				}
+				$fragment .= $value;
 			}
 		}