dialect/sql/schema: mock result in write driver if returning clause is present (#3369)

dialect/sql/schema/writer.go

@@ -111,7 +111,46 @@ func (w *WriteDriver) Query(ctx context.Context, query string, args, res any) er
 			return err
 		}
 		if rr, ok := res.(*sql.Rows); ok {
-			*rr = sql.Rows{ColumnScanner: noRows{}}
+			cols := func() []string {
+				// If the query has a RETURNING clause, mock the result.
+				var clause string
+			outer:
+				for i := 0; i < len(query); i++ {
+					switch q := query[i]; {
+					case q == '\'', q == '"', q == '`': // string or identifier
+						_, skip := skipQuoted(query, i)
+						if skip == -1 {
+							return nil // malformed SQL
+						}
+						i = skip
+						continue
+					case reReturning.MatchString(query[i:]):
+						var j int
+					inner:
+						// Forward until next unquoted ';' appears, or we reach the end of the query.
+						for j = i; j < len(query); j++ {
+							switch query[j] {
+							case '\'', '"', '`': // string or identifier
+								_, skip := skipQuoted(query, j)
+								if skip == -1 {
+									return nil // malformed RETURNING clause
+								}
+								j = skip
+							case ';':
+								break inner
+							}
+						}
+						clause = query[i:j]
+						break outer
+					}
+				}
+				cols := strings.Split(reReturning.ReplaceAllString(clause, ""), ",")
+				for i := range cols {
+					cols[i] = strings.TrimSpace(cols[i])
+				}
+				return cols
+			}()
+			*rr = sql.Rows{ColumnScanner: &noRows{cols: cols}}
 		}
 		return nil
 	}
@@ -237,22 +276,7 @@ var reReturning = regexp.MustCompile(`(?i)^\s?RETURNING`)
 // trimReturning trims any RETURNING suffix from INSERT/UPDATE queries.
 // Note, that the output may be incorrect or unsafe SQL and require manual changes.
 func trimReturning(query []byte) []byte {
-	var returning = []byte("returning")
-	var (
-		b          bytes.Buffer
-		skipQuoted = func(query []byte, idx int) ([]byte, int) {
-			for j := idx + 1; j < len(query); j++ {
-				switch query[j] {
-				case '\\':
-					j++
-				case query[idx]:
-					return query[idx : j+1], j
-				}
-			}
-			// Unexpected EOS.
-			return query, -1
-		}
-	)
+	var b bytes.Buffer
 loop:
 	for i := 0; i < len(query); i++ {
 		switch q := query[i]; {
@@ -266,7 +290,7 @@ loop:
 			continue
 		case reReturning.Match(query[i:]):
 			// Forward until next unquoted ';' appears.
-			for j := i + len(returning); j < len(query); j++ {
+			for j := i; j < len(query); j++ { // skip "RETURNING"
 				switch query[j] {
 				case '\'', '"', '`': // string or identifier
 					_, skip := skipQuoted(query, j)
@@ -286,6 +310,19 @@ loop:
 	return b.Bytes()
 }
 
+func skipQuoted[T []byte | string](query T, idx int) (T, int) {
+	for j := idx + 1; j < len(query); j++ {
+		switch query[j] {
+		case '\\':
+			j++
+		case query[idx]:
+			return query[idx : j+1], j
+		}
+	}
+	// Unexpected EOS.
+	return query, -1
+}
+
 // Tx writes the transaction start.
 func (w *WriteDriver) Tx(context.Context) (dialect.Tx, error) {
 	return dialect.NopTx(w), nil
@@ -298,11 +335,23 @@ func (noResult) LastInsertId() (int64, error) { return 0, nil }
 func (noResult) RowsAffected() (int64, error) { return 0, nil }
 
 // noRows represents no rows.
-type noRows struct{ sql.ColumnScanner }
+type noRows struct {
+	sql.ColumnScanner
+	cols []string
+	done bool
+}
 
-func (noRows) Close() error { return nil }
-func (noRows) Err() error   { return nil }
-func (noRows) Next() bool   { return false }
+func (*noRows) Close() error { return nil }
+func (*noRows) Err() error   { return nil }
+func (r *noRows) Next() bool {
+	if !r.done {
+		r.done = true
+		return true
+	}
+	return false
+}
+func (r *noRows) Columns() ([]string, error) { return r.cols, nil }
+func (*noRows) Scan(...any) error            { return nil }
 
 type nopDriver struct {
 	dialect.Driver