Add ErrDuplicateMigration typed error

source/httpfs/driver.go

@@ -10,6 +10,17 @@ import (
 	"github.com/golang-migrate/migrate/v4/source"
 )
 
+// ErrDuplicateMigration is an error type for reporting duplicate migration
+// files.
+type ErrDuplicateMigration struct {
+	Filename string
+}
+
+// Error implements error interface.
+func (e ErrDuplicateMigration) Error() string {
+	return fmt.Sprintf("duplicate migration file: %s", e.Filename)
+}
+
 // Driver is a migration source driver for reading migrations from
 // http.FileSystem instances. It implements source.Driver interface and can be
 // used as a migration source for the main migrate library.
@@ -61,7 +72,9 @@ func (h *Driver) Init(fs http.FileSystem, path string) error {
 		}
 
 		if !ms.Append(m) {
-			return fmt.Errorf("duplicate migration file: %v", file.Name())
+			return ErrDuplicateMigration{
+				Filename: file.Name(),
+			}
 		}
 	}