Merge pull request #620 from golang-migrate/fix-source-file-driver

fix source/file driver

Author: dhui

source/file/file.go

@@ -6,12 +6,34 @@ import (
 	"path/filepath"
 
 	"github.com/golang-migrate/migrate/v4/source"
+	"github.com/golang-migrate/migrate/v4/source/iofs"
 )
 
 func init() {
 	source.Register("file", &File{})
 }
 
+type File struct {
+	iofs.PartialDriver
+	url  string
+	path string
+}
+
+func (f *File) Open(url string) (source.Driver, error) {
+	p, err := parseURL(url)
+	if err != nil {
+		return nil, err
+	}
+	nf := &File{
+		url:  url,
+		path: p,
+	}
+	if err := nf.Init(os.DirFS(p), "."); err != nil {
+		return nil, err
+	}
+	return nf, nil
+}
+
 func parseURL(url string) (string, error) {
 	u, err := nurl.Parse(url)
 	if err != nil {