backends: remove log.Fatal and replace with error returns #5234

This changes the Config interface so that it returns an error.

backend/drive/drive.go

@@ -14,7 +14,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"log"
 	"mime"
 	"net/http"
 	"path"
@@ -183,13 +182,12 @@ func init() {
 		Description: "Google Drive",
 		NewFs:       NewFs,
 		CommandHelp: commandHelp,
-		Config: func(ctx context.Context, name string, m configmap.Mapper) {
+		Config: func(ctx context.Context, name string, m configmap.Mapper) error {
 			// Parse config into Options struct
 			opt := new(Options)
 			err := configstruct.Set(m, opt)
 			if err != nil {
-				fs.Errorf(nil, "Couldn't parse config into struct: %v", err)
-				return
+				return errors.Wrap(err, "couldn't parse config into struct")
 			}
 
 			// Fill in the scopes
@@ -202,13 +200,14 @@ func init() {
 			if opt.ServiceAccountFile == "" && opt.ServiceAccountCredentials == "" {
 				err = oauthutil.Config(ctx, "drive", name, m, driveConfig, nil)
 				if err != nil {
-					log.Fatalf("Failed to configure token: %v", err)
+					return errors.Wrap(err, "failed to configure token")
 				}
 			}
 			err = configTeamDrive(ctx, opt, m, name)
 			if err != nil {
-				log.Fatalf("Failed to configure Shared Drive: %v", err)
+				return errors.Wrap(err, "failed to configure Shared Drive")
 			}
+			return nil
 		},
 		Options: append(driveOAuthOptions(), []fs.Option{{
 			Name: "scope",
@@ -522,7 +521,7 @@ If this flag is set then rclone will ignore shortcut files completely.
 	} {
 		for mimeType, extension := range m {
 			if err := mime.AddExtensionType(extension, mimeType); err != nil {
-				log.Fatalf("Failed to register MIME type %q: %v", mimeType, err)
+				fs.Errorf("Failed to register MIME type %q: %v", mimeType, err)
 			}
 		}
 	}