Fix stderr usages (#26477)

cmd/admin_user_create.go

@@ -6,7 +6,6 @@ package cmd
 import (
 	"errors"
 	"fmt"
-	"os"
 
 	auth_model "code.gitea.io/gitea/models/auth"
 	user_model "code.gitea.io/gitea/models/user"
@@ -87,7 +86,7 @@ func runCreateUser(c *cli.Context) error {
 		username = c.String("username")
 	} else {
 		username = c.String("name")
-		fmt.Fprintf(os.Stderr, "--name flag is deprecated. Use --username instead.\n")
+		_, _ = fmt.Fprintf(c.App.ErrWriter, "--name flag is deprecated. Use --username instead.\n")
 	}
 
 	ctx, cancel := installSignals()

models/migrations/migrations.go

@@ -7,7 +7,6 @@ package migrations
 import (
 	"context"
 	"fmt"
-	"os"
 
 	"code.gitea.io/gitea/models/migrations/v1_10"
 	"code.gitea.io/gitea/models/migrations/v1_11"
@@ -608,8 +607,7 @@ Please try upgrading to a lower version first (suggested v1.6.4), then upgrade t
 		if !setting.IsProd {
 			msg += fmt.Sprintf("\nIf you are in development and really know what you're doing, you can force changing the migration version by executing: UPDATE version SET version=%d WHERE id=1;", minDBVersion+len(migrations))
 		}
-		_, _ = fmt.Fprintln(os.Stderr, msg)
-		log.Fatal(msg)
+		log.Fatal("Migration Error: %s", msg)
 		return nil
 	}
 

services/gitdiff/gitdiff.go

@@ -13,7 +13,6 @@ import (
 	"html/template"
 	"io"
 	"net/url"
-	"os"
 	"sort"
 	"strings"
 	"time"
@@ -1152,14 +1151,15 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 	}()
 
 	go func() {
+		stderr := &bytes.Buffer{}
 		cmdDiff.SetDescription(fmt.Sprintf("GetDiffRange [repo_path: %s]", repoPath))
 		if err := cmdDiff.Run(&git.RunOpts{
 			Timeout: time.Duration(setting.Git.Timeout.Default) * time.Second,
 			Dir:     repoPath,
-			Stderr:  os.Stderr,
 			Stdout:  writer,
+			Stderr:  stderr,
 		}); err != nil {
-			log.Error("error during RunWithContext: %w", err)
+			log.Error("error during GetDiff(git diff dir: %s): %v, stderr: %s", repoPath, err, stderr.String())
 		}
 
 		_ = writer.Close()