Improve tree not found page (#26570)

Before:

![before](https://github.com/go-gitea/gitea/assets/18380374/383822d5-7d77-4ec3-b49b-4ab1e8b167ce)

After:

![after](https://github.com/go-gitea/gitea/assets/18380374/32afa0a3-fa05-4087-b96e-7d067f0ed756)

In Github:
https://github.com/yp05327/test/blob/main/test.drawio

Updated:
UI changed

![image](https://github.com/go-gitea/gitea/assets/18380374/41ed07ff-b815-4b4e-9779-5ab36b5f3980)

![image](https://github.com/go-gitea/gitea/assets/18380374/5d7b28d6-a2fc-4d4c-8d6d-d93f9c9a270b)

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

4 files changed, 29 insertions, 7 deletions

diff --git a/routers/web/repo/blame.go b/routers/web/repo/blame.go
index e4506a857e..1f1cca897e 100644
--- a/routers/web/repo/blame.go
+++ b/routers/web/repo/blame.go
@@ -70,7 +70,7 @@ func RefBlame(ctx *context.Context) {
 	// Get current entry user currently looking at.
 	entry, err := ctx.Repo.Commit.GetTreeEntryByPath(ctx.Repo.TreePath)
 	if err != nil {
-		ctx.NotFoundOrServerError("Repo.Commit.GetTreeEntryByPath", git.IsErrNotExist, err)
+		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
 		return
 	}
 
diff --git a/routers/web/repo/editor.go b/routers/web/repo/editor.go
index 9d9fee3a77..1ad091b70f 100644
--- a/routers/web/repo/editor.go
+++ b/routers/web/repo/editor.go
@@ -123,7 +123,7 @@ func editFile(ctx *context.Context, isNewFile bool) {
 	if !isNewFile {
 		entry, err := ctx.Repo.Commit.GetTreeEntryByPath(ctx.Repo.TreePath)
 		if err != nil {
-			ctx.NotFoundOrServerError("GetTreeEntryByPath", git.IsErrNotExist, err)
+			HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
 			return
 		}
 
diff --git a/routers/web/repo/helper.go b/routers/web/repo/helper.go
index f8cdefdc8e..a98abe566f 100644
--- a/routers/web/repo/helper.go
+++ b/routers/web/repo/helper.go
@@ -4,9 +4,12 @@
 package repo
 
 import (
+	"net/url"
 	"sort"
 
 	"code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/git"
 )
 
 func MakeSelfOnTop(doer *user.User, users []*user.User) []*user.User {
@@ -20,3 +23,22 @@ func MakeSelfOnTop(doer *user.User, users []*user.User) []*user.User {
 	}
 	return users
 }
+
+func HandleGitError(ctx *context.Context, msg string, err error) {
+	if git.IsErrNotExist(err) {
+		refType := ""
+		switch {
+		case ctx.Repo.IsViewBranch:
+			refType = "branch"
+		case ctx.Repo.IsViewTag:
+			refType = "tag"
+		case ctx.Repo.IsViewCommit:
+			refType = "commit"
+		}
+		ctx.Data["NotFoundPrompt"] = ctx.Locale.Tr("repo.tree_path_not_found_"+refType, ctx.Repo.TreePath, url.PathEscape(ctx.Repo.RefName))
+		ctx.Data["NotFoundGoBackURL"] = ctx.Repo.RepoLink + "/src/" + refType + "/" + url.PathEscape(ctx.Repo.RefName)
+		ctx.NotFound(msg, err)
+	} else {
+		ctx.ServerError(msg, err)
+	}
+}
diff --git a/routers/web/repo/view.go b/routers/web/repo/view.go
index 91c00b049e..0b1b064409 100644
--- a/routers/web/repo/view.go
+++ b/routers/web/repo/view.go
@@ -692,7 +692,7 @@ func checkCitationFile(ctx *context.Context, entry *git.TreeEntry) {
 	}
 	tree, err := ctx.Repo.Commit.SubTree(ctx.Repo.TreePath)
 	if err != nil {
-		ctx.NotFoundOrServerError("Repo.Commit.SubTree", git.IsErrNotExist, err)
+		HandleGitError(ctx, "Repo.Commit.SubTree", err)
 		return
 	}
 	allEntries, err := tree.ListEntries()
@@ -783,7 +783,7 @@ func LastCommit(ctx *context.Context) {
 func renderDirectoryFiles(ctx *context.Context, timeout time.Duration) git.Entries {
 	tree, err := ctx.Repo.Commit.SubTree(ctx.Repo.TreePath)
 	if err != nil {
-		ctx.NotFoundOrServerError("Repo.Commit.SubTree", git.IsErrNotExist, err)
+		HandleGitError(ctx, "Repo.Commit.SubTree", err)
 		return nil
 	}
 
@@ -792,12 +792,12 @@ func renderDirectoryFiles(ctx *context.Context, timeout time.Duration) git.Entri
 	// Get current entry user currently looking at.
 	entry, err := ctx.Repo.Commit.GetTreeEntryByPath(ctx.Repo.TreePath)
 	if err != nil {
-		ctx.NotFoundOrServerError("Repo.Commit.GetTreeEntryByPath", git.IsErrNotExist, err)
+		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
 		return nil
 	}
 
 	if !entry.IsDir() {
-		ctx.NotFoundOrServerError("Repo.Commit.GetTreeEntryByPath", git.IsErrNotExist, err)
+		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
 		return nil
 	}
 
@@ -963,7 +963,7 @@ func renderCode(ctx *context.Context) {
 	// Get current entry user currently looking at.
 	entry, err := ctx.Repo.Commit.GetTreeEntryByPath(ctx.Repo.TreePath)
 	if err != nil {
-		ctx.NotFoundOrServerError("Repo.Commit.GetTreeEntryByPath", git.IsErrNotExist, err)
+		HandleGitError(ctx, "Repo.Commit.GetTreeEntryByPath", err)
 		return
 	}