Inherit submodules from template repository content (#16237)

Fix #10316

---------

Signed-off-by: Steffen Schröter <steffen@vexar.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/submodule.go

@@ -0,0 +1,66 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"os"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+type TemplateSubmoduleCommit struct {
+	Path   string
+	Commit string
+}
+
+// GetTemplateSubmoduleCommits returns a list of submodules paths and their commits from a repository
+// This function is only for generating new repos based on existing template, the template couldn't be too large.
+func GetTemplateSubmoduleCommits(ctx context.Context, repoPath string) (submoduleCommits []TemplateSubmoduleCommit, _ error) {
+	stdoutReader, stdoutWriter, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	opts := &RunOpts{
+		Dir:    repoPath,
+		Stdout: stdoutWriter,
+		PipelineFunc: func(ctx context.Context, cancel context.CancelFunc) error {
+			_ = stdoutWriter.Close()
+			defer stdoutReader.Close()
+
+			scanner := bufio.NewScanner(stdoutReader)
+			for scanner.Scan() {
+				entry, err := parseLsTreeLine(scanner.Bytes())
+				if err != nil {
+					cancel()
+					return err
+				}
+				if entry.EntryMode == EntryModeCommit {
+					submoduleCommits = append(submoduleCommits, TemplateSubmoduleCommit{Path: entry.Name, Commit: entry.ID.String()})
+				}
+			}
+			return scanner.Err()
+		},
+	}
+	err = NewCommand(ctx, "ls-tree", "-r", "--", "HEAD").Run(opts)
+	if err != nil {
+		return nil, fmt.Errorf("GetTemplateSubmoduleCommits: error running git ls-tree: %v", err)
+	}
+	return submoduleCommits, nil
+}
+
+// AddTemplateSubmoduleIndexes Adds the given submodules to the git index.
+// It is only for generating new repos based on existing template, requires the .gitmodules file to be already present in the work dir.
+func AddTemplateSubmoduleIndexes(ctx context.Context, repoPath string, submodules []TemplateSubmoduleCommit) error {
+	for _, submodule := range submodules {
+		cmd := NewCommand(ctx, "update-index", "--add", "--cacheinfo", "160000").AddDynamicArguments(submodule.Commit, submodule.Path)
+		if stdout, _, err := cmd.RunStdString(&RunOpts{Dir: repoPath}); err != nil {
+			log.Error("Unable to add %s as submodule to repo %s: stdout %s\nError: %v", submodule.Path, repoPath, stdout, err)
+			return err
+		}
+	}
+	return nil
+}