feat: implement branch/commit comparison API

- Add a new API endpoint for comparing differences between branches or commits
- Implement a new function `CompareDiff` in the `repo` package to handle the comparison logic
- Create a new file `compare.go` in the `common` package to parse and process comparison information
- Define a new `CompareInfo` struct to hold comparison details
- Add logic to determine the base and head repositories for comparison, including handling of forks and permission checks
- Implement comparison logic to fetch and compare information between branches or commits, including support for file-only comparisons

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

routers/api/v1/api.go

@@ -1066,6 +1066,8 @@ func Routes() *web.Route {
 			m.Post("/migrate", reqToken(), bind(api.MigrateRepoOptions{}), repo.Migrate)
 
 			m.Group("/{username}/{reponame}", func() {
+				m.Get("/compare/*", repo.CompareDiff)
+
 				m.Combo("").Get(reqAnyRepoReader(), repo.Get).
 					Delete(reqToken(), reqOwner(), repo.Delete).
 					Patch(reqToken(), reqAdmin(), bind(api.EditRepoOption{}), repo.Edit)

routers/api/v1/repo/compare.go

@@ -0,0 +1,83 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"net/http"
+
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/gitrepo"
+	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/routers/common"
+	"code.gitea.io/gitea/services/context"
+	"code.gitea.io/gitea/services/convert"
+)
+
+// CompareDiff compare two branches or commits
+func CompareDiff(ctx *context.APIContext) {
+	// swagger:operation GET /repos/{owner}/{repo}/compare/{diff} Get compared branches information
+	// ---
+	// summary: Get compared branches information
+	// produces:
+	// - application/json
+	// parameters:
+	// - name: owner
+	//   in: path
+	//   description: owner of the repo
+	//   type: string
+	//   required: true
+	// - name: repo
+	//   in: path
+	//   description: name of the repo
+	//   type: string
+	//   required: true
+	// - name: diff
+	//   in: path
+	//   description: compare two branches or commits
+	//   type: string
+	//   required: true
+	// responses:
+	//   "200":
+	//     "$ref": "#/responses/Repository"
+	//   "404":
+	//     "$ref": "#/responses/notFound"
+
+	if ctx.Repo.GitRepo == nil {
+		gitRepo, err := gitrepo.OpenRepository(ctx, ctx.Repo.Repository)
+		if err != nil {
+			ctx.Error(http.StatusInternalServerError, "OpenRepository", err)
+			return
+		}
+		ctx.Repo.GitRepo = gitRepo
+		defer gitRepo.Close()
+	}
+
+	ci := common.ParseCompareInfo(ctx)
+	defer func() {
+		if ci != nil && ci.HeadGitRepo != nil {
+			ci.HeadGitRepo.Close()
+		}
+	}()
+	if ctx.Written() {
+		return
+	}
+
+	apiCommits := make([]*api.Commit, 0, len(ci.CompareInfo.Commits))
+	userCache := make(map[string]*user_model.User)
+	for i := 0; i < len(ci.CompareInfo.Commits); i++ {
+		apiCommit, err := convert.ToCommit(ctx, ctx.Repo.Repository, ctx.Repo.GitRepo, ci.CompareInfo.Commits[i], userCache,
+			convert.ToCommitOptions{
+				Stat:         true,
+				Verification: ctx.FormBool("verification"),
+				Files:        ctx.FormBool("files"),
+			})
+		if err != nil {
+			ctx.ServerError("toCommit", err)
+			return
+		}
+		apiCommits = append(apiCommits, apiCommit)
+	}
+
+	ctx.JSON(http.StatusOK, &apiCommits)
+}