Add API Endpoint for Branch Creation (#11607)

* [FEATURE] [API] Add Endpoint for Branch Creation

Issue: https://github.com/go-gitea/gitea/issues/11376

This commit introduces an API endpoint for branch creation.

The added route is POST /repos/{owner}/{repo}/branches.
A JSON with the name of the new branch and the name of the old branch is
required as parameters.

Signed-off-by: Terence Le Huu Phuong <terence@qwasar.io>

* Put all the logic into CreateBranch and removed CreateRepoBranch

* - Added the error ErrBranchDoesNotExist in error.go
- Made the CreateNewBranch function return an errBranchDoesNotExist error
when the OldBranch does not exist
- Made the CreateBranch API function checks that the repository is not
empty and that branch exists.

* - Added a resetFixtures helper function in integration_test.go to
fine-tune test env resetting
- Added api test for CreateBranch
- Used resetFixture instead of the more general prepareTestEnv in the
repo_branch_test CreateBranch tests

* Moved the resetFixtures call inside the loop for APICreateBranch function

* Put the prepareTestEnv back in repo_branch_test

* fix import order/sort api branch test

Co-authored-by: zeripath <art27@cantab.net>

routers/api/v1/repo/branch.go

@@ -182,6 +182,96 @@ func DeleteBranch(ctx *context.APIContext) {
 	ctx.Status(http.StatusNoContent)
 }
 
+// CreateBranch creates a branch for a user's repository
+func CreateBranch(ctx *context.APIContext, opt api.CreateBranchRepoOption) {
+	// swagger:operation POST /repos/{owner}/{repo}/branches repository repoCreateBranch
+	// ---
+	// summary: Create a branch
+	// consumes:
+	// - application/json
+	// 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: body
+	//   in: body
+	//   schema:
+	//     "$ref": "#/definitions/CreateBranchRepoOption"
+	// responses:
+	//   "201":
+	//     "$ref": "#/responses/Branch"
+	//   "404":
+	//     description: The old branch does not exist.
+	//   "409":
+	//     description: The branch with the same name already exists.
+
+	if ctx.Repo.Repository.IsEmpty {
+		ctx.Error(http.StatusNotFound, "", "Git Repository is empty.")
+		return
+	}
+
+	if len(opt.OldBranchName) == 0 {
+		opt.OldBranchName = ctx.Repo.Repository.DefaultBranch
+	}
+
+	err := repo_module.CreateNewBranch(ctx.User, ctx.Repo.Repository, opt.OldBranchName, opt.BranchName)
+
+	if err != nil {
+		if models.IsErrBranchDoesNotExist(err) {
+			ctx.Error(http.StatusNotFound, "", "The old branch does not exist")
+		}
+		if models.IsErrTagAlreadyExists(err) {
+			ctx.Error(http.StatusConflict, "", "The branch with the same tag already exists.")
+
+		} else if models.IsErrBranchAlreadyExists(err) || git.IsErrPushOutOfDate(err) {
+			ctx.Error(http.StatusConflict, "", "The branch already exists.")
+
+		} else if models.IsErrBranchNameConflict(err) {
+			ctx.Error(http.StatusConflict, "", "The branch with the same name already exists.")
+
+		} else {
+			ctx.Error(http.StatusInternalServerError, "CreateRepoBranch", err)
+
+		}
+		return
+	}
+
+	branch, err := repo_module.GetBranch(ctx.Repo.Repository, opt.BranchName)
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "GetBranch", err)
+		return
+	}
+
+	commit, err := branch.GetCommit()
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "GetCommit", err)
+		return
+	}
+
+	branchProtection, err := ctx.Repo.Repository.GetBranchProtection(branch.Name)
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "GetBranchProtection", err)
+		return
+	}
+
+	br, err := convert.ToBranch(ctx.Repo.Repository, branch, commit, branchProtection, ctx.User, ctx.Repo.IsAdmin())
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "convert.ToBranch", err)
+		return
+	}
+
+	ctx.JSON(http.StatusCreated, br)
+}
+
 // ListBranches list all the branches of a repository
 func ListBranches(ctx *context.APIContext) {
 	// swagger:operation GET /repos/{owner}/{repo}/branches repository repoListBranches