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>

integrations/api_branch_test.go

@@ -6,6 +6,7 @@ package integrations
 
 import (
 	"net/http"
+	"net/url"
 	"testing"
 
 	api "code.gitea.io/gitea/modules/structs"
@@ -100,6 +101,72 @@ func TestAPIGetBranch(t *testing.T) {
 	}
 }
 
+func TestAPICreateBranch(t *testing.T) {
+	onGiteaRun(t, testAPICreateBranches)
+}
+
+func testAPICreateBranches(t *testing.T, giteaURL *url.URL) {
+
+	username := "user2"
+	ctx := NewAPITestContext(t, username, "my-noo-repo")
+	giteaURL.Path = ctx.GitPath()
+
+	t.Run("CreateRepo", doAPICreateRepository(ctx, false))
+	tests := []struct {
+		OldBranch          string
+		NewBranch          string
+		ExpectedHTTPStatus int
+	}{
+		// Creating branch from default branch
+		{
+			OldBranch:          "",
+			NewBranch:          "new_branch_from_default_branch",
+			ExpectedHTTPStatus: http.StatusCreated,
+		},
+		// Creating branch from master
+		{
+			OldBranch:          "master",
+			NewBranch:          "new_branch_from_master_1",
+			ExpectedHTTPStatus: http.StatusCreated,
+		},
+		// Trying to create from master but already exists
+		{
+			OldBranch:          "master",
+			NewBranch:          "new_branch_from_master_1",
+			ExpectedHTTPStatus: http.StatusConflict,
+		},
+		// Trying to create from other branch (not default branch)
+		{
+			OldBranch:          "new_branch_from_master_1",
+			NewBranch:          "branch_2",
+			ExpectedHTTPStatus: http.StatusCreated,
+		},
+		// Trying to create from a branch which does not exist
+		{
+			OldBranch:          "does_not_exist",
+			NewBranch:          "new_branch_from_non_existent",
+			ExpectedHTTPStatus: http.StatusNotFound,
+		},
+	}
+	for _, test := range tests {
+		defer resetFixtures(t)
+		session := ctx.Session
+		token := getTokenForLoggedInUser(t, session)
+		req := NewRequestWithJSON(t, "POST", "/api/v1/repos/user2/my-noo-repo/branches?token="+token, &api.CreateBranchRepoOption{
+			BranchName:    test.NewBranch,
+			OldBranchName: test.OldBranch,
+		})
+		resp := session.MakeRequest(t, req, test.ExpectedHTTPStatus)
+
+		var branch api.Branch
+		DecodeJSON(t, resp, &branch)
+
+		if test.ExpectedHTTPStatus == http.StatusCreated {
+			assert.EqualValues(t, test.NewBranch, branch.Name)
+		}
+	}
+}
+
 func TestAPIBranchProtection(t *testing.T) {
 	defer prepareTestEnv(t)()