Handle setting default branch via API (#9030)

routers/api/v1/api.go

@@ -606,7 +606,7 @@ func RegisterRoutes(m *macaron.Macaron) {
 			m.Group("/:username/:reponame", func() {
 				m.Combo("").Get(reqAnyRepoReader(), repo.Get).
 					Delete(reqToken(), reqOwner(), repo.Delete).
-					Patch(reqToken(), reqAdmin(), bind(api.EditRepoOption{}), repo.Edit)
+					Patch(reqToken(), reqAdmin(), bind(api.EditRepoOption{}), context.RepoRef(), repo.Edit)
 				m.Group("/hooks", func() {
 					m.Combo("").Get(repo.ListHooks).
 						Post(bind(api.CreateHookOption{}), repo.CreateHook)

routers/api/v1/repo/repo.go

@@ -17,6 +17,7 @@ import (
 	"code.gitea.io/gitea/modules/auth"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/convert"
+	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/migrations"
 	"code.gitea.io/gitea/modules/notification"
@@ -687,6 +688,17 @@ func updateBasicProperties(ctx *context.APIContext, opts api.EditRepoOption) err
 		repo.IsTemplate = *opts.Template
 	}
 
+	// Default branch only updated if changed and exist
+	if opts.DefaultBranch != nil && repo.DefaultBranch != *opts.DefaultBranch && ctx.Repo.GitRepo.IsBranchExist(*opts.DefaultBranch) {
+		if err := ctx.Repo.GitRepo.SetDefaultBranch(*opts.DefaultBranch); err != nil {
+			if !git.IsErrUnsupportedVersion(err) {
+				ctx.Error(http.StatusInternalServerError, "SetDefaultBranch", err)
+				return err
+			}
+		}
+		repo.DefaultBranch = *opts.DefaultBranch
+	}
+
 	if err := models.UpdateRepository(repo, visibilityChanged); err != nil {
 		ctx.Error(http.StatusInternalServerError, "UpdateRepository", err)
 		return err