Make "update file" API can create a new file when SHA is not set (#35738)

Fix #19008, use GitHub's behavior (empty SHA to create a new file)

routers/api/v1/repo/file.go

@@ -525,7 +525,7 @@ func CreateFile(ctx *context.APIContext) {
 func UpdateFile(ctx *context.APIContext) {
 	// swagger:operation PUT /repos/{owner}/{repo}/contents/{filepath} repository repoUpdateFile
 	// ---
-	// summary: Update a file in a repository
+	// summary: Update a file in a repository if SHA is set, or create the file if SHA is not set
 	// consumes:
 	// - application/json
 	// produces:
@@ -554,6 +554,8 @@ func UpdateFile(ctx *context.APIContext) {
 	// responses:
 	//   "200":
 	//     "$ref": "#/responses/FileResponse"
+	//   "201":
+	//     "$ref": "#/responses/FileResponse"
 	//   "403":
 	//     "$ref": "#/responses/error"
 	//   "404":
@@ -572,8 +574,9 @@ func UpdateFile(ctx *context.APIContext) {
 		ctx.APIError(http.StatusUnprocessableEntity, err)
 		return
 	}
+	willCreate := apiOpts.SHA == ""
 	opts.Files = append(opts.Files, &files_service.ChangeRepoFile{
-		Operation:     "update",
+		Operation:     util.Iif(willCreate, "create", "update"),
 		ContentReader: contentReader,
 		SHA:           apiOpts.SHA,
 		FromTreePath:  apiOpts.FromPath,
@@ -587,7 +590,7 @@ func UpdateFile(ctx *context.APIContext) {
 		handleChangeRepoFilesError(ctx, err)
 	} else {
 		fileResponse := files_service.GetFileResponseFromFilesResponse(filesResponse, 0)
-		ctx.JSON(http.StatusOK, fileResponse)
+		ctx.JSON(util.Iif(willCreate, http.StatusCreated, http.StatusOK), fileResponse)
 	}
 }