Fix bug webhook milestone is not right. (#34419)

Fix #34400

---------

Co-authored-by: silverwind <me@silverwind.io>

tests/integration/repo_webhook_test.go

@@ -404,6 +404,78 @@ func Test_WebhookIssue(t *testing.T) {
 	})
 }
 
+func Test_WebhookIssueMilestone(t *testing.T) {
+	var payloads []api.IssuePayload
+	var triggeredEvent string
+	provider := newMockWebhookProvider(func(r *http.Request) {
+		content, _ := io.ReadAll(r.Body)
+		var payload api.IssuePayload
+		err := json.Unmarshal(content, &payload)
+		assert.NoError(t, err)
+		payloads = append(payloads, payload)
+		triggeredEvent = "issues"
+	}, http.StatusOK)
+	defer provider.Close()
+
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		// create a new webhook with special webhook for repo1
+		session := loginUser(t, "user2")
+		repo1 := unittest.AssertExistsAndLoadBean(t, &repo.Repository{ID: 1})
+		testAPICreateWebhookForRepo(t, session, "user2", "repo1", provider.URL(), "issue_milestone")
+
+		t.Run("assign a milestone", func(t *testing.T) {
+			// trigger the webhook
+			testIssueChangeMilestone(t, session, repo1.Link(), 1, 1)
+
+			// validate the webhook is triggered
+			assert.Equal(t, "issues", triggeredEvent)
+			assert.Len(t, payloads, 1)
+			assert.Equal(t, "milestoned", string(payloads[0].Action))
+			assert.Equal(t, "repo1", payloads[0].Issue.Repo.Name)
+			assert.Equal(t, "user2/repo1", payloads[0].Issue.Repo.FullName)
+			assert.Equal(t, "issue1", payloads[0].Issue.Title)
+			assert.Equal(t, "content for the first issue", payloads[0].Issue.Body)
+			assert.EqualValues(t, 1, payloads[0].Issue.Milestone.ID)
+		})
+
+		t.Run("change a milestong", func(t *testing.T) {
+			// trigger the webhook again
+			triggeredEvent = ""
+			payloads = make([]api.IssuePayload, 0, 1)
+			// change milestone to 2
+			testIssueChangeMilestone(t, session, repo1.Link(), 1, 2)
+
+			// validate the webhook is triggered
+			assert.Equal(t, "issues", triggeredEvent)
+			assert.Len(t, payloads, 1)
+			assert.Equal(t, "milestoned", string(payloads[0].Action))
+			assert.Equal(t, "repo1", payloads[0].Issue.Repo.Name)
+			assert.Equal(t, "user2/repo1", payloads[0].Issue.Repo.FullName)
+			assert.Equal(t, "issue1", payloads[0].Issue.Title)
+			assert.Equal(t, "content for the first issue", payloads[0].Issue.Body)
+			assert.EqualValues(t, 2, payloads[0].Issue.Milestone.ID)
+		})
+
+		t.Run("remove a milestone", func(t *testing.T) {
+			// trigger the webhook again
+			triggeredEvent = ""
+			payloads = make([]api.IssuePayload, 0, 1)
+			// change milestone to 0
+			testIssueChangeMilestone(t, session, repo1.Link(), 1, 0)
+
+			// validate the webhook is triggered
+			assert.Equal(t, "issues", triggeredEvent)
+			assert.Len(t, payloads, 1)
+			assert.Equal(t, "demilestoned", string(payloads[0].Action))
+			assert.Equal(t, "repo1", payloads[0].Issue.Repo.Name)
+			assert.Equal(t, "user2/repo1", payloads[0].Issue.Repo.FullName)
+			assert.Equal(t, "issue1", payloads[0].Issue.Title)
+			assert.Equal(t, "content for the first issue", payloads[0].Issue.Body)
+			assert.Nil(t, payloads[0].Issue.Milestone)
+		})
+	})
+}
+
 func Test_WebhookPullRequest(t *testing.T) {
 	var payloads []api.PullRequestPayload
 	var triggeredEvent string