[v14.0/forgejo] fix(ui): process dynamically added content via htmx (#10630)

**Backport:** https://codeberg.org/forgejo/forgejo/pulls/10572

When new content is added via JS and htmx is not used for this change,
htmx need to be informed that DOM changes happened and that it needs to
reprocess the DOM (or at least the changed parts).

When a diff is really large, it is hidden by default. The user can press
a button to load the diff, which then will be added via JS.
The diff contains buttons to expand it, which are using htmx behind the
scenes. Therefore a reprocessing via htmx needs to be triggered after
adding the large diff.

Fixes #10570

Co-authored-by: Beowulf <beowulf@beocode.eu>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/10630
Reviewed-by: Beowulf <beowulf@beocode.eu>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>

tests/e2e/declare_repos_test.go

@@ -6,6 +6,7 @@ package e2e
 import (
 	"fmt"
 	"os"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -144,6 +145,34 @@ body:
 			addCommitToBranch(t, user, repo, "test-branch", "test-branch", "test-README.md", commit2Sha,
 				readStringFile(t, "tests/e2e/declarative-repo/long-diff-test/3-README.md"))
 		}),
+		newRepo(t, 2, "huge-diff-test", nil, []FileChanges{{
+			Filename: "glossary.po",
+			Versions: []string{
+				func() string {
+					var sb strings.Builder
+					sb.Write([]byte("0"))
+					for i := 1; i < 2000; i++ {
+						sb.WriteString(strconv.Itoa(i))
+						sb.WriteByte('\n')
+					}
+					return sb.String()
+				}(),
+			},
+		}}, func(user *user_model.User, repo *repo_model.Repository) {
+			addCommitToBranch(t, user, repo, "main", "main-2", "glossary.po", "",
+				func() string {
+					var sb strings.Builder
+					sb.Write([]byte("0"))
+					for i := 1; i < 2000; i++ {
+						sb.WriteString(strconv.Itoa(i))
+						if i%12 == 0 {
+							sb.WriteString("Blub")
+						}
+						sb.WriteByte('\n')
+					}
+					return sb.String()
+				}())
+		}),
 		// add your repo declarations here
 	}
 

tests/e2e/file-diff.test.e2e.ts

@@ -0,0 +1,41 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// @watch start
+// templates/repo/diff/**
+// web_src/css/review.css
+// web_src/js/features/repo-diff.js
+// @watch end
+
+import {expect} from '@playwright/test';
+import {test} from './utils_e2e.ts';
+
+test.use({user: 'user2'});
+
+test('Expand Large diff', async ({page}) => {
+  let response = await page.goto('/user2/huge-diff-test/src/branch/main-2', {waitUntil: 'domcontentloaded'});
+  expect(response?.status()).toBe(200);
+
+  const commitUrl = await page.locator('.commit-summary a').getAttribute('href');
+
+  response = await page.goto(commitUrl, {waitUntil: 'domcontentloaded'});
+  expect(response?.status()).toBe(200);
+
+  const loadDiff = page.locator('.diff-load-button');
+  const expandDiff = page.locator('.code-expander-button');
+  const diffLines = page.locator('.file-body tbody > tr');
+
+  await expect(loadDiff).toBeVisible();
+
+  loadDiff.click();
+  await page.waitForLoadState('load');
+
+  await expect(expandDiff).toHaveCount(167);
+  await expect(diffLines).toHaveCount(1495);
+
+  await expandDiff.first().click();
+  await page.waitForLoadState('load');
+
+  await expect(expandDiff).toHaveCount(166);
+  await expect(diffLines).toHaveCount(1502);
+});

web_src/js/features/repo-diff.js

@@ -1,4 +1,5 @@
 import $ from 'jquery';
+import htmx from 'htmx.org';
 import {initCompReactionSelector} from './comp/ReactionSelector.js';
 import {initRepoIssueContentHistory} from './repo-issue-content.js';
 import {initDiffFileTree} from './repo-diff-filetree.js';
@@ -151,6 +152,7 @@ function onShowMoreFiles() {
   initViewedCheckboxListenerFor();
   countAndUpdateViewedFiles();
   initImageDiff();
+  htmx.process(document.body);
 }
 
 export async function loadMoreFiles(url) {