fix(web): normalize content for edit history diff and fix comment history dropdown (#39616) (#39627)

Backport #39616 by @SergioBenitez

Editing a comment as follows:

```diff
# Deployment checklist

- Timeout: 30 seconds.
+ Timeout: 60 seconds.
Restart the worker before deploying.
Check the logs after deployment.
```

Gitea would render the history this way, before, inserting spurious new
lines:

<img width="1280" height="720" alt="before"
src="https://github.com/user-attachments/assets/5391167b-ac04-4746-b544-add926230ad8"
/>

With this change, it now renders it like this:

<img width="1280" height="720" alt="after"
src="https://github.com/user-attachments/assets/369f1f19-0eaf-4da5-99e5-aeedbac6050c"
/>

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Sergio Benitez <SergioBenitez@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/issue_content_history.go

@@ -4,8 +4,6 @@
 package repo
 
 import (
-	"bytes"
-	"html"
 	"html/template"
 	"net/http"
 	"strings"
@@ -15,6 +13,7 @@ import (
 	"gitea.dev/modules/htmlutil"
 	"gitea.dev/modules/log"
 	"gitea.dev/modules/templates"
+	"gitea.dev/modules/util"
 	"gitea.dev/services/context"
 
 	"github.com/sergi/go-diff/diffmatchpatch"
@@ -110,6 +109,34 @@ func canSoftDeleteContentHistory(ctx *context.Context, issue *issues_model.Issue
 	return canSoftDelete
 }
 
+func diffContentHistory(oldContent, newContent string) template.HTML {
+	// compare the current history revision with the previous one
+	dmp := diffmatchpatch.New()
+	// `checklines=false` makes better diff result
+	diff := dmp.DiffMain(util.NormalizeStringEOL(oldContent), util.NormalizeStringEOL(newContent), false)
+	diff = dmp.DiffCleanupEfficiency(diff)
+
+	// use chroma to render the diff html
+	buf := &htmlutil.HTMLBuilder{}
+	buf.WriteHTML(`<pre class="chroma">`)
+	for _, it := range diff {
+		switch it.Type {
+		case diffmatchpatch.DiffInsert:
+			buf.WriteHTML(`<span class="gi">`)
+			buf.WriteString(it.Text)
+			buf.WriteHTML("</span>")
+		case diffmatchpatch.DiffDelete:
+			buf.WriteHTML(`<span class="gd">`)
+			buf.WriteString(it.Text)
+			buf.WriteHTML("</span>")
+		default:
+			buf.WriteString(it.Text)
+		}
+	}
+	buf.WriteHTML("</pre>")
+	return buf.HTMLString()
+}
+
 // GetContentHistoryDetail get detail
 func GetContentHistoryDetail(ctx *context.Context) {
 	issue := GetActionIssue(ctx)
@@ -144,36 +171,11 @@ func GetContentHistoryDetail(ctx *context.Context) {
 		prevHistoryContentText = prevHistory.ContentText
 	}
 
-	// compare the current history revision with the previous one
-	dmp := diffmatchpatch.New()
-	// `checklines=false` makes better diff result
-	diff := dmp.DiffMain(prevHistoryContentText, history.ContentText, false)
-	diff = dmp.DiffCleanupEfficiency(diff)
-
-	// use chroma to render the diff html
-	diffHTMLBuf := bytes.Buffer{}
-	diffHTMLBuf.WriteString("<pre class='chroma'>")
-	for _, it := range diff {
-		switch it.Type {
-		case diffmatchpatch.DiffInsert:
-			diffHTMLBuf.WriteString("<span class='gi'>")
-			diffHTMLBuf.WriteString(html.EscapeString(it.Text))
-			diffHTMLBuf.WriteString("</span>")
-		case diffmatchpatch.DiffDelete:
-			diffHTMLBuf.WriteString("<span class='gd'>")
-			diffHTMLBuf.WriteString(html.EscapeString(it.Text))
-			diffHTMLBuf.WriteString("</span>")
-		default:
-			diffHTMLBuf.WriteString(html.EscapeString(it.Text))
-		}
-	}
-	diffHTMLBuf.WriteString("</pre>")
-
 	ctx.JSON(http.StatusOK, map[string]any{
 		"canSoftDelete": canSoftDeleteContentHistory(ctx, issue, comment, history),
 		"historyId":     historyID,
 		"prevHistoryId": prevHistoryID,
-		"diffHtml":      diffHTMLBuf.String(),
+		"diffHtml":      diffContentHistory(prevHistoryContentText, history.ContentText),
 	})
 }
 

routers/web/repo/issue_content_history_test.go

@@ -0,0 +1,17 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDiffContentHistory(t *testing.T) {
+	out := diffContentHistory("<\r\n&\r\n>", "<\nXXX\n>")
+	assert.Equal(t, `<pre class="chroma">&lt;
+<span class="gd">&amp;</span><span class="gi">XXX</span>
+&gt;</pre>`, string(out))
+}

web_src/fomantic/build/components/dropdown.js

@@ -521,10 +521,14 @@ $.fn.dropdown = function(parameters) {
             : function(){}
           ;
           const dataKeyRemoteQueried = 'remote-queried';
-          if(module.is.remote() && !$module.data(dataKeyRemoteQueried)) {
+          // if the dropdown uses remote API, then it needs to query if:
+          // * its content is empty (can not show: no menu item)
+          // * it has not queried before (it has content, but we still need to query the remote API, e.g.: issue author list)
+          if(module.is.remote() && (!module.can.show() || !$module.data(dataKeyRemoteQueried))) {
             module.debug('No API results retrieved, searching before show');
             $module.data(dataKeyRemoteQueried, true)
             module.queryRemote(module.get.query(), module.show);
+            // can continue to "show" if there are menu items to avoid the lag of waiting for the remote API response
           }
           if( module.can.show() && !module.is.active() ) {
             module.debug('Showing dropdown');