Avoid emoji mismatch and allow to only enable chosen emojis (#35692) (#35705)

Backport #35692 by wxiaoguang

Fix #23635

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/markup/html_emoji.go

@@ -5,6 +5,7 @@ package markup
 
 import (
 	"strings"
+	"unicode"
 
 	"code.gitea.io/gitea/modules/emoji"
 	"code.gitea.io/gitea/modules/setting"
@@ -66,26 +67,31 @@ func emojiShortCodeProcessor(ctx *RenderContext, node *html.Node) {
 		}
 		m[0] += start
 		m[1] += start
-
 		start = m[1]
 
 		alias := node.Data[m[0]:m[1]]
-		alias = strings.ReplaceAll(alias, ":", "")
-		converted := emoji.FromAlias(alias)
-		if converted == nil {
-			// check if this is a custom reaction
-			if _, exist := setting.UI.CustomEmojisMap[alias]; exist {
-				replaceContent(node, m[0], m[1], createCustomEmoji(ctx, alias))
-				node = node.NextSibling.NextSibling
-				start = 0
-				continue
-			}
+
+		var nextChar byte
+		if m[1] < len(node.Data) {
+			nextChar = node.Data[m[1]]
+		}
+		if nextChar == ':' || unicode.IsLetter(rune(nextChar)) || unicode.IsDigit(rune(nextChar)) {
 			continue
 		}
 
-		replaceContent(node, m[0], m[1], createEmoji(ctx, converted.Emoji, converted.Description))
-		node = node.NextSibling.NextSibling
-		start = 0
+		alias = strings.Trim(alias, ":")
+		converted := emoji.FromAlias(alias)
+		if converted != nil {
+			// standard emoji
+			replaceContent(node, m[0], m[1], createEmoji(ctx, converted.Emoji, converted.Description))
+			node = node.NextSibling.NextSibling
+			start = 0 // restart searching start since node has changed
+		} else if _, exist := setting.UI.CustomEmojisMap[alias]; exist {
+			// custom reaction
+			replaceContent(node, m[0], m[1], createCustomEmoji(ctx, alias))
+			node = node.NextSibling.NextSibling
+			start = 0 // restart searching start since node has changed
+		}
 	}
 }