Add link to user profile in markdown mention only if user exists (#21533)

Previously mentioning a user would link to its profile, regardless of
whether the user existed. This change tests if the user exists and only
if it does - a link to its profile is added.

* Fixes #3444

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/markup/html.go

@@ -603,8 +603,14 @@ func mentionProcessor(ctx *RenderContext, node *html.Node) {
 			start = loc.End
 			continue
 		}
-		replaceContent(node, loc.Start, loc.End, createLink(util.URLJoin(setting.AppURL, mention[1:]), mention, "mention"))
-		node = node.NextSibling.NextSibling
+		mentionedUsername := mention[1:]
+
+		if processorHelper.IsUsernameMentionable != nil && processorHelper.IsUsernameMentionable(ctx.Ctx, mentionedUsername) {
+			replaceContent(node, loc.Start, loc.End, createLink(util.URLJoin(setting.AppURL, mentionedUsername), mention, "mention"))
+			node = node.NextSibling.NextSibling
+		} else {
+			node = node.NextSibling
+		}
 		start = 0
 	}
 }

modules/markup/markdown/markdown_test.go

@@ -38,6 +38,11 @@ func TestMain(m *testing.M) {
 	if err := git.InitSimple(context.Background()); err != nil {
 		log.Fatal("git init failed, err: %v", err)
 	}
+	markup.Init(&markup.ProcessorHelper{
+		IsUsernameMentionable: func(ctx context.Context, username string) bool {
+			return username == "r-lyeh"
+		},
+	})
 	os.Exit(m.Run())
 }
 

modules/markup/renderer.go

@@ -19,8 +19,18 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 )
 
+type ProcessorHelper struct {
+	IsUsernameMentionable func(ctx context.Context, username string) bool
+}
+
+var processorHelper ProcessorHelper
+
 // Init initialize regexps for markdown parsing
-func Init() {
+func Init(ph *ProcessorHelper) {
+	if ph != nil {
+		processorHelper = *ph
+	}
+
 	NewSanitizer()
 	if len(setting.Markdown.CustomURLSchemes) > 0 {
 		CustomLinkURLSchemes(setting.Markdown.CustomURLSchemes)