cleanup code `issueFullPattern` in modules/markup (#16419)

fix #16415

modules/markup/html.go

@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+	"sync"
 
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/emoji"
@@ -71,9 +72,6 @@ var (
 // CSS class for action keywords (e.g. "closes: #1")
 const keywordClass = "issue-keyword"
 
-// regexp for full links to issues/pulls
-var issueFullPattern *regexp.Regexp
-
 // IsLink reports whether link fits valid format.
 func IsLink(link []byte) bool {
 	return isLink(link)
@@ -88,12 +86,17 @@ func isLinkStr(link string) bool {
 	return validLinksPattern.MatchString(link)
 }
 
-// FIXME: This function is not concurrent safe
+// regexp for full links to issues/pulls
+var issueFullPattern *regexp.Regexp
+
+// Once for to prevent races
+var issueFullPatternOnce sync.Once
+
 func getIssueFullPattern() *regexp.Regexp {
-	if issueFullPattern == nil {
+	issueFullPatternOnce.Do(func() {
 		issueFullPattern = regexp.MustCompile(regexp.QuoteMeta(setting.AppURL) +
 			`\w+/\w+/(?:issues|pulls)/((?:\w{1,10}-)?[1-9][0-9]*)([\?|#]\S+.(\S+)?)?\b`)
-	}
+	})
 	return issueFullPattern
 }
 

modules/markup/renderer.go

@@ -19,7 +19,6 @@ import (
 
 // Init initialize regexps for markdown parsing
 func Init() {
-	getIssueFullPattern()
 	NewSanitizer()
 	if len(setting.Markdown.CustomURLSchemes) > 0 {
 		CustomLinkURLSchemes(setting.Markdown.CustomURLSchemes)