Fix various trivial problems (#36921)

* Fix #36915
* Fix #36919
* Close #36600
* Close #36601
* Fix incorrect oauth2 error message display

models/issues/pull.go

@@ -9,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"regexp"
 	"strings"
 
 	"code.gitea.io/gitea/models/db"
@@ -24,6 +23,7 @@ import (
 	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/util"
 
+	"github.com/dlclark/regexp2"
 	"xorm.io/builder"
 )
 
@@ -861,7 +861,7 @@ func GetCodeOwnersFromContent(ctx context.Context, data string) ([]*CodeOwnerRul
 }
 
 type CodeOwnerRule struct {
-	Rule     *regexp.Regexp
+	Rule     *regexp2.Regexp // it supports negative lookahead, does better for end users
 	Negative bool
 	Users    []*user_model.User
 	Teams    []*org_model.Team
@@ -877,7 +877,8 @@ func ParseCodeOwnersLine(ctx context.Context, tokens []string) (*CodeOwnerRule,
 
 	warnings := make([]string, 0)
 
-	rule.Rule, err = regexp.Compile(fmt.Sprintf("^%s$", strings.TrimPrefix(tokens[0], "!")))
+	expr := fmt.Sprintf("^%s$", strings.TrimPrefix(tokens[0], "!"))
+	rule.Rule, err = regexp2.Compile(expr, regexp2.None)
 	if err != nil {
 		warnings = append(warnings, fmt.Sprintf("incorrect codeowner regexp: %s", err))
 		return nil, warnings