fix 500 when use a duplicat email instead of giving an error tip (#1040)

models/login_source.go

@@ -20,9 +20,9 @@ import (
 	"github.com/go-xorm/xorm"
 
 	"code.gitea.io/gitea/modules/auth/ldap"
+	"code.gitea.io/gitea/modules/auth/oauth2"
 	"code.gitea.io/gitea/modules/auth/pam"
 	"code.gitea.io/gitea/modules/log"
-	"code.gitea.io/gitea/modules/auth/oauth2"
 )
 
 // LoginType represents an login type.
@@ -624,6 +624,16 @@ func UserSignIn(username, password string) (*User, error) {
 	var user *User
 	if strings.Contains(username, "@") {
 		user = &User{Email: strings.ToLower(strings.TrimSpace(username))}
+		// check same email
+		cnt, err := x.Count(user)
+		if err != nil {
+			return nil, err
+		}
+		if cnt > 1 {
+			return nil, ErrEmailAlreadyUsed{
+				Email: user.Email,
+			}
+		}
 	} else {
 		user = &User{LowerName: strings.ToLower(strings.TrimSpace(username))}
 	}

routers/user/auth.go

@@ -7,20 +7,20 @@ package user
 import (
 	"errors"
 	"fmt"
+	"net/http"
 	"net/url"
-
+	"strings"
-	"github.com/go-macaron/captcha"
 
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/auth"
+	"code.gitea.io/gitea/modules/auth/oauth2"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
-	"net/http"
+
-	"code.gitea.io/gitea/modules/auth/oauth2"
+	"github.com/go-macaron/captcha"
 	"github.com/markbates/goth"
-	"strings"
 )
 
 const (
@@ -144,6 +144,8 @@ func SignInPost(ctx *context.Context, form auth.SignInForm) {
 	if err != nil {
 		if models.IsErrUserNotExist(err) {
 			ctx.RenderWithErr(ctx.Tr("form.username_password_incorrect"), tplSignIn, &form)
+		} else if models.IsErrEmailAlreadyUsed(err) {
+			ctx.RenderWithErr(ctx.Tr("form.email_been_used"), tplSignIn, &form)
 		} else {
 			ctx.Handle(500, "UserSignIn", err)
 		}