Make allowed Visiblity modes configurable for Users (#16271)

Now that #16069 is merged, some sites may wish to enforce that users are all public, limited or private, and/or disallow users from becoming private.

This PR adds functionality and settings to constrain a user's ability to change their visibility.

Co-authored-by: zeripath <art27@cantab.net>

models/user_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/util"
 
 	"github.com/stretchr/testify/assert"
@@ -189,6 +190,7 @@ func TestDeleteUser(t *testing.T) {
 
 func TestEmailNotificationPreferences(t *testing.T) {
 	assert.NoError(t, PrepareTestDatabase())
+
 	for _, test := range []struct {
 		expected string
 		userID   int64
@@ -467,3 +469,23 @@ ssh-dss AAAAB3NzaC1kc3MAAACBAOChCC7lf6Uo9n7BmZ6M8St19PZf4Tn59NriyboW2x/DZuYAz3ib
 		}
 	}
 }
+
+func TestUpdateUser(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+	user := AssertExistsAndLoadBean(t, &User{ID: 2}).(*User)
+
+	user.KeepActivityPrivate = true
+	assert.NoError(t, UpdateUser(user))
+	user = AssertExistsAndLoadBean(t, &User{ID: 2}).(*User)
+	assert.True(t, user.KeepActivityPrivate)
+
+	setting.Service.AllowedUserVisibilityModesSlice = []bool{true, false, false}
+	user.KeepActivityPrivate = false
+	user.Visibility = structs.VisibleTypePrivate
+	assert.Error(t, UpdateUser(user))
+	user = AssertExistsAndLoadBean(t, &User{ID: 2}).(*User)
+	assert.True(t, user.KeepActivityPrivate)
+
+	user.Email = "no mail@mail.org"
+	assert.Error(t, UpdateUser(user))
+}