fix: 500 error when updating user visibility (#38480)

## How to reproduce this bug

1. Create a user with `visibility=public`
2. Update `ALLOWED_USER_VISIBILITY_MODES` setting to `limited, private`
3. Modify any field other than "User visibility" (e.g. "Full Name")
4. UI shows 500 error

## Fix

Only update the visibility field when it actually changes.

services/user/update.go

@@ -145,7 +145,8 @@ func UpdateUser(ctx context.Context, u *user_model.User, opts *UpdateOptions) er
 		}
 	}
 
-	if opts.Visibility.Has() {
+	// only validate and persist the visibility when it actually changes
+	if opts.Visibility.Has() && opts.Visibility.Value() != u.Visibility {
 		if !u.IsOrganization() && !setting.Service.AllowedUserVisibilityModesSlice.IsAllowedVisibility(opts.Visibility.Value()) {
 			return fmt.Errorf("visibility mode not allowed: %s", opts.Visibility.Value().String())
 		}

services/user/update_test.go

@@ -10,7 +10,9 @@ import (
 	user_model "gitea.dev/models/user"
 	password_module "gitea.dev/modules/auth/password"
 	"gitea.dev/modules/optional"
+	"gitea.dev/modules/setting"
 	"gitea.dev/modules/structs"
+	"gitea.dev/modules/test"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -121,3 +123,33 @@ func TestUpdateAuth(t *testing.T) {
 		Password: optional.Some("aaaa"),
 	}), password_module.ErrMinLength)
 }
+
+func TestUpdateUserVisibility(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	// user28's current visibility is public, e.g. an account created before public was disallowed
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 28})
+	assert.Equal(t, structs.VisibleTypePublic, user.Visibility)
+
+	// public is no longer an allowed visibility mode, e.g. ALLOWED_USER_VISIBILITY_MODES = limited, private
+	defer test.MockVariableValue(&setting.Service.AllowedUserVisibilityModesSlice, setting.AllowedVisibility{false, true, true})()
+
+	// re-submitting the unchanged (now-disallowed) visibility must not fail the whole update
+	assert.NoError(t, UpdateUser(t.Context(), user, &UpdateOptions{
+		FullName:   optional.Some("Changed Name"),
+		Visibility: optional.Some(structs.VisibleTypePublic),
+	}))
+	assert.Equal(t, "Changed Name", user.FullName)
+	assert.Equal(t, structs.VisibleTypePublic, user.Visibility)
+
+	// changing to an allowed visibility still works
+	assert.NoError(t, UpdateUser(t.Context(), user, &UpdateOptions{
+		Visibility: optional.Some(structs.VisibleTypePrivate),
+	}))
+	assert.Equal(t, structs.VisibleTypePrivate, user.Visibility)
+
+	// genuinely changing to a disallowed visibility is still rejected
+	assert.Error(t, UpdateUser(t.Context(), user, &UpdateOptions{
+		Visibility: optional.Some(structs.VisibleTypePublic),
+	}))
+}