refactor: form binding validation (#38832)

Make "form-fetch-action" highlight the invalid field as "error"

modules/web/middleware/binding_test.go

@@ -0,0 +1,31 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"gitea.dev/modules/translation"
+
+	"gitea.com/go-chi/binding"
+	"github.com/stretchr/testify/assert"
+)
+
+type testRangeForm struct {
+	Hours int `binding:"Range(0,1000)"`
+}
+
+func (f *testRangeForm) Validate(_ *http.Request, errs binding.Errors) binding.Errors { return errs }
+
+func TestBuildValidationErrorForUser(t *testing.T) {
+	// an out-of-range value must reach its own message instead of the panicking "default" branch
+	form := &testRangeForm{Hours: 2000}
+	errs := binding.Validate(httptest.NewRequest(http.MethodPost, "/", nil), form)
+	errorMessage, errorFieldName, fieldNames := BuildValidationErrorForUser(form, translation.MockLocale{}, errs)
+	assert.Equal(t, "form.range_error:Hours,0,1000", errorMessage)
+	assert.Equal(t, "Hours", errorFieldName)
+	assert.Equal(t, []string{"Hours"}, fieldNames)
+}