fix core: UASSERT for non-empty label name

commit_hash:5d5788305043304a8e076ab6c67b848fa2b8ed4f

Author: ArkadyRudenko

core/include/userver/utils/statistics/labels.hpp

@@ -7,6 +7,8 @@
 #include <string_view>
 #include <type_traits>
 
+#include <userver/utils/assert.hpp>
+
 USERVER_NAMESPACE_BEGIN
 
 namespace utils::statistics {
@@ -16,10 +18,12 @@ class Label;
 /// @brief Non owning label name+value storage.
 class LabelView final {
 public:
-    LabelView() = default;
+    LabelView() = delete;
     LabelView(Label&& label) = delete;
-    explicit LabelView(const Label& label) noexcept;
-    constexpr LabelView(std::string_view name, std::string_view value) noexcept : name_(name), value_(value) {}
+    explicit LabelView(const Label& label);
+    constexpr LabelView(std::string_view name, std::string_view value) : name_(name), value_(value) {
+        UINVARIANT(!name_.empty(), "The lable name must not be empty.");
+    }
 
     template <class T, std::enable_if_t<std::is_arithmetic_v<T>>* = nullptr>
     constexpr LabelView(std::string_view, T) {

core/src/utils/statistics/labels.cpp

@@ -6,7 +6,9 @@ USERVER_NAMESPACE_BEGIN
 
 namespace utils::statistics {
 
-LabelView::LabelView(const Label& label) noexcept : name_(label.Name()), value_(label.Value()) {}
+LabelView::LabelView(const Label& label) : name_(label.Name()), value_(label.Value()) {
+    UINVARIANT(!name_.empty(), "The lable name must not be empty.");
+}
 
 LabelsSpan::LabelsSpan(const LabelView* begin, const LabelView* end) noexcept : begin_(begin), end_(end) {
     UASSERT(begin <= end);

core/src/utils/statistics/writer.cpp

@@ -201,7 +201,8 @@ void Writer::ResetState() noexcept {
             kFixitHint
         )
     );
-    state_->add_labels.resize(initial_labels_size_);
+    auto& labels = state_->add_labels;
+    labels.erase(labels.begin() + initial_labels_size_, labels.end());
 
     state_ = nullptr;
 }