[clang-tools-extra] [clang-tidy] Add a new check 'modernize-use-string-view' (PR #172170)

[Yanzuo Liu via cfe-commits]

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@@ -0,0 +1,373 @@
+// RUN: %check_clang_tidy \
+// RUN: -std=c++17-or-later %s modernize-use-string-view %t -- \
+// RUN: -- -isystem %clang_tidy_headers
+
+#include <string>
+
+namespace std {
+namespace literals {
+namespace string_literals {
+  string operator""s(const char *, size_t);
+}
+namespace string_view_literals {
+  string_view operator""sv(const char *, size_t);
+}
+}
+template <class T, class U> struct is_same { static constexpr bool value = false; };
+template <class T> struct is_same<T, T> { static constexpr bool value = true; };
+template <class T, class U> constexpr bool is_same_v = is_same<T, U>::value;
+} // namespace std
+
+
+// ==========================================================
+// Positive tests
+// ==========================================================
+
+std::string simpleLiteral() {
+// CHECK-MESSAGES:[[@LINE-1]]:1: warning: consider using 'std::string_view' to avoid unnecessary copying and allocations [modernize-use-string-view]
+// CHECK-FIXES: std::string_view simpleLiteral() {
+  return "simpleLiteral";
+}
+
+std::wstring simpleLiteralW() {
+// CHECK-MESSAGES:[[@LINE-1]]:1: warning: consider using 'std::wstring_view' to avoid unnecessary copying and allocations [modernize-use-string-view]
+// CHECK-FIXES: std::wstring_view simpleLiteralW() {
+  return L"wide literal";
+}
+
+std::string simpleRLiteral() {
+// CHECK-MESSAGES:[[@LINE-1]]:1: warning: consider using 'std::string_view' to avoid unnecessary copying and allocations [modernize-use-string-view]
+// CHECK-FIXES: std::string_view simpleRLiteral() {
+  return R"(simpleLiteral)";
+}
+
+[[nodiscard]] std::string Attributed() {
+// CHECK-MESSAGES:[[@LINE-1]]:15: warning: consider using 'std::string_view' to avoid unnecessary copying and allocations [modernize-use-string-view]
+// CHECK-FIXES: {{\[\[nodiscard\]\]}} std::string_view Attributed() {
+  return "attributed";
+}
+
+const std::string Const() {
+// CHECK-MESSAGES:[[@LINE-1]]:7: warning: consider using 'std::string_view' to avoid unnecessary copying and allocations [modernize-use-string-view]
+// CHECK-FIXES: const std::string_view Const() {
+  return "Const";
+}
+
+auto Trailing() -> std::string {
+// CHECK-MESSAGES:[[@LINE-1]]:1: warning: consider using 'std::string_view' to avoid unnecessary copying and allocations [modernize-use-string-view]
+// TODO: support fixes for deduced types
----------------
zwuis wrote:

This is trailing return type, not deduced return type.

https://github.com/llvm/llvm-project/pull/172170