[clang-tools-extra] [clang-tidy] Add a new check 'performance-string-view-conversions' (PR #174288)

[via cfe-commits]

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@@ -0,0 +1,134 @@
+// RUN: %check_clang_tidy -std=c++17-or-later %s performance-string-view-conversions %t -- \
+// RUN:   -- -isystem %clang_tidy_headers
+
+#include <string>
+
+using namespace std::literals::string_literals;
+using namespace std::literals::string_view_literals;
+
+// Support for std::move
+namespace std {
+template <typename>
+struct remove_reference;
+
+template <typename _Tp>
+struct remove_reference {
+  typedef _Tp type;
+};
+
+template <typename _Tp>
+struct remove_reference<_Tp &> {
+  typedef _Tp type;
+};
+
+template <typename _Tp>
+struct remove_reference<_Tp &&> {
+  typedef _Tp type;
+};
+
+template <typename _Tp>
+constexpr typename std::remove_reference<_Tp>::type &&move(_Tp &&__t) {
+  return static_cast<typename std::remove_reference<_Tp>::type &&>(__t);
+}
+} // namespace std
+
+void foo_sv(int p1, std::string_view p2, double p3);
+void foo_wsv(int p1, std::wstring_view p2, double p3);
+void foo_wsv(std::wstring_view p2);
+void foo_str(int p1, const std::string& p2, double p3);
+void foo_wstr(int p1, const std::wstring& p2, double p3);
+
+std::string foo_str(int p1);
+std::wstring foo_wstr(int, const std::string&);
+std::string_view foo_sv(int p1);
+
+void positive(std::string_view sv, std::wstring_view wsv) {
+  // string(string_view)
+  //
+  foo_sv(42, std::string(sv), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, sv, 3.14);
+
+  foo_sv(42, std::string("Hello, world"), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, "Hello, world", 3.14);
+
+  // TODO: support for ""sv literals
+  foo_sv(42, "Hello, world"s, 3.14);
+
+  foo_sv(42, std::string{"Hello, world"}, 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, "Hello, world", 3.14);
+
+  const char *ptr = "Hello, world";
+  foo_sv(42, std::string(ptr), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, ptr, 3.14);
+
+  char arr[] = "Hello, world";
+  foo_sv(42, std::string(arr), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, arr, 3.14);
+
+  foo_sv(42, std::string(foo_sv(42)), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, foo_sv(42), 3.14);
+
+  std::string s = "hello";
+  foo_sv(42, std::string(s), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, s, 3.14);
+
+  foo_sv(42, std::string{s}, 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: redundant conversion to 'std::string' (aka 'basic_string<char>') and then back to 'std::string_view' (aka 'basic_string_view<char>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_sv(42, s, 3.14);
+
+  // wstring(wstring_view)
+  //
+  foo_wsv(42, std::wstring(wsv), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: redundant conversion to 'std::wstring' (aka 'basic_string<wchar_t>') and then back to 'std::wstring_view' (aka 'basic_string_view<wchar_t>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_wsv(42, wsv, 3.14);
+
+  const wchar_t *wptr = L"Hello, world";
+  foo_wsv(42, std::wstring(wptr), 3.14);
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: redundant conversion to 'std::wstring' (aka 'basic_string<wchar_t>') and then back to 'std::wstring_view' (aka 'basic_string_view<wchar_t>') [performance-string-view-conversions]
+  // CHECK-FIXES: foo_wsv(42, wptr, 3.14);
+}
+
+void negative(std::string_view sv, std::wstring_view wsv) {
+  // No warnings expected: already string_view
----------------
zeyi2 wrote:

Could we add a new testcase like: `foo_sv(42, std::string("Hello, world", 5), 3.14);`

(To make sure that no wrong fix-it is generated, by reading the implementation I suspect that it may generate `std::string("Hello, world")`, which seems off. We likely need to add `argumentCountIs(1)` to the matcher to prevent this.)

https://github.com/llvm/llvm-project/pull/174288