[libc++] Implement P0980R1 (constexpr std::string)

Reviewed By: #libc, ldionne

Spies: daltenty, sdasgup3, ldionne, arichardson, MTC, ChuanqiXu, mehdi_amini, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, aartbik, liufengdb, stephenneuendorffer, Joonsoo, grosul1, Kayjukh, jurahul, msifontes, tatianashp, rdzhabarov, teijeong, cota, dcaballe, Chia-hungDuan, wrengr, wenzhicui, arphaman, Mordante, miscco, Quuxplusone, smeenai, libcxx-commits

Differential Revision: https://reviews.llvm.org/D110598

libcxx/test/std/strings/basic.string/string.capacity/capacity.pass.cpp

@@ -8,7 +8,7 @@
 
 // <string>
 
-// size_type capacity() const;
+// size_type capacity() const; // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -18,11 +18,9 @@
 
 #include "test_macros.h"
 
-test_allocator_statistics alloc_stats;
-
 template <class S>
 TEST_CONSTEXPR_CXX20 void
-test(S s)
+test(S s, test_allocator_statistics& alloc_stats)
 {
     alloc_stats.throw_after = 0;
 #ifndef TEST_HAS_NO_EXCEPTIONS
@@ -42,17 +40,18 @@ test(S s)
     alloc_stats.throw_after = INT_MAX;
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
+    test_allocator_statistics alloc_stats;
     typedef std::basic_string<char, std::char_traits<char>, test_allocator<char> > S;
     S s((test_allocator<char>(&alloc_stats)));
-    test(s);
+    test(s, alloc_stats);
     s.assign(10, 'a');
     s.erase(5);
-    test(s);
+    test(s, alloc_stats);
     s.assign(100, 'a');
     s.erase(50);
-    test(s);
+    test(s, alloc_stats);
   }
 #if TEST_STD_VER >= 11
   {
@@ -69,7 +68,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/clear.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// void clear();
+// void clear(); // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -24,7 +26,7 @@ test(S s)
     assert(s.size() == 0);
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     S s;
@@ -61,7 +63,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/empty.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// bool empty() const noexcept;
+// bool empty() const noexcept; // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -24,7 +26,7 @@ test(const S& s)
     assert(s.empty() == (s.size() == 0));
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     test(S());
@@ -47,7 +49,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/empty.verify.cpp

@@ -10,7 +10,7 @@
 
 // class deque
 
-// bool empty() const noexcept;
+// bool empty() const noexcept; // constexpr since C++20
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 
@@ -18,7 +18,7 @@
 
 #include "test_macros.h"
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   std::string c;
   c.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
 
@@ -29,7 +29,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/length.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// size_type length() const;
+// size_type length() const; // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -17,13 +19,13 @@
 #include "min_allocator.h"
 
 template <class S>
-void
+TEST_CONSTEXPR_CXX20 void
 test(const S& s)
 {
     assert(s.length() == s.size());
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     test(S());
@@ -46,7 +48,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp

@@ -9,7 +9,7 @@
 // UNSUPPORTED: no-exceptions
 // <string>
 
-// size_type max_size() const;
+// size_type max_size() const; // constexpr since C++20
 
 // NOTE: asan and msan will fail for one of two reasons
 // 1. If allocator_may_return_null=0 then they will fail because the allocation
@@ -25,7 +25,7 @@
 #include "min_allocator.h"
 
 template <class S>
-void
+TEST_CONSTEXPR_CXX20 void
 test1(const S& s)
 {
     S s2(s);
@@ -36,7 +36,7 @@ test1(const S& s)
 }
 
 template <class S>
-void
+TEST_CONSTEXPR_CXX20 void
 test2(const S& s)
 {
     S s2(s);
@@ -47,7 +47,7 @@ test2(const S& s)
 }
 
 template <class S>
-void
+TEST_CONSTEXPR_CXX20 void
 test(const S& s)
 {
     assert(s.max_size() >= s.size());
@@ -55,7 +55,7 @@ test(const S& s)
     test2(s);
 }
 
-bool test() {
+void test() {
   {
     typedef std::string S;
     test(S());
@@ -70,15 +70,25 @@ bool test() {
     test(S("12345678901234567890123456789012345678901234567890"));
   }
 #endif
+}
+
+#if TEST_STD_VER > 17
+constexpr bool test_constexpr() {
+  std::string str;
+
+  size_t size = str.max_size();
+  assert(size > 0);
 
   return true;
 }
+#endif
 
 int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  test_constexpr();
+  static_assert(test_constexpr());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/over_max_size.pass.cpp

@@ -16,7 +16,7 @@
 
 // <string>
 
-// size_type max_size() const;
+// size_type max_size() const; // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -59,9 +59,6 @@ bool test() {
 int main(int, char**)
 {
   test();
-#if TEST_STD_VER > 17
-  // static_assert(test());
-#endif
 
   return 0;
 }

libcxx/test/std/strings/basic.string/string.capacity/reserve.pass.cpp

@@ -20,7 +20,7 @@
 #include "min_allocator.h"
 
 template <class S>
-TEST_CONSTEXPR_CXX20 void
+void
 test(typename S::size_type min_cap, typename S::size_type erased_index)
 {
     S s(min_cap, 'a');
@@ -63,9 +63,6 @@ bool test() {
 int main(int, char**)
 {
   test();
-#if TEST_STD_VER > 17
-  // static_assert(test());
-#endif
 
   return 0;
 }

libcxx/test/std/strings/basic.string/string.capacity/reserve_size.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// void reserve(size_type res_arg);
+// void reserve(size_type res_arg); // constexpr since C++20
 
 // This test relies on https://llvm.org/PR45368 being fixed, which isn't in
 // older Apple dylibs
@@ -62,7 +64,7 @@ test(typename S::size_type min_cap, typename S::size_type erased_index, typename
 #endif
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     {
@@ -105,7 +107,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp

@@ -90,18 +90,14 @@ int main(int, char**) {
   test<char16_t>();
   test<char32_t>();
 
-#if defined(__cpp_lib_constexpr_string) && __cpp_lib_constexpr_string >= 201907L
   static_assert(test<char>());
   static_assert(test<char8_t>());
   static_assert(test<char16_t>());
   static_assert(test<char32_t>());
-#endif
 
 #ifndef TEST_HAS_NO_WIDE_CHARACTERS
   test<wchar_t>();
-#if defined(__cpp_lib_constexpr_string) && __cpp_lib_constexpr_string >= 201907L
   static_assert(test<wchar_t>());
-#endif
 #endif
   return 0;
 }

libcxx/test/std/strings/basic.string/string.capacity/resize_size.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// void resize(size_type n);
+// void resize(size_type n); // constexpr since C++20
 
 #include <string>
 #include <stdexcept>
@@ -43,7 +45,7 @@ test(S s, typename S::size_type n, S expected)
 #endif
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     test(S(), 0, S());
@@ -92,7 +94,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/resize_size_char.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// void resize(size_type n, charT c);
+// void resize(size_type n, charT c); // constexpr since C++20
 
 #include <string>
 #include <stdexcept>
@@ -43,7 +45,7 @@ test(S s, typename S::size_type n, typename S::value_type c, S expected)
 #endif
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     test(S(), 0, 'a', S());
@@ -92,7 +94,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/shrink_to_fit.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// void shrink_to_fit();
+// void shrink_to_fit(); // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -29,7 +31,7 @@ test(S s)
     assert(s.capacity() >= s.size());
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     S s;
@@ -66,7 +68,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;

libcxx/test/std/strings/basic.string/string.capacity/size.pass.cpp

@@ -6,9 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: LIBCXX-AIX-FIXME
+
 // <string>
 
-// size_type size() const;
+// size_type size() const; // constexpr since C++20
 
 #include <string>
 #include <cassert>
@@ -23,7 +25,7 @@ test(const S& s, typename S::size_type c)
     assert(s.size() == c);
 }
 
-bool test() {
+TEST_CONSTEXPR_CXX20 bool test() {
   {
     typedef std::string S;
     test(S(), 0);
@@ -46,7 +48,7 @@ int main(int, char**)
 {
   test();
 #if TEST_STD_VER > 17
-  // static_assert(test());
+  static_assert(test());
 #endif
 
   return 0;