[libc++] Remove assertions from <string_view> that are unreachable (llvm#148598)

When assertions are enabled it is impossible to construct a
`string_view` which contains a null pointer and a non-zero size, so
assertions where we check for that on an already constructed
`string_view` are unreachable.

Author: philnik777

libcxx/include/string_view

@@ -320,7 +320,7 @@ public:
   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI basic_string_view(const _CharT* __s, size_type __len) _NOEXCEPT
       _LIBCPP_DIAGNOSE_NULLPTR_IF(__len != 0 && __s == nullptr, " if len is not zero")
       : __data_(__s), __size_(__len) {
-#  if _LIBCPP_STD_VER >= 14
+#  if !defined(_LIBCPP_CXX03_LANG) && (!defined(_LIBCPP_COMPILER_GCC) || _LIBCPP_STD_VER >= 14)
     // Allocations must fit in `ptrdiff_t` for pointer arithmetic to work. If `__len` exceeds it, the input
     // range could not have been valid. Most likely the caller underflowed some arithmetic and inadvertently
     // passed in a negative length.
@@ -502,7 +502,6 @@ public:
   // find
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI size_type
   find(basic_string_view __s, size_type __pos = 0) const _NOEXCEPT {
-    _LIBCPP_ASSERT_NON_NULL(__s.size() == 0 || __s.data() != nullptr, "string_view::find(): received nullptr");
     return std::__str_find<value_type, size_type, traits_type, npos>(data(), size(), __s.data(), __pos, __s.size());
   }
 
@@ -527,7 +526,6 @@ public:
   // rfind
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI size_type
   rfind(basic_string_view __s, size_type __pos = npos) const _NOEXCEPT {
-    _LIBCPP_ASSERT_NON_NULL(__s.size() == 0 || __s.data() != nullptr, "string_view::find(): received nullptr");
     return std::__str_rfind<value_type, size_type, traits_type, npos>(data(), size(), __s.data(), __pos, __s.size());
   }
 
@@ -553,7 +551,6 @@ public:
   // find_first_of
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI size_type
   find_first_of(basic_string_view __s, size_type __pos = 0) const _NOEXCEPT {
-    _LIBCPP_ASSERT_NON_NULL(__s.size() == 0 || __s.data() != nullptr, "string_view::find_first_of(): received nullptr");
     return std::__str_find_first_of<value_type, size_type, traits_type, npos>(
         data(), size(), __s.data(), __pos, __s.size());
   }
@@ -580,7 +577,6 @@ public:
   // find_last_of
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI size_type
   find_last_of(basic_string_view __s, size_type __pos = npos) const _NOEXCEPT {
-    _LIBCPP_ASSERT_NON_NULL(__s.size() == 0 || __s.data() != nullptr, "string_view::find_last_of(): received nullptr");
     return std::__str_find_last_of<value_type, size_type, traits_type, npos>(
         data(), size(), __s.data(), __pos, __s.size());
   }
@@ -607,8 +603,6 @@ public:
   // find_first_not_of
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI size_type
   find_first_not_of(basic_string_view __s, size_type __pos = 0) const _NOEXCEPT {
-    _LIBCPP_ASSERT_NON_NULL(
-        __s.size() == 0 || __s.data() != nullptr, "string_view::find_first_not_of(): received nullptr");
     return std::__str_find_first_not_of<value_type, size_type, traits_type, npos>(
         data(), size(), __s.data(), __pos, __s.size());
   }
@@ -635,8 +629,6 @@ public:
   // find_last_not_of
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI size_type
   find_last_not_of(basic_string_view __s, size_type __pos = npos) const _NOEXCEPT {
-    _LIBCPP_ASSERT_NON_NULL(
-        __s.size() == 0 || __s.data() != nullptr, "string_view::find_last_not_of(): received nullptr");
     return std::__str_find_last_not_of<value_type, size_type, traits_type, npos>(
         data(), size(), __s.data(), __pos, __s.size());
   }

libcxx/test/libcxx/strings/string.view/assert.ctor.length.pass.cpp

@@ -7,7 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 // REQUIRES: has-unix-headers
-// UNSUPPORTED: c++03, c++11
+// UNSUPPORTED: c++03
+// UNSUPPORTED: c++11 && gcc
 // REQUIRES: libcpp-hardening-mode={{extensive|debug}}
 // XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
 
@@ -17,10 +18,17 @@
 #include <string_view>
 
 #include "check_assertion.h"
+#include "test_macros.h"
+
+// We're testing for assertions here, so let's not diagnose the misuses at compile time
+// FIXME: This should really be in ADDITIONAL_COMPILE_FLAGS, but it that doesn't work due to a Clang bug
+TEST_CLANG_DIAGNOSTIC_IGNORED("-Wnonnull")
 
 int main(int, char**) {
   char c = 0;
   TEST_LIBCPP_ASSERT_FAILURE(
       std::string_view(&c, -1), "string_view::string_view(_CharT *, size_t): length does not fit in difference_type");
+  TEST_LIBCPP_ASSERT_FAILURE(
+      std::string_view(nullptr, 1), "string_view::string_view(_CharT *, size_t): received nullptr");
   return 0;
 }