[libcxx] [test] Fixed possible loss of data warnings in tests on amd64

[BillyONeal]

Summary

Fix possible loss of data warnings on amd64

In T_size_size.pass, there is an explicit template argument to std::min to ask
for unsigned, to avoid type deduction errors. However, C1XX' warnings still
hate this use, because a 64 bit value (a size_t) is being passed to a function
accepting an unsigned (a 32 bit value).

Instead, change the tests to pass around std::size_t instances, and explicitly
narrow when constructing the string type under test. This also allows
removal of explicit template arguments to std::min.

[EricWF]

LGTM after addressing inline comments.

test/std/strings/basic.string/string.cons/T_size_size.pass.cpp

40

The cast should happen after the subtraction, not before.

73

The cast should happen after the subtraction, not before.

[BillyONeal]

test/std/strings/basic.string/string.cons/T_size_size.pass.cpp

40

The cast happens before the subtraction because the invariant that size() is less than unsigned max is established on line 36 (by passing in an unsigned as the length).

Alternately, would it be better to just pass around size_ts here so that no casts would be necessary any longer?

[EricWF]

test/std/strings/basic.string/string.cons/T_size_size.pass.cpp

40

Alternately, would it be better to just pass around size_ts here so that no casts would be necessary any longer?

Yeah, that seems more correct to me. Good catch.

[BillyONeal]

Instead, change the tests to pass around std::size_t instances, and explicitly
narrow when constructing the string type under test. This also allows
removal of explicit template arguments to std::min.

[EricWF]

Still LGTM.

test/std/strings/basic.string/string.cons/T_size_size.pass.cpp

 #include <cassert>
 
 #include "test_macros.h"
 #include "test_allocator.h"
 #include "min_allocator.h"
 
 template <class S, class SV>
 void
-test(SV sv, unsigned pos, unsigned n)
+test(SV sv, std::size_t pos, std::size_t n)
 {
     typedef typename S::traits_type T;
     typedef typename S::allocator_type A;
+    typedef typename S::size_type Size;
     if (pos <= sv.size())
     {
-        S s2(sv, pos, n);
+        S s2(sv, static_cast<Size>(pos), static_cast<Size>(n));
         LIBCPP_ASSERT(s2.__invariants());
         assert(pos <= sv.size());
-        unsigned rlen = std::min<unsigned>(sv.size() - pos, n);
+        std::size_t rlen = std::min(sv.size() - pos, n);
         assert(s2.size() == rlen);
         assert(T::compare(s2.data(), sv.data() + pos, rlen) == 0);
         assert(s2.get_allocator() == A());
         assert(s2.capacity() >= s2.size());
     }
 #ifndef TEST_HAS_NO_EXCEPTIONS
     else
     {
         try
         {
-            S s2(sv, pos, n);
+            S s2(sv, static_cast<Size>(pos), static_cast<Size>(n));
             assert(false);
         }
         catch (std::out_of_range&)
         {
             assert(pos > sv.size());
         }
     }
 #endif
 }
 
 template <class S, class SV>
 void
-test(SV sv, unsigned pos, unsigned n, const typename S::allocator_type& a)
+test(SV sv, std::size_t pos, std::size_t n, const typename S::allocator_type& a)
 {
     typedef typename S::traits_type T;
+    typedef typename S::size_type Size;
     if (pos <= sv.size())
     {
-        S s2(sv, pos, n, a);
+        S s2(sv, static_cast<Size>(pos), static_cast<Size>(n), a);
         LIBCPP_ASSERT(s2.__invariants());
         assert(pos <= sv.size());
-        unsigned rlen = std::min<unsigned>(sv.size() - pos, n);
+        std::size_t rlen = std::min(sv.size() - pos, n);
         assert(s2.size() == rlen);
         assert(T::compare(s2.data(), sv.data() + pos, rlen) == 0);
         assert(s2.get_allocator() == a);
         assert(s2.capacity() >= s2.size());
     }
 #ifndef TEST_HAS_NO_EXCEPTIONS
     else
     {
         try
         {
-            S s2(sv, pos, n, a);
+            S s2(sv, static_cast<Size>(pos), static_cast<Size>(n), a);
             assert(false);
         }
         catch (std::out_of_range&)
         {
             assert(pos > sv.size());
         }
     }
 #endif