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[libc++] Restore `basic_ios`'s implicit conversion to `bool` in C++03 mode. 

efriedma noted that D104682 broke this test case, reduced from SPEC2006.

    #include <istream>
    bool a(std::istream a) {
        return a.getline(0,0) == 0;
    }

We can unbreak it by restoring the conversion to something-convertible-to-bool.
We chose `void*` in order to match libstdc++.

For more ancient history, see PR19460: https://bugs.llvm.org/show_bug.cgi?id=19460

Differential Revision: https://reviews.llvm.org/D107663
This commit is contained in:
Arthur O'Dwyer 2021-08-06 14:50:09 -04:00
parent b2c262cfb1
commit c1a8f12873
2 changed files with 15 additions and 2 deletions
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7
libcxx/include/ios
View File

@ -607,8 +607,15 @@ public:
static_assert((is_same<_CharT, typename traits_type::char_type>::value),
"traits_type::char_type must be the same type as CharT");
#ifdef _LIBCPP_CXX03_LANG
// Preserve the ability to compare with literal 0,
// and implicitly convert to bool, but not implicitly convert to int.
_LIBCPP_INLINE_VISIBILITY
operator void*() const {return fail() ? nullptr : (void*)this;}
#else
_LIBCPP_INLINE_VISIBILITY
explicit operator bool() const {return !fail();}
#endif
_LIBCPP_INLINE_VISIBILITY bool operator!() const {return fail();}
_LIBCPP_INLINE_VISIBILITY iostate rdstate() const {return ios_base::rdstate();}

10
libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
View File

@ -24,10 +24,16 @@ int main(int, char**)
assert(static_cast<bool>(ios) == !ios.fail());
ios.setstate(std::ios::failbit);
assert(static_cast<bool>(ios) == !ios.fail());
static_assert((!std::is_convertible<std::ios, void*>::value), "");
static_assert((!std::is_convertible<std::ios, int>::value), "");
static_assert((!std::is_convertible<std::ios const&, int>::value), "");
static_assert((!std::is_convertible<std::ios, bool>::value), "");
#if TEST_STD_VER >= 11
static_assert(!std::is_convertible<std::ios, void*>::value, "");
static_assert(!std::is_convertible<std::ios, bool>::value, "");
#else
static_assert(std::is_convertible<std::ios, void*>::value, "");
static_assert(std::is_convertible<std::ios, bool>::value, "");
(void)(ios == 0); // SPEC2006 apparently relies on this to compile
#endif
return 0;
}