[llvm-bugs] [Bug 41819] New: Bad diagnostic when trying to copy an uncopyable type

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41819

            Bug ID: 41819
           Summary: Bad diagnostic when trying to copy an uncopyable type
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: barry.revzin at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Same issue as gcc's bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90413):

template<class T>
struct Bar {
    Bar() {}
    Bar(const Bar&) {
        static_assert(sizeof(T) == 1, "");
    }
};
template<class T>
struct Foo {
    Foo() {}
#ifdef DEFAULT
    Foo(const Foo&) = default;
#else
    Foo(const Foo& o) : b(o.b) {}
#endif
    Bar<T> b;
};

int main() { 
    Foo<int> f;
    Foo<int> g = f;
}

Without -DDEFAULT, the error points to the offending line (you can see the
construction of 'g' in the error trace):

source>:5:9: error: static_assert failed due to requirement 'sizeof(int) == 1'
""
        static_assert(sizeof(T) == 1, "");
        ^             ~~~~~~~~~~~~~~
<source>:14:25: note: in instantiation of member function 'Bar<int>::Bar'
requested here
    Foo(const Foo& o) : b(o.b) {}
                        ^
<source>:21:18: note: in instantiation of member function 'Foo<int>::Foo'
requested here
    Foo<int> g = f;
                 ^
1 error generated.
Compiler returned: 1

With -DDEFAULT, the error does not point to the offending line at all:

source>:5:9: error: static_assert failed due to requirement 'sizeof(int) == 1'
""
        static_assert(sizeof(T) == 1, "");
        ^             ~~~~~~~~~~~~~~
<source>:12:5: note: in instantiation of member function 'Bar<int>::Bar'
requested here
    Foo(const Foo&) = default;
    ^
1 error generated.
Compiler returned: 1

In larger examples, this makes it very hard to determine the actual source of
problem -- since it doesn't even appear.

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