[LLVMbugs] [Bug 12692] New: Confusing error message when using illegal explicitly-defaulted function

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12692

             Bug #: 12692
           Summary: Confusing error message when using illegal
                    explicitly-defaulted function
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: martin.desharnais at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


#include <utility>

struct A
{
    A(int& i) : m_i(i) { } 

    A(const A&) = delete;
    A(A&&) = default; // Illegal (C++11 12.1.5): non-static data member with no
brace-or-equal-initializer is of reference type

    A& operator=(const A&) = delete;
    A& operator=(A&&) = default;

    int& m_i;
};

int main()
{
    int i = 10; 
    A a1(i);
    A a2(i);

    a1 = std::move(a2);
}

In the above code, it we can not ask the compiler to generate a default
move-constructor since we have a non-static reference type. But the error
message is criptic.

main.cpp:22:5: error: overload resolution selected implicitly-deleted move
assignment operator
        a1 = std::move(a2);
           ^
main.cpp:11:5: note: candidate function has been explicitly deleted
        A& operator=(A&&) = default;
           ^
main.cpp:10:5: note: candidate function has been explicitly deleted
        A& operator=(const A&) = delete;
           ^
1 error generated.


I see two problems with this output:
1. The error message point out that the constructor have been
implicitly-deleted. But we can wonder why since we explicitly asked the
compiler to generate a default implementation.
2. The note message said that the constructor have been explicitly deleted and
show us a call to an explicitly defaulted constructor.

I think the error message should explained that the compiler was unable to
generate the default implementation because of the reference type present in
the class.

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