[llvm-bugs] [Bug 39649] New: clang fails to generate defaulted move constructor upon template instantiation

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39649

            Bug ID: 39649
           Summary: clang fails to generate defaulted move constructor
                    upon template instantiation
           Product: clang
           Version: unspecified
          Hardware: All
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: wdehnen64 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

I couldn't reduce the error below this three file example:

// file unit.h:
#include <vector>

template<typename T>
struct foo
{
    std::vector<T> data;
    foo(foo&&) = default;        // no code generated, even if odr-used.
    foo(std::vector<T>&&v) : data(std::move(v)) {}
};

extern template struct foo<int>; // indicates instantiation elsewhere


// file unit.cc:
#include "unit.h"
template struct foo<int>;        // forces instantiation


// file main.cc:
#include "unit.h"

struct bar
{
    foo<int> f;
    bar(foo<int>&&x) : f(std::move(x)) {}
};

bar makeBar()
{
    foo<int> f(std::vector<int>(5));
    return {std::move(f)};
}

int main()
{
    bar x=makeBar();
}


clang++ -std=c++11 main.cc unit.cc
produces:

Undefined symbols for architecture x86_64:
  "foo<int>::foo(foo<int>&&)", referenced from:
      bar::bar(foo<int>&&) in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

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