[llvm-bugs] [Bug 32766] New: Return type deduction for auto fails for member function in struct nested in lambda nested in function template

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=32766

            Bug ID: 32766
           Summary: Return type deduction for auto fails for member
                    function in struct nested in lambda nested in function
                    template
           Product: clang
           Version: 4.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: arnetheduck at gmail.com
                CC: llvm-bugs at lists.llvm.org

Here's a snippet which I *think* should compile (it does so with gcc/icc), but
fails under clang 4.0 - https://godbolt.org/g/8oCnrm

It works if any of the following are true:
* f is not a template function
* xxx is not a auto parameter
* v does not return auto
* R is not nested in y

template <typename F>
void f() {
     auto y = [=] (auto xxx) {
         struct R {
             static constexpr auto v() { return 42; }
         };
     };

     y(32);
}

void x() {
    f<int>();
}

<source>:5:49: error: cannot initialize return object of type 'auto' with an
rvalue of type 'int'
             static constexpr auto v() { return 42; }
                                                ^~
<source>:4:17: note: in instantiation of member function 'f()::(anonymous
class)::operator()(type-parameter-0-0)::R::v' requested here
         struct R {
                ^
<source>:13:5: note: in instantiation of function template specialization
'f<int>' requested here
    f<int>();
    ^
1 error generated.
Compiler exited with result code 1


The example looks a little convoluted but comes from real life in some
callback-heavy async code, deep down in a library.

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