[llvm-bugs] [Bug 34005] New: Compiler confused when compiling template variable initialized by lambda-expression with default parameter.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34005

            Bug ID: 34005
           Summary: Compiler confused when compiling template variable
                    initialized by lambda-expression with default
                    parameter.
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: shirayama.kazatsuyu at gmail.com
                CC: llvm-bugs at lists.llvm.org

The code below fail to be compile.

// prog.cc

template<int> struct X {};
template<int n> constexpr void f(X<n>) {}
template<typename> constexpr int v = [](int r = 0l) constexpr { return r; }();

int main() {
    f<v<int>>(X<0>());
}

$ clang++ -std=c++1z prog.cc

prog.cc:6:5: error: no matching function for call to 'f'
    f<v<int>>(X<0>());
    ^~~~~~~~~
prog.cc:2:32: note: candidate function not viable: no known conversion from
'X<...>' to 'X<...>' for 1st argument
template<int n> constexpr void f(X<n>) {}
                               ^
1 error generated.


I think v<T> is always 0, so f<v<int>>(X<0>()) should match f<0>(X<0>);

And if lambda's default parameter type is int,

template<typename> constexpr int v = [](int r = 0) constexpr { return r; }();

There are no errors.

This link is the result executed by wandbox.
https://wandbox.org/permlink/yjKqrYKQyl2YZ6PO

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