[llvm-bugs] [Bug 46648] New: template lambda with default value can't be called if passing argument type doesn't match default value type

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46648

            Bug ID: 46648
           Summary: template lambda with default value can't be called if
                    passing argument type doesn't match default value type
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++2a
          Assignee: unassignedclangb...@nondot.org
          Reporter: iurii.shty...@gmail.com
                CC: blitzrak...@gmail.com, erik.pilking...@gmail.com,
                    llvm-bugs@lists.llvm.org, richard-l...@metafoo.co.uk

interactive: https://godbolt.org/z/mM9hY8

code: 
_________________________
#include <string>

using std::literals::operator""s;
int main(){
    auto error_lambda = []<class T = int>(T def = 1) -> T {
        return def;
    };

    error_lambda(1);
    error_lambda("error"s);

    //but it works if default value = 0
    auto good_lambda = []<class T = int>(T def = 0) -> T {
        return def;
    };

    good_lambda(1);
    good_lambda("good"s);
}
_________________________

output:

<source>:10:5: error: no matching function for call to object of type '(lambda
at <source>:5:25)'
    error_lambda("error"s);
    ^~~~~~~~~~~~
<source>:5:25: note: candidate template ignored: substitution failure [with T =
std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char>>]: no viable conversion from 'int' to
'std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char>>'
    auto error_lambda = []<class T = int>(T def = 1) -> T {
                        ^                   ~~~
1 error generated.
Compiler returned: 1

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