Overload resolution bug in Clang

[h0nzZik]

Problem description

12.3.3.2/4.2 says:

A conversion that promotes an enumeration whose underlying type is fixed to its underlying type is better than one that promotes to the promoted underlying type, if the two are different.

Therefore, in the following program, the overload resolution should choose the int bar(short) overload.

enum E : short {
	Foo = 1
};

int bar(int) { return 1; }
int bar(short) { return 0; }

int main() {
	return bar(Foo);
}

This is indeed the case for GCC, but Clang reject the program, saying

error: call to 'bar' is ambiguous

The situation is the same when the underlying type of E is char.

What to do

• fill a bug report for clang
• test the C++ semantics

Unfortunately, the Clang parser rejects the above program as well. I can see two ways to test the semantics:

1. Make sure the clang parser outputs kast earlier in the pipeline, before overload resolution happens in Clang. However, this probably goes against our attempt to let the parser emit implicitly-defined functions and template specializations.
2. Create a manual test case, consisting of two files: test.C.ignore with the source code of the example, and test.C.kast with hand-crafted KAST. The kcc script would be run the test.C.kast file and skip the parsing part.

Btw we should add references to the standard even to our test files.

[h0nzZik]

The bug report: https://bugs.llvm.org/show_bug.cgi?id=42318