[Issue 20576] TemplateTypeParameter and TemplateValueParameter default values are not checked

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20576

--- Comment #4 from Basile-z <b2.temp at gmx.com> ---
other example:

struct Foo {
    Foo opBinary(string op="-")(Foo f) {
        return Foo();
    }
}
void main() {
    auto Foo = Foo() + Foo();
}

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