Operator overloading fails to follow aliasing rules of mixin templates

[dlangBugzillaToGithub]

Benjamin Schaaf reported this on 2017-12-24T12:13:04Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18118

Description

When you have 2 mixin templates that both overload the same operator, you can't use alias declarations to combine overloads.

Tested on dmd-2.076.1 and dmd-2.073.2

```
mixin template A() {
    auto opBinary(string op, T)(T other) if (op == "in") {
        return other;
    }
}

mixin template B() {
    auto opBinary(string op, T)(T other) if (op == "&") {
        return other;
    }
}

mixin template C() {
    mixin A a;
    mixin B b;

    alias opBinary = a.opBinary;
    alias opBinary = b.opBinary;
}

struct Foo {
    mixin A a;
    mixin B b;

    alias opBinary = a.opBinary;
    alias opBinary = b.opBinary;
}

struct Bar {
    mixin C;
}

struct TestA {
    mixin A;
}

struct TestB {
    mixin B;
}

void main() {
    // These examples work
    auto test1 = Foo().opBinary!"in"("foo");
    auto test2 = Foo().opBinary!"&"("foo");

    auto testa = TestA() in "foo";
    auto testb = TestB() & "foo";

    // These fail to compile
    auto test4 = Foo() in "foo";
    auto test5 = Foo() & "foo";

    auto test6 = Bar() in "bar";
    auto test7 = Bar() & "bar";
}

```