Give D2-style operator overload priority over D1-style, reinstate the latter's deprecation

[Geod24]

It was merged accidentally, see #10716 (comment)

[dlang-bot]

Thanks for your pull request, @Geod24!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	18665	enhancement	Deprecate Undocumented Operator Overloads

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#10725"

[Geod24]

@don-clugston-sociomantic : Can you review ? Hope this will suit you. The only downside I can see is that the following is not supported:

class DontDoThat {
   int opAdd(int) {}
   int opBinary(string op)(int) if (op == "-") { return 0; }
}

void main ()
{
     scope o = new DontDoThat();
    // This will now error out because the compiler does not consider `opAdd`,
    // as it sees an `opBinary`... I don't think that's a big deal but you tell us.
     o + 42;
}

[don-clugston-sociomantic]

That looks great! From there, we can mark the D1 names as deprecated in our own code, so that we can flush out existing uses. Nice solution.

[don-clugston-sociomantic]

The only downside I can see is that the following is not supported:

class DontDoThat {
   int opAdd(int) {}
   int opBinary(string op)(int) if (op == "-") { return 0; }
}

void main ()
{
     scope o = new DontDoThat();
    // This will now error out because the compiler does not consider `opAdd`,
    // as it sees an `opBinary`... I don't think that's a big deal but you tell us.
     o + 42;
}

I think that's good behaviour actually. Any code affected by that deserves to be broken.

[don-clugston-sociomantic]

LGTM. This is a good solution.

[schveiguy]

Nice! Note that I found even an alias works, and should be exactly equivalent to the original (no inlining necessary):

class C
{
    int *opIn_r(int x) { return null; }
    alias opBinaryRight(string s : "in") = opIn_r;
}

This should not error now, I would think (it did not error if the virtual call was not named opIn_r).

[don-clugston-sociomantic]

Can we get this merged into stable, please?

[Geod24]

#10760