[Issue 24479] New: [REG2.104] Error on getAttributes on getOverloads of templates

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24479

          Issue ID: 24479
           Summary: [REG2.104] Error on getAttributes on getOverloads of
                    templates
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: johanengelen at weka.io

Testcase, https://d.godbolt.org/z/cheqP1eof:
```
import std.meta : Filter;

struct S {
    S opBinary(string op: "-")(S rhs) const pure nothrow @nogc {
        return rhs;
    }
    S opBinary(string op: "*")(S dur) const pure nothrow @nogc {
        return dur;
    }
}

private enum hasExternalUDA(alias A) = is(A == External) || is(typeof(A) ==
External);

void foo() {
    static foreach (t; __traits(getOverloads, S, "opBinary", true)) {
        static assert( Filter!(hasExternalUDA, __traits(getAttributes,
t)).length == 0 );
    }

    static foreach (t; __traits(getOverloads, S, "opBinary", true))
        static foreach(attr; __traits(getAttributes, t))
            pragma(msg, attr);

    static assert(__traits(getOverloads, S, "opBinary", true).length == 2);
    alias A = __traits(getAttributes, __traits(getOverloads, S, "opBinary",
true)[1]);
}
```

Fails (deprecations are errors!) since dlang 2.104, with deprecations:
```
<source>(16): Deprecation: `__traits(getAttributes)` may only be used for
individual functions, not overload sets such as: `opBinary`
<source>(16):        the result of `__traits(getOverloads)` may be used to
select the desired function to extract attributes from
<source>(20): Deprecation: `__traits(getAttributes)` may only be used for
individual functions, not overload sets such as: `opBinary`
<source>(20):        the result of `__traits(getOverloads)` may be used to
select the desired function to extract attributes from
<source>(24): Deprecation: `__traits(getAttributes)` may only be used for
individual functions, not overload sets such as: `opBinary`
<source>(24):        the result of `__traits(getOverloads)` may be used to
select the desired function to extract attributes from
```

Loosely related to https://issues.dlang.org/show_bug.cgi?id=23966.

I don't know a workaround, because iterating with explicit indexing as
suggested in 23966 also does not work (last line of testcase).

--