Usability of "allMembers and derivedMembers traits now only return visible symbols"

[Basile B. via Digitalmars-d]

On Tuesday, 30 August 2016 at 22:24:12 UTC, Ali Çehreli wrote:
> v2.071.2-b3 is bringing a change for this bug:
>
>   https://issues.dlang.org/show_bug.cgi?id=15907
>
> I don't agree with the current solution:
>
>   
> http://dlang.org/changelog/2.071.2.html#traits-members-visibility
>
> Modules should be able to use library templates without needing 
> to mix them in first.
>
> Do you think the solution in the change log usable? I don't 
> think so because silently skipping my private members is an 
> unexpected behavior that will cause bugs.
>
> Further, do I understand the example right? Am I supposed to 
> mixin the same template twice for two different types? The 
> following code which adds another struct does not compile:
>
> import std.stdio;
> import std.traits;
>
> enum UDA;
> struct S
> {
>     @UDA int visible;
>     @UDA private int invisible;
> }
>
> // only returns symbols visible from std.traits
> static assert(getSymbolsByUDA!(S, UDA).length == 1);
> // mixin the template instantiation, using a name to avoid 
> namespace pollution
> mixin getSymbolsByUDA!(S, UDA) symbols;
> // as the template is instantiated in the current scope, it can 
> see private members
> static assert(symbols.getSymbolsByUDA.length == 2);
>
> // --- The following is added by Ali: ---
>
> struct S2 {
>     @UDA int s2;
> }
>
> mixin getSymbolsByUDA!(S2, UDA) symbolsS2;    // COMPILATION 
> ERROR:
> // Error: mixin deneme.getSymbolsByUDA!(S2, UDA) TList isn't a 
> template
>
> static assert(symbolsS2.getSymbolsByUDA.length == 1);
>
> void main() {
>     foreach (i; 0 .. symbols.getSymbolsByUDA.length) {
>         // ...
>     }
> }
>
> I can't wrap my head around the fact that a library template 
> called by my module cannot see my private members.
>
> Ali

Yes I agree, a change of the specifications in a dot release 
seems a bit extreme, especially since there was a deeper problem 
**before** the broken imports were fixed.

This problem was discovered a while back when the library traits 
related to UDAs were added to phobos.

The little story began here: 
https://issues.dlang.org/show_bug.cgi?id=15335. Then the proposal 
to give super powers to certain traits verbs: 
https://issues.dlang.org/show_bug.cgi?id=15371.