__traits(compiles, ...) fails to see valid enum symbols

[dlangBugzillaToGithub]

det reported this on 2014-04-06T16:23:40Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=12532

CC List

Description

under certain circumstances, eg when called from a template using mixin and static if, __traits(compiles, ...)  fails to see valid enum symbols. (if 'enum' in following example is replaced by 'const bool' or 'immutable bool' all symbols are found.)

=== EXAMPLE ===

template valid(string mem){
    pragma(msg, "instantiation of 'valid' with: "~mem);
    static if( !__traits( compiles, mixin(mem) ) ){
        enum valid = false;
    }else{
        enum valid =  true;
     }
}

enum ok = valid!"works";
pragma(msg, "found 'works'? "~ok.stringof );
// true - fine, recognizes 'works' later in module scope

enum foo = valid!"bar";
pragma(msg, "found 'bar'? "~foo.stringof );
// true - fine, recognizes 'bar' laterin module scope

enum bar = valid!"foo";
pragma(msg, "found 'foo'? "~bar.stringof );
// false - fails to see 'foo' earlier in module scope!

enum works = true;

void main(){}

[dlangBugzillaToGithub]

monarchdodra commented on 2014-04-06T23:09:32Z

Reduced:

//----
enum a = is(typeof(b));
enum b = is(typeof(a));

pragma(msg, a); //true
pragma(msg, b); //false
//----

I'm not sure this is actually resolvable...?

[dlangBugzillaToGithub]

2krnk commented on 2014-04-07T07:20:53Z

(In reply to comment #1)
> Reduced:
> 
> //----
> enum a = is(typeof(b));
> enum b = is(typeof(a));
> 
> pragma(msg, a); //true
> pragma(msg, b); //false
> //----
> 
> I'm not sure this is actually resolvable...?

sorry, i should have reduced it to

enum a = __traits(compiles, b);
pragma(msg, a);                 // true
enum b = __traits(compiles, a);
pragma(msg, b);                 // false

guess i was too preoccupied with issue 12533. however, i think b should be true, __traits(compiles, ...) should not need the value or type of a. in other words, it should be able to see that a symbol is defined without caring what it actually is. as a matter of fact, in

enum c;
pragma(msg, typeof(c));         // _error_
pragma(msg, is(typeof(c)) );    // false
enum d = __traits(compiles, c);
pragma(msg, d);                 // true

this is kinda happening.