instantiated template using __traits(compiles, ...) causes semantic errors when reused

[dlangBugzillaToGithub]

det reported this on 2014-04-06T16:39:50Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=12533

Description

compilation fails for no reason in given example involving a template using mixin, static if and __traits(compiles, ...) code reflection. see details in example as it is too complicated to describe.

might be related to issue 12532. however, example fails as well when 'enum' is replaced by 'const'

=== 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 works = valid!"fails";
pragma(msg, "found 'fails' (via 'works')? "~works.stringof );
// compiles but produces 'false': issue 12532

enum dummy = valid!"fails";
pragma(msg, "found 'fails' (via 'dummy')? "~dummy.stringof );
// compiles but produces 'false': issue 12532

enum fails = valid!"fails";
// Error: variable demo.fails had semantic errors when compiling
// NOTE: if you comment out the first two usages of valid!"fails",
// it will work here - but give 'false' again.

//  pragma(msg, "found 'fails' (via 'fails')? "~fails.stringof );

void main(){}

[dlangBugzillaToGithub]

2krnk commented on 2014-04-07T22:50:35Z

(In reply to comment #0)

might be caused by issue 12541.