Separate compilation changes result of __traits(compiles)

[dlangBugzillaToGithub]

Paul Backus (@pbackus) reported this on 2018-11-20T20:11:02Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19417

Description

The following program prints "true" when compiled together, and "false" when compiled separately:

--- dub.json
{
    "name": "example"
}

--- source/app.d
import node;

void main()
{
    import std.stdio;
    writeln(__traits(compiles, Struct.init == Struct.init));
}

--- source/node.d
import example;

alias Node = Example!Struct;
struct Struct { Node[] nodes; }

--- source/example.d
struct Example(T)
{
    T t;

    static if (__traits(compiles, T.init == T.init)) {
        bool opEquals(Example!T rhs) { return this.t == rhs.t; }
    } else {
        @disable bool opEquals(Example!T rhs);
    }
}

---

To build and run with dub:

$ dub --quiet build --build-mode=singleFile --force && dub --quiet run                                                                                   
false
$ dub --quiet build --force && dub --quiet run                                                                                                           
true