https://issues.dlang.org/show_bug.cgi?id=13666

          Issue ID: 13666
           Summary: Undefined Symbols for __gshared data symbols in
                    templates
           Product: D
           Version: D2
          Hardware: x86
                OS: Windows
            Status: NEW
          Severity: major
          Priority: P1
         Component: DMD
          Assignee: nobody@puremagic.com
          Reporter: r.sagitario@gmx.de

Compile this module to a library:

module test;

template drt_envvars_enabled()
{
    extern(C) __gshared bool drt_envvars_enabled = false;
}

bool foo()
{
    return drt_envvars_enabled!();
}

///////////
> dmd -lib test.d

Then link it with main.d:

import test;

int main()
{
    return foo();
}

//////////////
> dmd main.d test.lib

OPTLINK (R) for Win32  Release 8.00.15
Copyright (C) Digital Mars 1989-2013  All rights reserved.
http://www.digitalmars.com/ctg/optlink.html
test.lib(test)
 Error 42: Symbol Undefined
__D4test25__T19drt_envvars_enabledZ19drt_envvars_enabledb
--- errorlevel 1

According to https://github.com/D-Programming-Language/druntime/pull/986, this fails for Win32 and OS/X, but works for other platform.

It also works if the variable is not "__gshared" or it is initialized to a non-zero value. It is probably caused by some bad BSS optimization.

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