dlib 0.19.1 seems to be failing linking with ldc2

[jeff thompson]

On Friday, 31 July 2020 at 22:26:26 UTC, jeff thompson wrote:
> On Friday, 31 July 2020 at 20:07:26 UTC, Dennis wrote:
>> On Friday, 31 July 2020 at 14:17:14 UTC, jeff thompson wrote:
>>> dlib.lib(dlib.audio.io.wav.obj) : error LNK2019: unresolved 
>>> external symbol 
>>> _D4core8internal7switch___T14__switch_errorZQrFNaNbNiNfAyamZv 
>>> referenced in function 
>>> _D3std6format__T10printFloatTfTaZQrFNaNfNkAafSQBsQBr__T10FormatSpecTaZQpEQCtQCs12RoundingModeZQCa
>>> dlib.lib(dlib.filesystem.local.obj) : error LNK2001: 
>>> unresolved external symbol 
>>> _D4core8internal7switch___T14__switch_errorZQrFNaNbNiNfAyamZv
>>> .dub\build\application-debug-windows-x86_64-ldc_2092-316AB5B187D20C1F6AFBA496E604908D\test.exe : fatal error LNK1120: 1 unresolved externals
>>
>>
>> The first thing you want to do is demangle the symbols so you 
>> know what they really are.
>> You can use the tool `ddemangle` for that:
>> ```
>> echo 
>> '_D3std6format__T10printFloatTfTaZQrFNaNfNkAafSQBsQBr__T10FormatSpecTaZQpEQCtQCs12RoundingModeZQCa' | ddemangle
>> ```
>>
>> You'll find that this symbol is missing:
>>
>> pure nothrow @nogc @safe void 
>> core.internal.switch_.__switch_error!().__switch_error(immutable(char)[], ulong)
>>
>> And it's used in this function:
>>
>> pure @safe char[] std.format.printFloat!(float, 
>> char).printFloat(return char[], float, 
>> std.format.FormatSpec!(char).FormatSpec, 
>> std.format.RoundingMode)
>>
>> The switch_error function is called when none of the cases of 
>> a `final switch` apply. There is a final switch in 
>> std.format.printFloat:
>> https://github.com/ldc-developers/phobos/blob/c43cafe53746a07dee8fa9e00d3a2256c7f05506/std/format.d#L7096
>>
>> So why is the compiler not emitting the final switch error 
>> template function? I am not sure, it could be a bug, or maybe 
>> you have some funky dub settings. You might be able to work 
>> around this by defining a final switch in you own code 
>> somewhere, or explicitly defining the function.
>>
>> ```
>> pragma(mangle, 
>> "_D4core8internal7switch___T14__switch_errorZQrFNaNbNiNfAyamZv")
>> void switchError(string file, ulong line) {
>>     assert(0, file);
>> }
>> ```
>>
>> I hope someone else with more familiarity of how template 
>> symbols are emitted can find the root of this problem and give 
>> a proper fix.
>
> Thanks! From looking at it, isn't happening in 
> dlib.lib(dlib.audio.io.wav.obj)? Also this is with a test 
> program with nothing but an empty main and a dependency on dlib 
> 0.19.1. I
>  guess ill post something in their github since it does compile 
> and link with dmd

Ok so the scenario is a dub project A that has a dependency on 
another dub project B who is using dlib. Compiling project A with 
the dependency with ldc produces the error