• Bastiaan Veelo (17/17) May 17 2018 Hi!
• Basile B. (4/8) May 17 2018 Hello. Yes, add `import core.stdc.stdarg;` in your module and it
• Bastiaan Veelo (4/13) May 17 2018 Great! Thanks a lot, Basile!
• Steven Schveighoffer (19/34) May 18 2018 Interestingly, the error was better before:

Bastiaan Veelo <Bastiaan Veelo.net> writes:

Hi!

The code in [1] compiles and runs flawlessly on Windows, but not 
on Linux (neither run.dlang nor Travis docker image). Any idea 
what can be done?

errors:
Error: undefined identifier __va_list_tag
onlineapp.d(282): Error: template instance 
`onlineapp.SetFactory!byte` error instantiating
Error: undefined identifier __va_list_tag
onlineapp.d(288): Error: template instance 
`onlineapp.SetFactory!(Count)` error instantiating
Error: undefined identifier __va_list_tag
onlineapp.d(290): Error: template instance 
`onlineapp.SetFactory!char` error instantiating

SetFactory is defined on row 233, and it seems that the problem 
relates to the vararg opIndex.

[1] https://run.dlang.io/gist/6dcbe4e82846cbeb3bf478e92a2b6e6f

Basile B. <b2.temp gmx.com> writes:

On Thursday, 17 May 2018 at 22:07:46 UTC, Bastiaan Veelo wrote:
 Hi!

 The code in [1] compiles and runs flawlessly on Windows, but 
 not on Linux (neither run.dlang nor Travis docker image). Any 
 idea what can be done?

Hello. Yes, add `import core.stdc.stdarg;` in your module and it 
works.
I don't know why it's not required on windows, this is strange.

Bastiaan Veelo <Bastiaan Veelo.net> writes:

On Thursday, 17 May 2018 at 23:18:32 UTC, Basile B. wrote:
 On Thursday, 17 May 2018 at 22:07:46 UTC, Bastiaan Veelo wrote:
 Hi!

 The code in [1] compiles and runs flawlessly on Windows, but 
 not on Linux (neither run.dlang nor Travis docker image). Any 
 idea what can be done?

 Hello. Yes, add `import core.stdc.stdarg;` in your module and 
 it works.
 I don't know why it's not required on windows, this is strange.

Great! Thanks a lot, Basile!

Seems there is room for improvement somewhere, a better error 
message at the least.

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 5/17/18 7:33 PM, Bastiaan Veelo wrote:
 On Thursday, 17 May 2018 at 23:18:32 UTC, Basile B. wrote:
 On Thursday, 17 May 2018 at 22:07:46 UTC, Bastiaan Veelo wrote:
 Hi!

 The code in [1] compiles and runs flawlessly on Windows, but not on 
 Linux (neither run.dlang nor Travis docker image). Any idea what can 
 be done?

 Hello. Yes, add `import core.stdc.stdarg;` in your module and it works.
 I don't know why it's not required on windows, this is strange.

 
 Great! Thanks a lot, Basile!
 
 Seems there is room for improvement somewhere, a better error message at 
 the least.

Interestingly, the error was better before:

https://run.dlang.io/is/BgvH4w

Tested on all compilers, up to 2.072.1, it results in:

onlineapp.d(1): Error: '__va_argsave_t' is not defined, perhaps you need 
to import core.vararg; ?
onlineapp.d(1): Error: function onlineapp.foo must import core.vararg to 
use variadic functions

In 2.072.2, it starts saying:

Error: undefined identifier '__va_list_tag'

The previous error was much better, but this to me is a huge code smell. 
Why do we have to import certain modules to use actual language 
features? Just to *define* a function, but not do anything inside it? 
I'd understand if this was a linker error, but surely the compiler can 
know to auto-import something, or at least spit out the proper extern(C) 
declarations?

Note that your code works if I import core.vararg outside the function, 
you don't need core.stdc.stdarg. The import cannot be *inside* the function.

-Steve