Build error "template with C linkage"

[NerdyProjects]

Trying to build falcon (AUR tudo-falcon 1.3.0-1) on a recent manjaro,

I get build errors:

[ 50%] Building CXX object src/eye/phy/CMakeFiles/eye_phy.dir/SubframeWorker.cc.o
In file included from /usr/include/glib-2.0/glib/gatomic.h:31,
                 from /usr/include/glib-2.0/glib/gthread.h:32,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:32,
                 from /usr/include/glib-2.0/glib.h:32,
                 from /usr/include/glib-2.0/gmodule.h:28,
                 from /usr/include/cmnalib/at_sierra_wireless_em7565.h:12,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/probe_modem.h:27,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/TrafficGeneratorEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/DummyEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/src/meas/DummyEventHandler.cc:21:
/usr/include/c++/11.1.0/type_traits:56:3: error: template with C linkage
   56 |   template<typename _Tp, _Tp __v>
      |   ^~~~~~~~
In file included from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/TrafficGeneratorEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/DummyEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/src/meas/DummyEventHandler.cc:21:
/home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/probe_modem.h:24:1: note: ‘extern "C"’ linkage started here
   24 | extern "C" {
      | ^~~~~~~~~~
In file included from /usr/include/glib-2.0/glib/gatomic.h:31,
                 from /usr/include/glib-2.0/glib/gthread.h:32,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:32,
                 from /usr/include/glib-2.0/glib.h:32,
                 from /usr/include/glib-2.0/gmodule.h:28,
                 from /usr/include/cmnalib/at_sierra_wireless_em7565.h:12,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/probe_modem.h:27,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/TrafficGeneratorEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/DummyEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/src/meas/DummyEventHandler.cc:21:
/usr/include/c++/11.1.0/type_traits:71:3: error: template with C linkage
   71 |   template<typename _Tp, _Tp __v>
      |   ^~~~~~~~
In file included from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/TrafficGeneratorEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/DummyEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/src/meas/DummyEventHandler.cc:21:
/home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/probe_modem.h:24:1: note: ‘extern "C"’ linkage started here
   24 | extern "C" {
      | ^~~~~~~~~~
In file included from /usr/include/glib-2.0/glib/gatomic.h:31,
                 from /usr/include/glib-2.0/glib/gthread.h:32,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:32,
                 from /usr/include/glib-2.0/glib.h:32,
                 from /usr/include/glib-2.0/gmodule.h:28,
                 from /usr/include/cmnalib/at_sierra_wireless_em7565.h:12,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/probe_modem.h:27,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/TrafficGeneratorEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/include/falcon/meas/DummyEventHandler.h:23,
                 from /home/matthias/.cache/yay/tudo-falcon/src/falcon-1.3.0/lib/src/meas/DummyEventHandler.cc:21:
/usr/include/c++/11.1.0/type_traits:80:3: error: template with C linkage
   80 |   template<bool __v>
      |   ^~~~~~~~

and am a bit too stupid to look into it myself. Any hints what requirement I am missing? :D

[NerdyProjects]

I temporarily downgraded glib2 to version 2.66.7-1 (as I had this lying around) and it worked :-) Found that related issue: https://gitlab.gnome.org/GNOME/glib/-/issues/2331

[bastian-src]

@NerdyProjects thanks a lot for your comment! With your links to the glib issue, I was able to resolve the build error such that falcon can easily be build with glib version 2.72.4 (default of Ubuntu 22.04).

Here is the patch:

It just changes the import and moves it before the extern "C" statement:

diff --git a/lib/include/falcon/meas/probe_modem.h b/lib/include/falcon/meas/probe_modem.h
index 5001867..09b93e1 100644
--- a/lib/include/falcon/meas/probe_modem.h
+++ b/lib/include/falcon/meas/probe_modem.h
@@ -20,11 +20,12 @@
  */
 #pragma once
 
+#include "cmnalib/at_sierra_wireless_em7565.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include "cmnalib/at_sierra_wireless_em7565.h"
 
 //#define DEFAULT_URL "mptcp1.pi21.de:5002"
 #define DEFAULT_URL "www.kn.e-technik.tu-dortmund.de"