Build-system: Force C linkage for all DNA type headers

Some DNA headers already did this, most did not. Even though many of them would
be included in C++ files and thus compiled as C++. This would be confusing and
developers may think they have to add `extern "C"` too a whole lot of
(indirect) includes to be able to use a C header in C++.

However, this is a misconception.
`extern "C"` does not cause code to be compiled with C rather than C++! It only
causes the linker to not use C++ function name mangling. See
https://stackoverflow.com/a/1041880.
Because extern DNA headers don't have function declarations, using `extern "C"`
actually should not have any effect. On the other hand, adding it causes no
harm and avoids confusion. So let's just have it consistently in C header
files.

Differential Revision: https://developer.blender.org/D9578

Reviewed by: Bastien Montagne, Sybren Stüvel

1 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_particle_types.h b/source/blender/makesdna/DNA_particle_types.h
index bd19498eba7..d48144f90e8 100644
--- a/source/blender/makesdna/DNA_particle_types.h
+++ b/source/blender/makesdna/DNA_particle_types.h
@@ -27,6 +27,10 @@
 #include "DNA_boid_types.h"
 #include "DNA_defs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct AnimData;
 
 typedef struct HairKey {
@@ -690,3 +694,7 @@ typedef enum eParticleTextureInfluence {
   PAMAP_CHILD = (PAMAP_CLUMP | PAMAP_KINK_FREQ | PAMAP_KINK_AMP | PAMAP_ROUGH | PAMAP_LENGTH |
                  PAMAP_TWIST),
 } eParticleTextureInfluence;
+
+#ifdef __cplusplus
+}
+#endif