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_fileglobal_types.h b/source/blender/makesdna/DNA_fileglobal_types.h
index bb660fb8eaa..dc43524a325 100644
--- a/source/blender/makesdna/DNA_fileglobal_types.h
+++ b/source/blender/makesdna/DNA_fileglobal_types.h
@@ -23,6 +23,10 @@
 
 #pragma once
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * FileGlobal stores a part of the current user-interface settings at
  * the moment of saving, and the file-specific settings.
@@ -53,3 +57,7 @@ typedef struct FileGlobal {
 /* example: if in 2.43 the meshes lose mesh data, minversion is 2.43 then too */
 /* or: in 2.42, subversion 1, same as above, minversion then is 2.42, min subversion 1 */
 /* (defines for version are in the BKE_blender_version.h file, for historic reasons) */
+
+#ifdef __cplusplus
+}
+#endif