* conf_post.h: Add comments for INLINE, EXTERN_INLINE, etc.

2 files changed, 35 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index c432c1ad8bb..f8d4063b352 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2013-06-18  Paul Eggert  <eggert@cs.ucla.edu>
+
+        * conf_post.h: Add comments for INLINE, EXTERN_INLINE, etc.
+
 2013-06-18  Kenichi Handa  <handa@gnu.org>
 
         * font.c (Ffont_spec): Signal an error for an invalid font name
diff --git a/src/conf_post.h b/src/conf_post.h
index 5cb385d9029..46aea32ef30 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -207,6 +207,37 @@ extern void _DebPrint (const char *fmt, ...);
 #undef noinline
 #endif
 
+/* Use Gnulib's extern-inline module for extern inline functions.
+   An include file foo.h should prepend FOO_INLINE to function
+   definitions, with the following overall pattern:
+
+      [#include any other .h files first.]
+      ...
+      INLINE_HEADER_BEGIN
+      #ifndef FOO_INLINE
+      # define FOO_INLINE INLINE
+      #endif
+      ...
+      FOO_INLINE int
+      incr (int i)
+      {
+        return i + 1;
+      }
+      ...
+      INLINE_HEADER_END
+
+   The corresponding foo.c file should do this:
+
+      #define FOO_INLINE EXTERN_INLINE
+
+   before including any .h file other than config.h.
+   Other .c files should not define FOO_INILNE.
+
+   C99 compilers compile functions like 'incr' as C99-style extern
+   inline functions.  Pre-C99 GCCs do something similar with
+   GNU-specific keywords.  Pre-C99 non-GCC compilers use static
+   functions, which bloats the code but is good enough.  */
+
 #define INLINE _GL_INLINE
 #define EXTERN_INLINE _GL_EXTERN_INLINE
 #define INLINE_HEADER_BEGIN _GL_INLINE_HEADER_BEGIN