[PATCH] ruby: extern linkage portability improvement

[Austin Clements]

Quoth Tomi Ollila on May 10 at  8:12 pm:
> Some C compilers are stricter when it comes to (tentative) definition
> of a variable -- in those compilers introducing variable without 'extern'
> keyword always allocates new 'storage' to the variable and linking all
> these modules fails due to duplicate symbols.
> 
> This change uses some macro trickery to avoid writing every variable twice.
> 
> This is reimplementation of Charlie Allom's patch:
> id:"1336481467-66356-1-git-send-email-charlie at mediasp.com"
> 
> combining information from other change made by Ali Polatel.
> ---
> 
> Charlie: could you test whether this patch actually work ? :)
> 
> Everyone: what do you think of the "hiding extern" macro trick ?

This seems like a hacky and nonstandard way to do this.  Granted, the
standard way to do this---always declare variables extern in .h files
and also give a non-extern definition in exactly one .c file---is more
verbose, but nobody will be surprised or confused by it.

>  bindings/ruby/defs.h |   56 +++++++++++++++++++++++++++----------------------
>  bindings/ruby/init.c |    2 +
>  2 files changed, 33 insertions(+), 25 deletions(-)
> 
> diff --git a/bindings/ruby/defs.h b/bindings/ruby/defs.h
> index 85d8205..2531760 100644
> --- a/bindings/ruby/defs.h
> +++ b/bindings/ruby/defs.h
> @@ -24,31 +24,37 @@
>  #include <ruby.h>
>  #include "notmuch.h"
>  
> -VALUE notmuch_rb_cDatabase;
> -VALUE notmuch_rb_cDirectory;
> -VALUE notmuch_rb_cFileNames;
> -VALUE notmuch_rb_cQuery;
> -VALUE notmuch_rb_cThreads;
> -VALUE notmuch_rb_cThread;
> -VALUE notmuch_rb_cMessages;
> -VALUE notmuch_rb_cMessage;
> -VALUE notmuch_rb_cTags;
> -
> -VALUE notmuch_rb_eBaseError;
> -VALUE notmuch_rb_eDatabaseError;
> -VALUE notmuch_rb_eMemoryError;
> -VALUE notmuch_rb_eReadOnlyError;
> -VALUE notmuch_rb_eXapianError;
> -VALUE notmuch_rb_eFileError;
> -VALUE notmuch_rb_eFileNotEmailError;
> -VALUE notmuch_rb_eNullPointerError;
> -VALUE notmuch_rb_eTagTooLongError;
> -VALUE notmuch_rb_eUnbalancedFreezeThawError;
> -VALUE notmuch_rb_eUnbalancedAtomicError;
> -
> -ID ID_call;
> -ID ID_db_create;
> -ID ID_db_mode;
> +#ifdef RUBY_INIT_C
> +#define extern
> +#endif
> +
> +extern VALUE notmuch_rb_cDatabase;
> +extern VALUE notmuch_rb_cDirectory;
> +extern VALUE notmuch_rb_cFileNames;
> +extern VALUE notmuch_rb_cQuery;
> +extern VALUE notmuch_rb_cThreads;
> +extern VALUE notmuch_rb_cThread;
> +extern VALUE notmuch_rb_cMessages;
> +extern VALUE notmuch_rb_cMessage;
> +extern VALUE notmuch_rb_cTags;
> +
> +extern VALUE notmuch_rb_eBaseError;
> +extern VALUE notmuch_rb_eDatabaseError;
> +extern VALUE notmuch_rb_eMemoryError;
> +extern VALUE notmuch_rb_eReadOnlyError;
> +extern VALUE notmuch_rb_eXapianError;
> +extern VALUE notmuch_rb_eFileError;
> +extern VALUE notmuch_rb_eFileNotEmailError;
> +extern VALUE notmuch_rb_eNullPointerError;
> +extern VALUE notmuch_rb_eTagTooLongError;
> +extern VALUE notmuch_rb_eUnbalancedFreezeThawError;
> +extern VALUE notmuch_rb_eUnbalancedAtomicError;
> +
> +extern ID ID_call;
> +extern ID ID_db_create;
> +extern ID ID_db_mode;
> +
> +#undef extern
>  
>  /* RSTRING_PTR() is new in ruby-1.9 */
>  #if !defined(RSTRING_PTR)
> diff --git a/bindings/ruby/init.c b/bindings/ruby/init.c
> index 3fe60fb..b2dc7f6 100644
> --- a/bindings/ruby/init.c
> +++ b/bindings/ruby/init.c
> @@ -18,7 +18,9 @@
>   * Author: Ali Polatel <alip at exherbo.org>
>   */
>  
> +#define RUBY_INIT_C
>  #include "defs.h"
> +#undef RUBY_INIT_C
>  
>  /*
>   * Document-module: Notmuch