Re: [PATCH] lib: fix clang build

[Tomi Ollila <tomi.ollila@iki.fi>]

On Sun, Aug 18 2013, Jani Nikula <jani@nikula.org> wrote:

> Long story short, fix build on recent (3.2+) clang.
>
> The long story for posterity follows.
>
> gcc 4.6 added new warnings about structs with greater visibility than
> their fields. The warnings were silenced by adjusting visibility in
>
> commit d5523ead90b6be2b07d4af745b8ed9b980a6b9f1
> Author: Carl Worth <cworth@cworth.org>
> Date:   Wed May 11 13:23:13 2011 -0700
>
>     Mark some structures in the library interface with visibility=default attribute.
>
> Later on,
>
> commit 3b76adf9e2c026dd03b820f4c6eab50e25444113
> Author: Austin Clements <amdragon@MIT.EDU>
> Date:   Sat Jan 14 19:17:33 2012 -0500
>
>     lib: Add support for automatically excluding tags from queries
>
> changed visibility of struct _notmuch_string_list for the same reason, and
>
> commit 1a53f9f116fa7c460cda3df532be921baaafb082
> Author: Mark Walters <markwalters1009@gmail.com>
> Date:   Thu Mar 1 22:30:38 2012 +0000
>
>     lib: Add the exclude flag to notmuch_query_search_threads
>
> split the struct _notmuch_string_list and its typedef
> notmuch_string_list_t as a way to make a forward declaration for
> _notmuch_thread_create().
>
> The subtle difference was that the struct definition now had 'visible'
> in it, while the typedef didn't, and it was within the #pragma GCC
> visibility push(hidden) block. This went unnoticed, as the then common
> versions of clang didn't care about this.
>
> A later change in clang (I did not dig into when this change was
> introduced) caused the following error:
>
> CXX  -O2 lib/database.o
> In file included from lib/database.cc:21:
> In file included from ./lib/database-private.h:33:
> ./lib/notmuch-private.h:479:8: error: visibility does not match previous declaration
> struct visible _notmuch_string_list {
>        ^
> ./lib/notmuch-private.h:67:33: note: expanded from macro 'visible'
>                                 ^
> ./lib/notmuch-private.h:52:13: note: previous attribute is here
>             ^
> 1 error generated.
> make: *** [lib/database.o] Error 1
>
> This is slightly misleading due to the reference to the #pragma. The
> real culprit is the typedef within the #pragma.
>
> We could just add 'visible' to the typedef, or move the typedef
> outside of the #pragma, and be done with it, but juggle the
> declarations a bit to accommodate moving the typedef back with the
> struct, and keep the visibility attribute in one place.
>
> The problem was originally reported by Simonas Kazlauskas
> <s@kazlauskas.me> in id:20130418102507.GA23688@godbox but I was only
> able to reproduce and investigate now that I upgraded clang.
> ---
>  lib/notmuch-private.h |   28 +++++++++++++---------------
>  1 file changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
> index eced03e..af185c7 100644
> --- a/lib/notmuch-private.h
> +++ b/lib/notmuch-private.h
> @@ -162,8 +162,6 @@ typedef enum _notmuch_find_flags {
>  
>  typedef struct _notmuch_doc_id_set notmuch_doc_id_set_t;

Looks good to me (except log message is a bit excessive (?) maybe
it is reasonable to have it, though (TL;DR ;)...
>  
> -typedef struct _notmuch_string_list notmuch_string_list_t;
> -

anyway, would

typedef struct visible _notmuch_string_list notmuch_string_list_t;

have helped here (if yes is your resolution nicer ?? :D )

Tomi


>  /* database.cc */
>  
>  /* Lookup a prefix value by name.
> @@ -228,17 +226,6 @@ _notmuch_directory_create (notmuch_database_t *notmuch,
>  unsigned int
>  _notmuch_directory_get_document_id (notmuch_directory_t *directory);
>  
> -/* thread.cc */
> -
> -notmuch_thread_t *
> -_notmuch_thread_create (void *ctx,
> -			notmuch_database_t *notmuch,
> -			unsigned int seed_doc_id,
> -			notmuch_doc_id_set_t *match_set,
> -			notmuch_string_list_t *excluded_terms,
> -			notmuch_exclude_t omit_exclude,
> -			notmuch_sort_t sort);
> -
>  /* message.cc */
>  
>  notmuch_message_t *
> @@ -476,11 +463,11 @@ typedef struct _notmuch_string_node {
>      struct _notmuch_string_node *next;
>  } notmuch_string_node_t;
>  
> -struct visible _notmuch_string_list {
> +typedef struct visible _notmuch_string_list {
>      int length;
>      notmuch_string_node_t *head;
>      notmuch_string_node_t **tail;
> -};
> +} notmuch_string_list_t;
>  
>  notmuch_string_list_t *
>  _notmuch_string_list_create (const void *ctx);
> @@ -509,6 +496,17 @@ notmuch_filenames_t *
>  _notmuch_filenames_create (const void *ctx,
>  			   notmuch_string_list_t *list);
>  
> +/* thread.cc */
> +
> +notmuch_thread_t *
> +_notmuch_thread_create (void *ctx,
> +			notmuch_database_t *notmuch,
> +			unsigned int seed_doc_id,
> +			notmuch_doc_id_set_t *match_set,
> +			notmuch_string_list_t *excluded_terms,
> +			notmuch_exclude_t omit_exclude,
> +			notmuch_sort_t sort);
> +
>  NOTMUCH_END_DECLS
>  
>  #ifdef __cplusplus
> -- 
> 1.7.10.4
>
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