[gvdb/wip/lantw/use-weak-symbols-in-gvdb] build: Use weak bindings in gvdb to fix linking with LLD

[Ting-Wei Lan <lantw src gnome org>]

commit a4594ceba433a8711ee8fc55ba35cab1bb7b6270
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Wed Oct 24 21:46:16 2018 +0800

    build: Use weak bindings in gvdb to fix linking with LLD
    
    Since tests/dconf-mock-gvdb.c has functions conflicting with the real
    gvdb and it is intended for the former to override the latter in tests,
    we have to make functions in gvdb library have weak bindings instead of
    the default strong bindings to avoid duplicate symbol errors.
    
    Fixes https://gitlab.gnome.org/GNOME/dconf/issues/47

 gvdb-reader.c |  1 +
 gvdb-reader.h | 35 +++++++++++++++++++++++++----------
 2 files changed, 26 insertions(+), 10 deletions(-)
---
diff --git a/gvdb-reader.c b/gvdb-reader.c
index 9509388..0d6bd7c 100644
--- a/gvdb-reader.c
+++ b/gvdb-reader.c
@@ -17,6 +17,7 @@
  * Author: Ryan Lortie <desrt desrt ca>
  */
 
+#define GVDB_USE_WEAK_SYMBOLS
 #include "gvdb-reader.h"
 #include "gvdb-format.h"
 
diff --git a/gvdb-reader.h b/gvdb-reader.h
index 9bf627f..79a97d3 100644
--- a/gvdb-reader.h
+++ b/gvdb-reader.h
@@ -22,40 +22,55 @@
 
 #include <glib.h>
 
+/* We cannot enable the weak attribute unconditionally here because both
+ * gvdb/gvdb-reader.c and tests/dconf-mock-gvdb.c include this file. The
+ * intention of using weak symbols here is to allow the latter to override
+ * functions defined in the former, so functions in tests/dconf-mock-gvdb.c
+ * must have strong bindings. */
+#ifdef GVDB_USE_WEAK_SYMBOLS
+# ifdef __GNUC__
+#  define GVDB_GNUC_WEAK __attribute__((weak))
+# else
+#  define GVDB_GNUC_WEAK
+# endif
+#else
+# define GVDB_GNUC_WEAK
+#endif
+
 typedef struct _GvdbTable GvdbTable;
 
 G_BEGIN_DECLS
 
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 GvdbTable *             gvdb_table_new_from_bytes                       (GBytes       *bytes,
                                                                          gboolean      trusted,
                                                                          GError      **error);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 GvdbTable *             gvdb_table_new                                  (const gchar  *filename,
                                                                          gboolean      trusted,
                                                                          GError      **error);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 void                    gvdb_table_free                                 (GvdbTable    *table);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 gchar **                gvdb_table_get_names                            (GvdbTable    *table,
                                                                          gsize        *length);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 gchar **                gvdb_table_list                                 (GvdbTable    *table,
                                                                          const gchar  *key);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 GvdbTable *             gvdb_table_get_table                            (GvdbTable    *table,
                                                                          const gchar  *key);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 GVariant *              gvdb_table_get_raw_value                        (GvdbTable    *table,
                                                                          const gchar  *key);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 GVariant *              gvdb_table_get_value                            (GvdbTable    *table,
                                                                          const gchar  *key);
 
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 gboolean                gvdb_table_has_value                            (GvdbTable    *table,
                                                                          const gchar  *key);
-G_GNUC_INTERNAL
+G_GNUC_INTERNAL GVDB_GNUC_WEAK
 gboolean                gvdb_table_is_valid                             (GvdbTable    *table);
 
 G_END_DECLS