docs: Drop outdated docs/debugging.txt

Most of the document was about traps, which have not existed since
commit 58cdf0b474, 10 years ago.

The rest of the document was about `GOBJECT_DEBUG`, and that information
would be more easily findable in the full GObject documentation — so
move it there and update it a bit.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

docs/debugging.txt

@@ -1,38 +0,0 @@
-
-Traps (G_BREAKPOINT) and traces for the debugging
-=================================================
-
-Some code portions contain trap variables that can be set during
-debugging time if G_ENABLE_DEBUG has been defined upon compilation
-(use the --buildtype=debug option to configure for this, macros.txt
-covers more details).
-Such traps lead to immediate code halts to examine the current
-program state and backtrace.
-Currently, the following trap variables exist:
-
-static volatile gulong g_trap_free_size;
-static volatile gulong g_trap_realloc_size;
-static volatile gulong g_trap_malloc_size;
-	If set to a size > 0, g_free(), g_realloc() and g_malloc()
-	respectively, will be intercepted if the size matches the
-	size of the corresponding memory block to free/reallocate/allocate.
-	This will only work with g_mem_set_vtable (glib_mem_profiler_table)
-	upon startup though, because memory profiling is required to match
-	on the memory block sizes.
-static volatile GObject *g_trap_object_ref;
-	If set to a valid object pointer, ref/unref will be intercepted
-	with G_BREAKPOINT ();
-static volatile gpointer *g_trap_instance_signals;
-static volatile gpointer *g_trace_instance_signals;
-       If set to a valid instance pointer, debugging messages
-       will be spewed about emissions of signals on this instance.
-       For g_trap_instance_signals matches, the emissions will
-       also be intercepted with G_BREAKPOINT ();
-
-Environment variables for debugging
-===================================
-When G_ENABLE_DEBUG was defined upon compilation, the GObject library 
-supports an environment variable GOBJECT_DEBUG that can be set to a
-combination of the flags passed in to g_type_init() (currently
-"objects" and "signals") to trigger debugging messages about
-object bookkeeping and signal emissions during runtime.

docs/macros.txt

@@ -48,11 +48,9 @@ G_ENABLE_DEBUG
 	be affected by it similar to G_DISABLE_ASSERT.
 	The additional code executed/compiled for this macro currently involve:
 	- extra validity checks for GDate
-	- memory profiling traps in gmem.c (consult debugging.txt for details)
 	- BREAKPOINT abortion for fatal log levels in gmessage.c instead of
 	  plain abort() to allow debuggers trapping and overriding them
 	- added verbosity of gscanner.c to catch deprecated code paths
 	- added verbosity of gutils.c to catch deprecated code paths
-	- object ref/unref traps (consult debugging.txt) and object bookkeeping
-	  in gobject.c
+	- object and type bookkeeping in gobject.c
 	- extra validity checks in gsignal.c

gobject/gtype.c

@@ -87,6 +87,20 @@
  * be at least three characters long. There is no upper length limit. The first
  * character must be a letter (a–z or A–Z) or an underscore (‘_’). Subsequent
  * characters can be letters, numbers or any of ‘-_+’.
+ *
+ * # Runtime Debugging
+ *
+ * When `G_ENABLE_DEBUG` is defined during compilation, the GObject library
+ * supports an environment variable `GOBJECT_DEBUG` that can be set to a
+ * combination of flags to trigger debugging messages about
+ * object bookkeeping and signal emissions during runtime.
+ *
+ * The currently supported flags are:
+ *  - `objects`: Tracks all #GObject instances in a global hash table called
+ *    `debug_objects_ht`, and prints the still-alive objects on exit.
+ *  - `instance-count`: Tracks the number of instances of every #GType and makes
+ *    it available via the g_type_get_instance_count() function.
+ *  - `signals`: Currently unused.
  */
 
 
@@ -3953,8 +3967,8 @@ g_type_query (GType       type,
  *
  * Returns the number of instances allocated of the particular type;
  * this is only available if GLib is built with debugging support and
- * the instance_count debug flag is set (by setting the GOBJECT_DEBUG
- * variable to include instance-count).
+ * the `instance-count` debug flag is set (by setting the `GOBJECT_DEBUG`
+ * variable to include `instance-count`).
  *
  * Returns: the number of instances allocated of the given type;
  *   if instance counts are not available, returns 0.
@@ -4468,7 +4482,7 @@ _g_type_boxed_init (GType          type,
  * flags.  Since GLib 2.36, the type system is initialised automatically
  * and this function does nothing.
  *
- * If you need to enable debugging features, use the GOBJECT_DEBUG
+ * If you need to enable debugging features, use the `GOBJECT_DEBUG`
  * environment variable.
  *
  * Deprecated: 2.36: the type system is now initialised automatically

gobject/gtype.h

@@ -714,7 +714,7 @@ struct _GTypeQuery
  * These flags used to be passed to g_type_init_with_debug_flags() which
  * is now deprecated.
  *
- * If you need to enable debugging features, use the GOBJECT_DEBUG
+ * If you need to enable debugging features, use the `GOBJECT_DEBUG`
  * environment variable.
  *
  * Deprecated: 2.36: g_type_init() is now done automatically