gdb: add all_objfiles_removed observer

The new_objfile observer is currently used to indicate both when a new
objfile is added to program space (when passed non-nullptr) and when all
objfiles of a program space were just removed (when passed nullptr).
I think this is confusing (and Andrew apparently thinks so too [1]).
Add a new "all_objfiles_removed" observer to remove the second role from
"new_objfile".

Some existing users of new_objfile do nothing if the passed objfile is
nullptr.  For them, we can simply drop the nullptr check.  For others,
add a new all_objfiles_removed callback, and refactor things a bit to
keep the existing behavior as much as possible.

Some callbacks relied on current_program_space, and following
the refactoring now use either objfile->pspace or the pspace passed to
all_objfiles_removed.  I think this should be relatively safe, and in
general a step in the right direction.

On the notify side, I found only one call site to change from
new_objfile to all_objfiles_removed, in clear_symtab_users.  It is not
entirely clear to me that this is entirely correct.  clear_symtab_users
appears to be called in spots that don't remove all objfiles
(functions finish_new_objfile, remove_symbol_file_command, reread_symbols,
do_module_cleanups).  But I think that this patch at least makes the
current code clearer.

[1] https://gitlab.com/gnutools/binutils-gdb/-/commit/a0a031bce0527b1521788b5dad640e7883b3a252

Change-Id: Icb648f72862e056267f30f44dd439bd4ec766f13
Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 4dc4055..a37e563 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -13884,7 +13884,7 @@ static struct cmd_list_element *show_ada_list;
 static void
 ada_new_objfile_observer (struct objfile *objfile)
 {
-  ada_clear_symbol_cache (current_program_space);
+  ada_clear_symbol_cache (objfile->pspace);
 }
 
 /* This module's 'free_objfile' observer.  */
@@ -13892,7 +13892,7 @@ ada_new_objfile_observer (struct objfile *objfile)
 static void
 ada_free_objfile_observer (struct objfile *objfile)
 {
-  ada_clear_symbol_cache (current_program_space);
+  ada_clear_symbol_cache (objfile->pspace);
 }
 
 /* Charsets known to GNAT.  */
@@ -14025,6 +14025,8 @@ DWARF attribute."),
 
   /* The ada-lang observers.  */
   gdb::observers::new_objfile.attach (ada_new_objfile_observer, "ada-lang");
+  gdb::observers::all_objfiles_removed.attach (ada_clear_symbol_cache,
+					       "ada-lang");
   gdb::observers::free_objfile.attach (ada_free_objfile_observer, "ada-lang");
   gdb::observers::inferior_exit.attach (ada_inferior_exit, "ada-lang");