gdb: Remove C++ symbol aliases from completion list

Consider debugging the following C++ program:

  struct object
  { int a; };

  typedef object *object_p;

  static int
  get_value (object_p obj)
  {
    return obj->a;
  }

  int
  main ()
  {
    object obj;
    obj.a = 0;

    return get_value (&obj);
  }

Now in a GDB session:

  (gdb) complete break get_value
  break get_value(object*)
  break get_value(object_p)

Or:

  (gdb) break get_va<TAB>
  (gdb) break get_value(object<RETURN>
  Function "get_value(object" not defined.
  Make breakpoint pending on future shared library load? (y or [n]) n

The reason this happens is that we add completions based on the
msymbol names and on the symbol names.  For C++ both of these names
include the parameter list, however, the msymbol names have some
differences from the symbol names, for example:

  + typedefs are resolved,
  + whitespace rules are different around pointers,
  + the 'const' keyword is placed differently.

What this means is that the msymbol names and symbol names appear to
be completely different to GDB's completion tracker, and therefore to
readline when it offers the completions.

This commit builds on the previous commit which reworked the
completion_tracker class.  It is now trivial to add a
remove_completion member function, this is then used along with
cp_canonicalize_string_no_typedefs to remove the msymbol aliases from
the completion tracker as we add the symbol names.

Now, for the above program GDB only presents a single completion for
'get_value', which is 'get_value(object_p)'.

It is still possible to reference the symbol using the msymbol name,
so a user can manually type out 'break get_value (object *)' if they
wish and will get the expected behaviour.

I did consider adding an option to make this alias exclusion optional,
in the end I didn't bother as I didn't think it would be very useful,
but I can easily add such an option if people think it would be
useful.

gdb/ChangeLog:

	* completer.c (completion_tracker::remove_completion): Define new
	function.
	* completer.h (completion_tracker::remove_completion): Declare new
	function.
	* symtab.c (completion_list_add_symbol): Remove aliasing msymbols
	when adding a C++ function symbol.

gdb/testsuite/ChangeLog:

	* gdb.linespec/cp-completion-aliases.cc: New file.
	* gdb.linespec/cp-completion-aliases.exp: New file.

Change-Id: Ie5c7c9fc8ecf973072cfb4a9650867104bf7f50c

1 files changed, 14 insertions, 0 deletions

diff --git a/gdb/completer.c b/gdb/completer.c
index 14c7a57..67dce30 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -1678,6 +1678,20 @@ completion_tracker::add_completions (completion_list &&list)
     add_completion (std::move (candidate));
 }
 
+/* See completer.h.  */
+
+void
+completion_tracker::remove_completion (const char *name)
+{
+  hashval_t hash = htab_hash_string (name);
+  if (htab_find_slot_with_hash (m_entries_hash, name, hash, NO_INSERT)
+      != NULL)
+    {
+      htab_remove_elt_with_hash (m_entries_hash, name, hash);
+      m_lowest_common_denominator_valid = false;
+    }
+}
+
 /* Helper for the make_completion_match_str overloads.  Returns NULL
    as an indication that we want MATCH_NAME exactly.  It is up to the
    caller to xstrdup that string if desired.  */