Refactor expression completion

This refactors the gdb expression completion code to make it easier to
add more types of completers.

In the old approach, just two kinds of completers were supported:
field names for some sub-expression, or tag names (like "enum
something").  The data for each kind was combined in single structure,
"expr_completion_state", and handled explicitly by
complete_expression.

In the new approach, the parser state just holds an object that is
responsible for implementing completion.  This way, new completion
types can be added by subclassing this base object.

The structop completer is moved into structop_base_operation, and new
objects are defined for use by the completion code.  This moves much
of the logic of expression completion out of completer.c as well.

1 files changed, 8 insertions, 84 deletions

diff --git a/gdb/completer.c b/gdb/completer.c
index a51c16ac7f8..63b4cd22d24 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -1055,107 +1055,31 @@ location_completer_handle_brkchars (struct cmd_list_element *ignore,
   location_completer (ignore, tracker, text, NULL);
 }
 
-/* Helper for expression_completer which recursively adds field and
-   method names from TYPE, a struct or union type, to the OUTPUT
-   list.  */
-
-static void
-add_struct_fields (struct type *type, completion_list &output,
-		   const char *fieldname, int namelen)
-{
-  int i;
-  int computed_type_name = 0;
-  const char *type_name = NULL;
-
-  type = check_typedef (type);
-  for (i = 0; i < type->num_fields (); ++i)
-    {
-      if (i < TYPE_N_BASECLASSES (type))
-	add_struct_fields (TYPE_BASECLASS (type, i),
-			   output, fieldname, namelen);
-      else if (type->field (i).name ())
-	{
-	  if (type->field (i).name ()[0] != '\0')
-	    {
-	      if (! strncmp (type->field (i).name (), 
-			     fieldname, namelen))
-		output.emplace_back (xstrdup (type->field (i).name ()));
-	    }
-	  else if (type->field (i).type ()->code () == TYPE_CODE_UNION)
-	    {
-	      /* Recurse into anonymous unions.  */
-	      add_struct_fields (type->field (i).type (),
-				 output, fieldname, namelen);
-	    }
-	}
-    }
-
-  for (i = TYPE_NFN_FIELDS (type) - 1; i >= 0; --i)
-    {
-      const char *name = TYPE_FN_FIELDLIST_NAME (type, i);
-
-      if (name && ! strncmp (name, fieldname, namelen))
-	{
-	  if (!computed_type_name)
-	    {
-	      type_name = type->name ();
-	      computed_type_name = 1;
-	    }
-	  /* Omit constructors from the completion list.  */
-	  if (!type_name || strcmp (type_name, name))
-	    output.emplace_back (xstrdup (name));
-	}
-    }
-}
-
 /* See completer.h.  */
 
 void
 complete_expression (completion_tracker &tracker,
 		     const char *text, const char *word)
 {
-  struct type *type = NULL;
-  gdb::unique_xmalloc_ptr<char> fieldname;
-  enum type_code code = TYPE_CODE_UNDEF;
+  expression_up exp;
+  std::unique_ptr<expr_completion_base> expr_completer;
 
   /* Perform a tentative parse of the expression, to see whether a
      field completion is required.  */
   try
     {
-      type = parse_expression_for_completion (text, &fieldname, &code);
+      exp = parse_expression_for_completion (text, &expr_completer);
     }
   catch (const gdb_exception_error &except)
     {
       return;
     }
 
-  if (fieldname != nullptr && type)
-    {
-      for (;;)
-	{
-	  type = check_typedef (type);
-	  if (!type->is_pointer_or_reference ())
-	    break;
-	  type = TYPE_TARGET_TYPE (type);
-	}
-
-      if (type->code () == TYPE_CODE_UNION
-	  || type->code () == TYPE_CODE_STRUCT)
-	{
-	  completion_list result;
-
-	  add_struct_fields (type, result, fieldname.get (),
-			     strlen (fieldname.get ()));
-	  tracker.add_completions (std::move (result));
-	  return;
-	}
-    }
-  else if (fieldname != nullptr && code != TYPE_CODE_UNDEF)
-    {
-      collect_symbol_completion_matches_type (tracker, fieldname.get (),
-					      fieldname.get (), code);
-      return;
-    }
+  /* Part of the parse_expression_for_completion contract.  */
+  gdb_assert ((exp == nullptr) == (expr_completer == nullptr));
+  if (expr_completer != nullptr
+      && expr_completer->complete (exp.get (), tracker))
+    return;
 
   complete_files_symbols (tracker, text, word);
 }