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, 20 insertions, 2 deletions

diff --git a/gdb/expression.h b/gdb/expression.h
index ff3990e..3ba68a2 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -232,8 +232,26 @@ extern expression_up parse_expression (const char *,
 extern expression_up parse_expression_with_language (const char *string,
 						     enum language lang);
 
-extern struct type *parse_expression_for_completion
-    (const char *, gdb::unique_xmalloc_ptr<char> *, enum type_code *);
+
+class completion_tracker;
+
+/* Base class for expression completion.  An instance of this
+   represents a completion request from the parser.  */
+struct expr_completion_base
+{
+  /* Perform this object's completion.  EXP is the expression in which
+     the completion occurs.  TRACKER is the tracker to update with the
+     results.  Return true if completion was possible (even if no
+     completions were found), false to fall back to ordinary
+     expression completion (i.e., symbol names).  */
+  virtual bool complete (struct expression *exp,
+			 completion_tracker &tracker) = 0;
+
+  virtual ~expr_completion_base () = default;
+};
+
+extern expression_up parse_expression_for_completion
+     (const char *, std::unique_ptr<expr_completion_base> *completer);
 
 class innermost_block_tracker;
 extern expression_up parse_exp_1 (const char **, CORE_ADDR pc,