Add completion for operations

This patch adds the necessary support for field name completion for
expressions using class operation.

This patch takes an approach similar to what is done today.  It might
be good, in the future, to change completion to be a method on the
base class, to enable context-sensitive completion in more areas.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* parser-defs.h (struct expr_completion_state) <expout_last_op>:
	New member.
	(struct parser_state) <mark_struct_expression>: New method.
	* parse.c (parser_state::mark_struct_expression): Update assert.
	(parser_state::mark_struct_expression): New method.
	(parser_state::mark_completion_tag): Update assert.
	(parse_expression_for_completion): Handle expout_last_op.

3 files changed, 45 insertions, 2 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 5fd0967..3436e4e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,15 @@
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
+	* parser-defs.h (struct expr_completion_state) <expout_last_op>:
+	New member.
+	(struct parser_state) <mark_struct_expression>: New method.
+	* parse.c (parser_state::mark_struct_expression): Update assert.
+	(parser_state::mark_struct_expression): New method.
+	(parser_state::mark_completion_tag): Update assert.
+	(parse_expression_for_completion): Handle expout_last_op.
+
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
 	* ada-exp.h (class ada_var_value_operation) <get_symbol>: Remove;
 	now in superclass.
 	* value.h (fetch_subexp_value): Add "op" parameter.
diff --git a/gdb/parse.c b/gdb/parse.c
index 68386f1..79b1ca1 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -507,10 +507,23 @@ parser_state::mark_struct_expression ()
 {
   gdb_assert (parse_completion
 	      && (m_completion_state.expout_tag_completion_type
-		  == TYPE_CODE_UNDEF));
+		  == TYPE_CODE_UNDEF)
+	      && m_completion_state.expout_last_op == nullptr);
   m_completion_state.expout_last_struct = expout_ptr;
 }
 
+/* See parser-defs.h.  */
+
+void
+parser_state::mark_struct_expression (expr::structop_base_operation *op)
+{
+  gdb_assert (parse_completion
+	      && (m_completion_state.expout_tag_completion_type
+		  == TYPE_CODE_UNDEF)
+	      && m_completion_state.expout_last_struct == -1);
+  m_completion_state.expout_last_op = op;
+}
+
 /* Indicate that the current parser invocation is completing a tag.
    TAG is the type code of the tag, and PTR and LENGTH represent the
    start of the tag name.  */
@@ -523,7 +536,8 @@ parser_state::mark_completion_tag (enum type_code tag, const char *ptr,
 	      && (m_completion_state.expout_tag_completion_type
 		  == TYPE_CODE_UNDEF)
 	      && m_completion_state.expout_completion_name == NULL
-	      && m_completion_state.expout_last_struct == -1);
+	      && m_completion_state.expout_last_struct == -1
+	      && m_completion_state.expout_last_op == nullptr);
   gdb_assert (tag == TYPE_CODE_UNION
 	      || tag == TYPE_CODE_STRUCT
 	      || tag == TYPE_CODE_ENUM);
@@ -1262,6 +1276,14 @@ parse_expression_for_completion (const char *string,
       return NULL;
     }
 
+  if (cstate.expout_last_op != nullptr)
+    {
+      expr::structop_base_operation *op = cstate.expout_last_op;
+      const std::string &fld = op->get_string ();
+      *name = make_unique_xstrdup (fld.c_str ());
+      return value_type (op->evaluate_lhs (exp.get ()));
+    }
+
   if (cstate.expout_last_struct == -1)
     return NULL;
 
diff --git a/gdb/parser-defs.h b/gdb/parser-defs.h
index a9ae198..9f70ff9 100644
--- a/gdb/parser-defs.h
+++ b/gdb/parser-defs.h
@@ -25,6 +25,7 @@
 
 #include "expression.h"
 #include "symtab.h"
+#include "expop.h"
 
 struct block;
 struct language_defn;
@@ -93,6 +94,11 @@ struct expr_completion_state
      field name.  It is -1 if no dereference operation was found.  */
   int expout_last_struct = -1;
 
+  /* The last struct expression directly before a '.' or '->'.  This
+     is set when parsing and is only used when completing a field
+     name.  It is nullptr if no dereference operation was found.  */
+  expr::structop_base_operation *expout_last_op = nullptr;
+
   /* If we are completing a tagged type name, this will be nonzero.  */
   enum type_code expout_tag_completion_type = TYPE_CODE_UNDEF;
 
@@ -156,6 +162,11 @@ struct parser_state : public expr_builder
 
   void mark_struct_expression ();
 
+  /* Mark the given operation as the starting location of a structure
+     expression.  This is used when completing on field names.  */
+
+  void mark_struct_expression (expr::structop_base_operation *op);
+
   /* Indicate that the current parser invocation is completing a tag.
      TAG is the type code of the tag, and PTR and LENGTH represent the
      start of the tag name.  */