Implement Ada assignment

Assignment is the most complicated Ada expression, because
implementing aggregate assignment involves several specialized
opcodes.

This patch does this implementation by introducing new abstract
classes that are used to represent the various parts of aggregate
assignment.  This makes the code somewhat cleaner, and, by avoiding
the over-use of 'operation' subclasses, avoids the need for dissection
using dynamic_cast (though a few are still needed here).

I believe this patch fixes a latent bug in the handling of
aggregate_assign_from_choices.  That code does:

      if (op == OP_DISCRETE_RANGE)
	{
	  choice_pos += 1;
	  lower = value_as_long (ada_evaluate_subexp (NULL, exp, pos,
						      EVAL_NORMAL));
	  upper = value_as_long (ada_evaluate_subexp (NULL, exp, pos,
						      EVAL_NORMAL));
	}

However, I think 'choice_pos' should be used in the calls, rather than
'pos'.

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

	* expprint.c (dump_for_expression): New overload.
	* expop.h (check_objfile, dump_for_expression): Declare new
	overloads.
	* ada-lang.c (check_objfile): New overload.
	(assign_component, ada_aggregate_component::uses_objfile)
	(ada_aggregate_component::dump, ada_aggregate_component::assign)
	(ada_aggregate_component::assign_aggregate)
	(ada_positional_component::uses_objfile)
	(ada_positional_component::dump, ada_positional_component::assign)
	(ada_discrete_range_association::uses_objfile)
	(ada_discrete_range_association::dump)
	(ada_discrete_range_association::assign)
	(ada_name_association::uses_objfile, ada_name_association::dump)
	(ada_name_association::assign)
	(ada_choices_component::uses_objfile, ada_choices_component::dump)
	(ada_choices_component::assign)
	(ada_others_component::uses_objfile, ada_others_component::dump)
	(ada_others_component::assign, ada_assign_operation::evaluate):
	New methods.
	* ada-exp.h (ada_string_operation) <get_name>: New method.
	(class ada_assign_operation): New.
	(class ada_component): New.
	(ada_component_up): New typedef.
	(class ada_aggregate_operation, class ada_aggregate_component)
	(class ada_positional_component, class ada_others_component)
	(class ada_association): New.
	(ada_association_up): New typedef.
	(class ada_choices_component)
	(class ada_discrete_range_association)
	(class ada_name_association): New.

1 files changed, 279 insertions, 0 deletions

diff --git a/gdb/ada-exp.h b/gdb/ada-exp.h
index 456aa89..ab910e8 100644
--- a/gdb/ada-exp.h
+++ b/gdb/ada-exp.h
@@ -122,6 +122,12 @@ public:
 
   using string_operation::string_operation;
 
+  /* Return the underlying string.  */
+  const char *get_name () const
+  {
+    return std::get<0> (m_storage).c_str ();
+  }
+
   value *evaluate (struct type *expect_type,
 		   struct expression *exp,
 		   enum noside noside) override;
@@ -447,6 +453,279 @@ public:
   { return OP_FUNCALL; }
 };
 
+/* An Ada assignment operation.  */
+class ada_assign_operation
+  : public assign_operation
+{
+public:
+
+  using assign_operation::assign_operation;
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override;
+
+  enum exp_opcode opcode () const override
+  { return BINOP_ASSIGN; }
+};
+
+/* This abstract class represents a single component in an Ada
+   aggregate assignment.  */
+class ada_component
+{
+public:
+
+  /* Assign to LHS, which is part of CONTAINER.  EXP is the expression
+     being evaluated.  INDICES, LOW, and HIGH indicate which
+     sub-components have already been assigned; INDICES should be
+     updated by this call.  */
+  virtual void assign (struct value *container,
+		       struct value *lhs, struct expression *exp,
+		       std::vector<LONGEST> &indices,
+		       LONGEST low, LONGEST high) = 0;
+
+  /* Same as operation::uses_objfile.  */
+  virtual bool uses_objfile (struct objfile *objfile) = 0;
+
+  /* Same as operation::dump.  */
+  virtual void dump (ui_file *stream, int depth) = 0;
+
+  virtual ~ada_component () = default;
+
+protected:
+
+  ada_component () = default;
+  DISABLE_COPY_AND_ASSIGN (ada_component);
+};
+
+/* Unique pointer specialization for Ada assignment components.  */
+typedef std::unique_ptr<ada_component> ada_component_up;
+
+/* An operation that holds a single component.  */
+class ada_aggregate_operation
+  : public tuple_holding_operation<ada_component_up>
+{
+public:
+
+  using tuple_holding_operation::tuple_holding_operation;
+
+  /* Assuming that LHS represents an lvalue having a record or array
+     type, evaluate an assignment of this aggregate's value to LHS.
+     CONTAINER is an lvalue containing LHS (possibly LHS itself).
+     Does not modify the inferior's memory, nor does it modify the
+     contents of LHS (unless == CONTAINER).  */
+
+  void assign_aggregate (struct value *container,
+			 struct value *lhs,
+			 struct expression *exp);
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override
+  {
+    error (_("Aggregates only allowed on the right of an assignment"));
+  }
+
+  enum exp_opcode opcode () const override
+  { return OP_AGGREGATE; }
+};
+
+/* A component holding a vector of other components to assign.  */
+class ada_aggregate_component : public ada_component
+{
+public:
+
+  explicit ada_aggregate_component (std::vector<ada_component_up> &&components)
+    : m_components (std::move (components))
+  {
+  }
+
+  void assign (struct value *container,
+	       struct value *lhs, struct expression *exp,
+	       std::vector<LONGEST> &indices,
+	       LONGEST low, LONGEST high) override;
+
+  bool uses_objfile (struct objfile *objfile) override;
+
+  void dump (ui_file *stream, int depth) override;
+
+private:
+
+  std::vector<ada_component_up> m_components;
+};
+
+/* A component that assigns according to a provided index (which is
+   relative to the "low" value).  */
+class ada_positional_component : public ada_component
+{
+public:
+
+  ada_positional_component (int index, operation_up &&op)
+    : m_index (index),
+      m_op (std::move (op))
+  {
+  }
+
+  void assign (struct value *container,
+	       struct value *lhs, struct expression *exp,
+	       std::vector<LONGEST> &indices,
+	       LONGEST low, LONGEST high) override;
+
+  bool uses_objfile (struct objfile *objfile) override;
+
+  void dump (ui_file *stream, int depth) override;
+
+private:
+
+  int m_index;
+  operation_up m_op;
+};
+
+/* A component which handles an "others" clause.  */
+class ada_others_component : public ada_component
+{
+public:
+
+  explicit ada_others_component (operation_up &&op)
+    : m_op (std::move (op))
+  {
+  }
+
+  void assign (struct value *container,
+	       struct value *lhs, struct expression *exp,
+	       std::vector<LONGEST> &indices,
+	       LONGEST low, LONGEST high) override;
+
+  bool uses_objfile (struct objfile *objfile) override;
+
+  void dump (ui_file *stream, int depth) override;
+
+private:
+
+  operation_up m_op;
+};
+
+/* An interface that represents an association that is used in
+   aggregate assignment.  */
+class ada_association
+{
+public:
+
+  /* Like ada_component::assign, but takes an operation as a
+     parameter.  The operation is evaluated and then assigned into LHS
+     according to the rules of the concrete implementation.  */
+  virtual void assign (struct value *container,
+		       struct value *lhs,
+		       struct expression *exp,
+		       std::vector<LONGEST> &indices,
+		       LONGEST low, LONGEST high,
+		       operation_up &op) = 0;
+
+  /* Same as operation::uses_objfile.  */
+  virtual bool uses_objfile (struct objfile *objfile) = 0;
+
+  /* Same as operation::dump.  */
+  virtual void dump (ui_file *stream, int depth) = 0;
+
+  virtual ~ada_association () = default;
+
+protected:
+
+  ada_association () = default;
+  DISABLE_COPY_AND_ASSIGN (ada_association);
+};
+
+/* Unique pointer specialization for Ada assignment associations.  */
+typedef std::unique_ptr<ada_association> ada_association_up;
+
+/* A component that holds a vector of associations and an operation.
+   The operation is re-evaluated for each choice.  */
+class ada_choices_component : public ada_component
+{
+public:
+
+  explicit ada_choices_component (operation_up &&op)
+    : m_op (std::move (op))
+  {
+  }
+
+  /* Set the vector of associations.  This is done separately from the
+     constructor because it was simpler for the implementation of the
+     parser.  */
+  void set_associations (std::vector<ada_association_up> &&assoc)
+  {
+    m_assocs = std::move (assoc);
+  }
+
+  void assign (struct value *container,
+	       struct value *lhs, struct expression *exp,
+	       std::vector<LONGEST> &indices,
+	       LONGEST low, LONGEST high) override;
+
+  bool uses_objfile (struct objfile *objfile) override;
+
+  void dump (ui_file *stream, int depth) override;
+
+private:
+
+  std::vector<ada_association_up> m_assocs;
+  operation_up m_op;
+};
+
+/* An association that uses a discrete range.  */
+class ada_discrete_range_association : public ada_association
+{
+public:
+
+  ada_discrete_range_association (operation_up &&low, operation_up &&high)
+    : m_low (std::move (low)),
+      m_high (std::move (high))
+  {
+  }
+
+  void assign (struct value *container,
+	       struct value *lhs, struct expression *exp,
+	       std::vector<LONGEST> &indices,
+	       LONGEST low, LONGEST high,
+	       operation_up &op) override;
+
+  bool uses_objfile (struct objfile *objfile) override;
+
+  void dump (ui_file *stream, int depth) override;
+
+private:
+
+  operation_up m_low;
+  operation_up m_high;
+};
+
+/* An association that uses a name.  The name may be an expression
+   that evaluates to an integer (for arrays), or an Ada string or
+   variable value operation.  */
+class ada_name_association : public ada_association
+{
+public:
+
+  explicit ada_name_association (operation_up val)
+    : m_val (std::move (val))
+  {
+  }
+
+  void assign (struct value *container,
+	       struct value *lhs, struct expression *exp,
+	       std::vector<LONGEST> &indices,
+	       LONGEST low, LONGEST high,
+	       operation_up &op) override;
+
+  bool uses_objfile (struct objfile *objfile) override;
+
+  void dump (ui_file *stream, int depth) override;
+
+private:
+
+  operation_up m_val;
+};
+
 } /* namespace expr */
 
 #endif /* ADA_EXP_H */