[Ada] Declare expressions

[Ada] Declare expressions

2020-06-16  Bob Duff  <duff@adacore.com>

gcc/ada/

	* par-ch4.adb (P_Case_Expression): Move to be local.
	(P_Declare_Expression): New parsing routine.
	(P_Unparen_Cond_Expr_Etc): New name for
	P_Unparen_Cond_Case_Quant_Expression which was missing one case
	in its name (iterated component association), and we're adding a
	new case (declare expression), so lets use "Etc" instead of
	trying to pack all those things into the name.  Add call to
	P_Declare_Expression, and check for missing parens.
	(P_Expression_If_OK, P_Expression_Or_Range_Attribute_If_OK): Add
	Tok_Declare.
	* par.adb (P_Basic_Declarative_Items): Add parameter
	Declare_Expression so we can tailor the error message about
	incorrect bodies.
	(P_Case_Expression): Move to body.
	* par-ch3.adb (P_Basic_Declarative_Items): Tailor the error
	message about incorrect bodies.
	* par-ch7.adb (P_Package): Pass Declare_Expression => False to
	P_Basic_Declarative_Items.
	* sem.ads (In_Declare_Expr): Counter used to determine whether
	we are analyzing a declare_expression. Needed to give errors
	about things that are not allowed in declare_expression, such as
	the 'Access attribute.
	* sem.adb (Do_Analyze): Save/restore In_Declare_Expr.
	* sem_ch4.adb (Analyze_Expression_With_Actions): Give this node
	its own scope.  That seems better in general, but it is
	necessary for declare_expressions.  For example, an identifier
	declared in a declare_expression should not clash with the same
	identifier in an outer scope.  If this is a declare_expression,
	indicated by Comes_From_Source, then check legality rules, and
	incr/decr In_Declare_Expr.
	* sem_aggr.adb (Resolve_Aggregate): Allow an applicable index
	constraint for a declare_expression, so if its expression is an
	array aggregate, it can have "others => ...".
	* sem_attr.adb (Analyze_Access_Attribute): Disallow these
	attributes in declare_expressions. Add comment to make it clear
	that Unrestricted_Access is included.
	* sinfo.ads, sinfo.adb, atree.ads, atree.adb: Remove the
	now-incorrect comment in sinfo.ads that says
	N_Expression_With_Actions has no proper scope.  Add 17-parameter
	versions of Nkind_In.  Remove the 16-parameter versions of
	Nkind_In.