[Ada] Ada 2020: Allow declarative items mixed with statements

This patch implements a syntactic language extension that allows
declarative items to appear in a sequence of statements.  For example:

    for X in S'Range loop
        Item : Character renames S (X);
        Item := Transform (Item);
    end loop;

Previously, declare/begin/end was required, which is just noise.

gcc/ada/

	* par.adb (P_Declarative_Items): New function to parse a
	sequence of declarative items.
	(P_Sequence_Of_Statements): Add Handled flag, to indicate
	whether to wrap the result in a block statement.
	* par-ch3.adb (P_Declarative_Item): Rename P_Declarative_Items
	to be P_Declarative_Item, because it really only parses a single
	declarative item, and to avoid conflict with the new
	P_Declarative_Items. Add In_Statements.  We keep the old
	error-recovery mechanisms in place when In_Statements is False.
	When True, we don't want to complain about statements, because
	we are parsing a sequence of statements.
	(P_Identifier_Declarations): If In_Statements, and we see what
	looks like a statement, we no longer give an error. We return to
	P_Sequence_Of_Statements with Done = True, so it can parse the
	statement.
	* par-ch5.adb (P_Sequence_Of_Statements): Call
	P_Declarative_Items to parse declarative items that appear in
	the statement list.  Remove error handling code that complained
	about such items.  Check some errors conservatively.  Wrap the
	result in a block statement when necessary.
	* par-ch11.adb (P_Handled_Sequence_Of_Statements): Pass
	Handled => True to P_Sequence_Of_Statements.
	* types.ads (No, Present): New functions for querying
	Source_Ptrs (equal, not equal No_Location).

1 files changed, 4 insertions, 0 deletions

diff --git a/gcc/ada/types.ads b/gcc/ada/types.ads
index 9ae1797..aae51a2 100644
--- a/gcc/ada/types.ads
+++ b/gcc/ada/types.ads
@@ -247,6 +247,10 @@ package Types is
    --  (very often we conditionalize so that we set No_Location in normal mode
    --  and the corresponding source line in -gnatD mode).
 
+   function No (Loc : Source_Ptr) return Boolean is (Loc = No_Location);
+   function Present (Loc : Source_Ptr) return Boolean is (not No (Loc));
+   --  Tests for No_Location / not No_Location
+
    Standard_Location : constant Source_Ptr := -2;
    --  Used for all nodes in the representation of package Standard other than
    --  nodes representing the contents of Standard.ASCII. Note that testing for