[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).