[Ada] Improve error recovery for bad comma/semicolon in expression

[Ada] Improve error recovery for bad comma/semicolon in expression

[Arnaud Charlet]

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This patch improves the error recovery for an errant comma or semicolon
after one condition in an expression when more conditions follow, as
shown in this example:

     1. procedure BadANDTHEN (X : Integer) is
     2. begin
     3.    if X > 10
     4.      and then X mod 4 = 2;
                                 |
        >>> extra ";" ignored

     5.      and then X mod 12 = 8
     6.    then
     7.       null;
     8.    end if;
     9. end;

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-10-20  Robert Dewar  <dewar@adacore.com>

	* par-ch4.adb (P_Expression): Handle extraneous comma/semicolon
	in middle of expression with logical operators.


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Index: par-ch4.adb
===================================================================
--- par-ch4.adb	(revision 216469)
+++ par-ch4.adb	(working copy)
@@ -1708,6 +1708,48 @@
             Node1 := New_Op_Node (Logical_Op, Op_Location);
             Set_Left_Opnd (Node1, Node2);
             Set_Right_Opnd (Node1, P_Relation);
+
+            --  Check for case of errant comma or semicolon
+
+            if Token = Tok_Comma or else Token = Tok_Semicolon then
+               declare
+                  Com        : constant Boolean := Token = Tok_Comma;
+                  Scan_State : Saved_Scan_State;
+                  Logop      : Node_Kind;
+
+               begin
+                  Save_Scan_State (Scan_State); -- at comma/semicolon
+                  Scan; -- past comma/semicolon
+
+                  --  Check for AND THEN or OR ELSE after comma/semicolon. We
+                  --  do not deal with AND/OR because those cases get mixed up
+                  --  with the select alternatives case.
+
+                  if Token = Tok_And or else Token = Tok_Or then
+                     Logop := P_Logical_Operator;
+                     Restore_Scan_State (Scan_State); -- to comma/semicolon
+
+                     if Nkind_In (Logop, N_And_Then, N_Or_Else) then
+                        Scan; -- past comma/semicolon
+
+                        if Com then
+                           Error_Msg_SP -- CODEFIX
+                             ("|extra "","" ignored");
+                        else
+                           Error_Msg_SP -- CODEFIX
+                             ("|extra "";"" ignored");
+                        end if;
+
+                     else
+                        Restore_Scan_State (Scan_State); -- to comma/semicolon
+                     end if;
+
+                  else
+                     Restore_Scan_State (Scan_State); -- to comma/semicolon
+                  end if;
+               end;
+            end if;
+
             exit when Token not in Token_Class_Logop;
          end loop;