[COMMITTED] ada: Better error message for bad Discard_Names configuration pragma

["Marc Poulhiès" <poulhies@adacore.com>]

From: Steve Baird <baird@adacore.com>

When a pragma Discard_Names is used as a configuration pragma, it does not
take an argument. If an argument is given, the resulting error message was
incorrect and confusing.

gcc/ada/

	* sem_prag.adb (Analyze_Pragma): Fix Is_Configuration_Pragma
	function to handle case where the pragma's parent is an
	N_Aspect_Specification node. In analyzing a Discard_Names pragma,
	do not assume that a nonzero number of arguments implies that the
	pragma is not a configuration pragma; that assumption only holds
	for legal programs.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/ada/sem_prag.adb | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb
index f3c23caeae4..555e09b74e9 100644
--- a/gcc/ada/sem_prag.adb
+++ b/gcc/ada/sem_prag.adb
@@ -7298,11 +7298,20 @@ package body Sem_Prag is
       --  the test below also permits use in a configuration pragma file.
 
       function Is_Configuration_Pragma return Boolean is
-         Lis : constant List_Id := List_Containing (N);
+         Lis : List_Id;
          Par : constant Node_Id := Parent (N);
          Prg : Node_Id;
 
       begin
+         --  Don't evaluate List_Containing (N) if Parent (N) could be
+         --  an N_Aspect_Specification node.
+
+         if not Is_List_Member (N) then
+            return False;
+         end if;
+
+         Lis := List_Containing (N);
+
          --  If no parent, then we are in the configuration pragma file,
          --  so the placement is definitely appropriate.
 
@@ -15729,8 +15738,13 @@ package body Sem_Prag is
 
             --  Deal with configuration pragma case
 
-            if Arg_Count = 0 and then Is_Configuration_Pragma then
-               Global_Discard_Names := True;
+            if Is_Configuration_Pragma then
+               if Arg_Count /= 0 then
+                  Error_Pragma
+                    ("nonzero number of arguments for configuration pragma%");
+               else
+                  Global_Discard_Names := True;
+               end if;
                return;
 
             --  Otherwise, check correct appropriate context
-- 
2.34.1