gdb/modula-2: parsing of multi-subscript arrays

Fix bug PR m2/26372, GDB's inability to parse multi-dimensional
modula-2 arrays.

We previously had two rules for handling the parsing of array
sub-scripts.  I have reproduced them here with the actual handler
blocks removed to make the bug clearer:

  exp     :    exp '[' non_empty_arglist ']'
          ;

  exp     :    exp '[' exp ']'
          ;

  non_empty_arglist
          :       exp
          ;

  non_empty_arglist
          :       non_empty_arglist ',' exp
          ;

This is ambiguous as the pattern "exp '[' exp" could match either of
the 'exp' rules.  Currently it just so happens that the parser picks
the second 'exp' rule which means we can only handle a single array
index.

As the handler code for the first 'exp' pattern will correctly handle
and number of array indexes then lets just remove the second pattern.

gdb/ChangeLog:

	PR m2/26372
        * m2-exp.y (exp): Improve comment for non_empty_arglist case, add
	an assert.  Remove single element array indexing pattern as the
	MULTI_SUBSCRIPT support will handle this case too.

gdb/testsuite/ChangeLog:

	PR m2/26372
        * gdb.modula2/multidim.c: New file.
        * gdb.modula2/multidim.exp: New file.

1 files changed, 6 insertions, 7 deletions

diff --git a/gdb/m2-exp.y b/gdb/m2-exp.y
index 70a3d9c..c79c1f2 100644
--- a/gdb/m2-exp.y
+++ b/gdb/m2-exp.y
@@ -293,21 +293,20 @@ set	:	'{' arglist '}'
 	;
 
 
-/* Modula-2 array subscript notation [a,b,c...] */
+/* Modula-2 array subscript notation [a,b,c...].  */
 exp     :       exp '['
                         /* This function just saves the number of arguments
 			   that follow in the list.  It is *not* specific to
 			   function types */
                         { pstate->start_arglist(); }
                 non_empty_arglist ']'  %prec DOT
-                        { write_exp_elt_opcode (pstate, MULTI_SUBSCRIPT);
+			{
+			  gdb_assert (pstate->arglist_len > 0);
+			  write_exp_elt_opcode (pstate, MULTI_SUBSCRIPT);
 			  write_exp_elt_longcst (pstate,
 						 pstate->end_arglist());
-			  write_exp_elt_opcode (pstate, MULTI_SUBSCRIPT); }
-        ;
-
-exp	:	exp '[' exp ']'
-			{ write_exp_elt_opcode (pstate, BINOP_SUBSCRIPT); }
+			  write_exp_elt_opcode (pstate, MULTI_SUBSCRIPT);
+			}
 	;
 
 exp	:	exp '('