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.

5 files changed, 96 insertions, 7 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 642cb64..4592b84 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2020-08-25  Gaius Mulley  <gaiusmod2@gmail.com>
+	    Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	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.
+
 2020-08-24  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* value.h (valprint_check_validity): Move declaration from
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 '('
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index b976a54..f5c258b 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-08-25  Gaius Mulley  <gaiusmod2@gmail.com>
+
+	PR m2/26372
+        * gdb.modula2/multidim.c: New file.
+        * gdb.modula2/multidim.exp: New file.
+
 2020-08-24  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* lib/gdb.exp (runto): Always emit fail on internal error.
diff --git a/gdb/testsuite/gdb.modula2/multidim.c b/gdb/testsuite/gdb.modula2/multidim.c
new file mode 100644
index 0000000..b0ce848
--- /dev/null
+++ b/gdb/testsuite/gdb.modula2/multidim.c
@@ -0,0 +1,39 @@
+/* This test script is part of GDB, the GNU debugger.
+
+   Copyright 2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+
+static int a[10][20];
+
+static void
+here (void)
+{
+}
+
+int
+main ()
+{
+  int i, j;
+  int count = 0;
+
+  for (i = 0; i < 10; i++)
+    for (j = 0; j < 20; j++)
+      {
+	a[i][j] = count;
+	count += 1;
+      }
+  here ();
+}
diff --git a/gdb/testsuite/gdb.modula2/multidim.exp b/gdb/testsuite/gdb.modula2/multidim.exp
new file mode 100644
index 0000000..ccccaa2
--- /dev/null
+++ b/gdb/testsuite/gdb.modula2/multidim.exp
@@ -0,0 +1,37 @@
+# Copyright 2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the gdb testsuite.  It contains tests for printing
+# the elements of an unbounded array using the Modula-2 language mode of
+# gdb.
+
+standard_testfile multidim.c
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile \
+	 {debug quiet}]} {
+    return -1
+}
+
+if ![runto here] then {
+    perror "couldn't run to breakpoint 'here'"
+    continue
+}
+
+gdb_test "set lang modula-2" ".*does not match.*" "switch to modula-2"
+
+gdb_test "print a\[1,2\]" ".*= 22.*" "second row third column"
+gdb_test "print a\[2,1\]" ".*= 41.*" "fifth row second column"
+gdb_test "print a\[a\[0,1\],a\[0,2\]\]" ".*= 22.*" \
+    "second row third column again"