[patch, libgfortran] PR43899 Wrong unused-variable warning with NAMELISTs

[Jerry DeLisle <jvdelisle at frontier dot com>]

This PR is about two issues.  The first is a bogus warning about the variable 
being unused when -Wall is being used.  The second issue has to do with warning 
a user when a namelist read of a character object is truncated. Only the second 
issue is addressed here.

As Tobias points out, the test case is legal.  The attached patch adds a new 
runtime warning function to libgfortran and uses it in list_read.c if the test 
case has been compiled with -fbounds-check.  The warning is issued to stderr, 
and execution proceeds normally.

This will give users an opportunity to debug code that may unintentionally have 
an issue.

The runtime warning will also be useful down the road.

Regression tested on x86-64-linux-gnu.  OK for trunk.

Regards,

Jerry

2010-11-02  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

	PR libgfortran/43899
	* runtime/error.c (generate_error): New function to generate a run
	time warning message. Fix some whitespace.
	* gfortran.map: Add symbol for new function.
	* libgfortran.h: Add prototype for new function.
	* io/list_read.c (nml_read_obj): Use new function to warn when a
	character namelist object is truncated.  Only warn if compiled
	with -fbounds-check.

Index: runtime/error.c
===================================================================
--- runtime/error.c	(revision 166182)
+++ runtime/error.c	(working copy)
@@ -443,6 +443,22 @@ generate_error (st_parameter_common *cmp, int fami
 }
 iexport(generate_error);
 
+
+/* generate_error()-- Similar to generate_error but just give a warning.  */
+
+void
+generate_warning (st_parameter_common *cmp, const char *message)
+{
+
+  if (message == NULL)
+    message = " ";
+
+  show_locus (cmp);
+  st_printf ("Fortran runtime warning: %s\n", message);
+}
+iexport(generate_warning);
+
+
 /* Whether, for a feature included in a given standard set (GFC_STD_*),
    we should issue an error or a warning, or be quiet.  */
 
@@ -462,7 +478,6 @@ notification_std (int std)
 }
 
 
-
 /* Possibly issue a warning/error about use of a nonstandard (or deleted)
    feature.  An error/warning will be issued if the currently selected
    standard does not contain the requested bits.  */
Index: gfortran.map
===================================================================
--- gfortran.map	(revision 166182)
+++ gfortran.map	(working copy)
@@ -1116,6 +1116,7 @@ GFORTRAN_1.4 {
     _gfortran_bessel_yn_r10;
     _gfortran_bessel_yn_r16;
     _gfortran_error_stop_numeric;
+    _gfortran_generate_warning;
     _gfortran_iall_i1;
     _gfortran_iall_i2;
     _gfortran_iall_i4;
Index: libgfortran.h
===================================================================
--- libgfortran.h	(revision 166182)
+++ libgfortran.h	(working copy)
@@ -733,6 +733,9 @@ internal_proto(translate_error);
 extern void generate_error (st_parameter_common *, int, const char *);
 iexport_proto(generate_error);
 
+extern void generate_warning (st_parameter_common *, const char *);
+iexport_proto(generate_warning);
+
 extern try notify_std (st_parameter_common *, int, const char *);
 internal_proto(notify_std);
 
Index: io/list_read.c
===================================================================
--- io/list_read.c	(revision 166182)
+++ io/list_read.c	(working copy)
@@ -2586,7 +2586,19 @@ nml_read_obj (st_parameter_dt *dtp, namelist_info
 	  break;
 
 	case BT_CHARACTER:
-	  m = (dlen < dtp->u.p.saved_used) ? dlen : dtp->u.p.saved_used;
+	  if (dlen < dtp->u.p.saved_used)
+	    {
+	      if (compile_options.bounds_check)
+		{
+		  snprintf (nml_err_msg, nml_err_msg_size,
+			    "Namelist object '%s' truncated on read.",
+			    nl->var_name);
+		  generate_warning (&dtp->common, nml_err_msg);
+		}
+	      m = dlen;
+	    }
+	  else
+	    m = dtp->u.p.saved_used;
 	  pdata = (void*)( pdata + clow - 1 );
 	  memcpy (pdata, dtp->u.p.saved_string, m);
 	  if (m < dlen)

Attachment: namelist_67.f90
Description: Text document