[patch, fortran] PR109662 Namelist input with comma after name accepted

[Jerry D <jvdelisle2@gmail.com>]

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The attached patch adds a check for the invalid comma and emits a 
runtime error if -std=f95,f2003,f2018 are specified at compile time.

Attached patch includes a new test case.

Regression tested on x86_64-linux-gnu.

OK for mainline?

Regards,

Jerry

Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Fri May 5 20:12:25 2023 -0700

     Fortran: Namelist read with invalid input accepted.

             PR fortran/109662

     libgfortran/ChangeLog:

             * io/list_read.c: Add a check for a comma after a namelist
             name in read input. Issue a runtime error message.

     gcc/testsuite/ChangeLog:

             * gfortran.dg/pr109662.f90: New test.

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diff --git a/gcc/testsuite/gfortran.dg/pr109662.f90 b/gcc/testsuite/gfortran.dg/pr109662.f90
new file mode 100644
index 00000000000..988cfab73cc
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr109662.f90
@@ -0,0 +1,15 @@
+! { dg-do run }
+! { dg-options "-std=f2003" }
+! PR109662 a comma after namelist name accepted on input. 
+program testnmlread
+  implicit none
+  character(16) :: list = '&stuff, n = 759/'
+  character(100)::message
+  integer       :: n, ioresult
+  namelist/stuff/n
+  message = ""
+  ioresult = 0
+  n = 99
+  read(list,nml=stuff,iostat=ioresult)
+  if (ioresult == 0) STOP 13
+end program testnmlread
diff --git a/libgfortran/io/list_read.c b/libgfortran/io/list_read.c
index 109313c15b1..78bfd9e8787 100644
--- a/libgfortran/io/list_read.c
+++ b/libgfortran/io/list_read.c
@@ -3596,8 +3596,12 @@ find_nml_name:
   if (dtp->u.p.nml_read_error)
     goto find_nml_name;
 
-  /* A trailing space is required, we give a little latitude here, 10.9.1.  */
+  /* A trailing space is required, we allow a comma with std=gnu.  */
   c = next_char (dtp);
+  if (c == ',' && !(compile_options.allow_std & GFC_STD_GNU))
+    generate_error (&dtp->common, LIBERROR_READ_VALUE,
+		    "Comma after namelist name not allowed");
+
   if (!is_separator(c) && c != '!')
     {
       unget_char (dtp, c);