Fortran: Detect missing quote in namelist read.

PR libfortran/123012

libgfortran/ChangeLog:

	* io/list_read.c (read_character): Add new check after
	get_string and provide better comments.

gcc/testsuite/ChangeLog:

	* gfortran.dg/namelist_101.f90: New test.

gcc/testsuite/gfortran.dg/namelist_101.f90

@@ -0,0 +1,16 @@
+! { dg-do run )
+! { dg-shouldfail "Missing quote" }
+program nml_quotes_bug
+  implicit none
+  integer      :: unit = 10
+  character(8) :: c1, c2
+  namelist /tovs_obs_chan/ c1, c2
+  open (unit ,file="nml-quotes-bug.nml")
+  write(unit,*) "&tovs_obs_chan"
+  write(unit,*) "  c1 = '1',"
+  write(unit,*) "  c2 =  2a ,"
+  write(unit,*) "/"
+  rewind(unit)
+  read (unit ,nml=tovs_obs_chan)
+  close(unit ,status="delete")
+end program nml_quotes_bug

libgfortran/io/list_read.c

@@ -1314,6 +1314,10 @@ read_character (st_parameter_dt *dtp, int length __attribute__ ((unused)))
 
 	CASE_SEPARATORS:
 	case EOF:
+	  /* At this point we have been reading a string of digits. Now we see
+	     the end of these digits without seeing the closing quote and not
+	     seeing the '*' for a repeat count.  When in namelist mode, if it
+	     was a string of digits it should have had the closing quote.  */
 	  if (dtp->u.p.namelist_mode)
 	    {
 	      snprintf (message, IOMSG_LEN, "Missing quote while reading item %d",
@@ -1367,6 +1371,16 @@ read_character (st_parameter_dt *dtp, int length __attribute__ ((unused)))
 
  get_string:
 
+  /* We could be at the beginning of a string or partially through a string
+     that began with all digits. Either way, the quote character for a namelist
+     read should have been set.  */
+  if (dtp->u.p.namelist_mode && (quote == ' '))
+    {
+      snprintf (message, IOMSG_LEN, "Missing quote while reading item %d",
+		dtp->u.p.item_count);
+      generate_error (&dtp->common, LIBERROR_READ_VALUE, message);
+    }
+
   for (;;)
     {
       if ((c = next_char (dtp)) == EOF)