[gcc r16-6142] Fortran: Fix bad read involving extra input text.

[Jerry DeLisle]

https://gcc.gnu.org/g:381fc8ed0f1530d0c30d5dbb6119b370fd91ba68

commit r16-6142-g381fc8ed0f1530d0c30d5dbb6119b370fd91ba68
Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Sun Dec 14 13:23:36 2025 -0800

    Fortran: Fix bad read involving extra input text.
    
            The problem here involved DTIO mixed with non-DTIO
            variables in list formatted reads.  The previous fix to
            PR105361 broke the test case here by mis-handling the
            end of file conditions. It was found that the code could
            be significantly reduced as well.
    
            PR libfortran/122936
    
    libgfortran/ChangeLog:
    
            * io/list_read.c (finish_list_read): Remove the use of hit_eof
            and free_line. Simplify the logic. Add comments to clarify.
    
    gcc/testsuite/ChangeLog:
    
            * gfortran.dg/pr122936.f90: New test.

Diff:
---
 gcc/testsuite/gfortran.dg/pr122936.f90 | 43 ++++++++++++++++++++++++++++++++++
 libgfortran/io/list_read.c             | 27 ++++++++++++++-------
 2 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/gcc/testsuite/gfortran.dg/pr122936.f90 b/gcc/testsuite/gfortran.dg/pr122936.f90
new file mode 100644
index 000000000000..88fa2cb050b3
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr122936.f90
@@ -0,0 +1,43 @@
+! { dg-do run }
+! PR122936, derived from the original provided by the reporter.
+! Before the patch this gave a runtime error.
+module test_io
+    TYPE :: MYTYPE
+        REAL :: value
+    END TYPE
+    INTERFACE read(formatted)
+        MODULE PROCEDURE read_formatted
+    END INTERFACE
+    PUBLIC :: read(formatted)
+contains
+    ! Formatted Input
+    SUBROUTINE read_formatted(dtv, unit, iotype, v_list, iostat, iomsg)
+        CLASS(MYTYPE), INTENT(INOUT) :: dtv
+        INTEGER, INTENT(IN)      :: unit
+        CHARACTER(*), INTENT(IN) :: iotype
+        INTEGER, INTENT(IN)      :: v_list(:)
+        INTEGER, INTENT(OUT)     :: iostat
+        CHARACTER(*), INTENT(INOUT) :: iomsg
+
+        REAL   :: tmp
+
+        READ(unit, FMT = *, IOSTAT=iostat, IOMSG=iomsg) tmp
+        IF (iostat == 0) dtv%value = tmp
+    END SUBROUTINE read_formatted
+
+end module
+
+PROGRAM MAIN
+    USE test_io
+    INTEGER, PARAMETER  :: NIN = 15
+    TYPE(MYTYPE)       :: V11, V12, V13
+    INTEGER            :: V21, V22, V23
+    OPEN(NIN, status='scratch')
+    WRITE(NIN,*) "    2.5 9 1.5, AValue for V1"
+    WRITE(NIN,*) "    15 2.4 17,  BValue for V2"
+    REWIND(NIN)
+    READ(NIN, FMT = *) V11, V23, V12
+    READ(NIN, FMT = *) V21, V13, V22
+    CLOSE(NIN)
+END PROGRAM MAIN
+
diff --git a/libgfortran/io/list_read.c b/libgfortran/io/list_read.c
index 7c22f61e5a70..c20900841e38 100644
--- a/libgfortran/io/list_read.c
+++ b/libgfortran/io/list_read.c
@@ -2554,6 +2554,7 @@ finish_list_read (st_parameter_dt *dtp)
       return;
     }
 
+  /* Only perform the following cleanup on external files or the stdin file.  */
   if (!is_internal_unit (dtp))
     {
       int c;
@@ -2561,23 +2562,31 @@ finish_list_read (st_parameter_dt *dtp)
       /* Set the next_char and push_char worker functions.  */
       set_workers (dtp);
 
-      if (likely (dtp->u.p.child_saved_iostat == LIBERROR_OK)
-	      && ((dtp->common.flags & IOPARM_DT_HAS_UDTIO) == 0))
+      /* Make sure there were no errors from a DTIO child read.  */
+      if (likely (dtp->u.p.child_saved_iostat == LIBERROR_OK))
 	{
+	  /* Peek ahead to see where we are in the parent read.  */
 	  c = next_char (dtp);
-	  if (c == EOF)
+	  unget_char (dtp, c);
+
+	  /* If the last read used DTIO, handle end conditions differently.  */
+	  if ((dtp->common.flags & IOPARM_DT_HAS_UDTIO) != 0)
 	    {
-	      free_line (dtp);
-	      hit_eof (dtp);
-	      return;
+	      if ((c == EOF) || (c == ' '))
+		return;
+	    }
+	  else
+	    {
+	      if (c == EOF)
+		{
+		  hit_eof (dtp);
+		  return;
+		}
 	    }
 	  if (c != '\n')
 	    eat_line (dtp);
 	}
     }
-
-  free_line (dtp);
-
 }
 
 /*			NAMELIST INPUT