Zero the initial file port revealed count.

Fixes <https://bugs.gnu.org/41204>.
Reported by Caleb Ristvedt <caleb.ristvedt@cune.org>.

Until now, Guile would leak the file descriptors of all the file ports
not explicitly closed.

* libguile/fports.c (scm_i_fdes_to_port): Initialize fp->revealed.
* test-suite/tests/ports.test ("initial revealed count")
("non-revealed port is closed"): New tests.
("close-port & revealed port"): Check (port-revealed port).
("revealed port fdes not closed"): Likewise.

libguile/fports.c

@@ -1,4 +1,4 @@
-/* Copyright 1995-2004,2006-2015,2017-2019
+/* Copyright 1995-2004,2006-2015,2017-2020
      Free Software Foundation, Inc.
 
    This file is part of Guile.
@@ -452,6 +452,7 @@ scm_i_fdes_to_port (int fdes, long mode_bits, SCM name, unsigned options)
                                                   "file port");
   fp->fdes = fdes;
   fp->options = options;
+  fp->revealed = 0;
 
   port = scm_c_make_port (scm_file_port_type, mode_bits, (scm_t_bits)fp);
   

test-suite/tests/ports.test

@@ -2,7 +2,7 @@
 ;;;; Jim Blandy <jimb@red-bean.com> --- May 1999
 ;;;;
 ;;;; 	Copyright (C) 1999, 2001, 2004, 2006, 2007, 2009, 2010,
-;;;;      2011, 2012, 2013, 2014, 2015, 2017, 2019 Free Software Foundation, Inc.
+;;;;      2011, 2012, 2013, 2014, 2015, 2017, 2019, 2020 Free Software Foundation, Inc.
 ;;;;
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -602,10 +602,40 @@
                           (pass-if "unread residue"
                                    (string=? (read-line) "moon"))))
 
+(pass-if-equal "initial revealed count"    ;<https://bugs.gnu.org/41204>
+    0
+  (let* ((port     (open-input-file "/dev/null"))
+         (revealed (port-revealed port)))
+    (close-port port)
+    revealed))
+
+(pass-if-equal "non-revealed port is closed"
+    EBADF
+  (let* ((port (open-input-file "/dev/null"))
+         (fdes (fileno port)))          ;leaves revealed count unchanged
+    (unless (zero? (port-revealed port))
+      (error "wrong revealed count" (port-revealed port)))
+
+    (set! port #f)
+    (gc)
+    (catch 'system-error
+      (lambda ()
+        (seek fdes 0 SEEK_CUR)
+
+        ;; If we get here, it might be because PORT was not GC'd, we
+        ;; don't know (and we can't use a guardian because it would keep
+        ;; PORT alive.)
+        (close-fdes fdes)
+        (throw 'unresolved))
+      (lambda args
+        (system-error-errno args)))))
+
 (pass-if-equal "close-port & revealed port"
     EBADF
   (let* ((port (open-file "/dev/null" "r0"))
          (fdes (port->fdes port)))    ;increments revealed count of PORT
+    (unless (= 1 (port-revealed port))
+      (error "wrong revealed count" (port-revealed port)))
     (close-port port)                 ;closes FDES as a side-effect
     (catch 'system-error
       (lambda ()
@@ -617,6 +647,9 @@
 (pass-if "revealed port fdes not closed"
   (let* ((port (open-file "/dev/null" "r0"))
          (fdes (port->fdes port)))
+    (unless (= 1 (port-revealed port))
+      (error "wrong revealed count" (port-revealed port)))
+
     (set! port #f)
     (gc)