Rework time-* functions in Tramp

* doc/misc/emacs-mime.texi (time-date): Add time-equal-p.

* lisp/net/tramp-compat.el (tramp-compat-time-equal-p): New defsubst.

* lisp/net/tramp.el (tramp-file-name-handler): Remove `debug'
error handler.
(tramp-half-a-year): Remove.
(tramp-time-dont-know, tramp-time-doesnt-exist): New defconst.
(tramp-time-diff): Remove compat code.
(tramp-handle-set-visited-file-modtime)
(tramp-handle-verify-visited-file-modtime):
* lisp/net/tramp-adb.el (tramp-do-parse-file-attributes-with-ls)
(tramp-adb-handle-set-file-times):
* lisp/net/tramp-sh.el (tramp-do-file-attributes-with-ls)
(tramp-sh-handle-set-visited-file-modtime)
(tramp-sh-handle-verify-visited-file-modtime)
(tramp-sh-handle-set-file-times)
(tramp-sh-handle-file-newer-than-file-p):
Use `tramp-time-dont-know', `tramp-time-doesnt-exist' and
`tramp-compat-time-equal-p'.
(tramp-sh-handle-verify-visited-file-modtime): Simplify check.

* lisp/net/tramp-smb.el (tramp-smb-handle-file-attributes)
(tramp-smb-read-file-entry): Use `tramp-time-dont-know'.
(tramp-smb-handle-insert-directory): Adapt half-a-year check.

* src/editfns.c (Ftime_equal_p): Adapt docstring.

* test/lisp/net/tramp-tests.el
(tramp-test19-directory-files-and-attributes)
(tramp-test22-file-times): Use `tramp-compat-time-equal-p' and
`tramp-time-dont-know'.
(tramp-test23-visited-file-modtime): Extend test.

10 files changed, 97 insertions, 84 deletions

diff --git a/doc/misc/emacs-mime.texi b/doc/misc/emacs-mime.texi
index 45f37fb8557..9280311b5c9 100644
--- a/doc/misc/emacs-mime.texi
+++ b/doc/misc/emacs-mime.texi
@@ -1561,6 +1561,9 @@ Here's a bunch of time/date/second/day examples:
 (time-less-p '(13818 19266) '(13818 19145))
 @result{} nil
 
+(time-equal-p '(13818 19266) '(13818 19145))
+@result{} nil
+
 (time-subtract '(13818 19266) '(13818 19145))
 @result{} (0 121)
 
@@ -1641,6 +1644,10 @@ return a ``zero'' time.
 Take two times and say whether the first time is less (i.e., earlier)
 than the second time.  (This is a built-in function.)
 
+@item time-equal-p
+Check, whether two time values are equal.  The time values must not be
+in the same format.  (This is a built-in function.)
+
 @item time-since
 Take a time and return a time saying how long it was since that time.
 
diff --git a/lisp/net/tramp-adb.el b/lisp/net/tramp-adb.el
index 35b0fdda623..36374f88e0d 100644
--- a/lisp/net/tramp-adb.el
+++ b/lisp/net/tramp-adb.el
@@ -411,9 +411,9 @@ pass to the OPERATION."
                  ;; no way to handle numeric ids in Androids ash
                  (if (eq id-format 'integer) 0 uid)
                  (if (eq id-format 'integer) 0 gid)
-                 '(0 0)                 ; atime
+                 tramp-time-dont-know   ; atime
                  (date-to-time date)    ; mtime
-                 '(0 0)                 ; ctime
+                 tramp-time-dont-know   ; ctime
                  size
                  mod-string
                  ;; fake
@@ -725,7 +725,9 @@ But handle the case, if the \"test\" command is not available."
   (with-parsed-tramp-file-name filename nil
     (tramp-flush-file-properties v (file-name-directory localname))
     (tramp-flush-file-properties v localname)
-    (let ((time (if (or (null time) (equal time '(0 0)))
+    (let ((time (if (or (null time)
+                        (tramp-compat-time-equal-p time tramp-time-doesnt-exist)
+                        (tramp-compat-time-equal-p time tramp-time-dont-know))
                     (current-time)
                   time)))
       (tramp-adb-send-command-and-check
diff --git a/lisp/net/tramp-cache.el b/lisp/net/tramp-cache.el
index b40a4d7edd6..ebb4254dab4 100644
--- a/lisp/net/tramp-cache.el
+++ b/lisp/net/tramp-cache.el
@@ -118,9 +118,8 @@ Returns DEFAULT if not set."
         (and (consp value)
              (or (null remote-file-name-inhibit-cache)
                  (and (integerp remote-file-name-inhibit-cache)
-                      (<=
-                       (tramp-time-diff (current-time) (car value))
-                       remote-file-name-inhibit-cache))
+                      (<= (tramp-time-diff (current-time) (car value))
+                          remote-file-name-inhibit-cache))
                  (and (consp remote-file-name-inhibit-cache)
                       (time-less-p
                        remote-file-name-inhibit-cache (car value)))))
diff --git a/lisp/net/tramp-compat.el b/lisp/net/tramp-compat.el
index bcfaf40ebc1..c3777e6e737 100644
--- a/lisp/net/tramp-compat.el
+++ b/lisp/net/tramp-compat.el
@@ -247,6 +247,14 @@ If NAME is a remote file name, the local part of NAME is unquoted."
             (funcall handler 'exec-path)
           exec-path)))))
 
+;; `time-equal-p' has appeared in Emacs 27.1.
+(if (fboundp 'time-equal-p)
+    (defalias 'tramp-compat-time-equal-p 'time-equal-p)
+  (defsubst tramp-compat-time-equal-p (t1 t2)
+    "Return non-nil if time value T1 is equal to time value T2.
+A nil value for either argument stands for the current time."
+    (equal (or t1 (current-time)) (or t2 (current-time)))))
+
 (add-hook 'tramp-unload-hook
           (lambda ()
             (unload-feature 'tramp-loaddefs 'force)
diff --git a/lisp/net/tramp-gvfs.el b/lisp/net/tramp-gvfs.el
index f46ddc68ae4..c150edf3f13 100644
--- a/lisp/net/tramp-gvfs.el
+++ b/lisp/net/tramp-gvfs.el
@@ -650,7 +650,7 @@ Return nil for null BYTE-ARRAY."
   (cond
    ((and (consp message) (characterp (car message)))
     (format "%S" (tramp-gvfs-dbus-byte-array-to-string message)))
-   ((and (consp message) (not (consp (cdr message))))
+   ((and (consp message) (atom (cdr message)))
     (cons (tramp-gvfs-stringify-dbus-message (car message))
           (tramp-gvfs-stringify-dbus-message (cdr message))))
    ((consp message)
diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 64d208175f9..b2be43395f8 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -1348,13 +1348,10 @@ component is used as the target of the symlink."
            res-uid
            ;; 3. File gid.
            res-gid
-           ;; 4. Last access time, as a list of integers.  Normally
-           ;; this would be in the same format as `current-time', but
-           ;; the subseconds part is not currently implemented, and
-           ;; (0 0) denotes an unknown time.
-           ;; 5. Last modification time, likewise.
-           ;; 6. Last status change time, likewise.
-           '(0 0) '(0 0) '(0 0)         ;CCC how to find out?
+           ;; 4. Last access time.
+           ;; 5. Last modification time.
+           ;; 6. Last status change time.
+           tramp-time-dont-know tramp-time-dont-know tramp-time-dont-know
            ;; 7. Size in bytes (-1, if number is out of range).
            res-size
            ;; 8. File modes, as a string of ten letters or dashes as in ls -l.
@@ -1420,13 +1417,10 @@ component is used as the target of the symlink."
       (with-parsed-tramp-file-name f nil
         (let* ((remote-file-name-inhibit-cache t)
                (attr (file-attributes f))
-               ;; '(-1 65535) means file doesn't exists yet.
                (modtime (or (tramp-compat-file-attribute-modification-time attr)
-                            '(-1 65535))))
+                            tramp-time-doesnt-exist)))
           (setq coding-system-used last-coding-system-used)
-          ;; We use '(0 0) as a don't-know value.  See also
-          ;; `tramp-do-file-attributes-with-ls'.
-          (if (not (equal modtime '(0 0)))
+          (if (not (tramp-compat-time-equal-p modtime tramp-time-dont-know))
               (tramp-run-real-handler 'set-visited-file-modtime (list modtime))
             (progn
               (tramp-send-command
@@ -1455,7 +1449,7 @@ of."
       ;; recorded last modification time, or there is no established
       ;; connection.
       (if (or (not f)
-              (eq (visited-file-modtime) 0)
+              (zerop (visited-file-modtime))
               (not (file-remote-p f nil 'connected)))
           t
         (with-parsed-tramp-file-name f nil
@@ -1466,16 +1460,10 @@ of."
 
             (cond
              ;; File exists, and has a known modtime.
-             ((and attr (not (equal modtime '(0 0))))
-              (< (abs (tramp-time-diff
-                       modtime
-                       ;; For compatibility, deal with both the old
-                       ;; (HIGH . LOW) and the new (HIGH LOW) return
-                       ;; values of `visited-file-modtime'.
-                       (if (atom (cdr mt))
-                           (list (car mt) (cdr mt))
-                         mt)))
-                 2))
+             ((and attr
+                   (not
+                    (tramp-compat-time-equal-p modtime tramp-time-dont-know)))
+              (< (abs (tramp-time-diff modtime mt)) 2))
              ;; Modtime has the don't know value.
              (attr
               (tramp-send-command
@@ -1491,7 +1479,7 @@ of."
                 v localname "visited-file-modtime-ild" "")))
              ;; If file does not exist, say it is not modified if and
              ;; only if that agrees with the buffer's record.
-             (t (equal mt '(-1 65535))))))))))
+             (t (tramp-compat-time-equal-p mt tramp-time-doesnt-exist)))))))))
 
 (defun tramp-sh-handle-set-file-modes (filename mode)
   "Like `set-file-modes' for Tramp files."
@@ -1510,9 +1498,12 @@ of."
     (when (tramp-get-remote-touch v)
       (tramp-flush-file-properties v (file-name-directory localname))
       (tramp-flush-file-properties v localname)
-      (let ((time (if (or (null time) (equal time '(0 0)))
-                      (current-time)
-                    time)))
+      (let ((time
+             (if (or (null time)
+                     (tramp-compat-time-equal-p time tramp-time-doesnt-exist)
+                     (tramp-compat-time-equal-p time tramp-time-dont-know))
+                 (current-time)
+               time)))
         (tramp-send-command-and-check
          v (format
             "env TZ=UTC %s %s %s"
@@ -1685,11 +1676,13 @@ be non-negative integers."
                  (fa2 (file-attributes file2)))
              (if (and
                   (not
-                   (equal (tramp-compat-file-attribute-modification-time fa1)
-                          '(0 0)))
+                   (tramp-compat-time-equal-p
+                    (tramp-compat-file-attribute-modification-time fa1)
+                    tramp-time-dont-know))
                   (not
-                   (equal (tramp-compat-file-attribute-modification-time fa2)
-                          '(0 0))))
+                   (tramp-compat-time-equal-p
+                    (tramp-compat-file-attribute-modification-time fa2)
+                    tramp-time-dont-know)))
                  (> 0 (tramp-time-diff
                        (tramp-compat-file-attribute-modification-time fa2)
                        (tramp-compat-file-attribute-modification-time fa1)))
diff --git a/lisp/net/tramp-smb.el b/lisp/net/tramp-smb.el
index 583acbde03c..a97b8017300 100644
--- a/lisp/net/tramp-smb.el
+++ b/lisp/net/tramp-smb.el
@@ -817,18 +817,18 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
             ;; Check result.
             (when entry
               (list (and (string-match "d" (nth 1 entry))
-                         t)        ;0 file type
-                    -1             ;1 link count
-                    uid            ;2 uid
-                    gid            ;3 gid
-                    '(0 0)         ;4 atime
-                    (nth 3 entry)  ;5 mtime
-                    '(0 0)         ;6 ctime
-                    (nth 2 entry)  ;7 size
-                    (nth 1 entry)  ;8 mode
-                    nil            ;9 gid weird
-                    inode          ;10 inode number
-                    device)))))))) ;11 file system number
+                         t)              ;0 file type
+                    -1                   ;1 link count
+                    uid                  ;2 uid
+                    gid                  ;3 gid
+                    tramp-time-dont-know ;4 atime
+                    (nth 3 entry)        ;5 mtime
+                    tramp-time-dont-know ;6 ctime
+                    (nth 2 entry)        ;7 size
+                    (nth 1 entry)        ;8 mode
+                    nil                  ;9 gid weird
+                    inode                ;10 inode number
+                    device))))))))       ;11 file system number
 
 (defun tramp-smb-do-file-attributes-with-stat (vec &optional id-format)
   "Implement `file-attributes' for Tramp files using stat command."
@@ -1085,8 +1085,9 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
                      (or (tramp-compat-file-attribute-group-id attr) "nogroup")
                      (or (tramp-compat-file-attribute-size attr) (nth 2 x))
                      (format-time-string
-                      (if (time-less-p (time-subtract (current-time) (nth 3 x))
-                           tramp-half-a-year)
+                      (if (time-less-p
+                           ;; Half a year.
+                           (time-since (nth 3 x)) (days-to-time 183))
                           "%b %e %R"
                         "%b %e  %Y")
                       (nth 3 x))))) ; date
@@ -1816,7 +1817,7 @@ Result is the list (LOCALNAME MODE SIZE MTIME)."
                  sec min hour day
                  (cdr (assoc (downcase month) parse-time-months))
                  year)
-              '(0 0)))
+              tramp-time-dont-know))
       (list localname mode size mtime))))
 
 (defun tramp-smb-get-cifs-capabilities (vec)
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 723b35c9e7b..e1602db1492 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -3602,13 +3602,11 @@ support symbolic links."
            (buffer-name)))
   (unless time-list
     (let ((remote-file-name-inhibit-cache t))
-      ;; '(-1 65535) means file doesn't exists yet.
       (setq time-list
             (or (tramp-compat-file-attribute-modification-time
                  (file-attributes (buffer-file-name)))
-                '(-1 65535)))))
-  ;; We use '(0 0) as a don't-know value.
-  (unless (equal time-list '(0 0))
+                tramp-time-doesnt-exist))))
+  (unless (tramp-compat-time-equal-p time-list tramp-time-dont-know)
     (tramp-run-real-handler 'set-visited-file-modtime (list time-list))))
 
 (defun tramp-handle-verify-visited-file-modtime (&optional buf)
@@ -3634,21 +3632,14 @@ of."
 
           (cond
            ;; File exists, and has a known modtime.
-           ((and attr (not (equal modtime '(0 0))))
-            (< (abs (tramp-time-diff
-                     modtime
-                     ;; For compatibility, deal with both the old
-                     ;; (HIGH . LOW) and the new (HIGH LOW) return
-                     ;; values of `visited-file-modtime'.
-                     (if (atom (cdr mt))
-                         (list (car mt) (cdr mt))
-                       mt)))
-               2))
+           ((and attr
+                 (not (tramp-compat-time-equal-p modtime tramp-time-dont-know)))
+            (< (abs (tramp-time-diff modtime mt)) 2))
            ;; Modtime has the don't know value.
            (attr t)
            ;; If file does not exist, say it is not modified if and
            ;; only if that agrees with the buffer's record.
-           (t (equal mt '(-1 65535)))))))))
+           (t (tramp-compat-time-equal-p mt tramp-time-doesnt-exist))))))))
 
 ;; This is used in tramp-gvfs.el and tramp-sh.el.
 (defconst tramp-gio-events
@@ -4531,17 +4522,19 @@ Invokes `password-read' if available, `read-passwd' else."
        :host ,host-port :port ,method))
     (password-cache-remove (tramp-make-tramp-file-name vec 'noloc 'nohop))))
 
-;; Snarfed code from time-date.el.
+;;;###tramp-autoload
+(defconst tramp-time-dont-know '(0 0 0 1000)
+  "An invalid time value, used as \"Don’t know\" value.")
 
-(defconst tramp-half-a-year '(241 17024)
-"Evaluated by \"(days-to-time 183)\".")
+;;;###tramp-autoload
+(defconst tramp-time-doesnt-exist '(-1 65535)
+  "An invalid time value, used as \"Doesn’t exist\" value.")
 
 ;;;###tramp-autoload
 (defun tramp-time-diff (t1 t2)
   "Return the difference between the two times, in seconds.
 T1 and T2 are time values (as returned by `current-time' for example)."
-  ;; Starting with Emacs 25.1, we could change this to use `time-subtract'.
-  (float-time (tramp-compat-funcall 'subtract-time t1 t2)))
+  (float-time (time-subtract t1 t2)))
 
 (defun tramp-unquote-shell-quote-argument (s)
   "Remove quotation prefix \"/:\" from string S, and quote it then for shell."
diff --git a/src/editfns.c b/src/editfns.c
index daea7463871..47509c23d04 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1677,7 +1677,9 @@ See `current-time-string' for the various forms of a time value.  */)
 }
 
 DEFUN ("time-equal-p", Ftime_equal_p, Stime_equal_p, 2, 2, 0,
-       doc: /* Return non-nil if T1 and T2 are equal time values.  */)
+       doc: /* Return non-nil if T1 and T2 are equal time values.
+A nil value for either argument stands for the current time.
+See `current-time-string' for the various forms of a time value.  */)
   (Lisp_Object t1, Lisp_Object t2)
 {
   return time_cmp (t1, t2) == 0 ? Qt : Qnil;
diff --git a/test/lisp/net/tramp-tests.el b/test/lisp/net/tramp-tests.el
index 79013558fdb..523c7afada8 100644
--- a/test/lisp/net/tramp-tests.el
+++ b/test/lisp/net/tramp-tests.el
@@ -2882,16 +2882,17 @@ This tests also `file-readable-p', `file-regular-p' and
             ;; able to return the date correctly.  They say "don't know".
             (dolist (elt attr)
               (unless
-                  (zerop
-                   (float-time
-                    (nth 5 (file-attributes
-                            (expand-file-name (car elt) tmp-name2)))))
+                  (tramp-compat-time-equal-p
+                   (nth
+                    5 (file-attributes (expand-file-name (car elt) tmp-name2)))
+                   tramp-time-dont-know)
                 (should
                  (equal (file-attributes (expand-file-name (car elt) tmp-name2))
                         (cdr elt)))))
             (setq attr (directory-files-and-attributes tmp-name2 'full))
             (dolist (elt attr)
-              (unless (zerop (float-time (nth 5 (file-attributes (car elt)))))
+              (unless (tramp-compat-time-equal-p
+                       (nth 5 (file-attributes (car elt))) tramp-time-dont-know)
                 (should
                  (equal (file-attributes (car elt)) (cdr elt)))))
             (setq attr (directory-files-and-attributes tmp-name2 nil "^b"))
@@ -3215,14 +3216,13 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
             (write-region "foo" nil tmp-name1)
             (should (file-exists-p tmp-name1))
             (should (consp (nth 5 (file-attributes tmp-name1))))
-            ;; A zero timestamp means don't know, and will be replaced by
-            ;; `current-time'.  Therefore, use timestamp 1.  Skip the
-            ;; test, if the remote handler is not able to set the
-            ;; correct time.
+            ;; Skip the test, if the remote handler is not able to set
+            ;; the correct time.
             (skip-unless (set-file-times tmp-name1 (seconds-to-time 1)))
             ;; Dumb remote shells without perl(1) or stat(1) are not
             ;; able to return the date correctly.  They say "don't know".
-            (unless (zerop (float-time (nth 5 (file-attributes tmp-name1))))
+            (unless (tramp-compat-time-equal-p
+                     (nth 5 (file-attributes tmp-name1)) tramp-time-dont-know)
               (should
                (equal (nth 5 (file-attributes tmp-name1)) (seconds-to-time 1)))
               (write-region "bla" nil tmp-name2)
@@ -3252,6 +3252,14 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
               (should (verify-visited-file-modtime))
               (set-visited-file-modtime (seconds-to-time 1))
               (should (verify-visited-file-modtime))
+              (should (= 1 (float-time (visited-file-modtime))))
+
+              ;; Checks with deleted file.
+              (delete-file tmp-name)
+              (dired-uncache tmp-name)
+              (should (verify-visited-file-modtime))
+              (set-visited-file-modtime (seconds-to-time 1))
+              (should (verify-visited-file-modtime))
               (should (= 1 (float-time (visited-file-modtime))))))
 
         ;; Cleanup.