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.

7 files changed, 69 insertions, 73 deletions

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."