bug#58842: 29.0.50/tramp; copy-file KEEP-TIME gives the target earlier time

[Sam Steingold]

One property of `copy-file' that I came to expect is:

(copy-file src dst ...) is successful
==>
(file-newer-than-file-p src dst) is false

This ensures that the same file is not copied over and over.

Alas, this does not hold in the following corner case:

1. src is local on mac
2. dst is remote on linux
3. KEEP-TIME is passed to `copy-file'

In this case, after `(copy-file src dst t t)`,
--8<---------------cut here---------------start------------->8---
(file-attribute-modification-time (file-attributes dst))
=> (25435 65247 0 0)
(file-attribute-modification-time (file-attributes src))
=> (25435 65247 279367 729000)
--8<---------------cut here---------------end--------------->8---

I understand this is bad behavior is covered by the `copy-file' doc
--8<---------------cut here---------------start------------->8---
Fourth arg KEEP-TIME non-nil means give the output file the same
last-modified time as the old one.  (This works on only some systems.)
--8<---------------cut here---------------end--------------->8---

but it would seem to be relatively easy to fix by rounding _up_ the time
before calling the tramp handler for `set-file-times'.

Thank you.


In GNU Emacs 29.0.50 (build 1, x86_64-apple-darwin21.6.0, NS
 appkit-2113.60 Version 12.6 (Build 21G115)) of 2022-10-24 built on
 3c22fb11fdab.ant.amazon.com
Repository revision: 366169450392c7025665f6477e5062be72c7280f
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-- 
Sam Steingold (https://aphar.dreamwidth.org/) on darwin Ns 10.3.2113
https://lastingimpactpsychology.com https://steingoldpsychology.com
http://think-israel.org https://www.dhimmitude.org https://memri.org
Do not worry about which side your bread is buttered on: you eat BOTH sides.