[sr #110989] Improve reliability of AT_MTIME_DELAY in test suite with a loop

URL:
  <https://savannah.gnu.org/support/?110989>

                 Summary: Improve reliability of AT_MTIME_DELAY in test suite
with a loop
                   Group: Autoconf
               Submitter: zackw
               Submitted: Fri 22 Dec 2023 04:21:35 PM UTC
                Priority: 5 - Unprioritized
                Severity: 1 - Wish
                  Status: Confirmed
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
        Operating System: None


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Follow-up Comments:


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Date: Fri 22 Dec 2023 04:21:35 PM UTC By: Zack Weinberg <zackw>
Recording this idea for the next release cycle:

On Fri, Dec 22, 2023, at 10:08 AM, Nick Bowler wrote:
> On 2023-12-22 09:28, Zack Weinberg wrote:
>> On Thu, Dec 21, 2023, at 10:07 PM, Jacob Bachmeyer wrote:
> [...]
>>> I suggest revising AT_MTIME_DELAY to actually create two files and
>>> loop touching one of them until the timestamps differ.
>> 
>> This won’t work, because whether *test* thinks two timestamps differ
>> may be different from whether *autom4te* thinks two timestamps differ
>> (due to the whole mess with Time::HiRes not necessarily being
>> available, timestamps getting rounded to the nearest IEEE double,
>> etc).  Also, test -nt isn’t portable, we’d have to do the same
>> mess with ls -t that’s in the code setting at_ts_resolution.
>
> Since for the purpose of testing autom4te behaviour one should be able
> to assume autom4te is available, a solution for this issue would be to
> simply add a mechanism to autom4te (or find a creative way to do it
> with existing autom4te) which compares two file timestamps, and use
> that in the loop.

Rather than adding it to autom4te itself, perhaps a tiny Perl script
that does the loop.  We would still need to detect whether automake
understands high-resolution timestamps.

It would also make sense for autom4te to ensure that its output file
is newer than its cache file.







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