Tcl Source Code

In my code, I frequently use the following method to get the epoch time of the next midnight:

set midnight [clock scan 24:00:00 -format %T]

In Tcl 9.0 that currently throws an error. Apparently I need to use the option -validate 0 to allow the Tcl 8.6 behavior.

First of all, there is no mention of the -validate option in the clock manual page. TIP #688 claims that the default value for the -validate option is 0. In practice it seems to actually be 1.

However, the biggest problem is that the produced value is incorrect. Clearly 24:00:00 should be 1 second after 23:59:59. But that is not the case. I wrote the following test script:

if {[package vsatisfies [package present Tcl] 9]} {
    set novalidate {-validate 0}
} else {
    set novalidate {}
}

set sec1 [clock scan 23:59:59 -format %T {*}$novalidate]
set sec2 [clock scan 24:00:00 -format %T {*}$novalidate]

puts [expr {$sec2 - $sec1}]

In Tcl 8.6 this produces a result of 1, as expected. In Tcl 9.0 it reports -86400 (possibly depending on the day of the week the script is executed).

Although I personally would rather use something like:
clock scan "+1 day"
instead of
clock scan 24:00:00
it is indeed a certain regression (which was not covered previously in the test suite).

I'll add related tests to 8.6+ and fix it ASAP in 8.7+.

By the way, instead of -validate 0 arguments, one could use ::tcl::unsupported::clock::configure -validate 0 (previously clock configure -validate 0) to restore previous behaviour (surely only after the issue with not incremented date gets fixed).