Update determine_time_zone function to check TZ

[kbravh]

Instead of defaulting immediately to /etc/filename for the timezone, we can first check whether the TZ environment variable is set. If so, we can pull the corresponding timezone file from /usr/share/zoneinfo. Closes #453.

[kbravh]

@poliorcetics Thanks for the feedback! I tried out the suggestion you made; I definitely like deconstructing the timezone from the environment variable instead of unwrapping, so I've added that change.

The only issue is that we have to use the return keyword from inside the if block; we can only omit the return if we want to return the last expression in a function, otherwise it returns an empty type (). So I've followed the pattern on the Rust docs function page and I'm using return for the first case where the TZ variable is set. Otherwise, I've left the final expression as the last statement so it's automatically returned.

if let Ok(file) = env::var("TZ") {
        return TimeZone::from_file(format!("/usr/share/zoneinfo/{}", file));
    }
    
TimeZone::from_file("/etc/localtime")

[poliorcetics]

That's because I put ; in my suggestion, the fix should be:

    if let Ok(file) = env::var("TZ") {
        TimeZone::from_file(format!("/usr/share/zoneinfo/{}", file)) // no ;
    } else {
        TimeZone::from_file("/etc/localtime") // no ;
    }

[kbravh]

@poliorcetics That did the trick! Thanks for the help.

[ogham]

Thanks for this!

[themadsens]

Just bitten by this .. Out of curisosity: Why not use libc::mktime instead of thinking you can outsmart libc? Then all of these timezone issues would just disappear!

[ariasuni]

@themadsens Well I can’t speak for ogham, but I would gladly use a libc function if it would make things easier. Right now, it wouldn’t be very useful, and #712 which is reasonably simple would fix the remaining issues.

It’s certainly an option to drop zoneinfo_compiled and datetime and just use a few C functions, but I think trying to do things in Rust as much as possible can be useful, either to push for more Rust libraries, or simply to for exa’s code to be an example.