Cross-platform compatibility

Note: I wrote this for my project Ara's README but it's useful for other projects too so I made a seperate page for this.

Previously ara had OpenBSD specific code & would simply fail to run on other OSes, now it runs on all platforms. There is still OpenBSD specific code but it's used only when ara detects to be running on OpenBSD.

use constant is_OpenBSD => $^O eq "openbsd";
require OpenBSD::Unveil
    if is_OpenBSD;
sub unveil {
    if (is_OpenBSD) {
        return OpenBSD::Unveil::unveil(@_);
    } else {
        return 1;
    }
}

is_OpenBSD is a constant so the if-else block is optimized at compile time. Another way would be to define the sub inside the if-else block which is what I did initially but that is not the same thing as this.

You cannot define sub like that in Perl because this step happens at compile time & so the if-else block is ignored, which means the code will be equivalent to else block being true all the time because that's what comes later.

if (is_OpenBSD) {
    require OpenBSD::Unveil;
    OpenBSD::Unveil->import;
} else {
    sub unveil { return 1; }
}

Above code block will override the unveil sub to be return 1; everytime, this was fixed in commit 245aebe3da915afc0feafc7257f025e2e66a987f.

This will still fail on OpenBSD if users don't have OpenBSD::Unveil in @INC, this shouldn't be an issue with Perl in base but if user runs custom Perl then it might not be in @INC, in that case user is expected to fix this by adding the path to OpenBSD:: in @INC.