Require a certain (or later) version of a package?

Question

Is there a way to enforce that a certain version, or a later version, of a package is loaded when building the document? I've found that compiling a document on another platform, where the package versions differ, can cause problems that may or may not be hard to pinpoint. Thus, I would like to be able to say, in the document, that "you need at least this version of this package", and produce an explicit error about it when it doesn't hold true.

Is there any way of doing this?

Answer 1

You can request a minimal version/date using the trailing optional argument of \usepackage[<options>]{<name>}[<min.date>] (or \RequirePackage). However, it will only print a warning text and not cause an error if the installed version is older than the requested version.

This feature is realized in the LaTeX core by the macro \@ifpackagelater{<name>}{<date>}{<yes>}{<no>}, which you can also use yourself (\makeatletter .. \makeatother is required if not used inside a package or class file).

You can use the following code to cause an error if the package is older than the given date. However, this only works after the package was loaded.

\makeatletter
\usepackage{<name>}%
\@ifpackagelater{<name>}{<date>}{%
    % Package is new enough
}{%
    \PackageError{<your package or document name>}{Package <name> is to old <...>}%
}
\makeatother

Note that despite the name \@ifpackagelater, AFAIK, the macro checks actually if the package date is later or equal. A more accurate name would be therefore ifpackagenotolder. If you want to check if a package is actually newer than a last version known to you, than simply add one day to the date.