Reproducibility of `Log4jPlugins.java`

[ppkarwasz]

The generation of the new plugin cache Log4jPlugins.java is non deterministic, which breaks reproducibility of 3.x builds.

As far as I can tell the problem is restricted to the order in which the plugins are declared.

[rgoers]

The way it is supposed to work is to find all the plugins in the module and then use the package that they all have in common and then create a plugins package there and add Log4jPlugins.java in that directory. The algorithm should be very deterministic until you add a new plugin that isn't common with the others. I also seem to recall that there is a way to specify the package the file should be placed in.

[jvz]

Well, this could be fixed fairly easily: alphabetize the entries before writing.

[jvz]

Seems to be a regression from LOG4J-2735, but I can't see that issue on Jira for some reason.

Edit: oops, that's a typo.

[jvz]

This is a regression that was otherwise address in 2.x in https://issues.apache.org/jira/browse/LOG4J2-2735

[jvz]

Fixed.