module A does a "use" on module B. module B does a "use" on module A. mod_perl breaks, and perl -wc on either module A or B will produce a lot of "subroutine redefined" warnings. There are various ways to fix this: 1) Check @INC if this module is already loaded, and don't load it if so. If we can do this simply, this is preferred since it's the most modular solution. However, it may not be possible. 2) Remove most "use" statements from libraries, and then re-order the "use" statements in CGIs so that the least-dependent things are first and the most-dependent things are last. 3) Move around a bunch of subroutines to eliminate dependency loops. Right now, this is a HUGE problem for us -- we have a LOT of dependency loops. We may want to fix the problem in several smaller bugs that block this bug. As we're doing this, we'll have to set rules on certain libraries as to what they can "use." There should be many libraries that say, "This library may not 'use' anything in the Bugzilla namespace."

Actually, we don't have as many dependency loops as we thought. Most of them disappeared with the checkin of bug 303413. Check the graph at http://www.justdave.net/BugzillaDeps.png Notice except for the 2 red lines we already knew about that all of the arrows point to the right. There are none going directly up/down, and none pointing left. This is a Good Thing. :) So our only problems in the way of dependency loops now are: Bugzilla::Attachment <-> Bugzilla::Flag and Bugzilla::Util <-> Bugzilla::Error

Here's a more-capable version of the module dependency graph creator that I posted to the other bug. This one completely parses out the pod docs, as well as having cross-dependency testing which turns the lines red if two modules cross-depend on each other (but it doesn't actually do loop checks yet).

And the current dependency graph, just for posterity.

This should be added to our test suite and throw a "not ok" for each interdependency.

Updated grapher script. This one detects all loops, not just direct cross-dependencies. It also properly deals with all current known instances of modules being loaded from a variable name (which in itself exposed several additional loops).

We should probably use that code as a base for bug 304600. Note that for the most part it's okay if a module "uses" one module, and that module "requires" it in return, since those will happen at different times. It's not okay for two modules to "require" each other, or two modules to "use" each other.

We don't seem to have any dep loops that are breaking mod_perl, anymore, so I'm changing the summary.

Also, this isn't actually blocking mod_perl work anymore.

Running an altered version of 010dependencies.t (where require Bugzilla::Foo inside routines are not considered as part of dependency loops) shows no dependency loops anymore. The checking of 010dependencies.t will now prevent new loops from appearing. Marking this bug as fixed.