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From Carl Myers <cmy...@palantirtech.com>
Subject Better Determine conflicting dependencies
Date Wed, 16 Dec 2009 00:34:31 GMT
Hey all,

It seems like a common problem (the way we are using ivy) to run into 
conflicts.  Unfortunately, if your dependency tree looks like this:

A: B C D E
C: F G
G: H-1.0
E: Z
Z: H-1.1

Here I have a conflict and get the message "H-1.0 (required by G) 
conflicts with H-1.1 (required by Z)".

Unfortunately, I am building A, and I have no clue where H comes from. 
If I look at my ivy.xml (the only ivy.xml that I have checked out and 
handy) all I see are A, B, C, D, and E.  I have potentially never heard 
of Z or G, nor do I care.  Some dependency changed and boned me, and I 
need more information than that to figure out how to fix it.

Specifically, I need the all packages on the path to the "lowest common 
ancestor" of the two conflicting packages in my dependency tree.  In 
this example, I would like to see:

H-1.1 (A->E->Z->H-1.1) conflicts with H-1.0 (A->C->G->H-1.0)

This should include the version numbers too, I am just leaving them out 
for clarity and brevity here.  The two lists of dependencies above are 
the two paths from the lowest common ancestor to each respective 
conflicting package.  It also happens to be a conprehensive list of 
*every* package I might potentially edit to fix this problem, giving me 
the data I need to analyze the problem.  In this example, the lowest 
common ancestor was A, the package I was working on, but you can easily 
come up with examples where even the LCA will be some package you have 
never heard of - but armed with that path, you can start your 
investigation and figure out what changed, and what needs to change to 
fix it.

Additionally, presently, Ivy bails out as soon as it finds a single 
dependency conflict, when there may be more than one.  This means you 
make some decision (like "I am reverting Z to H-1.0") and fix that 
problem, only to realize some other package (Maybe, in this example, F) 
also depends on H-1.1.  How frustrating!

My questions are as follows:
1. Is there some "tell me more" setting which will make Ivy print out 
more info like I am asking for, or list all conflicts it can find 
instead of dying on the first one?

2. If I want to write a tool to analyze dependencies, for example:
getDownstreamDependencies(pkgName, pkgVersion)
getUpstreamDependencies(pkgName, pkgVersion)
getDirectDownstreamDependencies(pkgName, pkgVersion)

Is there some library which can parse ivy.xml files which can easily be 
used outside the ivy code base?  I haven't looked the code yet but I 
thought I'd run it by you guys before I tried anything drastic

3. RFC?  (Requests for comments) - should I consider submitting a patch 
for Ivy to do what I described above?

Thanks!
-- 
Carl Myers
Palantir Technologies | Internal Tools Software Engineer
cmyers@palantirtech.com

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