Dwins’s Weblog


Workaround: SBT/Maven “Inconsistent module descriptor”

Posted in Development,Open Source Software by dwins on October 15, 2011
Tags: , , ,

Here’s an issue I’ve been dealing with in GeoScript.scala for a while: when fetching dependencies I get an error message:

update: sbt.ResolveException: unresolved dependency: xml-apis#xml-apis-xerces;2.7.1: java.text.ParseException: inconsistent module descriptor file found in ‘http://download.osgeo.org/webdav/geotools/xml-apis/xml-apis-xerces/2.7.1/xml-apis-xerces-2.7.1.pom’: bad module name: expected=’xml-apis-xerces’ found=’xml-apis’; bad revision: expected=’2.7.1′ found=’xerces-2.7.1′;

Sure enough, when I go to http://download.osgeo.org/webdav/geotools/xml-apis/xml-apis-xerces/2.7.1/xml-apis-xerces-2.7.1.pom I can see that even though the URL suggests the artifact would be (group: xml-apis, artifact: xml-apis-xerces, version: 2.7.1), it is in fact listed as (group: xml-apis, artifact: xml-apis, version: xerces-2.7.1).  Apparently Maven doesn’t verify those details when fetching dependencies, but Ivy (by default) does.  According to this JIRA issue I found there is an option to disable it, but SBT doesn’t seem to expose it (I fiddled around a bit with an ivysettings.xml file and the ivyXML setting but to no avail.)

Finally I just added an entry to my libraryDependencies setting like this:

“xml-apis” % “xml-apis-xerces” % “2.7.1” from “http://download.osgeo.org/webdav/xml-apis/xml-apis-xerces/2.7.1/xml-apis-xerces-2.7.1.jar

This doesn’t avoid the warning but does let me go ahead with my build.  Good enough I guess.

But recently I’ve been hearing some complaints from folks checking out my code (that’s right, potential contributors!) who’ve been confused by the error.  Since first encountering this issue I’ve been informed that xerces is actually not even needed, the API it implements is included in modern JVMs or something, so I tried just adding a dependency exclusion to my SBT build file.  Success! Not only was I able to run the ‘update’ command with no scary errors, but the test suite even runs.  Ticket closed.

Except, as it turns out, Ivy needs that metadata to handle the exclusion (or something, I didn’t dig in too deep.)  I already had it in a local cache, thanks to having run the build with that explicit URL, but when benqua from Github attempted a build from scratch he ran into the same issues again.  ARRGH.

Finally I ended up sticking with the exclusion, but now the GeoScript build includes a dummy subproject that has the xml-apis dependency with the explicit URL.  The intermodule dependencies are set up so that it always runs before the main “library” subproject, meaning that the xml-api-xerces project, with correct metadata, is in the local cache before any dependency resolution involving GeoTools begins.  Not incredibly elegant, but it does work.

I’ll be in touch with the GeoTools guys to see about just fixing the metadata in the repository – since Maven appears to ignore it I don’t see this breaking any existing builds.

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