maven/USE-CASES.txt

Trying to get a large set of use cases that we can use to help drive
development in the right direction. I would like to collect some here and then
post them to the wiki as examples users can template to express what their
use cases are. So my first example is something I chatted about with Aslak
this morning. So they are brief and possibly naive but a huge collection
of these would help I think.

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- Being able to write artifact handler that would operate to install an
xdoclet plugin correctly when an xdoclet plugin is stated as a dependency.
  * Maybe this pattern could be generalized so you could register arbitrary
  ArtifactInterceptors (possibly a DAG of them) that will be called to handle
  events and operations on artifacts. They could even be used to actually
  implement the operation (ie have a interceptor actually fetch the artifact
  on request). This is basically an expansion of handler system as it stands
  so you can add more context and generalize how artifact operations are
  handled. (PD)

- With Maven installed it should be a simple command that allows you to
checkout the sources for a project.
  * Maybe this could be generalized so that if you reference a remote
  descriptor it will download the project. Something like

  $ maven --project http://www.realityforge.org/daedalus-project.xml

  would result in download of project either from remote location or
  maybe from scm declarations in project descriptor.

  As part of this remote downloading though the user may be asked for
  input of particular configuration data (ie username etc). (PD)

- Unified source directory structure that is analagous to the repository
itself. This way locations of intermediary artifacts of a build would be
in a known location.  This would also help with developer setup i.e. getting
new developers up and running. They could run a maven command and have all
their source trees set up in the same way as their collegues.

- I would like to be able to execute some goals (like 'clean') even when
  not all dependencies are satisfied.
  * hell yes!!!! Maybe dependency resolution could be a plugin that
  other plugins depend upon (PD)

- Support for "specification" dependencies. I would like to be able to
  say that I depend on a "specification" dependency such as
  "javax.jaxp.parser" with specific version. It is possible that multiple
  artifacts exist that satisfy this specification. ie Several versions
  of Crimson and Xerces may implement the "specification" and I want maven
  to select one and just use it. I dont care which does it but preferrably
  the one with the latest version. (PD)

- Support for retrieval of compatible versions for objects. For example I may
  say that I want version 1.1 of Crimson but Maven may return 1.1.1, 1.1.4 etc
  as it knows that these are compatible. This means aadding in some versioning
  specification or different strategies for resolution. (PD)

- Support for transitive and group dependencies
  * I would like to see this dependency information either encoded directly
  into the artifacts where possible (ie META-INF/maven/dependencies.xml in
  jar files) or accessible from repository at peer level for each artifact
  much like signature data is accessible for each artifact. (PD)

- It should be easy to create a single report without a need to (call like it has place now)
  maven:site. It will be nice if report generators can produce docs in few diffrent formats
  (e.g pdf, html, rtf) and this format can be also choosen for group of reports.

- groupId
 - Let's assume that there exists an artifact type "web-component"
   which is a zip file containg css/js/gifs/jpegs etc
   Example of such artifact is for example distribution of tigris style.

   Say an user has declared the following dependency:

   <depenedency>
      <groupId>org.tigris</groupId>
      <artifactId>style</artifactId>
      <type>web-component</type>
      <version>2.0</version>
   </depenedency>

   A dependency of this type should be processed only when users assembles the web application
   (war:webapp goal in maven-old)

   In short:  user can be able to declare goal decorators and goals should be fine-grained
   * This very similar to only resolving some dependencies depending on what goals
   are running as specified above. (PD)

- Maven is Java Build Tool. It should be well defined what does it mean to "build java project".
  It means that stages of the process should be well defined.

  pre-compile (this is when tools like JAXB, XDoclet)
  compile (javac, aspectj)
  post-compile (aspectj? )
  pre-jar
  ...
  etc

  It should e.g be possible to use Castor, JAXB plugin, XDoclet plugin without writing a single line
  of build script. In the ideal case it should be just enough to plug-in XDoclet into process simply
  by "checking the checkbox in IDE".
  This is someting what Vincent Massol started in maven-caller plugin. It will be nice to explore this idea.

- Reorganization of repository layout - are we going to map groupId : "a.b.c.d"  to path "a/b/c/d"?
  Are there some better alternatives?
  * I am not sure that is such a good idea - how can you tell when a
  directory is an artifact container (ie jar, sar, distribution etc) and when
  it is a group container (ie a/b/c/d). (PD)

- (Michal)  I have tried to implement "platform dependend dependecies".

   <depenedency>
      <groupId>a</groupId>
      <artifactId>b</artifactId>
      <type>native</type>
      <version>2.0</version>
   </depenedency>

    is resolved as

   a/b-2.0.dll (on windows) or a/b-2.0.so (unix)


   Maybe it can/should be done differently?
   What other "platform depended" artifact type do we have?
   exe? shell-script?

   * the problem with this approach is that most things that load native libs
   expect the name of the lib to follow a very specific name which usually will
   not conform to maven naming conventions (ie probably wont have -version on
   end). No idea how to fix this. (PD)

 - how to declare a dependency on JDK and what are possible implications of such dependency
  (e.g javac/javadoc target jdk)

 - I don't know if this will add too much complexity, but being able to generate multiple
   and compound artifacts from a single project would be nice. If we want to have a
   "Ant Compatibility Layer", then this would be required.
   
   Think of a project for a web application, it will have java code as well as web resources.
   The java code is collected into a JAR file, and then that is packaged with the web
   resources into a WAR.
   
   Of course, none of this is really required, as it can all be accomplished by breaking the
   project out into multiple projects with a reactor, per the Maven 1 guidelines. But if this
   limitation was removed, it might help Marvin adoption. (PR)