Martin Desruisseaux created MNG-8015:
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Summary: Control the type of path where each dependency can be
placed
Key: MNG-8015
URL: https://issues.apache.org/jira/browse/MNG-8015
Project: Maven
Issue Type: Improvement
Components: Core
Affects Versions: 4.0.0-alpha-12
Reporter: Martin Desruisseaux
Make possible to declare where each dependency can be placed: on the
module-path, class-path, agent path, doclet path, taglet path, annotation
processing path, _etc._ The proposed improvement consists in adding a new
{{PATH_TYPES}} property that can be associated to dependencies. The property
value is an array of {{PathType}}, a new enumeration-like class with values
such as {{CLASSES}}, {{MODULES}}, {{DOCLET}}, _etc._ Contrarily to real Java
enumerations, this enumeration-like class is extensible: plugins can add their
own enumeration values. This is required at least for the {{--patch-module}}
option, where a new {{PathType}} enumeration value need to be created for each
module to patch.
Users can control indirectly the {{PathType}} of a dependency by specifying the
dependency type. Note that there is no direct mapping between the dependency
type and where the dependency will be placed, but only an indirect mapping
caused by the fact that using a dependency type implies implicit values of some
properties such as classifier, and (with this proposal) path types:
* {{<type>jar</type>}} implies {{PathType.CLASSES}} and {{PathType.MODULES}}.
* {{<type>modular-jar</type>}} implies {{PathType.MODULES}} only.
* {{<type>classpath-jar</type>}} implies {{PathType.CLASSES}} only.
* _etc._
When a plugin requests the paths of dependencies, the plugin specifies the
types of path it is interested in. For example, a Java compiler plugin can
specify that it is interested in {{PathType.CLASSES}} and {{PathType.MODULES}},
but not {{PathType.DOCLET}}. If a dependency declared that it can be placed on
the class-path or the doclet-path, only the class-path is left after
intersection with plugin's request. This is important for the next step.
If, after all filtering such as above paragraph are applied, a dependency has
only one {{PathType}} left, then there is no ambiguity and we are done.
Combined with above-cited dependency types like {{modular-jar}} or
{{classpath-jar}}, this rule allows users to control where the dependency will
be placed. But if there are two or more {{PathType}} left after filtering, then
a choice needs to be done. For example if there are both {{PathType.CLASSES}}
and {{PathType.MODULES}} (which may happen when {{<type>jar</type>}} is used),
then an heuristic rule similar to Maven 3 can be applied: check if a
{{module-info.class}} file or an {{Automatic-Name}} manifest attribute is
present, and base the decision on that.
This proposal aims to fix MNG-7855.
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