Peter De Maeyer created MCLEAN-125:
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Summary: Clean all modules in multi-module project beforehand
Key: MCLEAN-125
URL: https://issues.apache.org/jira/browse/MCLEAN-125
Project: Maven Clean Plugin
Issue Type: Improvement
Affects Versions: 3.4.0
Reporter: Peter De Maeyer
In complex multi-module projects with custom plugins, there is often a
situation where one module populates the {{target/}} directory of _another_
(typically sibling or parent) module. While I agree that is not ideal and not
recommended practice, it is sometimes the only way to work around limitations
in plugins or build setups.
In such a case, one sooner or later bumps into the situation where {{mvn clean
verify}} fails while {{mvn clean; mvn verify}} (note the semicolon) succeeds.
The reason is that in the first case the {{target/}} directory is cleared at
the start of every module's build life cycle, clearing any needed files that a
previous module has put there. The workaround {{mvn clean; mvn verify}} works,
but it requires understanding of the user to correctly build the multi-module
project, which is suboptimal. It would be better if that knowledge were
embedded in the build script.
To better support these situations, it would be useful to have for example a
{{cleanAtStart}} option to the {{maven-clean-plugin}} that would clean _all_
modules during the "clean" phase of the first one. It would be similar and
complementary to the {{installAtEnd}} option of the {{maven-install-plugin}},
or the {{deployAtEnd}} option of the {{maven-deploy-plugin}}. This would move
the responsibility for correctly cleaning the project from the user to the
build, where it belongs. Then users could do a plain {{mvn clean install}}
while trusting the build script to take care of any of its own multi-module
intricacies.
I did some preliminary analysis of what it would take to implement this, using
the {{maven-invoker-plugin}}'s {{installAtEnd}} as inspiration, but it's not so
simple. The advantage that the {{maven-install-plugin}} has is that it can
visit all the plugin executions of all the modules in a normal way and merely
needs to defer the actual installation. Here, for the {{maven-clean-plugin}},
it is different: it needs to clean modules at the very start, before anything
else, based on information that is not available yet 'coz the executions of the
next modules hasn't been visited yet.
Another idea for an implementation I had was to monitor the file system for
files that were added during the build (by other modules) and exclude those
from cleaning, which is also (too) complicated to implement correctly.
Anyway, difficulty of implementation aside, I think this would be a good
feature that would complement existing features such as {{installAtEnd}} and
{{deployAtEnd}}. Ideally in a 3.x version.
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