[MCHECKSTYLE-444] Support exclusion of generated (test) resources

[jira-importer]

Stephan Schroevers opened MCHECKSTYLE-444 and commented

In the context of MCHECKSTYLE-412 a new excludeGeneratedSources option was introduced. This feature does not exclude generated {}resources{}, however. Generated resources are not uncommon:

1. The license-maven-plugin attaches a THIRD-PARTY.txt file.
2. The hisrc-basicjaxb plugin attaches a META-INF/sun-jaxb.episode file, located in a directory that also contains generated sources ((!)).

As a result, if one sets

<excludeGeneratedSources>true</excludeGeneratedSources>
<resourceIncludes>**/*</resourceIncludes>

Then the plugin will flag THIRD-PARTY.txt files (not completely unexpected) as well as XJC-generated Java files (very unexpected).

Possible fixes:

1. Update the excludeGeneratedSources flag to also cover (test) resource directories.
2. Introduce an analogous excludeGeneratedResources flag.

(The first option may seem less flexible, but would be less surprising i.c.w. plugins that generate sources and resources into the same directory, as in example (2) above.)

I'm open to contributing a PR for this change; it would be nice to first hear from the maintainers whether they prefer approach (1) or (2).

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Affects: 3.3.1

Issue Links:

• MCHECKSTYLE-412 Add option to exclude generated sources/test-sources from default source/test-source directories

[jira-importer]

Michael Osipov commented

Why is this a bug? Sources and resources are two distinct entities. I'd expect that there would be a separate flag, no?

[jira-importer]

Stephan Schroevers commented

TBH, when I first read about excludeGeneratedSources, I did expect all generated files to be covered. I guess that this is in part because when Maven plugins generate files, they generally allow users to specify the target directory, but not whether the result is designated "source" or "resource". But I'm willing to admit that this is simply "user error" from my side.

The second scenario I describe however does point at a bug proper: excludeGeneratedSources excludes generated sources in a directory X only if X isn't also designated a resource directory. That's what happens in case of META-INF/sun-jaxb.episode, which causes all generated Java files to be analyzed by Checkstyle. One can work around that by setting e.g. resourceIncludes to accept only .properties files (which happens to be the default), but from a user perspective it does not make sense that by restricting resources, I actually exclude source files.

Put another way: the plugin current doesn't properly distinguish between (generated) sources and resources. If I read the code correctly, one can also see that here, where all sources and resources are eventually collected in a single place for input to Checkstyle.

That said, my ticket title does hint a feature request, not a bug report, and the existing properties already distinguish between sources and resources. So indeed it makes more sense to introduce a separate flag. I guess it means I should have filed two distinct tickets:

1. One to suggest the introduction of an excludeGeneratedResources flag.
2. One to flag that the plugin doesn't properly keep sources and resources apart.

For our use case a solution to (1) would suffice, as we'd simply configure both excludeGeneratedSources and excludeGeneratedResources. On cursory inspection this change would likely not be too hard; I can open a PR for that. A solution to (2) looks like it'd require a larger refactoring; it's unlikely I'll find time for that any time soon.