ImportControl: allow to load files from resources

[romani]

base on #3358

ImportControl does not appear to be able to find configurations that are resources, only files. So this does not seem to be usable at all if checkstyle.xml is in your project as a resource rather than a file.

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[jochenvdv]

I will implement this.

[jochenvdv]

Should the resource loading be like the way it is done in for example SuppressionFilter?

[romani]

yes, by URI (web, filesystem, classpath) - https://github.com/checkstyle/checkstyle/blob/master/src/main/java/com/puppycrawl/tools/checkstyle/ConfigurationLoader.java#L177

[jochenvdv]

SuppresionFilter has a single property file which is interpreted as a filename or URL and resource as a fallback method,
but ImportControlCheck has already separate properties for file and URL.

Shall I make a separate property resource which accepts a path like my/package/resource.ext?

<module name="ImportControl">
    <property name="resource" value="/my/package/import-control.xml"/>
</module>

Or shall I use the file property and fall back to trying to load as a resource if the file could not be found?

<module name="ImportControl">
    <!-- File my/package/import-control.xml not found, so interpreted as resource in classpath -->
    <property name="file" value="/my/package/import-control.xml"/>
</module>

BTW, the file you link loads Checkstyle's main configuration, but the checks seem to use their own implementation which also extends AbstractLoader (see ImportControlLoader).

When CommonUtils.getUriByFilename() is used, it tries to load as a file, URL or resource, so implementing it this way would be easiest but inconsistent with having separate properties file, url and resource.

We could unite those into a single property but that would be a backwards incompatible change.

Tell me what you think. For now I have started implementing this using a new resource property. It is trivial to implement so I will make a PR soon.

[romani]

but ImportControlCheck has already separate properties for file and URL.

it is legacy. It exists only because we can not easily remove property without breaking backward compatibility. That is why we wait for major release to do this. Please create separate issue on this , i will put "checkstyle8" label on it.
Please use "file", it ok to use CommonUtils. If there is some own implementation of loading - create separate issue.

[jochenvdv]

OK. I will change the implementation of the file property to use CommonUtils. This will make it able to load files, URLs and resources. I will document it as well.

I will create a separate issue for removing the url property.
Should I already document it as deprecated in my PR or do this in a separate PR?

[romani]

Should I already document it as deprecated in my PR or do this in a separate PR?

to mark as deprecated please do by separate issue to explain the reason and prove that certain property is odd. Our releasenotes have links to issues, there all details should be.

[romani]

fix is merged.