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https://issues.apache.org/jira/browse/MSOURCES-95?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Plamen Totev updated MSOURCES-95:
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Attachment: reproduce-project.zip
> When one of the source folders is empty the source jar is recreated even when
> sources not changed
> -------------------------------------------------------------------------------------------------
>
> Key: MSOURCES-95
> URL: https://issues.apache.org/jira/browse/MSOURCES-95
> Project: Maven Source Plugin
> Issue Type: Bug
> Reporter: Plamen Totev
> Priority: Minor
> Attachments: reproduce-project.zip
>
>
> There is issue opened in Plexus Archive project -
> https://github.com/codehaus-plexus/plexus-archiver/issues/24
> In short if you download the attached zip and build it several times you'll
> see that the source jar is build every time no matter that the source are not
> changed. That's because {{target/generated-sources/annotations}} is empty. I
> think the reason for this behavior is that the default inclusion pattern in
> {{AbstractSourceJarMojo}} is {{\*\*/\*}}. If it's {{\*\*/\*\*}} then the jar
> will not be rebuilded. Is there any reason why it's {{\*\*/\*}} and not
> {{\*\*/\*\*}} ?
> In the next paragraphs I'll try to explain why the second patter work and the
> first not.
> Let's say we have the following directory:
> {code}
> + src
> +--+ main
> +--+ java
> +--+ app
> | +--+ App.java
> |
> +--+ empty_dir
> {code}
> when added to {{JarArchiver}} with prefix "" (empty string) this is how
> Plexus Archiver "sees" them:
> {code}
> src/main/java -> "" (empty string)
> src/main/java/app -> "app"
> src/main/java/app/App.java -> "app/App.java"
> src/main/java/empty_dir -> "empty_dir"
> {code}
> To decide which entries to add Plexus Archives applies inclusion and
> exclusion patterns. Internally it uses
> {{org.codehaus.plexus.util.DirectoryScanner}}
> (https://github.com/codehaus-plexus/plexus-utils/blob/master/src/main/java/org/codehaus/plexus/util/DirectoryScanner.java).
> The JavaDoc contains nice explanation how the patterns are applied but in
> the next paragraph I'll try to explain in short what happens.
> When the pattern is set to {{\*\*/\*}} will match all but /src/main/java
> (("", "app", "app/App.java", "empty_dir")). This is because the pattern
> matches zero or more path segments, followed by any path segment.
> src/main/java is mapped to "" so the pattern will not match it (it's empty
> path segment followed by nothing). So far so good. But what if the source
> directory is empty(src/main/java). Then nothing will be matched and we'll end
> with empty resource collection to add to the archive. And because it's empty
> there is no way to know when it was last modified so Plexus Archiver will do
> the safe thing and recreate the archive. After all when the archive was
> created the pattern may have matched something and the archive is not empty
> so it's outdated.
> What if the pattern is set to {{\*\*/\*\*}}. Then it matches zero or more
> path segments, followed by zero or more path segments - in other words
> everything (my understanding is that it's the same as {{\*\*}} - match
> everything). So if /src/main/java is empty we'll end up with collection
> containing only "" - file resource with empty name. Because of the empty name
> it won't be added to the archive(and that's exactly what we want) but there
> is at least one resource with last modification date so now Plexus Archiver
> knows if the archive is up to date or not. If there were files in the
> directory and now there in none then the directory mast modification date
> will be newer than the one of the archive.
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