Plamen Totev created MSOURCES-95:
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Summary: 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
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 {{\*\*/\*\*}}. 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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