ant checksum directory does not reflect removed files - ant

Question

I have the following ant targets defined. The idea is to do the heavy work only, if some contents of a folder have changed.
<target name="checksumAssets">
<echo message="verify checksums" />
<checksum todir="${bin.loc}/../checksums" verifyproperty="checksum.isUpToDate.test">
<fileset dir="${bin.loc}/assets/" id="filelist">
<include name="somefolder/" />
<exclude name="somefolder/result.swf"/>
</fileset>
</checksum>
<echo message="${toString:filelist}"/>
<echoproperties regex="checksum.isUpToDate.test"/>
</target>
<target name="createAsset" depends="checksumAssets" unless="${checksum.isUpToDate.test}">
<!-- do create the assets and other magic -->
<echo message="create checksum files" />
<checksum todir="${bin.loc}/../checksums" >
<fileset refid="filelist" />
</checksum>
</target>
somefolder contains images which will be processed and result in a swf file containing these assets.
i want this heavy processing only to take place if something in the asset folder changes.
this works as espected in two cases:
i add a new file to somefolder
i change an existing file in somefolder
my problem is:
it does not work when i delete a file from this folder.
this means, the createAsset Target is not called on ant createAsset if i remove a file from the folder in question. it is called in the two aforementioned cases and if there are no checksum files present in the checksums folder.
is there something i missed?
ant version is 1.8.2

Answer 1

i've found a workaround.
since <checksum> only saves the checksum of single files, it cannot know if a file is missing from a previous run. for this it would need to save the checksum of a complete filelist on disk.
this is what i accomplished:
<target name="checksumAssets">
<echo message="verify checksums" />
<!-- generate filelist.txt with actual content of somefolder -->
<fileset dir="${bin.loc}/assets/somefolder/" id="filelist">
<exclude name="result.swf"/>
<exclude name="filelist.txt"/>
</fileset>
<concat destfile="${bin.loc}/assets/somefolder/filelist.txt" fixlastline="true">${toString:filelist}</concat>
<!-- checksum folder including the filelist.txt -->
<checksum todir="${bin.loc}/../checksums" verifyproperty="checksum.isUpToDate.test">
<fileset dir="${bin.loc}/assets/" id="checkedlist">
<include name="somefolder/" />
<exclude name="somefolder/result.swf"/>
</fileset>
</checksum>
</target>
<target name="createAsset" depends="checksumAssets" unless="${checksum.isUpToDate.test}">
<!-- do create the assets and other magic -->
<echo message="create checksum files" />
<checksum todir="${bin.loc}/../checksums" >
<fileset refid="checkedlist" />
</checksum>
</target>
first i generate a filelist.txt with the content of the current folder.
then i generate checksums of all files in this folder, including the filelist.txt
on every an run, filelist.txt will be generated and checked against the filelist.txt from the last successful run of createAsset.
now the createAsset target is run if a content file changes or if the content of this folder changes.
mission accomplished ;)