Hi,
According to
https://wiki.eclipse.org/Tycho/Reproducible_Version_Qualifiers, only source code changes trigger the build of a new artifact version of a project. This concept leads to problems in cases where there are only binary changes (due to source code changes in another project).
Assume a project p.helloworld containing a source file Hello.java with a source code line Printer.print("Hello World"). That project has a dependency on another project named p.commons, containing a source file Printer.java with a method print(String s). Furthermore, assume the last source code change in p.commons was made today at 01:00, the last change in p.helloworld was made today at 05:00.
At 20:00 the method signature in Printer.java is changed to print(CharSequence s), no source code changes are made in Hello.java (the application still works as expected). But Hello.class will change, as it contains the signature of the referenced method. Now we've got the following artifacts:
p.commons_1.0.0.20140924-0100.jar - OK
p.commons_1.0.0.20140924-2000.jar - OK
p.helloworld_1.0.0.20140924-0500.jar - containing the "old" Hello.class
p.helloworld_1.0.0.20140924-0500.jar - containing the "new" Hello.class (!)
The last artifact for p.helloworld contains class files newer than the timestamp denoted by the artifact's filename. The content of the two artifacts built for p.helloworld differ, while the filenames are the same (so it's considered the same artifact/file/version).
When resolving/updating dependencies in yet another project (assuming a dependency on p.helloworld) the "old" p.helloworld artifact will possibly (happened in our team) not be replaced with the "new" p.helloworld artifact because it seems the correct artifact is already there.
This then leads to runtime errors (NoSuchMethodError) because the (outdated) Hello.class is still looking for a method print(String s) while there is only a method print(CharSequence s) available.
How can this be avoided? Should projects also check for source code changes in (explicit and implicit) dependencies to trigger a new artifact version? Could there be a post-check to ensure an artifact with the same version/filename as the previous build also has the same content/checksum (otherwise the version of the new build will be adjusted)?
What do you recommend?
Cheers
Michael
