Eclipse: How can I install an older plugin version from an update site?

Question

I want to determine if downgrading one of my Eclipse plugins to the previous version fixes the problem I have. I was wondering if there is a general method using the plugin's Eclipse update site that I can use Eclipse's install GUI to install an older version of the plugin.

If it matters, the tool of interest is the Scala-IDE at this update site: http://download.scala-ide.org/releases-28/2.0.0-beta

What I want is the previous build of the 2.0.0-beta.

Answer 1

Mirco Dotta answered this for me on the Scala IDE Forum.

If the previous plugin version had been installed in the past, and if the update site maintains older releases of the plugin, it should be possible to revert to a previous version you have installed by performing the following:

1. Uninstall the current plugin version (Eclipse -> About -> Installation Details -> Installed Software)
2. Re-install a previous version using the "Installation History" (Eclipse -> About -> Installation Details -> Installed History).

Note that in the case of the plugin I'm using, the update site does not maintain older versions, so this technique wouldn't help.

Answer 2

To downgrade Scala IDE, what I did was first uninstall [1] the current Scala plugin, and the reinstall the desired older version.

Special note: when reinstalling the older version, there's an annoying bug you have to sidestep. As per Iulian Dragos' last comment on that ticket, make sure you disable 'Contact all update sites during install to find required software' when installing the older version. After this, I encountered a bug about an illegal charset name for a file that no longer existed: /Applications/eclipse/configuration/org.eclipse.osgi/bundles/3801/1/.cp/lib:misc/scala-dev/plugins. The bug report you linked in the comments shows the solution: launch Eclipse with eclipse -clean. I got another error related to -Xpluginsdir, but this was fixed by cleaning and rebuilding the project.

[1] To uninstall the current plugin, you can go to [Help Menu] -> [Install new software...] -> [What is already installed]. Then select three items JDT Weaving, Scala IDE for Eclipse, Scala IDE for Eclipse Source and click uninstall.

Edit: I guess this doesn't answer your question about where to find an update site with the previous version. I couldn't find previous betas on the website. Maybe you'll have to ask on the mailing list.