Of invalid references to system libraries and execution environments

Picture this:

• You have a plugin that is supposed to be compatible with systems running even on 1.4 JRE i.e. your plugin execution environment is 1.4.
• An unsuspecting developer unintentionally checks out this plugin project into his workspace where he uses a 1.6 JRE by default.
• He starts writing Generics and is even allowed to do so because a 1.6 library is associated with the project in his workspace. The poor guy doesn't yet know what blunder he has done! :)

See an example below where in a plugin with 1.6 compliance, a developer accidentally used Autocloseable (coming from his workspace default 1.7 JRE).

API tooling provides a mechanism to figure out such illegal references to system libraries. In order to set up API tooling for your plugin project, right click on the project > PDE tools > API Tooling setup. Choose your project and click next. When it shows "Add API nature and API analysis builder", click finish. Now make sure your project settings for API tooling (right click > Properties > Plug-in development > API errors/warnings) are set as shown below:

By default, the "Supported Environments" will have no Execution Environments descriptions installed (From 3.8 onwards you will get an error whenever no execution environment description is installed). To install these EE descriptions, click on "install them now" or go to the "Install New Software.." page. Choose the "Eclipse Project update site" if already available or add the URL http://download.eclipse.org/eclipse/updates/<version> , where <version> = 3.6, 3.7, etc.

Uncheck "group by category" option and search for descriptions. Install these descriptions and you're all set to go. (Note: the above steps should be taken if you move to 3.8 Juno and suddenly find the "Missing EE descriptions" error in your project). 

Now with the above "invalid references to system libraries" option set to error/warning, you should get a warning for usage of Autocloseable in the above plugin project, as shown below:

These settings when done once on the project level and released into the repository will make sure that nobody accidentally references any API/class one is not supposed to. Read Olivier's post to know more about project vs. workspace settings