Sigasi has incompatibilities with the Visual Source Safe plugin . The VSS plugin blocks an Eclipse framework feature that Sigasi needs to run. Sigasi uses Eclipse’s Linked resource mechanism to add the common VHDL libraries to your project (std and ieee). But VSS does not support Linked resources —The last update of the VSS plugin was in 2007 for Eclipse 3.3— and it inhibits Sigasi from creating these links.
As a result, if you use Sigasi together with VSS, Sigasi can not add the std and ieee libraries to your project.
Workaround: Sigasi allows you to use your own custom std and ieee libraries. You can use this feature to manually add the std and ieee files.