You probably do not have Java >= 8 environment installed or you have multiple Java installations and version >= 8 is not the default one.
In case of former, just install the newest Java (JDK or JRE).
In case of later, you must point Eclipse to the right Java environment. To do so you need to add proper path to the eclipse.ini configuration file, for example:
Sometimes C/C++ indexer used for parsing GLSL files breaks down and you have to manually force it to reindex. To do so just click RMB on the project containing your shader and choose Index -> Rebuild