WordPress is one of the most known and used CMS in the web.
Eclipse is one of the most know and used IDE in the web.
Why they shouldn’t love each other???
The answer is simply: they do… if you edit 2 files.
Code Completion is one of the absolutely needed feature for an Integrated Development Environment such as Eclipse.
Eclipse, born for Java developing, nowadays support almost every open language with the help of an huge number of plugins.
PHP is included in this list. There is a ready to use suite codenamed PDT (PHP Developing Tools) and tons of how-to install it.