textDocument/completion support via gocode

[Contextualist]

Support textDocument/completion by vendoring nsf/gocode. Gocode maintains a separated package cache, thus this implementation is not optimal for memory.

Known issues:

• No VFS support, because gocode uses exclusively .a binary cache
• Vendor import gets ignored, probably a bug of gocode (fix vendor import get ignored nsf/gocode#485)
• Built-in types get ignored

Commit ff980ce also fixes #215 .
This closes #27, closes #77, and closes #201

[keegancsmith]

Thanks!! I'll take a look at this tomorrow. cc @sqs @slimsag

[keegancsmith]

Apologies I won't have time today, I've put it onto my TODO list to review on Monday though.

[Contextualist]

@keegancsmith That's fine. I also need some time to test the feature with some corner cases as well as with real-world setting.

[keegancsmith]

So this code assumes that we never have more than one langserver running in a process. However, the only place this isn't true (that I know of) is Sourcegraph.com and we don't do autocompletion on sourcegraph. So this LGTM! Thanks so much for the PR!

[keegancsmith]

you are setting a global variable here, but langserver supports multiple instances running at once in the same process.

[keegancsmith]

@ramya-rao-a you may be interested in trying out the completion support in go-langserver this PR added. You need to ensure you are on latest master and run the langserver with the flag -gocodecompletion.

Thanks again @Contextualist!

[ramya-rao-a]

nice, will give it a try

[ramya-rao-a]

This works pretty well, nice job @Contextualist

There are a few extra things that the Go extension to VS Code does for completions apart from what gocode returns. Once I figure out how they can play well with the basic completions from the language server, I can include this.