Breaking Changes – Part 1: Parser

Rubberduck 2.0 flips everything around.

When numbering versions, incrementing the “major” digit is reserved for breaking changes – and that’s exactly what Rubberduck 2.0 will introduce.

I have these changes in my own personal fork at the moment, not yet PR’d into the main repository.. but as more and more people fork the main repo I feel a need to go over some of the changes that are about to happen to the code base.

If you’re wondering, it’s becoming clearer now, that Rubberduck 2.0 will not be released until another couple of months – at this rate we’re looking at something like the end of winter 2016… but it’s going to be worth the wait.


 

Parser State

Parsing in Rubberduck 1.x was relatively simple:

  • User clicks on a command that requires a fresh parse tree;
  • Parser knows which modules have been modified since the last parse, so only the modified modules are processed by the ANTLR parser;
  • Once we have a parse tree and a set of Declaration objects for everything (modules, procedures, variables, etc.), we resolve the identifier usages we encounter as we walk the parse tree again, to one of these declarations;
  • Once identifier resolution is completed, the command can run.

The parse results were cached, so that if the Code Explorer processed the entire code base to show up, and then the user wanted to run code inspections or one of the refactor commands, they could be reused as long as none of the modules were modified.

Parsing in Rubberduck 2.0 flips this around and completely centralizes the parser state, which means the commands that require a fresh parse tree can be disabled until a fresh parse tree is available.

We’ve implemented a key hook that tells the parser whenever the user has pressed a key that’s changed the content of the active code pane. When the 2.0 parser receives this message, it cancels the parse task (wherever it’s at) for that module, and starts it over; anytime there’s a “ready” parse tree for all modules, the expensive identifier resolution step begins in the background – and once that step completes, the parser sends a message to whoever is listening, essentially saying “If you ever need to analyze some code, I have everything you need right here”.

Sounds great! So… What does it mean?

It means the Code Explorer and Find Symbol features no longer need to trigger a parse, and no longer need to even wait for identifier resolution to complete before they can do their thing.

It means no feature ever needs to trigger a parse anymore, and Rubberduck will be able to disable the relevant menu commands until parser state is ready to handle what you want to do, like refactor/rename, find all references or go to implementation.

It means despite the VBE not having a status bar, we can (read: will) use a command bar to display the current parser state in real-time (as you type!), and let you click that parser state command button to expand the parser/resolver progress and see exactly what little ducky’s working on in the background.


To be continued…
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