RSense Knows Your Code

Rsense brings the kind of static analysis tooling to Ruby that programmers in other languages take for granted. The kind of tooling I kept hearing was impossible to implement for Ruby. Accurate type inference, code completion, definition finding, and eventually so much more. How about a real refactoring tool, or the ability to find whole classes of bugs without executing the code? This is where Rsense is headed.

Learn how Rsense does its magic, hear the story of how one determined noob brought it back to life, and find out how you can use it to improve your daily coding experience.

Talk given at JRubyConfEU/eurucamp 2014 (Berlin, Germany)

http://rsense.github.io/
https://github.com/rsense/rsense

Transcript

1. Sees All
2. http://rsense.github.io/ twitter: @e_dub_kendo github: @edubkendo esw9999@gmail.com
3. — Ruby developer at LonelyPlanet — Former JRuby GSoC participant — Maintainer of Rsense
4. RSense is a static-analysis, type- inference tool for Ruby code. ie. It reads in source code and provides information about it.
5. This means we can build tools with this information: — code completion — find-definition — bug-detection — refactoring (Can your ctags do all that?)
6. I wanted Ruby code completion in Sublime Text.
8. Sometimes, I'd try "this one weird trick" and get it sort of working.
9. Never quite works right. Does not work with JRuby.
10. Everything I read suggested that doing good type-inference on Ruby was extremely difficult or impossible .
11. "Meta-programming makes the type inference problem equivalent to the halting problem." -raganwald
13. Rsense: The most useful development tools for Ruby ?
14. Rsense was created by Tomohiro Matsuyama.
15. Unfortunately...abandoned
16. Difficult to install, only works on 1.8 syntax. Using ANCIENT version of JRuby for parsing.
17. I'll just swap out the jar-file!
18. Google Summer of Code GSoC pays students a stipend to work on an open- source project. In 2013, JRuby was selected to be a participating organization. (As they had the year prior.)
19. Tom Enebo helps me fix over 800 errors and 100 failing tests.
20. No gems found!
21. Why wasn't rsense more widely adopted when it originally debuted? — People had a hard time installing it. — Written in Java.
22. Needed a better install story. Also needed MOAR ruby.
23. One year later...
25. gem install rsense and install the editor plugin of choice. Works for either MRI or JRuby.
26. Rsense gem uses Spoon (based on posix_spawn) to launch a jruby process (via the jruby-jars gem).
27. This runs rsense-server which communicates between editor plugins and rsense-core (a very thin wrapper around the rsense.jar).
28. The line of communication
29. Rsense is implemented with a variation on the Cartesian Product Algorithm (CPA).
30. Cartesian Product Algorithm CPA was first implemented for the language Self, by Ole Agesen. There is a paper describing a project called Ecstatic that appears to have been a major influence on Rsense. (Search ecstatic ruby type inference to find it.)
31. How RSense implements CPA
32. Code is read in and parsed into an Abstact Syntax Tree by jruby-parser.
33. Abstract Syntax Tree The representation of source code in a tree structure.
37. Source code is parsed into an AST so that compilers and interpreters have a structure more suitable for processing.
39. jruby-parser Library originally extracted from JRuby. Parser with special methods for use by IDEs and tools. Especially tracks source code position.
40. Rsense walks the AST, building up a graph of the nodes in the AST via an Abstract Interpreter.
41. Abstract Interpreter A Virtual Ruby. It interprets the code in order to make sense of branches, conditionals, etc without executing any code.
42. Constraint Propagation Propagates types along the edges to the nodes in the graph.
44. Stubbed out builtin methods.
45. Rsense relies on stubbed out copies of the Ruby core libs and std_lib to fill in missing information.
47. This would be almost enough, however, Ruby's dynamic metaprogramming feature does mean that a small subset of valid Ruby expressions cannot be type- inferred.
49. Fortunately, Rsense has a solution for this too.
50. Annotation Resolver The annotation resolver uses a special type annotation syntax in the comments to allow these rare edge cases to be resolved. Otherwise the failed inferences would bleed into the results and taint them or prevent types from propagating altogether.
51. This is mostly only necessary in the built-in stubs, because outside of the std_lib these techniques are less common.
52. Still, I'd like to move Rsense off of the unconventional annotation syntax and towards using something many Rubyists already use (YARD).
54. Demo from previous slide can be viewed at http:// rsense.github.io/demo
55. Where does Rsense stand today?
59. Works great for:
60. Currently, Rails plus all its dependencies is too big for the graph.
61. TODO: — Vim & Emacs plugins — Caching the type graph (fix Rails) — Switch to YARD for annotations — Expose find-definition, where, type-inference — Build bug detection, refactoring tools on top
62. This cat wishes he could use Rsense
63. http://rsense.github.io/
64. Any questions? — twitter: @e_dub_kendo — github: @edubkendo