Move fast and fix things

An introduction to Scalafix, presented at Scala IO 2017

Transcript

1. Move fast and BREAK FIX things
2. ME, HI!
3. STUFF I DO (BY DAY)
4. STUFF I DO (BY NIGHT) Scala and JS open-source
5. AGENDA 1. Intro and context 2. ASTs and related workflows 3. Scalameta 4. Scalafix 5. Live examples
6. WHAT IS SCALAFIX Scalafix is a rewrite and linting tool for Scala — scalacenter.github.io/scalafix
7. EXAMPLE 1 - NOPROCEDURESYNTAX // before def main(args: Seq[String]) { println("Hello world!") } // after def main(args: Seq[String]): Unit = { println("Hello world!") }
8. EXAMPLE 2 - NOAUTOTUPLING // before def someMethod(t: (Int, String)) = ??? someMethod(1, "something") // after def someMethod(t: (Int, String)) = ??? someMethod((1, "something"))
9. EXAMPLE 3 - REMOVECARTESIANBUILDER // before import cats.syntax.cartesian._ val o1: Option[Int] = Some(42) val o2: Option[String] = Some("hello") o1 |@| o2 map (_ + _) // after import cats.syntax.apply._ val o1: Option[Int] = Some(42) val o2: Option[String] = Some("hello") (o1, o2).mapN(_ + _)
10. EXAMPLE 4 - NOINFER val myList = List(Some(42), Right("foo")) // ^ // |__ ⚠ Product with Serializable
11. LET'S TALK ABOUT MAINTAINERS
12. PURE EVIL BREAK CODE WITHOUT DOCUMENTING WHAT BROKE
13. MILD EVIL BREAK CODE DOCUMENTING WHAT BROKE (OR LINKING TO A SUPER-LONG ISSUE)
14. GOOD EFFORT BREAK CODE AND DOCUMENT HOW TO FIX IT
15. YOU ROCK! BREAK CODE AFTER A DEPRECATION CYCLE AND EXPLAIN HOW TO FIX IT
16. SUPERHERO BREAK CODE AFTER A DEPRECATION CYCLE AND PROVIDE AN AUTOMATIC REWRITE
17. SCI-FI?
18. MEANWHILE IN SWIFT
19. MEANWHILE IN JAVASCRIPT
20. MEANWHILE IN JAVASCRIPT 3 paragraphs later
21. The JS tooling landscape is living in the future — Ólafur Páll Geirsson, author of Scalafix
22. IT'S TIME WE JUMP INTO THE FUTURE
23. HOW? LET'S TAKE A STEP BACK
24. A WORD ABOUT ASTS SO... AST?
25. ABSTRACT SYNTAX TREE
26. WHY ABSTRACT?
27. val answer = 42; val answer = 42 val answer = 42 val answer = 42
28. ASTS... WHY SHOULD I CARE?
29. AST WORKFLOW 1: SCALAC
30. AST WORKFLOW 2: MACROS
31. AST WORKFLOW 3: SCALAFMT
32. AST WORKFLOW 4: SCALAFIX
33. AST WORKFLOW 4: SCALAFIX Woops, copy-paste?
34. WHAT SCALAFIX COULD DO: // before def someMethod(string: String) { // I like trees println(string.trim.split("/").lastOption) } // after def someMethod(string: String): Unit = println( string .trim .split("/") .lastOption )
36. WHAT SCALAFIX DOES INSTEAD: // before def someMethod(string: String) { // I like trees println(string.trim.split("/").lastOption) } // after def someMethod(string: String): Unit = { // I like trees println(string.trim.split("/").lastOption) }
37. "AST" WORKFLOW 4: SCALAFIX
38. OK, LET'S DO THIS!
40. Introducing SCALAMETA
41. Scalameta is a modern metaprogramming library for Scala — scalameta.org
42. METAPROGRAMMING?
43. METAPROGRAMMING DEVTOOLS! ▸ code formatting ▸ code fixing ▸ code browsing ▸ and many more applications!
44. SCALAMETA VADEMECUM ▸ Trees ▸ Tokens ▸ Parser ▸ Tree manipulation primitives ▸ Semantic API ▸ (pretty-printer)
45. SEMANTIC INFORMATION List(1, 2, 3) // Symbol _root_.scala.collection.immutable.List. // Denotation final object List // Synthetic [2..7): apply => _root_.scala.collection.immutable.List.apply (Lscala/collection/Seq;)
47. SCALAFIX FINALLY!
48. Rule Rewrite
49. Rule A rule can be: ▸ checked ▸ fixed
50. Patch
51. Patch A Scalafix Patch is a patch in the diff sense of patch. It boils down to a list of -/+ to apply to the source code.
52. RuleCtx
53. RuleCtx The toolbox for writing rules. It provides the API for producing patches.
54. SemanticdbIndex
55. SemanticdbIndex A index for looking up data in a scalameta's Semantic Database. It contains all the available semantic information.
57. LIVE
58. WHAT'S NEXT?
59. SHORT-TERM ▸ more linter rules ▸ rule "bundles" ▸ more robust expansion of inferred types / implicits
60. MEDIUM TERM ▸ editor integrations ▸ stable API
62. Questions? @gabro27 @buildoHQ @ScalaItaly