Scala Abide: A lint tool for Scala
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This document provides an overview of Abide, a static checker tool for Scala based on type-checked ASTs. It has the goals of unifying existing rule-based approaches, making it easy to write and use rules, and providing reasonable performance and good integrations. Rules are decoupled from the tool and can come from core, extra, or project-specific packages. The document gives examples of core rules and rules for Akka and describes Abide's architecture, use, anatomy including traversers, directives, and how rules are coded. It encourages contributing rules to help the value of the tool.
Scala Abide: A lint tool for Scala
- 2. Overview • Static checker tool • Based on type-checked ASTs • Easy to use and write rules
- 3. Goals • Unify existing approaches in one platform • Easy to write rules • Easy to use other people’s rules • Reasonable performance • Good integrations
- 4. Abide • Rules are decoupled from the tool • rule packages • project-specific rules • Integrates with Sbt • planned: Maven, Eclipse
- 5. Examples • Core package • Unused members • Vars that are never re-assigned • Renamed arguments with defaults • Akka • sender method called inside future
- 7. Use addSbtPlugin("com.typesafe" % "sbt-abide" % "0.1.0") libraryDependencies += "com.typesafe" %% "abide-core" % “0.1.0” % "abide" libraryDependencies += "com.typesafe" %% "abide-extra" % “0.1.0” % "abide" Project(...).dependsOn(rules % "abide")
- 8. Anatomy
- 9. Traversers • Fused: one-pass for all rules • Optimised: rules are filtered on what they match
- 10. Directives • Shared context between rules • compiler universe • user-defined mix-ins
- 11. Rules val step = { case varDef @ q"$mods var $name : $tpt = $value" => nok(varDef.symbol, Warning(varDef)) case q"$rcv = $expr" => ok(rcv.symbol) } quasi-quote state helpers Replace `var` with `val`
- 12. Rules • partial function Tree => Unit • collect keys that can do one transition • nok (not ok) • ok (stable state)
- 13. Rules • existential rules (what we’ve seen) • scoping rules • helpers to maintain nesting • enter (no need for removing, handled by the library) • path rules • like scoping, but richer state checks
- 14. Coding a rule
- 15. For example..
- 16. Mutation inside iteration • Let’s forbid mutating the underlying collection while iterating for (x <- xs) xs -= x xs map { x => xs -= x } ys foreach { case (k, v) => ys remove 1 } for (p <- icodes; x <- xs) { icodes -= p._1 xs remove x }
- 17. Simplifying assumptions • purely syntactical matching (no points-to analysis) • name-based xs map { x => xs -= x }
- 18. Let’s code
- 19. Future
- 20. Next • SupressWarning support • Integrations: maven and IDEs • More rules
- 21. Contribute! • The value is in rules • Contribute to scala/scala-abide • ..or write your own rule package
- 22. Acknowledgements Nicolas Voirol (@samarion) did all the work during his internship at Typesafe Switzerland
- 23. Thank you