I was invited to give this talk at the Wix Backend Guild Day, an internal event which was broadcast live internationally, on 2018-04-12 Video: https://youtu.be/cQ7UvUybceA These days sbt is the de-facto build tool for Scala, but most of us just write the minimum viable build.sbt file, import the libraries we need (and maybe throw in some sbt-assembly) and forget about it. In this Good Practices session, you will learn about making your build safer and more robust by making the Scala compiler work for you and through using some sbt plugins. This talk will be quite high-level. There will be no need for prior knowledge of sbt and it should be beneficial for you even if you don’t use sbt.

1. Power Up Your Build
OMER VAN KLOETEN

2. This talk
 We can all do better
 Good, not best, practices
 No one-size-fits-all
 Not just green-field
 Open discussion

3. Who?
 Omer van Kloeten
 16 years in the industry
 Scala and sbt since 2012
 @omervk everywhere

4. A Good Build
 Explicit Compiler Behavior
 Robust and Repeatable
 Fast(-ish)
 Promotes Idiomatic Scala
 At the Right Level

5. Build Tools
 sbt
 cbt
 Mill
 Bazel
 Maven
 Gradle
 Pants

6. The Compiler

7. “
”
THE COMPILER IS YOUR FRIEND
AND FRIENDS TELL FRIENDS
WHEN THEY TRY TO DO STUPID THINGS
Hila Noga, “From Prehistoric to a New Age”, Scalapeño 2016
https://www.youtube.com/watch?v=N9loHZAI1NM

8. Build Passes! 🎉

9. Youhavediedofcompilerwarnings.

10. Out of sight, out of mind

11. “
”
-Xfatal-warnings
IS LIKE GLOBAL WARMING
YOU WANT TO DO SOMETHING ABOUT IT
BUT YOU NEVER DO
AND NOW IT'S TOO LATE
Andrew Phillips, “Essential vs Accidental Complexity in Scala & Dotty” (paraphrased),
ScalaWorld 2016
https://www.youtube.com/watch?v=Ay-9aanosUM

12. scalac Flags
 -deprecation
 -unchecked
 case _: Option[Int] =>
 -feature
 What level of Scala are you on?
 -language:implicitConversions (use splain)

13. scalac Flags
 Advanced Settings: -X
 -Xcheckinit ※
 -Xfuture
 -Xlint
 Run scalac –X for a list
class Foo {
val bar = baz // not yet
val baz = 1
}

14. scalac Flags
def print(x: (Int, Int)) =
println("Tupled")
def print(t: Int, x: Int) =
println("Untupled")
print(1, 2)

15. scalac Flags
def print(x: (Int, Int)) =
println("Tupled")
print(1, 2)

16. scalac Flags
 “Private” Settings: -Y
 -Yno-adapted-args
 -Ywarn-*
 Run scalac –Y for a list

17. YMMV
 Do what’s right for you
 “Recommended Scalac Flags for 2.12” by Rob Norris (@tpolecat)
https://tpolecat.github.io/2017/04/25/scalac-flags.html

18. Promoting Better Code

19. Linters
 FindBugs
 Linter
 Abide
 Scalastyle
 scapegoat

20. Linters
(that you should care about)
 -Xlint:*
 WartRemover
 Scalafix
 IntelliJ IDEA
 Leif Wickland, “Toward A Safer Scala”, ScalaDays SF 2015
https://www.youtube.com/watch?v=CQY5ef6R_eg

21. WartRemover
 All rules are opt-in
 No “Better Java”
 AsInstanceOf / IsInstanceOf
 Null
 Return

22. WartRemover
 Good Practices
 ExplicitImplicitTypes
 PublicInference
implicit def foo(): Bar = new Bar()
def foo(): Bar = new Bar()

23. WartRemover
 Language Best Practices
 FinalCaseClass
 LeakingSealed
final case class Foo()
sealed trait A
sealed trait B extends A
final class C extends A

24. WartRemover
 Standard Library Best Practices
 ArrayEquals
 JavaConversions
Array(1.toByte) == Array(1.toByte)
javaList.asScala

25. WartRemover
 Avoid Throwing
 OptionPartial
 TraversableOps
 TryPartial
none.get
emptyList.head
emptyList.reduce(_ + _)
failedTry.get

26. wartremover-contrib
 ExposedTuples
 OldTime
 SomeApply
def foo(): (Int, String)
new java.util.Date()
val foo = Some(null)

27. “
”
ANY STYLE GUIDE WRITTEN IN ENGLISH
IS EITHER SO BRIEF THAT IT’S AMBIGUOUS,
OR SO LONG THAT NO ONE READS IT
Bob Nystrom, "Hardest Program I've Ever Written”
http://journal.stuffwithstuff.com/2015/09/08/the-hardest-program-ive-ever-written/

28. Styleguides
 Infinite
 Unwritten Rules
 “Feels Right”
 Unenforceable

29. Automated Code Formatting
 Auto-reformat code on compile
 Be hated by peers
 scalafmt
 sbt-scalafmt
 IntelliJ IDEA

30. Versioning

31. Versions
 Metadata
 Easy Consensus
 Semantic Versioning
 Breaking.BackCompat.Patch
 Marketing.New.BugFix
 Copy of Copy of Software Final (3).docx

32. Types of Versions
 Canonical versions
 1.2.3
 Non-canonical versions
 Between 1.2.3 and 1.2.4
 Date? Branch? Hash?
 Not even a version
 Snapshots

33. Versioning
 git describe --tags
 2.15.1-29-g866b31dfe-SNAPSHOT
 Use sbt-git
enablePlugins(GitVersioning)
git.useGitDescribe := true

34. Dependencies

35. sbt-coursier
 Pure Scala Ivy Replacement
 Parallel Downloads (Fast!)
 No Global Lock
 Coming natively to sbt
sbt/librarymanagement/pull/190

36. Zero Pending Updates Policy
 First commit after release
 Can’t upgrade?
 Triage
 Open issues
 Fix bugs
 Schedule upgrade

37. Ivy
 Dynamic Revisions
 1.11.+
 [1.0,2.0)

38. JitPack
 GitHub’s Auto-Repository
 DEPEND ON ANYTHING
 Release
 Tag
 Branch
 Commit
 On-demand
 Free!
resolvers += "jitpack" at "https://jitpack.io"
libraryDependencies += "com.github.User" % "Repo" % "Tag”

39. sbt-updates
 Makes Life Easy
 Explained Upgrade Path
> dependencyUpdates
[info] Found 3 dependency updates for test-project
[info] ch.qos.logback:logback-classic : 0.8.1 -> 0.9.30 -> 1.2.3
[info] org.scala-lang:scala-library : 2.11.5 -> 2.11.12 -> 2.12.5
[info] org.slf4j:slf4j-api : 1.7.21 -> 1.7.25

40. sbt-dependency-check
 Security Issues Check
 Uses the Open Web Application Security Project (OWASP)

41. sbt-dependency-graph
 What’s Using What
 It’s always Jackson or Guava
> dependencyGraph
[info] com.omervk:mylib_2.12:0.0.1-ga480c6e-SNAPSHOT [S]
[info] +-com.amazonaws:aws-java-sdk-s3:1.11.160
[info] | +-com.amazonaws:aws-java-sdk-core:1.11.160
[info] | | +-com.fasterxml.jackson.core:jackson-databind:2.6.6
[info] | | | +-com.fasterxml.jackson.core:jackson-annotations:2.6.0
[info] | | | +-com.fasterxml.jackson.core:jackson-core:2.6.6
[info] | | |
[info] | | +-com.fasterxml.jackson.dataformat:jackson-dataformat-cbor:2.6.6
[info] | | | +-com.fasterxml.jackson.core:jackson-core:2.6.6
[info] | | |
[info] | | +-joda-time:joda-time:2.8.1
[info] | | +-org.apache.httpcomponents:httpclient:4.5.2
[info] | | | +-commons-codec:commons-codec:1.9
[info] | | | +-org.apache.httpcomponents:httpcore:4.4.4
[info] | | |
[info] | | +-software.amazon.ion:ion-java:1.0.2
[info] | |

42. Honorable Mentions
 sbt-assembly
 sbt-native-packager

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