zio / zio-shield   0.1.0

Apache License 2.0 GitHub

Enforce best coding practices with ZIO

Scala versions: 2.12
sbt plugins: 1.0

ZIO Shield 🛡️

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Project stage

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ZIO Shield statically analyses the source code, enforcing best coding practices with ZIO.
It aims to keep your code pure, total and clean with the help of powerful ZIO ecosystem.

Powered by Scalafix and Scalazzi rules.



Add zio-shield sbt plugin to your project/plugins.sbt:

addSbtPlugin("dev.zio" % "zio-shield" % "0.1.0")

It will add semanticdb-scalac compiler plugin and -Yrangepos scalac option to your project settings if they doesn't exist. They are needed to generate SemanticDb files for static analysis.


Running shield command will start the analysis.

> shield
[warn] ZioShieldShowcase.scala:23:7: error: possibly nullable
[warn]   def nullable(): Response = {
[warn]       ^^^^^^^^
[warn] ZioShieldShowcase.scala:24:18: error: nullable: null usage
[warn]     GoodResponse(null)
[warn]                  ^^^^
[warn] ZioShieldShowcase.scala:27:7: error: possibly nullable
[warn]   def handleResponse(response: Response): Unit = {
[warn]       ^^^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:40:24: error: possibly nullable
[warn]         handleResponse(nullable())
[warn]                        ^^^^^^^^
[warn] ZioShieldShowcase.scala:27:7: error: possible partial symbol
[warn]   def handleResponse(response: Response): Unit = {
[warn]       ^^^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:32:7: error: not total: throwing exceptions
[warn]       throw new RuntimeException("Bad response!")
[warn]       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:28:18: error: type casting
[warn]     if (response.isInstanceOf[BadResponse]) {
[warn]                  ^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:29:34: error: type casting
[warn]       val badResponse = response.asInstanceOf[BadResponse]
[warn]                                  ^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:34:35: error: type casting
[warn]       val goodResponse = response.asInstanceOf[GoodResponse]
[warn]                                   ^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:39:9: error: ignored expression
[warn]         handleResponse(alwaysGood())
[warn]         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:40:9: error: ignored expression
[warn]         handleResponse(nullable())
[warn]         ^^^^^^^^^^^^^^^^^^^^^^^^^^
[warn] ZioShieldShowcase.scala:8:7: error: Future returning method
[warn]   def bigComputation(data: String): Future[Int] = Future {
[warn]       ^^^^^^^^^^^^^^

ZioShieldShowcase.scala source code located here.


You can set shieldFatalWarnings sbt setting to make all warnings fatal, blocking you build if there are any problems detected by ZIO Shield.

shieldFatalWarnings := true
> shield
[error] ZioShieldShowcase.scala:23:7: error: possibly nullable
[error]   def nullable(): Response = {
[error]       ^^^^^^^^

To exlude specific rules from analysis you can create .shield.yaml file in the project root and specify exludedRules option.

# .shield.yaml
excludedRules: [ZioShieldNoIgnoredExpressions]


For using ZIO Shield with metals you should provide custom version of metals language server.

In vscode it can be done in your settings.json:

  "metals.customRepositories": ["central", "bintray:vovapolu/maven"],
  "metals.serverVersion": "0.7.6-zio-shield-RC0"

And then run Metals: Restart server command or just restart the editor.




  • Warnings are not shown

    Run Metals: Import build in vscode. If it doesn't help restart the editor and try again.


  • ZioShieldNoFutureMethods blocks any val or def that has type of Future[...]
  • ZioShieldNoIgnoredExpressions blocks ignored expressions except in ZIO.effect* blocks
  • ZioShieldNoReflection blocks all methods from scala.reflect, java.lang.reflect and java.lang.Class
  • ZioShieldNoTypeCasting blocks asInstanceOf, isInstanceOf and any case x: Y except in ZIO.effect* blocks
  • ZioShieldNoImpurity blocks direct usages of Unit returning methods and indirect usages through other methods except in ZIO.effect* blocks
  • ZioShieldNoIndirectUse blocks "effectful" methods, which contain usages of ZIO.effect*, expect when they are defined in ancestors of "pure" traits, i.e. traits without methods that use ZIO.effect*.
  • ZioShieldNoNull blocks direct null usages and indirect usages through other methods except in ZIO.effect* blocks
  • ZioShieldNoPartial blocks direct throw and try {...} catch ... usages and indirect usages through other methods except in ZIO.effect* blocks