support RemoveUnused on Scala 3

Author: bjaglin

.scalafix.conf

@@ -9,7 +9,7 @@ ExplicitResultTypes {
 OrganizeImports {
  groupedImports = Explode
  expandRelative = true
- removeUnused = true # done already by RemoveUnused rule
+ removeUnused = true
  groups = [
    "re:javax?\\."
    "scala."

build.sbt

@@ -180,8 +180,7 @@ lazy val input = projectMatrix
     noPublishAndNoMima,
     scalacOptions ~= (_.filterNot(_ == "-Yno-adapted-args")),
     scalacOptions ++= warnAdaptedArgs.value, // For NoAutoTupling
-    scalacOptions ++= warnUnusedImports.value, // For RemoveUnused
-    scalacOptions ++= warnUnused.value, // For RemoveUnusedTerms
+    scalacOptions += warnUnused.value, // For RemoveUnusedTerms
     logLevel := Level.Error, // avoid flood of compiler warnings
     libraryDependencies ++= testsDependencies.value,
     coverageEnabled := false
@@ -194,7 +193,6 @@ lazy val output = projectMatrix
   .in(file("scalafix-tests/output"))
   .settings(
     noPublishAndNoMima,
-    scalacOptions --= warnUnusedImports.value,
     libraryDependencies ++= testsDependencies.value,
     coverageEnabled := false
   )

docs/rules/RemoveUnused.md

@@ -14,15 +14,12 @@ example diff from running `sbt "scalafix RemoveUnused"`.
 
 To use this rule:
 
-- Enable the Scala compiler option `-Ywarn-unused` (or `-Wunused` in 2.13). In
-  sbt, this is done with `scalacOptions += "-Ywarn-unused"`.
+- Enable the Scala compiler option `-Ywarn-unused` (2.12.x), `-Wunused`
+  (2.13.x), or `-Wunused:all` (>=3.3.0).
 - Disable `-Xfatal-warnings` if you have it enabled. This is required so the
   compiler warnings do not fail the build before running Scalafix. If you are
   running 2.13.2 or later, you may keep `-Xfatal-warnings` by modifying how
   specific warnings are handled via `scalacOptions += "-Wconf:cat=unused:info"`.
-- This rule **can't work** yet on Scala 3 projects since the compiler option `warn-unused`
-  is not yet available in Scala 3. You need to remove `RemoveUnused` 
-  from `.scalafix.conf` for Scala 3 projects.
 
 ## Examples
 
@@ -129,21 +126,56 @@ import scalafix.internal.rule._
 println(scalafix.website.rule("RemoveUnused", RemoveUnusedConfig.default))
 ```
 
-## -Ywarn-unused
+## More granular scalac options
 
-Consult `scala -Y` in the command-line for more information about using
-`-Ywarn-unused`.
+You may request more granular warnings to the compiler if you opt-out
+from some rewrites in the rule configuration. 
 
 ```
-$ scala -Ywarn-unused:help
-Enable or disable specific `unused' warnings
-  imports    Warn if an import selector is not referenced.
-  patvars    Warn if a variable bound in a pattern is unused.
-  privates   Warn if a private member is unused.
-  locals     Warn if a local definition is unused.
-  explicits  Warn if an explicit parameter is unused.
-  implicits  Warn if an implicit parameter is unused.
-  params     Enable -Ywarn-unused:explicits,implicits.
-  linted     -Xlint:unused.
+$ scala212 -Wunused:help
+Enable or disable specific `unused` warnings
+  imports     Warn if an import selector is not referenced.
+  patvars     Warn if a variable bound in a pattern is unused.
+  privates    Warn if a private member is unused.
+  locals      Warn if a local definition is unused.
+  explicits   Warn if an explicit parameter is unused.
+  implicits   Warn if an implicit parameter is unused.
+  synthetics  Warn if a synthetic implicit parameter (context bound) is unused.
+  nowarn      Warn if a @nowarn annotation does not suppress any warnings.
+  params      Enable -Wunused:explicits,implicits,synthetics.
+  linted      -Xlint:unused.
 Default: All choices are enabled by default.
-```
+```
+
+```
+$ scala3 -W
+...
+       -Wunused  Enable or disable specific `unused` warnings
+                 Choices : 
+                 - nowarn, 
+                 - all, 
+                 - imports :
+                 	Warn if an import selector is not referenced.
+                 	NOTE : overrided by -Wunused:strict-no-implicit-warn, 
+                 - privates :
+                 	Warn if a private member is unused, 
+                 - locals :
+                 	Warn if a local definition is unused, 
+                 - explicits :
+                 	Warn if an explicit parameter is unused, 
+                 - implicits :
+                 	Warn if an implicit parameter is unused, 
+                 - params :
+                 	Enable -Wunused:explicits,implicits, 
+                 - linted :
+                 	Enable -Wunused:imports,privates,locals,implicits, 
+                 - strict-no-implicit-warn :
+                 	Same as -Wunused:import, only for imports of explicit named
+                 members.
+                 	NOTE : This overrides -Wunused:imports and NOT set by
+                 -Wunused:all,
+                 - unsafe-warn-patvars :
+                 	(UNSAFE) Warn if a variable bound in a pattern is unused.
+                 	This warning can generate false positive, as warning cannot be
+                 	suppressed yet.
+```

project/ScalafixBuild.scala

@@ -46,14 +46,10 @@ object ScalafixBuild extends AutoPlugin with GhpagesKeys {
     lazy val isScala212 = Def.setting {
       scalaVersion.value.startsWith("2.12")
     }
-    lazy val warnUnusedImports = Def.setting {
-      if (isScala3.value) Nil
-      else if (isScala213.value) Seq("-Wunused:imports")
-      else Seq("-Ywarn-unused-import")
-    }
     lazy val warnUnused = Def.setting {
-      if (isScala2.value) Seq("-Ywarn-unused")
-      else Nil
+      if (isScala3.value) "-Wunused:all" 
+      else if (isScala213.value) "-Wunused" 
+      else "-Ywarn-unused"
     }
     lazy val targetJvm = Def.setting {
       if (isScala3.value) Seq("-Xtarget:8")
@@ -80,13 +76,13 @@ object ScalafixBuild extends AutoPlugin with GhpagesKeys {
       scalaXml +: otherLibs
     }
     lazy val compilerOptions = Def.setting(
-      warnUnusedImports.value ++
-        targetJvm.value ++
+      targetJvm.value ++
         Seq(
           "-encoding",
           "UTF-8",
           "-feature",
-          "-unchecked"
+          "-unchecked",
+          warnUnused.value
         )
     )
 

scalafix-rules/src/main/scala/scalafix/internal/rule/RemoveUnused.scala

@@ -26,7 +26,7 @@ class RemoveUnused(config: RemoveUnusedConfig)
   def this() = this(RemoveUnusedConfig.default)
 
   override def description: String =
-    "Removes unused imports and terms that reported by the compiler under -Ywarn-unused"
+    "Removes unused imports and terms that reported by the compiler under -Wunused"
   override def isRewrite: Boolean = true
 
   private def warnUnusedPrefix = List("-Wunused", "-Ywarn-unused")
@@ -36,16 +36,11 @@ class RemoveUnused(config: RemoveUnusedConfig)
       warnUnusedPrefix.exists(prefix => option.startsWith(prefix)) ||
         warnUnusedString.contains(option)
     )
-    if (config.scalaVersion.startsWith("3"))
+    if (!hasWarnUnused) {
       Configured.error(
-        "This rule is specific to Scala 2, because the compiler option `-Ywarn-unused` is not available yet in scala 3 " +
-          "To fix this error, remove RemoveUnused from .scalafix.conf"
-      )
-    else if (!hasWarnUnused) {
-      Configured.error(
-        s"""|The Scala compiler option "-Ywarn-unused" is required to use RemoveUnused.
-          |To fix this problem, update your build to use at least one Scala compiler
-          |option like -Ywarn-unused, -Xlint:unused (2.12.2 or above), or -Wunused (2.13 only)""".stripMargin
+        """|A Scala compiler option is required to use RemoveUnused. To fix this problem,
+          |update your build to add -Ywarn-unused (2.12.x), -Wunused (2.13.x), or 
+          |-Wunused:all (>=3.3.0)""".stripMargin
       )
     } else {
       config.conf

scalafix-rules/src/main/scala/scalafix/internal/rule/RemoveUnusedConfig.scala

@@ -12,13 +12,9 @@ case class RemoveUnusedConfig(
     privates: Boolean = true,
     @Description("Remove unused local definitions")
     locals: Boolean = true,
-    @Description(
-      "Remove unused pattern match variables (compatible with Scala 2.12 and 2.13)"
-    )
+    @Description("Remove unused pattern match variables")
     patternvars: Boolean = true,
-    @Description(
-      "Remove unused function parameters (compatible with Scala 2.12 and 2.13)"
-    )
+    @Description("Remove unused function parameters")
     params: Boolean = true
 )