RemoveUnused.params on Scala 3 Next

scala/scala3#20894

Author: bjaglin

docs/rules/RemoveUnused.md

@@ -90,7 +90,7 @@ On Scala 2.13.15+, canonical patterns (vars with the same names as the
 attributes) do not trigger unused warnings, so the input above will not
 be rewritten. See https://github.com/scala/bug/issues/13035.
 
-### Remove unused function parameters (Scala 2 only)
+### Remove unused function parameters
 
 ```scala
 // before

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

@@ -96,7 +96,10 @@ class RemoveUnused(config: RemoveUnusedConfig)
         isUnusedPattern += diagnostic.position
       } else if (
         config.params &&
-        (msg.startsWith("parameter") && msg.endsWith("is never used"))
+        (
+          msg.startsWith("parameter") && msg.endsWith("is never used") ||
+            msg == "unused explicit parameter"
+        )
       ) {
         isUnusedParam += diagnostic.position
       }
@@ -189,7 +192,7 @@ class RemoveUnused(config: RemoveUnusedConfig)
         case Term.Function(params, _) =>
           params.collect {
             case param @ Term.Param(_, name, _, _)
-                if isUnusedParam(param.pos) =>
+                if isUnusedParam(param.pos) || isUnusedParam(name.pos) =>
               Patch.replaceTree(name, "_")
           }.asPatch
       }.asPatch

scalafix-tests/input/src/main/scala-2/test/removeUnused/RemoveUnusedParams.scala

@@ -3,8 +3,6 @@ rule = RemoveUnused
  */
 package test.removeUnused
 
-// Not available as of Scala 3.4.1
-// https://github.com/scalacenter/scalafix/issues/1937
 object UnusedParams {
   val f: String => Unit = unused => println("f")
   val ff = (unused: String) => println("f")

scalafix-tests/input/src/main/scala-3next/test/removeUnused/RemoveUnusedParams.scala

@@ -0,0 +1,12 @@
+/*
+rule = RemoveUnused
+ */
+package test.removeUnused
+
+object UnusedParams {
+  val f: String => Unit = unused => println("f")
+  val ff = (unused: String) => println("f")
+  val fs = (used: String, unused: Long) => println(used)
+  def g(x: String => Unit): Unit = ???
+  g{implicit string => println("g")}
+}

scalafix-tests/output/src/main/scala-2/test/removeUnused/RemoveUnusedParams.scala

@@ -1,7 +1,5 @@
 package test.removeUnused
 
-// Not available as of Scala 3.4.1
-// https://github.com/scalacenter/scalafix/issues/1937
 object UnusedParams {
   val f: String => Unit = _ => println("f")
   val ff = (_: String) => println("f")

scalafix-tests/output/src/main/scala-3next/test/removeUnused/RemoveUnusedParams.scala

@@ -0,0 +1,9 @@
+package test.removeUnused
+
+object UnusedParams {
+  val f: String => Unit = _ => println("f")
+  val ff = (_: String) => println("f")
+  val fs = (used: String, _: Long) => println(used)
+  def g(x: String => Unit): Unit = ???
+  g{implicit string => println("g")}
+}