RemoveUnused: pattern vars updates post 3.7.0

- document deprecation of `-Wunused:unsafe-warn-patvars`
- document fragmented canonical patvars behavior

Author: bjaglin

docs/rules/RemoveUnused.md

@@ -72,7 +72,10 @@ case class AB(a: Int, b: String)
 object Main {
   val example = AB(42, "lol")
   example match {
-    case AB(a, b) => println("Not used")
+    case AB(foo, bar) => println("Not used")
+  }
+  example match {
+    case AB(a, b) => println("Not used, but canonical names")
   }
 }
 // after
@@ -81,14 +84,14 @@ object Main {
   example match {
     case AB(_, _) => println("Not used")
   }
+  example match {
+    case AB(a, b) => println("Not used, but canonical names")
+  }
 }
 ```
 
-On Scala 3, `-Wunused:unsafe-warn-patvars` is required.
-
-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.
+On Scala 3, an additional `-Wunused:unsafe-warn-patvars` option is required
+until Scala 3.7.0.
 
 ### Remove unused function parameters
 

project/Dependencies.scala

@@ -6,7 +6,7 @@ import sbt._
 
 object Dependencies {
   val scala212 = sys.props.getOrElse("scala212.nightly", "2.12.20")
-  val scala213 = sys.props.getOrElse("scala213.nightly", "2.13.16")
+  val scala213 = sys.props.getOrElse("scala213.nightly", "2.13.16") // remove 2.13.14 hack in RuleSuite when bumping
   val scala33 = "3.3.5"
   val scala35 = "3.5.2"
   val scala36 = "3.6.4"

project/ScalafixBuild.scala

@@ -84,7 +84,11 @@ object ScalafixBuild extends AutoPlugin with GhpagesKeys {
       scalaVersion.value.startsWith("2.12")
     }
     lazy val warnUnused = Def.setting {
-      if (isScala3.value) Seq("-Wunused:all", "-Wunused:unsafe-warn-patvars")
+      if (isScala3.value)
+        Seq(
+          "-Wunused:all",
+          "-Wunused:unsafe-warn-patvars" // only needed for <3.7.0
+        )
       else if (isScala213.value) Seq("-Wunused")
       else Seq("-Ywarn-unused")
     }

scalafix-tests/expect/src/test/scala/scalafix/tests/rule/RuleSuite.scala

@@ -36,16 +36,23 @@ class RuleSuite extends AbstractSemanticRuleSuite with AnyFunSuiteLike {
   override def runOn(diffTest: RuleTest): Unit = {
     def stripPatch(v: String) = v.split('.').take(2).mkString(".")
 
+    val inputSV = props.scalaVersion
+    val path = diffTest.path.input.toNIO.toString
+
     val versionMismatch =
-      stripPatch(RulesBuildInfo.scalaVersion) != stripPatch(props.scalaVersion)
+      stripPatch(RulesBuildInfo.scalaVersion) != stripPatch(inputSV)
     val explicitResultTypesTest =
-      diffTest.path.input.toNIO.toString.contains(
+      path.contains(
         "explicitResultTypes" + java.io.File.separator // don't skip tests with a suffix
       )
 
-    // ExplicitResultTypes can only run against sources compiled with the sam
-    // binary version as the one used to compile the rule
-    if (versionMismatch && explicitResultTypesTest) return
+    if (
+      // ExplicitResultTypes can only run against sources compiled with the same
+      // binary version as the one used to compile the rule
+      (versionMismatch && explicitResultTypesTest) ||
+      // RemoveUnusedPatternVars has the old 2.12.x behavior for 2.13.14
+      (inputSV == "2.13.14" && path.endsWith("RemoveUnusedPatternVars.scala"))
+    ) return
     else super.runOn(diffTest)
   }
 

scalafix-tests/input/src/main/scala/test/removeUnused/RemoveUnusedPatternVars.scala renamed to scalafix-tests/input/src/main/scala-2/test/removeUnused/RemoveUnusedPatternVars.scala

@@ -12,6 +12,9 @@ object ob {
   // Add code that needs fixing here.
   val example = AB(42, "lol")
 
+  example match {
+    case AB(aa, bb) => println("https://github.com/scala/bug/issues/13035")
+  }
   example match {
     case AB(_, _) => println("Not used, good")
   }