Support OrganizeImports.removeUnused in Scala 3

Once this PR scala/scala3#17835
has merged and released, scalafix-organize-imports should be
able to run OrganizeImports.removeUnused based on the
diagnostics information in SemanticDB emit from Scala3 compiler.

In order to make OrganizeImports rule to work with Scala 3,
this commit added a few adjustments to the rule.

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

@@ -3,6 +3,8 @@ package scalafix.internal.rule
 import scala.annotation.tailrec
 import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
+import scala.util.Failure
+import scala.util.Success
 import scala.util.Try
 
 import scala.meta.Import
@@ -28,6 +30,7 @@ import metaconfig.ConfEncoder
 import metaconfig.ConfOps
 import metaconfig.Configured
 import metaconfig.internal.ConfGet
+import scalafix.internal.config.ScalaVersion
 import scalafix.internal.rule.ImportMatcher.*
 import scalafix.internal.rule.ImportMatcher.---
 import scalafix.internal.rule.ImportMatcher.parse
@@ -72,7 +75,8 @@ class OrganizeImports(config: OrganizeImportsConfig)
 
   override def fix(implicit doc: SemanticDocument): Patch = {
     unusedImporteePositions ++= doc.diagnostics.collect {
-      case d if d.message == "Unused import" => d.position
+      // Scala2 says "Unused import" while Scala3 says "unused import"
+      case d if d.message.toLowerCase == "unused import" => d.position
     }
 
     val (globalImports, localImports) = collectImports(doc.tree)
@@ -88,8 +92,16 @@ class OrganizeImports(config: OrganizeImportsConfig)
     diagnostics.map(Patch.lint).asPatch + globalImportsPatch + localImportsPatch
   }
 
-  private def isUnused(importee: Importee): Boolean =
-    unusedImporteePositions contains positionOf(importee)
+  private def isUnused(importee: Importee): Boolean = {
+    // positionOf returns the position of `bar` for `import foo.{bar => baz}`
+    // this position matches with the diagnostics from Scala2,
+    // but Scala3 diagnostics has a position for `bar => baz`, which doesn't match with
+    // the return value of `positionOf`.
+    // We could adjust the behavior of `positionOf` based on Scala version,
+    // but this implementation just checking the unusedImporteePosition includes the importee pos, for simplicity.
+    val pos = positionOf(importee)
+    unusedImporteePositions.exists(unused => unused.start <= pos.start && pos.end <= unused.end)
+  }
 
   private def organizeGlobalImports(
       imports: Seq[Import]
@@ -707,32 +719,40 @@ object OrganizeImports {
       scalacOptions: List[String],
       scalaVersion: String
   ): Configured[Rule] = {
-    val hasCompilerSupport = scalaVersion.startsWith("2")
-
-    val hasWarnUnused = hasCompilerSupport && {
-      val warnUnusedPrefix = Set("-Wunused", "-Ywarn-unused")
-      val warnUnusedString = Set("-Xlint", "-Xlint:unused")
-      scalacOptions exists { option =>
-        (warnUnusedPrefix exists option.startsWith) || (warnUnusedString contains option)
-      }
-    }
+    ScalaVersion.from(scalaVersion).map { v =>
+        v.isScala2 || (
+          v.isScala3 &&
+            v.minor.getOrElse(0) >= 3 &&
+            v.patch.getOrElse(0) >= 1
+        )
+    } match {
+      case Failure(exception) => Configured.error(exception.getMessage())
+      case Success(hasCompilerSupport) =>
+        val hasWarnUnused = hasCompilerSupport && {
+          val warnUnusedPrefix = Set("-Wunused", "-Ywarn-unused")
+          val warnUnusedString = Set("-Xlint", "-Xlint:unused")
+          scalacOptions exists { option =>
+            (warnUnusedPrefix exists option.startsWith) || (warnUnusedString contains option)
+          }
+        }
 
-    if (!conf.removeUnused || hasWarnUnused)
-      Configured.ok(new OrganizeImports(conf))
-    else if (hasCompilerSupport)
-      Configured.error(
-        "The Scala compiler option \"-Ywarn-unused\" is required to use OrganizeImports with"
-          + " \"OrganizeImports.removeUnused\" set to true. To fix this problem, update your"
-          + " build to use at least one Scala compiler option like -Ywarn-unused-import (2.11"
-          + " only), -Ywarn-unused, -Xlint:unused (2.12.2 or above) or -Wunused (2.13 only)."
-      )
-    else
-      Configured.error(
-        "\"OrganizeImports.removeUnused\" is not supported on Scala 3 as the compiler is"
-          + " not providing enough information. Run the rule with"
-          + " \"OrganizeImports.removeUnused\" set to false to organize imports while keeping"
-          + " potentially unused imports."
-      )
+        if (!conf.removeUnused || hasWarnUnused)
+          Configured.ok(new OrganizeImports(conf))
+        else if (hasCompilerSupport)
+          Configured.error(
+            "The Scala compiler option \"-Ywarn-unused\" is required to use OrganizeImports with"
+              + " \"OrganizeImports.removeUnused\" set to true. To fix this problem, update your"
+              + " build to use at least one Scala compiler option like -Ywarn-unused-import (2.11"
+              + " only), -Ywarn-unused, -Xlint:unused (2.12.2 or above) or -Wunused (2.13 only)."
+          )
+        else
+          Configured.error(
+            "\"OrganizeImports.removeUnused\"" + s"is not supported on $scalaVersion as the compiler is"
+              + " not providing enough information. Please upgrade Scala 3 version to 3.3.1 or greater."
+              + " Otherwise, run the rule with \"OrganizeImports.removeUnused\" set to false"
+              + " to organize imports while keeping potentially unused imports."
+          )
+        }
   }
 
   private def buildImportMatchers(