Support OrganizeImports.removeUnused in Scala 3.4+

docs/rules/OrganizeImports.md

@@ -52,15 +52,11 @@ do not rewrite import statements in ways that conflict with
 
 Known limitations:
 
-1.  The [`removeUnused`](OrganizeImports.md#removeunused) option must be
-    explicitly set to `false` - the rule currently doesn’t remove unused
-    imports as it is currently not supported by the compiler.
-
-2.  Usage of [deprecated package
+1.  Usage of [deprecated package
     objects](http://dotty.epfl.ch/docs/reference/dropped-features/package-objects.html)
     may result in incorrect imports.
 
-3.  The
+2.  The
     [`groupExplicitlyImportedImplicitsSeparately`](OrganizeImports.md#groupexplicitlyimportedimplicitsseparately)
     option has no effect.
 
@@ -1279,12 +1275,9 @@ Remove unused imports.
 > using Scala compilation diagnostics information, and the compilation phase
 > happens before Scalafix rules get applied.
 
-> The `removeUnused` option is currently not supported for source files
-> compiled with Scala 3, as the [compiler cannot issue warnings for unused
-> imports
-> yet](https://docs.scala-lang.org/scala3/guides/migration/options-lookup.html#warning-settings).
-> As a result, you must set `removeUnused` to `false` when running the
-> rule on source files compiled with Scala 3.
+> The `removeUnused` option is not supported for source files compiled with
+> early versions of Scala 3 as these do not export SemanticDB diagnostics for
+> unused imports. You must compile with Scala 3.4.0 or later to use it.
 
 ### Value type
 
@@ -1299,7 +1292,7 @@ Boolean
 ```conf
 OrganizeImports {
   groups = ["javax?\\.", "scala.", "*"]
-  removeUnused = true // not supported in Scala 3
+  removeUnused = true
 }
 ```
 

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

@@ -863,7 +863,9 @@ object OrganizeImports {
       scalacOptions: List[String],
       scalaVersion: String
   ): Configured[Rule] = {
-    val hasCompilerSupport = scalaVersion.startsWith("2")
+    val hasCompilerSupport =
+      Seq("3.0", "3.1", "3.2", "3.3")
+        .forall(v => !scalaVersion.startsWith(v))
 
     val hasWarnUnused = hasCompilerSupport && {
       val warnUnusedPrefix = Set("-Wunused", "-Ywarn-unused")
@@ -911,17 +913,17 @@ object OrganizeImports {
       )
     else if (hasCompilerSupport)
       Configured.error(
-        "The Scala compiler option \"-Ywarn-unused\" is required to use OrganizeImports with"
+        "A Scala compiler option 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)."
+          + " build to add `-Ywarn-unused` (2.12), `-Wunused:imports` (2.13), or"
+          + " `-Wunused:import` (3.4+)."
       )
     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."
+        "\"OrganizeImports.removeUnused\"" + s"is not supported on $scalaVersion as the compiler is"
+          + " not providing enough information. Please upgrade the Scala compiler to 3.4.0 or greater."
+          + " Otherwise, run the rule with \"OrganizeImports.removeUnused\" set to false"
+          + " to organize imports while keeping potentially unused imports."
       )
   }
 
@@ -1105,12 +1107,24 @@ object OrganizeImports {
   class UnusedImporteePositions(implicit doc: SemanticDocument) {
     private val positions: Seq[Position] =
       doc.diagnostics.toSeq.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
       }
 
     /** Returns true if the importee was marked as unused by the compiler */
-    def apply(importee: Importee): Boolean =
-      positions contains positionOf(importee)
+    def apply(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)
+      positions.exists { unused =>
+        unused.start <= pos.start && pos.end <= unused.end
+      }
+    }
   }
 
   implicit private class SymbolExtension(symbol: Symbol) {