Support rewrite

Author: som-snytt

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -24,6 +24,7 @@ import reporting._
 import io.{AbstractFile, NoAbstractFile, PlainFile, Path}
 import scala.io.Codec
 import collection.mutable
+import parsing.Parsers
 import printing._
 import config.{JavaPlatform, SJSPlatform, Platform, ScalaSettings, ScalaRelease}
 import classfile.ReusableDataReader
@@ -1025,6 +1026,7 @@ object Contexts:
   /** Collect information about the run for purposes of additional diagnostics.
    */
   class Usages:
+    import rewrites.Rewrites.patch
     private val selectors   = mutable.Map.empty[ImportInfo, Set[untpd.ImportSelector]].withDefaultValue(Set.empty)
     private val importInfos = mutable.Map.empty[CompilationUnit, List[(ImportInfo, Symbol)]].withDefaultValue(Nil)
 
@@ -1048,19 +1050,56 @@ object Contexts:
         end if
         def checkUsed(info: ImportInfo, owner: Symbol): Unit =
           val used = selectors(info)
+          var needsPatch = false
           def cull(toCheck: List[untpd.ImportSelector]): Unit =
             toCheck match
               case selector :: rest =>
                 cull(rest) // reverse
                 if !selector.isMask && !used(selector) then
                   unusages ::= ((info, owner, selector))
+                  needsPatch = true
               case _ =>
           cull(info.selectors)
+          val decidingFactor = false // whether to apply patches
+          if decidingFactor && needsPatch && !ctx.settings.rewrite.value.isEmpty then
+            val retained = info.selectors.filter(sel => sel.isMask || used(sel))
+            val infoPos = info.qualifier.sourcePos
+            val lineText = infoPos.lineContent
+            val src = ctx.compilationUnit.source
+            val lineSpan = src.lineSpan(infoPos.start)
+            val selectorSpan = info.selectors.map(_.span).reduce(_ union _)
+            val lineSource = SourceFile.virtual(name = "import-line.scala", content = lineText)
+            val parser = Parsers.Parser(lineSource)
+            val lineTree = parser.parse()
+            val PackageDef(_, pieces) = lineTree: @unchecked
+            // patch if there's just one import on the line, i.e., not import a.b, c.d
+            if pieces.length == 1 then
+              if retained.isEmpty then
+                patch(src, lineSpan, "")  // line deletion
+              else if retained.size == 1 && info.selectors.size > 1 then
+                var starting = info.selectors.head.span.start
+                while starting > lineSpan.start && src.content()(starting) != '{' do starting -= 1
+                var ending = info.selectors.last.span.end
+                while ending <= lineSpan.end && src.content()(ending) != '}' do ending += 1
+                if ending < lineSpan.end then ending += 1  // past the close brace
+                val widened = selectorSpan.withStart(starting).withEnd(ending)
+                patch(src, widened, toText(retained))  // try to remove braces
+              else
+                patch(src, selectorSpan, toText(retained))
         end checkUsed
         importInfos.remove(ctx.compilationUnit).foreach(_.foreach(checkUsed))
       unusages
     end unused
 
+    // just the selectors, no need to add braces
+    private def toText(retained: List[untpd.ImportSelector])(using Context): String =
+      def selected(sel: untpd.ImportSelector) =
+        if sel.isGiven then "given"
+        else if sel.isWildcard then "*"
+        else if sel.name == sel.rename then sel.name.show
+        else s"${sel.name.show} as ${sel.rename.show}"
+      retained.map(selected).mkString(", ")
+
     def clear()(using Context): Unit =
       importInfos.clear()
       selectors.clear()

compiler/src/dotty/tools/dotc/util/SourceFile.scala

@@ -9,13 +9,10 @@ import core.Contexts._
 import scala.io.Codec
 import Chars._
 import scala.annotation.internal.sharable
-import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
 
-import java.io.IOException
 import java.nio.charset.StandardCharsets
 import java.util.Optional
-import java.util.concurrent.atomic.AtomicInteger
 import java.util.regex.Pattern
 
 object ScriptSourceFile {
@@ -56,7 +53,6 @@ object ScriptSourceFile {
 }
 
 class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends interfaces.SourceFile {
-  import SourceFile._
 
   private var myContent: Array[Char] = null
 
@@ -194,6 +190,10 @@ class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends
   def lineContent(offset: Int): String =
     content.slice(startOfLine(offset), nextLine(offset)).mkString
 
+  /** The span of the line containing position `offset` */
+  def lineSpan(offset: Int): Span =
+    Spans.Span(startOfLine(offset), nextLine(offset))
+
   /** The column corresponding to `offset`, starting at 0 */
   def column(offset: Int): Int = {
     var idx = startOfLine(offset)

compiler/src/dotty/tools/dotc/util/Spans.scala

@@ -1,6 +1,5 @@
 package dotty.tools.dotc
 package util
-import language.implicitConversions
 
 /** The offsets part of a full position, consisting of 2 or 3 entries:
  *    - start:  the start offset of the span, in characters from start of file
@@ -143,6 +142,10 @@ object Spans {
     def ==(that: Span): Boolean = this.coords == that.coords
     def !=(that: Span): Boolean = this.coords != that.coords
   }
+  object Span:
+    extension (span: Span)
+      def spread: Int = span.end - span.start
+  end Span
 
   private def fromOffsets(start: Int, end: Int, pointDelta: Int) =
     //assert(start <= end || start == 1 && end == 0, s"$start..$end")

project/Build.scala

@@ -750,9 +750,10 @@ object Build {
         "-Ddotty.tests.classes.dottyTastyInspector=" + jars("scala3-tasty-inspector"),
       )
     },
-    scalacOptions ++= Seq(
-      //"-Wunused:imports",
-    ),
+    //scalacOptions ++= Seq(
+    //  "-Wunused:imports",
+    //  "-rewrite",
+    //),
     packageAll := {
       (`scala3-compiler` / packageAll).value ++ Seq(
         "scala3-compiler" -> (Compile / packageBin).value.getAbsolutePath,