Respect prefix when checking if selector selects

Use miniphase api instead of traversing.

Share a megaphase with CheckShadowing.

Perform more expensive checks last. Avoid intermediate collections.

Tighten allowance for serialization methods.

Don't ignore params of public methods.

Show misplaced warn comment, unfulfilled expectations.

Warn for unused patvars.
Don't warn about canonical names (case class element names).
Warn unassigned mutable patvars

No transparent inline exclusion. Handle match types.
No warn inline proxy. Detect summon inline.

Unused import diagnostics have an origin.

Original of literal.

Typos in build. Handle aliased boolean settings.

Resolve imports post inlining.

Excuse only empty interfaces as unused bound.

Use result of TypeTest.

Author: som-snytt

compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala

@@ -818,7 +818,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
 
       methSymbol  = dd.symbol
       jMethodName = methSymbol.javaSimpleName
-      returnType  = asmMethodType(dd.symbol).returnType
+      returnType  = asmMethodType(methSymbol).returnType
       isMethSymStaticCtor = methSymbol.isStaticConstructor
 
       resetMethodBookkeeping(dd)
@@ -915,7 +915,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
             for (p <- params) { emitLocalVarScope(p.symbol, veryFirstProgramPoint, onePastLastProgramPoint, force = true) }
           }
 
-          if (isMethSymStaticCtor) { appendToStaticCtor(dd) }
+          if (isMethSymStaticCtor) { appendToStaticCtor() }
         } // end of emitNormalMethodBody()
 
         lineNumber(rhs)
@@ -936,7 +936,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
      *
      *  TODO document, explain interplay with `fabricateStaticInitAndroid()`
      */
-    private def appendToStaticCtor(dd: DefDef): Unit = {
+    private def appendToStaticCtor(): Unit = {
 
       def insertBefore(
             location: asm.tree.AbstractInsnNode,

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -7,7 +7,6 @@ import typer.{TyperPhase, RefChecks}
 import parsing.Parser
 import Phases.Phase
 import transform.*
-import dotty.tools.backend
 import backend.jvm.{CollectSuperCalls, GenBCode}
 import localopt.StringInterpolatorOpt
 
@@ -34,8 +33,7 @@ class Compiler {
   protected def frontendPhases: List[List[Phase]] =
     List(new Parser) ::             // Compiler frontend: scanner, parser
     List(new TyperPhase) ::         // Compiler frontend: namer, typer
-    List(new CheckUnused.PostTyper) :: // Check for unused elements
-    List(new CheckShadowing) :: // Check shadowing elements
+    List(CheckUnused.PostTyper(), CheckShadowing()) :: // Check for unused, shadowed elements
     List(new YCheckPositions) ::    // YCheck positions
     List(new sbt.ExtractDependencies) :: // Sends information on classes' dependencies to sbt via callbacks
     List(new semanticdb.ExtractSemanticDB.ExtractSemanticInfo) :: // Extract info into .semanticdb files
@@ -51,10 +49,10 @@ class Compiler {
     List(new sbt.ExtractAPI) ::     // Sends a representation of the API of classes to sbt via callbacks
     List(new Inlining) ::           // Inline and execute macros
     List(new PostInlining) ::       // Add mirror support for inlined code
-    List(new CheckUnused.PostInlining) ::  // Check for unused elements
     List(new Staging) ::            // Check staging levels and heal staged types
     List(new Splicing) ::           // Replace level 1 splices with holes
     List(new PickleQuotes) ::       // Turn quoted trees into explicit run-time data structures
+    List(new CheckUnused.PostInlining) ::  // Check for unused elements
     Nil
 
   /** Phases dealing with the transformation from pickled trees to backend trees */

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -47,6 +47,14 @@ object desugar {
    */
   val UntupledParam: Property.Key[Unit] = Property.StickyKey()
 
+  /** An attachment key to indicate that a ValDef originated from a pattern.
+   */
+  val PatternVar: Property.Key[Unit] = Property.StickyKey()
+
+  /** An attachment key for Trees originating in for-comprehension, such as tupling of assignments.
+   */
+  val ForArtifact: Property.Key[Unit] = Property.StickyKey()
+
   /** An attachment key to indicate that a ValDef is an evidence parameter
    *  for a context bound.
    */
@@ -1507,7 +1515,7 @@ object desugar {
       val matchExpr =
         if (tupleOptimizable) rhs
         else
-          val caseDef = CaseDef(pat, EmptyTree, makeTuple(ids))
+          val caseDef = CaseDef(pat, EmptyTree, makeTuple(ids).withAttachment(ForArtifact, ()))
           Match(makeSelector(rhs, MatchCheck.IrrefutablePatDef), caseDef :: Nil)
       vars match {
         case Nil if !mods.is(Lazy) =>
@@ -1537,6 +1545,7 @@ object desugar {
                   ValDef(named.name.asTermName, tpt, selector(n))
                     .withMods(mods)
                     .withSpan(named.span)
+                    .withAttachment(PatternVar, ())
                 )
           flatTree(firstDef :: restDefs)
       }
@@ -1922,6 +1931,7 @@ object desugar {
     val vdef = ValDef(named.name.asTermName, tpt, rhs)
       .withMods(mods)
       .withSpan(original.span.withPoint(named.span.start))
+      .withAttachment(PatternVar, ())
     val mayNeedSetter = valDef(vdef)
     mayNeedSetter
   }
@@ -2167,7 +2177,7 @@ object desugar {
               case _ => Modifiers()
             makePatDef(valeq, mods, defpat, rhs)
           }
-          val rhs1 = makeFor(nme.map, nme.flatMap, GenFrom(defpat0, gen.expr, gen.checkMode) :: Nil, Block(pdefs, makeTuple(id0 :: ids)))
+          val rhs1 = makeFor(nme.map, nme.flatMap, GenFrom(defpat0, gen.expr, gen.checkMode) :: Nil, Block(pdefs, makeTuple(id0 :: ids).withAttachment(ForArtifact, ())))
           val allpats = gen.pat :: pats
           val vfrom1 = GenFrom(makeTuple(allpats), rhs1, GenCheckMode.Ignore)
           makeFor(mapName, flatMapName, vfrom1 :: rest1, body)

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -173,28 +173,20 @@ private sealed trait WarningSettings:
     choices = List(
       ChoiceWithHelp("nowarn", ""),
       ChoiceWithHelp("all", ""),
-      ChoiceWithHelp(
-        name = "imports",
-        description = "Warn if an import selector is not referenced.\n" +
-        "NOTE : overrided by -Wunused:strict-no-implicit-warn"),
+      ChoiceWithHelp("imports", "Warn if an import selector is not referenced."),
       ChoiceWithHelp("privates", "Warn if a private member is unused"),
       ChoiceWithHelp("locals", "Warn if a local definition is unused"),
       ChoiceWithHelp("explicits", "Warn if an explicit parameter is unused"),
       ChoiceWithHelp("implicits", "Warn if an implicit parameter is unused"),
       ChoiceWithHelp("params", "Enable -Wunused:explicits,implicits"),
+      ChoiceWithHelp("patvars","Warn if a variable bound in a pattern is unused"),
+      //ChoiceWithHelp("inlined", "Apply -Wunused to inlined expansions"), // TODO
       ChoiceWithHelp("linted", "Enable -Wunused:imports,privates,locals,implicits"),
       ChoiceWithHelp(
         name = "strict-no-implicit-warn",
         description = "Same as -Wunused:import, only for imports of explicit named members.\n" +
         "NOTE : This overrides -Wunused:imports and NOT set by -Wunused:all"
       ),
-      // ChoiceWithHelp("patvars","Warn if a variable bound in a pattern is unused"),
-      ChoiceWithHelp(
-        name = "unsafe-warn-patvars",
-        description = "(UNSAFE) Warn if a variable bound in a pattern is unused.\n" +
-        "This warning can generate false positive, as warning cannot be\n" +
-        "suppressed yet."
-      )
     ),
     default = Nil
   )
@@ -206,7 +198,6 @@ private sealed trait WarningSettings:
     // Is any choice set for -Wunused?
     def any(using Context): Boolean = Wall.value || Wunused.value.nonEmpty
 
-    // overrided by strict-no-implicit-warn
     def imports(using Context) =
       (allOr("imports") || allOr("linted")) && !(strictNoImplicitWarn)
     def locals(using Context) =
@@ -220,9 +211,8 @@ private sealed trait WarningSettings:
     def params(using Context) = allOr("params")
     def privates(using Context) =
       allOr("privates") || allOr("linted")
-    def patvars(using Context) =
-      isChoiceSet("unsafe-warn-patvars") // not with "all"
-      // allOr("patvars") // todo : rename once fixed
+    def patvars(using Context) = allOr("patvars")
+    def inlined(using Context) = isChoiceSet("inlined")
     def linted(using Context) =
       allOr("linted")
     def strictNoImplicitWarn(using Context) =

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

@@ -494,6 +494,8 @@ class Definitions {
     @tu lazy val Predef_undefined: Symbol = ScalaPredefModule.requiredMethod(nme.???)
   @tu lazy val ScalaPredefModuleClass: ClassSymbol = ScalaPredefModule.moduleClass.asClass
 
+  @tu lazy val SameTypeClass: ClassSymbol = requiredClass("scala.=:=")
+  @tu lazy val SameType_refl: Symbol = SameTypeClass.companionModule.requiredMethod(nme.refl)
   @tu lazy val SubTypeClass: ClassSymbol = requiredClass("scala.<:<")
   @tu lazy val SubType_refl: Symbol = SubTypeClass.companionModule.requiredMethod(nme.refl)
 
@@ -834,6 +836,7 @@ class Definitions {
   @tu lazy val QuotedExprClass: ClassSymbol = requiredClass("scala.quoted.Expr")
 
   @tu lazy val QuotesClass: ClassSymbol = requiredClass("scala.quoted.Quotes")
+    @tu lazy val Quotes_reflectModule: Symbol = QuotesClass.requiredClass("reflectModule")
     @tu lazy val Quotes_reflect: Symbol = QuotesClass.requiredValue("reflect")
       @tu lazy val Quotes_reflect_asTerm: Symbol = Quotes_reflect.requiredMethod("asTerm")
       @tu lazy val Quotes_reflect_Apply: Symbol = Quotes_reflect.requiredValue("Apply")
@@ -955,6 +958,7 @@ class Definitions {
   def NonEmptyTupleClass(using Context): ClassSymbol = NonEmptyTupleTypeRef.symbol.asClass
     lazy val NonEmptyTuple_tail: Symbol = NonEmptyTupleClass.requiredMethod("tail")
   @tu lazy val PairClass: ClassSymbol = requiredClass("scala.*:")
+    @tu lazy val PairClass_unapply: Symbol = PairClass.companionModule.requiredMethod("unapply")
 
   @tu lazy val TupleXXLClass: ClassSymbol = requiredClass("scala.runtime.TupleXXL")
   def TupleXXLModule(using Context): Symbol = TupleXXLClass.companionModule
@@ -1062,6 +1066,7 @@ class Definitions {
   @tu lazy val UntrackedCapturesAnnot: ClassSymbol = requiredClass("scala.caps.untrackedCaptures")
   @tu lazy val UseAnnot:  ClassSymbol = requiredClass("scala.caps.use")
   @tu lazy val VolatileAnnot: ClassSymbol = requiredClass("scala.volatile")
+  @tu lazy val LanguageFeatureMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.languageFeature")
   @tu lazy val BeanGetterMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.beanGetter")
   @tu lazy val BeanSetterMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.beanSetter")
   @tu lazy val FieldMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.field")

compiler/src/dotty/tools/dotc/report.scala

@@ -1,15 +1,12 @@
 package dotty.tools.dotc
 
-import reporting.*
-import Diagnostic.*
-import util.{SourcePosition, NoSourcePosition, SrcPos}
-import core.*
-import Contexts.*, Flags.*, Symbols.*, Decorators.*
-import config.SourceVersion
 import ast.*
-import config.Feature.sourceVersion
+import core.*, Contexts.*, Flags.*, Symbols.*, Decorators.*
+import config.Feature.sourceVersion, config.{MigrationVersion, SourceVersion}
+import reporting.*, Diagnostic.*
+import util.{SourcePosition, NoSourcePosition, SrcPos}
+
 import java.lang.System.currentTimeMillis
-import dotty.tools.dotc.config.MigrationVersion
 
 object report:
 
@@ -55,6 +52,9 @@ object report:
     else issueWarning(new FeatureWarning(msg, pos.sourcePos))
   end featureWarning
 
+  def warning(msg: Message, pos: SrcPos, origin: String)(using Context): Unit =
+    issueWarning(LintWarning(msg, addInlineds(pos), origin))
+
   def warning(msg: Message, pos: SrcPos)(using Context): Unit =
     issueWarning(new Warning(msg, addInlineds(pos)))
 

compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala

@@ -36,6 +36,18 @@ object Diagnostic:
     pos: SourcePosition
   ) extends Error(msg, pos)
 
+  /** A Warning with an origin. The semantics of `origin` depend on the warning.
+   *  For example, an unused import warning has an origin that specifies the unused selector.
+   *  The origin of a deprecation is the deprecated element.
+   */
+  trait OriginWarning(val origin: String):
+    self: Warning =>
+
+  /** Lints are likely to be filtered. Provide extra axes for filtering by `-Wconf`.
+   */
+  class LintWarning(msg: Message, pos: SourcePosition, origin: String)
+  extends Warning(msg, pos), OriginWarning(origin)
+
   class Warning(
     msg: Message,
     pos: SourcePosition
@@ -73,13 +85,9 @@ object Diagnostic:
     def enablingOption(using Context): Setting[Boolean] = ctx.settings.unchecked
   }
 
-  class DeprecationWarning(
-    msg: Message,
-    pos: SourcePosition,
-    val origin: String
-  ) extends ConditionalWarning(msg, pos) {
+  class DeprecationWarning(msg: Message, pos: SourcePosition, origin: String)
+  extends ConditionalWarning(msg, pos), OriginWarning(origin):
     def enablingOption(using Context): Setting[Boolean] = ctx.settings.deprecation
-  }
 
   class MigrationWarning(
     msg: Message,
@@ -104,5 +112,5 @@ class Diagnostic(
   override def diagnosticRelatedInformation: JList[interfaces.DiagnosticRelatedInformation] =
     Collections.emptyList()
 
-  override def toString: String = s"$getClass at $pos: $message"
+  override def toString: String = s"$getClass at $pos L${pos.line+1}: $message"
 end Diagnostic

compiler/src/dotty/tools/dotc/reporting/WConf.scala

@@ -14,11 +14,13 @@ import scala.annotation.internal.sharable
 import scala.util.matching.Regex
 
 enum MessageFilter:
-  def matches(message: Diagnostic): Boolean = this match
+  def matches(message: Diagnostic): Boolean =
+    import Diagnostic.*
+    this match
     case Any => true
-    case Deprecated => message.isInstanceOf[Diagnostic.DeprecationWarning]
-    case Feature => message.isInstanceOf[Diagnostic.FeatureWarning]
-    case Unchecked => message.isInstanceOf[Diagnostic.UncheckedWarning]
+    case Deprecated => message.isInstanceOf[DeprecationWarning]
+    case Feature => message.isInstanceOf[FeatureWarning]
+    case Unchecked => message.isInstanceOf[UncheckedWarning]
     case MessageID(errorId) => message.msg.errorId == errorId
     case MessagePattern(pattern) =>
       val noHighlight = message.msg.message.replaceAll("\\e\\[[\\d;]*[^\\d;]","")
@@ -31,7 +33,7 @@ enum MessageFilter:
       pattern.findFirstIn(path).nonEmpty
     case Origin(pattern) =>
       message match
-      case message: Diagnostic.DeprecationWarning => pattern.findFirstIn(message.origin).nonEmpty
+      case message: OriginWarning => pattern.findFirstIn(message.origin).nonEmpty
       case _ => false
     case None => false
 
@@ -56,12 +58,12 @@ object WConf:
   private type Conf = (List[MessageFilter], Action)
 
   def parseAction(s: String): Either[List[String], Action] = s match
-    case "error" | "e"            => Right(Error)
-    case "warning" | "w"          => Right(Warning)
-    case "verbose" | "v"          => Right(Verbose)
-    case "info" | "i"             => Right(Info)
-    case "silent" | "s"           => Right(Silent)
-    case _                        => Left(List(s"unknown action: `$s`"))
+    case "error"   | "e" => Right(Error)
+    case "warning" | "w" => Right(Warning)
+    case "verbose" | "v" => Right(Verbose)
+    case "info"    | "i" => Right(Info)
+    case "silent"  | "s" => Right(Silent)
+    case _               => Left(List(s"unknown action: `$s`"))
 
   private def regex(s: String) =
     try Right(s.r)

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -3290,22 +3290,24 @@ extends TypeMsg(ConstructorProxyNotValueID):
        |companion value with the (term-)name `A`. However, these context bound companions
        |are not values themselves, they can only be referred to in selections."""
 
-class UnusedSymbol(errorText: String)(using Context)
+class UnusedSymbol(errorText: String, val actions: List[CodeAction] = Nil)(using Context)
 extends Message(UnusedSymbolID) {
   def kind = MessageKind.UnusedSymbol
 
   override def msg(using Context) = errorText
   override def explain(using Context) = ""
-}
-
-object UnusedSymbol {
-    def imports(using Context): UnusedSymbol = new UnusedSymbol(i"unused import")
-    def localDefs(using Context): UnusedSymbol = new UnusedSymbol(i"unused local definition")
-    def explicitParams(using Context): UnusedSymbol = new UnusedSymbol(i"unused explicit parameter")
-    def implicitParams(using Context): UnusedSymbol = new UnusedSymbol(i"unused implicit parameter")
-    def privateMembers(using Context): UnusedSymbol = new UnusedSymbol(i"unused private member")
-    def patVars(using Context): UnusedSymbol = new UnusedSymbol(i"unused pattern variable")
-}
+  override def actions(using Context) = this.actions
+}
+
+object UnusedSymbol:
+  def imports(actions: List[CodeAction])(using Context): UnusedSymbol = UnusedSymbol(i"unused import", actions)
+  def localDefs(using Context): UnusedSymbol = UnusedSymbol(i"unused local definition")
+  def explicitParams(using Context): UnusedSymbol = UnusedSymbol(i"unused explicit parameter")
+  def implicitParams(using Context): UnusedSymbol = UnusedSymbol(i"unused implicit parameter")
+  def privateMembers(using Context): UnusedSymbol = UnusedSymbol(i"unused private member")
+  def patVars(using Context): UnusedSymbol = UnusedSymbol(i"unused pattern variable")
+  def unsetLocals(using Context): UnusedSymbol = UnusedSymbol(i"unset local variable, consider using an immutable val instead")
+  def unsetPrivates(using Context): UnusedSymbol = UnusedSymbol(i"unset private variable, consider using an immutable val instead")
 
 class NonNamedArgumentInJavaAnnotation(using Context) extends SyntaxMsg(NonNamedArgumentInJavaAnnotationID):