Revert pattern matching improvements introducing regressions in 3.5.2

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

@@ -405,7 +405,7 @@ abstract class Message(val errorId: ErrorMessageID)(using Context) { self =>
     override def canExplain = true
 
   /** Override with `true` for messages that should always be shown even if their
-   *  position overlaps another message of a different class. On the other hand
+   *  position overlaps another messsage of a different class. On the other hand
    *  multiple messages of the same class with overlapping positions will lead
    *  to only a single message of that class to be issued.
    */

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -35,6 +35,13 @@ class PatternMatcher extends MiniPhase {
 
   override def runsAfter: Set[String] = Set(ElimRepeated.name)
 
+  private val InInlinedCode = new util.Property.Key[Boolean]
+  private def inInlinedCode(using Context) = ctx.property(InInlinedCode).getOrElse(false)
+
+  override def prepareForInlined(tree: Inlined)(using Context): Context =
+    if inInlinedCode then ctx
+    else ctx.fresh.setProperty(InInlinedCode, true)
+
   override def transformMatch(tree: Match)(using Context): Tree =
     if (tree.isInstanceOf[InlineMatch]) tree
     else {
@@ -46,10 +53,13 @@ class PatternMatcher extends MiniPhase {
         case rt => tree.tpe
       val translated = new Translator(matchType, this).translateMatch(tree)
 
-      // Skip analysis on inlined code (eg pos/i19157)
-      if !tpd.enclosingInlineds.nonEmpty then
+      if !inInlinedCode then
         // check exhaustivity and unreachability
         SpaceEngine.checkMatch(tree)
+      else
+        // only check exhaustivity, as inlining may generate unreachable code 
+        // like in i19157.scala
+        SpaceEngine.checkMatchExhaustivityOnly(tree)
 
       translated.ensureConforms(matchType)
     }

compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala

@@ -74,7 +74,7 @@ object TypeTestsCasts {
     }.apply(tp)
 
     /** Returns true if the type arguments of `P` can be determined from `X` */
-    def typeArgsDeterminable(X: Type, P: AppliedType)(using Context) = inContext(ctx.fresh.setExploreTyperState().setFreshGADTBounds) {
+    def typeArgsTrivial(X: Type, P: AppliedType)(using Context) = inContext(ctx.fresh.setExploreTyperState().setFreshGADTBounds) {
       val AppliedType(tycon, _) = P
 
       def underlyingLambda(tp: Type): TypeLambda = tp.ensureLambdaSub match {
@@ -161,7 +161,7 @@ object TypeTestsCasts {
               val tparams = x.typeParams
               if tparams.isEmpty then x else x.appliedTo(tparams.map(_ => WildcardType))
             TypeComparer.provablyDisjoint(xApplied, tpe.derivedAppliedType(tycon, targs.map(_ => WildcardType)))
-            || typeArgsDeterminable(X, tpe)
+            || typeArgsTrivial(X, tpe)
             ||| i"its type arguments can't be determined from $X"
         }
       case AndType(tp1, tp2)    => recur(X, tp1) && recur(X, tp2)

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -3,9 +3,7 @@ package dotc
 package transform
 package patmat
 
-import core.*
-import Constants.*, Contexts.*, Decorators.*, Flags.*, NullOpsDecorator.*, Symbols.*, Types.*
-import Names.*, NameOps.*, StdNames.*
+import core.*, Constants.*, Contexts.*, Decorators.*, Flags.*, Names.*, NameOps.*, StdNames.*, Symbols.*, Types.*
 import ast.*, tpd.*
 import config.Printers.*
 import printing.{ Printer, * }, Texts.*
@@ -352,7 +350,7 @@ object SpaceEngine {
       val funRef = fun1.tpe.asInstanceOf[TermRef]
       if (fun.symbol.name == nme.unapplySeq)
         val (arity, elemTp, resultTp) = unapplySeqInfo(fun.tpe.widen.finalResultType, fun.srcPos)
-        if fun.symbol.owner == defn.SeqFactoryClass && pat.tpe.hasClassSymbol(defn.ListClass) then
+        if (fun.symbol.owner == defn.SeqFactoryClass && defn.ListType.appliedTo(elemTp) <:< pat.tpe)
           // The exhaustivity and reachability logic already handles decomposing sum types (into its subclasses)
           // and product types (into its components).  To get better counter-examples for patterns that are of type
           // List (or a super-type of list, like LinearSeq) we project them into spaces that use `::` and Nil.
@@ -372,7 +370,7 @@ object SpaceEngine {
       project(pat)
 
     case Typed(_, tpt) =>
-      Typ(erase(tpt.tpe.stripAnnots, isValue = true, isTyped = true), decomposed = false)
+      Typ(erase(tpt.tpe.stripAnnots, isValue = true), decomposed = false)
 
     case This(_) =>
       Typ(pat.tpe.stripAnnots, decomposed = false)
@@ -457,13 +455,13 @@ object SpaceEngine {
         tp.derivedAppliedType(erase(tycon, inArray, isValue = false), args2)
 
       case tp @ OrType(tp1, tp2) =>
-        OrType(erase(tp1, inArray, isValue, isTyped), erase(tp2, inArray, isValue, isTyped), tp.isSoft)
+        OrType(erase(tp1, inArray, isValue), erase(tp2, inArray, isValue), tp.isSoft)
 
       case AndType(tp1, tp2) =>
-        AndType(erase(tp1, inArray, isValue, isTyped), erase(tp2, inArray, isValue, isTyped))
+        AndType(erase(tp1, inArray, isValue), erase(tp2, inArray, isValue))
 
       case tp @ RefinedType(parent, _, _) =>
-        erase(parent, inArray, isValue, isTyped)
+        erase(parent, inArray, isValue)
 
       case tref: TypeRef if tref.symbol.isPatternBound =>
         if inArray then erase(tref.underlying, inArray, isValue, isTyped)
@@ -524,26 +522,14 @@ object SpaceEngine {
     val mt: MethodType = unapp.widen match {
       case mt: MethodType => mt
       case pt: PolyType   =>
-          val locked = ctx.typerState.ownedVars
           val tvars = constrained(pt)
           val mt = pt.instantiate(tvars).asInstanceOf[MethodType]
           scrutineeTp <:< mt.paramInfos(0)
           // force type inference to infer a narrower type: could be singleton
           // see tests/patmat/i4227.scala
           mt.paramInfos(0) <:< scrutineeTp
-          maximizeType(mt.paramInfos(0), Spans.NoSpan)
-          if !(ctx.typerState.ownedVars -- locked).isEmpty then
-            // constraining can create type vars out of wildcard types
-            // (in legalBound, by using a LevelAvoidMap)
-            // maximise will only do one pass at maximising the type vars in the target type
-            // which means we can maximise to types that include other type vars
-            // this fails TreeChecker's "non-empty constraint at end of $fusedPhase" check
-            // e.g. run-macros/string-context-implicits
-            // I can't prove that a second call won't also create type vars,
-            // but I'd rather have an unassigned new-new type var, than an infinite loop.
-            // After all, there's nothing strictly "wrong" with unassigned type vars,
-            // it just fails TreeChecker's linting.
-            maximizeType(mt.paramInfos(0), Spans.NoSpan)
+          instantiateSelected(mt, tvars)
+          isFullyDefined(mt, ForceDegree.all)
           mt
     }
 
@@ -557,7 +543,7 @@ object SpaceEngine {
     // Case unapplySeq:
     // 1. return the type `List[T]` where `T` is the element type of the unapplySeq return type `Seq[T]`
 
-    val resTp = wildApprox(ctx.typeAssigner.safeSubstMethodParams(mt, scrutineeTp :: Nil).finalResultType)
+    val resTp = ctx.typeAssigner.safeSubstMethodParams(mt, scrutineeTp :: Nil).finalResultType
 
     val sig =
       if (resTp.isRef(defn.BooleanClass))
@@ -578,14 +564,20 @@ object SpaceEngine {
           if (arity > 0)
             productSelectorTypes(resTp, unappSym.srcPos)
           else {
-            val getTp = extractorMemberType(resTp, nme.get, unappSym.srcPos)
+            val getTp = resTp.select(nme.get).finalResultType match
+              case tp: TermRef if !tp.isOverloaded =>
+                // Like widenTermRefExpr, except not recursively.
+                // For example, in i17184 widen Option[foo.type]#get
+                // to Option[foo.type] instead of Option[Int].
+                tp.underlying.widenExpr
+              case tp => tp
             if (argLen == 1) getTp :: Nil
             else productSelectorTypes(getTp, unappSym.srcPos)
           }
         }
       }
 
-    sig.map { case tp: WildcardType => tp.bounds.hi case tp => tp }
+    sig.map(_.annotatedToRepeated)
   }
 
   /** Whether the extractor covers the given type */
@@ -624,36 +616,14 @@ object SpaceEngine {
       case tp if tp.classSymbol.isAllOf(JavaEnum)      => tp.classSymbol.children.map(_.termRef)
         // the class of a java enum value is the enum class, so this must follow SingletonType to not loop infinitely
 
-      case Childless(tp @ AppliedType(Parts(parts), targs)) =>
+      case tp @ AppliedType(Parts(parts), targs) if tp.classSymbol.children.isEmpty =>
         // It might not obvious that it's OK to apply the type arguments of a parent type to child types.
         // But this is guarded by `tp.classSymbol.children.isEmpty`,
         // meaning we'll decompose to the same class, just not the same type.
         // For instance, from i15029, `decompose((X | Y).Field[T]) = [X.Field[T], Y.Field[T]]`.
         parts.map(tp.derivedAppliedType(_, targs))
 
-      case tpOriginal if tpOriginal.isDecomposableToChildren =>
-        // isDecomposableToChildren uses .classSymbol.is(Sealed)
-        // But that classSymbol could be from an AppliedType
-        // where the type constructor is a non-class type
-        // E.g. t11620 where `?1.AA[X]` returns as "sealed"
-        // but using that we're not going to infer A1[X] and A2[X]
-        // but end up with A1[<?>] and A2[<?>].
-        // So we widen (like AppliedType superType does) away
-        // non-class type constructors.
-        //
-        // Can't use `tpOriginal.baseType(cls)` because it causes
-        // i15893 to return exhaustivity warnings, because instead of:
-        //    <== refineUsingParent(N, class Succ, []) = Succ[<? <: NatT>]
-        //    <== isSub(Succ[<? <: NatT>] <:< Succ[Succ[<?>]]) = true
-        // we get
-        //    <== refineUsingParent(NatT, class Succ, []) = Succ[NatT]
-        //    <== isSub(Succ[NatT] <:< Succ[Succ[<?>]]) = false
-        def getAppliedClass(tp: Type): Type = tp match
-          case tp @ AppliedType(_: HKTypeLambda, _)                        => tp
-          case tp @ AppliedType(tycon: TypeRef, _) if tycon.symbol.isClass => tp
-          case tp @ AppliedType(tycon: TypeProxy, _)                       => getAppliedClass(tycon.superType.applyIfParameterized(tp.args))
-          case tp                                                          => tp
-        val tp = getAppliedClass(tpOriginal)
+      case tp if tp.isDecomposableToChildren =>
         def getChildren(sym: Symbol): List[Symbol] =
           sym.children.flatMap { child =>
             if child eq sym then List(sym) // i3145: sealed trait Baz, val x = new Baz {}, Baz.children returns Baz...
@@ -706,12 +676,6 @@ object SpaceEngine {
   final class PartsExtractor(val get: List[Type]) extends AnyVal:
     def isEmpty: Boolean = get == ListOfNoType
 
-  object Childless:
-    def unapply(tp: Type)(using Context): Result =
-      Result(if tp.classSymbol.children.isEmpty then tp else NoType)
-    class Result(val get: Type) extends AnyVal:
-      def isEmpty: Boolean = !get.exists
-
   /** Show friendly type name with current scope in mind
    *
    *  E.g.    C.this.B     -->  B     if current owner is C
@@ -808,15 +772,12 @@ object SpaceEngine {
     doShow(s)
   }
 
-  extension (self: Type) private def stripUnsafeNulls()(using Context): Type =
-    if Nullables.unsafeNullsEnabled then self.stripNull() else self
-
-  private def exhaustivityCheckable(sel: Tree)(using Context): Boolean = trace(i"exhaustivityCheckable($sel ${sel.className})") {
+  private def exhaustivityCheckable(sel: Tree)(using Context): Boolean = {
     val seen = collection.mutable.Set.empty[Symbol]
 
     // Possible to check everything, but be compatible with scalac by default
-    def isCheckable(tp: Type): Boolean = trace(i"isCheckable($tp ${tp.className})"):
-      val tpw = tp.widen.dealias.stripUnsafeNulls()
+    def isCheckable(tp: Type): Boolean =
+      val tpw = tp.widen.dealias
       val classSym = tpw.classSymbol
       classSym.is(Sealed) && !tpw.isLargeGenericTuple || // exclude large generic tuples from exhaustivity
                                                          // requires an unknown number of changes to make work
@@ -851,7 +812,7 @@ object SpaceEngine {
   /** Return the underlying type of non-module, non-constant, non-enum case singleton types.
    *  Also widen ExprType to its result type, and rewrap any annotation wrappers.
    *  For example, with `val opt = None`, widen `opt.type` to `None.type`. */
-  def toUnderlying(tp: Type)(using Context): Type = trace(i"toUnderlying($tp ${tp.className})")(tp match {
+  def toUnderlying(tp: Type)(using Context): Type = trace(i"toUnderlying($tp)")(tp match {
     case _: ConstantType                            => tp
     case tp: TermRef if tp.symbol.is(Module)        => tp
     case tp: TermRef if tp.symbol.isAllOf(EnumCase) => tp
@@ -862,7 +823,7 @@ object SpaceEngine {
   })
 
   def checkExhaustivity(m: Match)(using Context): Unit = trace(i"checkExhaustivity($m)") {
-    val selTyp = toUnderlying(m.selector.tpe.stripUnsafeNulls()).dealias
+    val selTyp = toUnderlying(m.selector.tpe).dealias
     val targetSpace = trace(i"targetSpace($selTyp)")(project(selTyp))
 
     val patternSpace = Or(m.cases.foldLeft(List.empty[Space]) { (acc, x) =>
@@ -940,6 +901,9 @@ object SpaceEngine {
   }
 
   def checkMatch(m: Match)(using Context): Unit =
-    if exhaustivityCheckable(m.selector) then checkExhaustivity(m)
+    checkMatchExhaustivityOnly(m)
     if reachabilityCheckable(m.selector) then checkReachability(m)
+
+  def checkMatchExhaustivityOnly(m: Match)(using Context): Unit =
+    if exhaustivityCheckable(m.selector) then checkExhaustivity(m)
 }

tests/pending/neg/i16451.check

@@ -0,0 +1,24 @@
+-- Error: tests/neg/i16451.scala:13:9 ----------------------------------------------------------------------------------
+13 |    case x: Wrapper[Color.Red.type] => Some(x) // error
+   |         ^
+   |the type test for Wrapper[(Color.Red : Color)] cannot be checked at runtime because its type arguments can't be determined from Wrapper[Color]
+-- Error: tests/neg/i16451.scala:21:9 ----------------------------------------------------------------------------------
+21 |    case x: Wrapper[Color.Red.type] => Some(x) // error
+   |         ^
+   |the type test for Wrapper[(Color.Red : Color)] cannot be checked at runtime because its type arguments can't be determined from Any
+-- Error: tests/neg/i16451.scala:25:9 ----------------------------------------------------------------------------------
+25 |    case x: Wrapper[Color.Red.type] => Some(x) // error
+   |         ^
+   |the type test for Wrapper[(Color.Red : Color)] cannot be checked at runtime because its type arguments can't be determined from Wrapper[Color]
+-- Error: tests/neg/i16451.scala:29:9 ----------------------------------------------------------------------------------
+29 |    case x: Wrapper[Color.Red.type] => Some(x) // error
+   |         ^
+   |the type test for Wrapper[(Color.Red : Color)] cannot be checked at runtime because its type arguments can't be determined from A1
+-- Error: tests/neg/i16451.scala:34:11 ---------------------------------------------------------------------------------
+34 |      case x: Wrapper[Color.Red.type] => x // error
+   |           ^
+   |the type test for Wrapper[(Color.Red : Color)] cannot be checked at runtime because its type arguments can't be determined from Wrapper[Color]
+-- Error: tests/neg/i16451.scala:39:11 ---------------------------------------------------------------------------------
+39 |      case x: Wrapper[Color.Red.type] => x // error
+   |           ^
+   |the type test for Wrapper[(Color.Red : Color)] cannot be checked at runtime because its type arguments can't be determined from Wrapper[Color]

tests/warn/i16451.scala → tests/pending/neg/i16451.scala

@@ -1,42 +1,38 @@
-//
+//> using options -Werror
 enum Color:
   case Red, Green
-//sealed trait Color
-//object Color:
-//  case object Red   extends Color
-//  case object Green extends Color
 
 case class Wrapper[A](value: A)
 
 object Test:
   def test_correct(x: Wrapper[Color]): Option[Wrapper[Color.Red.type]] = x match
-    case x: Wrapper[Color.Red.type]   => Some(x)                      // warn: unchecked
-    case x: Wrapper[Color.Green.type] => None    // warn: unreachable // also: unchecked (hidden)
+    case x: Wrapper[Color.Red.type] => Some(x) // error
+    case null                       => None
 
   def test_different(x: Wrapper[Color]): Option[Wrapper[Color]] = x match
     case x @ Wrapper(_: Color.Red.type)   => Some(x)
     case x @ Wrapper(_: Color.Green.type) => None
 
   def test_any(x: Any): Option[Wrapper[Color.Red.type]] = x match
-    case x: Wrapper[Color.Red.type]   => Some(x)                      // warn: unchecked
-    case x: Wrapper[Color.Green.type] => None    // warn: unreachable // also: unchecked (hidden)
+    case x: Wrapper[Color.Red.type] => Some(x) // error
+    case _                          => None
 
   def test_wrong(x: Wrapper[Color]): Option[Wrapper[Color.Red.type]] = x match
-    case x: Wrapper[Color.Red.type] => Some(x) // warn: unchecked
+    case x: Wrapper[Color.Red.type] => Some(x) // error
     case null                       => None
 
   def t2[A1 <: Wrapper[Color]](x: A1): Option[Wrapper[Color.Red.type]] = x match
-    case x: Wrapper[Color.Red.type] => Some(x) // warn: unchecked
+    case x: Wrapper[Color.Red.type] => Some(x) // error
     case null                       => None
 
   def test_wrong_seq(xs: Seq[Wrapper[Color]]): Seq[Wrapper[Color.Red.type]] =
     xs.collect {
-      case x: Wrapper[Color.Red.type] => x // warn: unchecked
+      case x: Wrapper[Color.Red.type] => x // error
     }
 
   def test_wrong_seq2(xs: Seq[Wrapper[Color]]): Seq[Wrapper[Color.Red.type]] =
     xs.collect { x => x match
-      case x: Wrapper[Color.Red.type] => x // warn: unchecked
+      case x: Wrapper[Color.Red.type] => x // error
     }
 
   def main(args: Array[String]): Unit =

tests/warn/i11178.scala

@@ -12,6 +12,7 @@ object Test1 {
   def test[A](bar: Bar[A]) =
     bar match {
       case _: Bar[Boolean] => ??? // warn
+      case _ => ???
     }
 }
 
@@ -22,6 +23,7 @@ object Test2 {
   def test[A](bar: Bar[A]) =
     bar match {
       case _: Bar[Boolean] => ??? // warn
+      case _ => ???
     }
 }
 
@@ -32,5 +34,6 @@ object Test3 {
   def test[A](bar: Bar[A]) =
     bar match {
       case _: Bar[Boolean] => ??? // warn
+      case _ => ???
     }
 }