Backport "Remove unnecessary and recursive Space decomposition" to LTS (#20804)

Backports #19216 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

Diff for: compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -2758,10 +2758,12 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
       case (tp1: TypeRef, tp2: TypeRef) if tp1.symbol.isClass && tp2.symbol.isClass =>
         val cls1 = tp1.classSymbol
         val cls2 = tp2.classSymbol
-        def isDecomposable(tp: Symbol): Boolean =
-           tp.is(Sealed) && !tp.hasAnonymousChild
+        val sameKind = tp1.hasSameKindAs(tp2)
+        def isDecomposable(sym: Symbol): Boolean =
+          sameKind && sym.is(Sealed) && !sym.hasAnonymousChild
         def decompose(sym: Symbol, tp: Type): List[Type] =
-          sym.children.map(x => refineUsingParent(tp, x)).filter(_.exists)
+          val tpSimple = tp.applyIfParameterized(tp.typeParams.map(_ => WildcardType))
+          sym.children.map(x => refineUsingParent(tpSimple, x)).filter(_.exists)
         if (cls1.derivesFrom(cls2) || cls2.derivesFrom(cls1))
           false
         else

Diff for: compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -838,33 +838,34 @@ object TypeOps:
       }
     }
 
-    /** Gather GADT symbols and `ThisType`s found in `tp2`, ie. the scrutinee. */
+    /** Gather GADT symbols and singletons found in `tp2`, ie. the scrutinee. */
     object TraverseTp2 extends TypeTraverser:
-      val thisTypes = util.HashSet[ThisType]()
-      val gadtSyms  = new mutable.ListBuffer[Symbol]
+      val singletons = util.HashMap[Symbol, SingletonType]()
+      val gadtSyms = new mutable.ListBuffer[Symbol]
 
-      def traverse(tp: Type) = {
+      def traverse(tp: Type) = try
         val tpd = tp.dealias
         if tpd ne tp then traverse(tpd)
         else tp match
-          case tp: ThisType if !tp.tref.symbol.isStaticOwner && !thisTypes.contains(tp) =>
-            thisTypes += tp
+          case tp: ThisType if !singletons.contains(tp.tref.symbol) && !tp.tref.symbol.isStaticOwner =>
+            singletons(tp.tref.symbol) = tp
             traverseChildren(tp.tref)
-          case tp: TypeRef if tp.symbol.isAbstractOrParamType =>
+          case tp: TermRef if tp.symbol.is(Param) =>
+            singletons(tp.typeSymbol) = tp
+            traverseChildren(tp)
+          case tp: TypeRef if !gadtSyms.contains(tp.symbol) && tp.symbol.isAbstractOrParamType =>
             gadtSyms += tp.symbol
             traverseChildren(tp)
-            val owners = Iterator.iterate(tp.symbol)(_.maybeOwner).takeWhile(_.exists)
-            for sym <- owners do
-              // add ThisType's for the classes symbols in the ownership of `tp`
-              // for example, i16451.CanForward.scala, add `Namer.this`, as one of the owners of the type parameter `A1`
-              if sym.isClass && !sym.isAnonymousClass && !sym.isStaticOwner then
-                traverse(sym.thisType)
+            // traverse abstract type infos, to add any singletons
+            // for example, i16451.CanForward.scala, add `Namer.this`, from the info of the type parameter `A1`
+            // also, i19031.ci-reg2.scala, add `out`, from the info of the type parameter `A1` (from synthetic applyOrElse)
+            traverseChildren(tp.info)
           case _ =>
             traverseChildren(tp)
-      }
+      catch case ex: Throwable => handleRecursive("traverseTp2", tp.show, ex)
     TraverseTp2.traverse(tp2)
-    val thisTypes = TraverseTp2.thisTypes
-    val gadtSyms  = TraverseTp2.gadtSyms.toList
+    val singletons = TraverseTp2.singletons
+    val gadtSyms   = TraverseTp2.gadtSyms.toList
 
     // Prefix inference, given `p.C.this.Child`:
     //   1. return it as is, if `C.this` is found in `tp`, i.e. the scrutinee; or
@@ -874,10 +875,13 @@ object TypeOps:
     class InferPrefixMap extends TypeMap {
       var prefixTVar: Type | Null = null
       def apply(tp: Type): Type = tp match {
-        case tp @ ThisType(tref) if !tref.symbol.isStaticOwner =>
+        case tp: TermRef if singletons.contains(tp.symbol) =>
+          prefixTVar = singletons(tp.symbol) // e.g. tests/pos/i19031.ci-reg2.scala, keep out
+          prefixTVar.uncheckedNN
+        case ThisType(tref) if !tref.symbol.isStaticOwner =>
           val symbol = tref.symbol
-          if thisTypes.contains(tp) then
-            prefixTVar = tp // e.g. tests/pos/i16785.scala, keep Outer.this
+          if singletons.contains(symbol) then
+            prefixTVar = singletons(symbol) // e.g. tests/pos/i16785.scala, keep Outer.this
             prefixTVar.uncheckedNN
           else if symbol.is(Module) then
             TermRef(this(tref.prefix), symbol.sourceModule)
@@ -912,7 +916,8 @@ object TypeOps:
     }
 
     def instantiate(): Type = {
-      for tp <- mixins.reverseIterator do protoTp1 <:< tp
+      for tp <- mixins.reverseIterator do
+        protoTp1 <:< tp
       maximizeType(protoTp1, NoSpan)
       wildApprox(protoTp1)
     }

Diff for: compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -55,8 +55,7 @@ class PatternMatcher extends MiniPhase {
 
       if !inInlinedCode then
         // check exhaustivity and unreachability
-        SpaceEngine.checkExhaustivity(tree)
-        SpaceEngine.checkRedundancy(tree)
+        SpaceEngine.checkMatch(tree)
 
       translated.ensureConforms(matchType)
     }

Diff for: compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -209,17 +209,13 @@ object SpaceEngine {
       case (a @ Typ(tp1, _), b @ Typ(tp2, _)) =>
         if isSubType(tp1, tp2) then a
         else if isSubType(tp2, tp1) then b
-        else if canDecompose(a) then intersect(Or(decompose(a)), b)
-        else if canDecompose(b) then intersect(a, Or(decompose(b)))
         else intersectUnrelatedAtomicTypes(tp1, tp2)(a)
       case (a @ Typ(tp1, _), Prod(tp2, fun, ss)) =>
         if isSubType(tp2, tp1) then b
-        else if canDecompose(a) then intersect(Or(decompose(a)), b)
         else if isSubType(tp1, tp2) then a // problematic corner case: inheriting a case class
         else intersectUnrelatedAtomicTypes(tp1, tp2)(b)
       case (Prod(tp1, fun, ss), b @ Typ(tp2, _)) =>
         if isSubType(tp1, tp2) then a
-        else if canDecompose(b) then intersect(a, Or(decompose(b)))
         else if isSubType(tp2, tp1) then a  // problematic corner case: inheriting a case class
         else intersectUnrelatedAtomicTypes(tp1, tp2)(a)
       case (a @ Prod(tp1, fun1, ss1), Prod(tp2, fun2, ss2)) =>
@@ -882,7 +878,7 @@ object SpaceEngine {
     case _                                          => tp
   })
 
-  def checkExhaustivity(m: Match)(using Context): Unit = if exhaustivityCheckable(m.selector) then trace(i"checkExhaustivity($m)", debug) {
+  def checkExhaustivity(m: Match)(using Context): Unit = trace(i"checkExhaustivity($m)", debug) {
     val selTyp = toUnderlying(m.selector.tpe).dealias
     debug.println(i"selTyp = $selTyp")
 
@@ -905,7 +901,7 @@ object SpaceEngine {
       report.warning(PatternMatchExhaustivity(showSpaces(deduped), m), m.selector)
   }
 
-  private def redundancyCheckable(sel: Tree)(using Context): Boolean =
+  private def reachabilityCheckable(sel: Tree)(using Context): Boolean =
     // Ignore Expr[T] and Type[T] for unreachability as a special case.
     // Quote patterns produce repeated calls to the same unapply method, but with different implicit parameters.
     // Since we assume that repeated calls to the same unapply method overlap
@@ -915,7 +911,7 @@ object SpaceEngine {
     && !sel.tpe.widen.isRef(defn.QuotedExprClass)
     && !sel.tpe.widen.isRef(defn.QuotedTypeClass)
 
-  def checkRedundancy(m: Match)(using Context): Unit = if redundancyCheckable(m.selector) then trace(i"checkRedundancy($m)", debug) {
+  def checkReachability(m: Match)(using Context): Unit = trace(i"checkReachability($m)", debug) {
     val cases = m.cases.toIndexedSeq
 
     val selTyp = toUnderlying(m.selector.tpe).dealias
@@ -967,4 +963,8 @@ object SpaceEngine {
       i += 1
     }
   }
+
+  def checkMatch(m: Match)(using Context): Unit =
+    if exhaustivityCheckable(m.selector) then checkExhaustivity(m)
+    if reachabilityCheckable(m.selector) then checkReachability(m)
 }

Diff for: scaladoc-js/common/src/utils/html.scala

@@ -26,7 +26,7 @@ object HTML {
         case ("id", id) => elem.id = id
         case ("class", value) => value.split("\\s+").foreach(cls => elem.classList.add(cls))
         case (attr, value) => elem.setAttribute(attr, value)
-        case s: Seq[AppliedAttr] => unpackAttributes(s*)
+        case s: Seq[AppliedAttr @unchecked] => unpackAttributes(s*)
       }
 
       unpackTags(tags:_*)
@@ -118,4 +118,4 @@ object HTML {
   val titleAttr =Attr("title")
   val onkeyup = Attr("onkeyup")
 
-}
+}

Diff for: tests/pos/i19031.ci-reg1.scala

@@ -0,0 +1,16 @@
+//> using options -Werror
+
+sealed trait Mark[T]
+
+trait Foo[T]
+class Bar1[T] extends Foo[T]
+class Bar2[T] extends Foo[T] with Mark[T]
+
+class Test:
+  def t1(foo: Foo[Int]): Unit = foo match
+    case _: Mark[t] =>
+    case _          =>
+
+  def t2[F <: Foo[Int]](foo: F): Unit = foo match
+    case _: Mark[t] =>
+    case _          =>

Diff for: tests/pos/i19031.ci-reg2.scala

@@ -0,0 +1,15 @@
+//> using options -Werror
+
+trait Outer:
+  sealed trait Foo
+  case class  Bar1() extends Foo
+  case class  Bar2() extends Foo
+  case object Bar3   extends Foo
+
+  def foos: List[Foo]
+
+class Test:
+  def t1(out: Outer) = out.foos.collect:
+    case out.Bar1() => 1
+    case out.Bar2() => 2
+    case out.Bar3   => 3

Diff for: tests/pos/i19031.scala

@@ -0,0 +1,9 @@
+//> using options -Werror
+
+sealed trait A:
+  class B extends A
+
+class Test:
+  def t1(a: A): Boolean =
+    a match
+      case b: A#B => true