Fix use of class terms in match analysis (#21848)

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

@@ -767,6 +767,67 @@ object TypeOps:
    *  Otherwise, return NoType.
    */
   private def instantiateToSubType(tp1: NamedType, tp2: Type, mixins: List[Type])(using Context): Type = trace(i"instantiateToSubType($tp1, $tp2, $mixins)", typr) {
+    /** Gather GADT symbols and singletons found in `tp2`, ie. the scrutinee. */
+    object TraverseTp2 extends TypeTraverser:
+      val singletons = util.HashMap[Symbol, SingletonType]()
+      val gadtSyms = new mutable.ListBuffer[Symbol]
+
+      def traverse(tp: Type) = try
+        val tpd = tp.dealias
+        if tpd ne tp then traverse(tpd)
+        else tp match
+          case tp: ThisType if !singletons.contains(tp.tref.symbol) && !tp.tref.symbol.isStaticOwner =>
+            singletons(tp.tref.symbol) = tp
+            traverseChildren(tp.tref)
+          case tp: TermRef =>
+            singletons(tp.typeSymbol) = tp
+            traverseChildren(tp)
+          case tp: TypeRef if !gadtSyms.contains(tp.symbol) && tp.symbol.isAbstractOrParamType =>
+            gadtSyms += tp.symbol
+            traverseChildren(tp)
+            // 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 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
+    //   2. replace it with `X.Child` where `X <: p.C`, stripping ThisType in `p` recursively.
+    //
+    // See tests/patmat/i3938.scala, tests/pos/i15029.more.scala, tests/pos/i16785.scala
+    class InferPrefixMap extends TypeMap {
+      var prefixTVar: Type | Null = null
+      def apply(tp: Type): Type = tp match {
+        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 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)
+          else if (prefixTVar != null)
+            this(tref.applyIfParameterized(tref.typeParams.map(_ => WildcardType)))
+          else {
+            prefixTVar = WildcardType  // prevent recursive call from assigning it
+            // e.g. tests/pos/i15029.more.scala, create a TypeVar for `Instances`' B, so we can disregard `Ints`
+            val tvars = tref.typeParams.map { tparam => newTypeVar(tparam.paramInfo.bounds, DepParamName.fresh(tparam.paramName)) }
+            val tref2 = this(tref.applyIfParameterized(tvars))
+            prefixTVar = newTypeVar(TypeBounds.upper(tref2), DepParamName.fresh(tref.name))
+            prefixTVar.uncheckedNN
+          }
+        case tp => mapOver(tp)
+      }
+    }
+
     // In order for a child type S to qualify as a valid subtype of the parent
     // T, we need to test whether it is possible S <: T.
     //
@@ -788,8 +849,15 @@ object TypeOps:
                                  // then to avoid it failing the <:<
                                  // we'll approximate by widening to its bounds
 
+        case tp: TermRef if singletons.contains(tp.symbol) =>
+          singletons(tp.symbol)
+
         case ThisType(tref: TypeRef) if !tref.symbol.isStaticOwner =>
-          tref
+          val symbol = tref.symbol
+          if singletons.contains(symbol) then
+            singletons(symbol)
+          else
+            tref
 
         case tp: TypeRef if !tp.symbol.isClass =>
           val lookup = boundTypeParams.lookup(tp)
@@ -840,67 +908,6 @@ object TypeOps:
       }
     }
 
-    /** Gather GADT symbols and singletons found in `tp2`, ie. the scrutinee. */
-    object TraverseTp2 extends TypeTraverser:
-      val singletons = util.HashMap[Symbol, SingletonType]()
-      val gadtSyms = new mutable.ListBuffer[Symbol]
-
-      def traverse(tp: Type) = try
-        val tpd = tp.dealias
-        if tpd ne tp then traverse(tpd)
-        else tp match
-          case tp: ThisType if !singletons.contains(tp.tref.symbol) && !tp.tref.symbol.isStaticOwner =>
-            singletons(tp.tref.symbol) = tp
-            traverseChildren(tp.tref)
-          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)
-            // 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 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
-    //   2. replace it with `X.Child` where `X <: p.C`, stripping ThisType in `p` recursively.
-    //
-    // See tests/patmat/i3938.scala, tests/pos/i15029.more.scala, tests/pos/i16785.scala
-    class InferPrefixMap extends TypeMap {
-      var prefixTVar: Type | Null = null
-      def apply(tp: Type): Type = tp match {
-        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 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)
-          else if (prefixTVar != null)
-            this(tref.applyIfParameterized(tref.typeParams.map(_ => WildcardType)))
-          else {
-            prefixTVar = WildcardType  // prevent recursive call from assigning it
-            // e.g. tests/pos/i15029.more.scala, create a TypeVar for `Instances`' B, so we can disregard `Ints`
-            val tvars = tref.typeParams.map { tparam => newTypeVar(tparam.paramInfo.bounds, DepParamName.fresh(tparam.paramName)) }
-            val tref2 = this(tref.applyIfParameterized(tvars))
-            prefixTVar = newTypeVar(TypeBounds.upper(tref2), DepParamName.fresh(tref.name))
-            prefixTVar.uncheckedNN
-          }
-        case tp => mapOver(tp)
-      }
-    }
-
     val inferThisMap = new InferPrefixMap
     val tvars = tp1.etaExpand match
       case eta: TypeLambda => constrained(eta)

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -1125,6 +1125,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         recur(fn) ~ "(" ~ toTextGlobal(explicitArgs, ", ") ~ ")"
       case TypeApply(fn, args) => recur(fn) ~ "[" ~ toTextGlobal(args, ", ") ~ "]"
       case Select(qual, nme.CONSTRUCTOR) => recur(qual)
+      case id @ Ident(tpnme.BOUNDTYPE_ANNOT) => "@" ~ toText(id.symbol.name)
       case New(tpt) => recur(tpt)
       case _ =>
         val annotSym = sym.orElse(tree.symbol.enclosingClass)

tests/warn/i21845.orig.scala

@@ -0,0 +1,33 @@
+trait Init[ScopeType]:
+  sealed trait Initialize[A1]
+  final class Bind[S, A1](val f: S => Initialize[A1], val in: Initialize[S])
+    extends Initialize[A1]
+  final class Value[A1](val value: () => A1) extends Initialize[A1]
+  final class ValidationCapture[A1](val key: ScopedKey[A1], val selfRefOk: Boolean)
+        extends Initialize[ScopedKey[A1]]
+  final class TransformCapture(val f: [x] => Initialize[x] => Initialize[x])
+        extends Initialize[[x] => Initialize[x] => Initialize[x]]
+  final class Optional[S, A1](val a: Option[Initialize[S]], val f: Option[S] => A1)
+        extends Initialize[A1]
+  object StaticScopes extends Initialize[Set[ScopeType]]
+
+  sealed trait Keyed[S, A1] extends Initialize[A1]
+  trait KeyedInitialize[A1] extends Keyed[A1, A1]
+  sealed case class ScopedKey[A](scope: ScopeType, key: AttributeKey[A]) extends KeyedInitialize[A]
+  sealed trait AttributeKey[A]
+
+abstract class EvaluateSettings[ScopeType]:
+    protected val init: Init[ScopeType]
+    import init._
+
+    val transform: [A] => Initialize[A] => Unit = [A] =>
+        (fa: Initialize[A]) =>
+          fa match
+            case k: Keyed[s, A]          => ???
+            case b: Bind[s, A]           => ???
+            case v: Value[A]             => ???
+            case v: ValidationCapture[a] => ??? // unrearchable warning
+            case t: TransformCapture     => ??? // unrearchable warning
+            case o: Optional[s, A]       => ??? // unrearchable warning
+            case StaticScopes            => ??? // unrearchable warning
+

tests/warn/i21845.scala

@@ -0,0 +1,15 @@
+trait Outer[O1]:
+  sealed trait Foo[A1]
+  final class Bar[A2] extends Foo[A2]
+  final class Baz[A4] extends Foo[Bar[A4]]
+  final class Qux     extends Foo[[a5] => Foo[a5] => Foo[a5]]
+
+trait Test[O2]:
+  val outer: Outer[O2]
+  import outer.*
+
+  def test[X](fa: Foo[X]): Unit =
+    fa match // was: inexhaustive: fail on _: (Outer[<?>] & (Test#outer : Outer[Test#O2]))#Qux
+      case _: Bar[X] => ???
+      case _: Baz[x] => ??? // was: unrearchable warning
+      case _: Qux    => ??? // was: unrearchable warning