Partial function synthesis changesOwner of selector

The selector expression may be non-trivial.

Author: som-snytt

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

@@ -865,7 +865,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
   /** An extractor for def of a closure contained the block of the closure. */
   object closureDef {
     def unapply(tree: Tree)(using Context): Option[DefDef] = tree match {
-      case Block((meth : DefDef) :: Nil, closure: Closure) if meth.symbol == closure.meth.symbol =>
+      case Block((meth: DefDef) :: Nil, closure: Closure) if meth.symbol == closure.meth.symbol =>
         Some(meth)
       case Block(Nil, expr) =>
         unapply(expr)

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

@@ -375,7 +375,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
    *      new parents { termForwarders; typeAliases }
    *
    *  @param parents        a non-empty list of class types
-   *  @param termForwarders a non-empty list of forwarding definitions specified by their name and the definition they forward to.
+   *  @param termForwarders a non-empty list of forwarding definitions specified by their name
+   *                        and the definition they forward to.
    *  @param typeMembers    a possibly-empty list of type members specified by their name and their right hand side.
    *  @param adaptVarargs   if true, allow matching a vararg superclass constructor
    *                        with a missing argument in superArgs, and synthesize an

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

@@ -6048,19 +6048,18 @@ object Types extends TypeUtils {
     end samParent
 
     def samClass(tp: Type)(using Context): Symbol = tp match
-      case tp: ClassInfo =>
-        val cls = tp.cls
+      case tp @ ClassInfo(_, cls, _, _, _) =>
         def takesNoArgs(tp: Type) =
           !tp.classSymbol.primaryConstructor.exists
               // e.g. `ContextFunctionN` does not have constructors
-          || tp.applicableConstructors(Nil, adaptVarargs = true).lengthCompare(1) == 0
+          || tp.applicableConstructors(argTypes = Nil, adaptVarargs = true).lengthCompare(1) == 0
               // we require a unique constructor so that SAM expansion is deterministic
         val noArgsNeeded: Boolean =
           takesNoArgs(tp)
-          && (!tp.cls.is(Trait) || takesNoArgs(tp.parents.head))
+          && (!cls.is(Trait) || takesNoArgs(tp.parents.head))
         def isInstantiable =
-          !tp.cls.isOneOf(FinalOrSealed) && (tp.appliedRef <:< tp.selfType)
-        if noArgsNeeded && isInstantiable then tp.cls
+          !cls.isOneOf(FinalOrSealed) && (tp.appliedRef <:< tp.selfType)
+        if noArgsNeeded && isInstantiable then cls
         else NoSymbol
       case tp: AppliedType =>
         samClass(tp.superType)

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

@@ -45,9 +45,9 @@ abstract class Dependencies(root: ast.tpd.Tree, @constructorOnly rootContext: Co
 
   /** A map from local methods and classes to the owners to which they will be lifted as members.
    *  For methods and classes that do not have any dependencies this will be the enclosing package.
-   *  symbols with packages as lifted owners will subsequently represented as static
+   *  Symbols with packages as lifted owners will be subsequently represented as static
    *  members of their toplevel class, unless their enclosing class was already static.
-   *  Note: During tree transform (which runs at phase LambdaLift + 1), liftedOwner
+   *  Note: During tree transform (which runs at phase LambdaLift + 1), logicOwner
    *  is also used to decide whether a method had a term owner before.
    */
   private val logicOwner = new LinkedHashMap[Symbol, Symbol]
@@ -75,8 +75,8 @@ abstract class Dependencies(root: ast.tpd.Tree, @constructorOnly rootContext: Co
     || owner.is(Trait) && isLocal(owner)
     || sym.isConstructor && isLocal(owner)
 
-  /** Set `liftedOwner(sym)` to `owner` if `owner` is more deeply nested
-   *  than the previous value of `liftedowner(sym)`.
+  /** Set `logicOwner(sym)` to `owner` if `owner` is more deeply nested
+   *  than the previous value of `logicOwner(sym)`.
    */
   private def narrowLogicOwner(sym: Symbol, owner: Symbol)(using Context): Unit =
     if sym.maybeOwner.isTerm
@@ -89,7 +89,7 @@ abstract class Dependencies(root: ast.tpd.Tree, @constructorOnly rootContext: Co
 
   /** Mark symbol `sym` as being free in `enclosure`, unless `sym` is defined
    *  in `enclosure` or there is an intermediate class properly containing `enclosure`
-   *  in which `sym` is also free. Also, update `liftedOwner` of `enclosure` so
+   *  in which `sym` is also free. Also, update `logicOwner` of `enclosure` so
    *  that `enclosure` can access `sym`, or its proxy in an intermediate class.
    *  This means:
    *
@@ -284,7 +284,7 @@ abstract class Dependencies(root: ast.tpd.Tree, @constructorOnly rootContext: Co
       changedFreeVars
     do ()
 
-  /** Compute final liftedOwner map by closing over caller dependencies */
+  /** Compute final logicOwner map by closing over caller dependencies */
   private def computeLogicOwners()(using Context): Unit =
     while
       changedLogicOwner = false

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

@@ -10,14 +10,15 @@ import Names.TypeName
 
 import NullOpsDecorator.*
 import ast.untpd
+import scala.collection.mutable.ListBuffer
 
 /** Expand SAM closures that cannot be represented by the JVM as lambdas to anonymous classes.
  *  These fall into five categories
  *
  *   1. Partial function closures, we need to generate isDefinedAt and applyOrElse methods for these.
  *   2. Closures implementing non-trait classes
  *   3. Closures implementing classes that inherit from a class other than Object
- *      (a lambda cannot not be a run-time subtype of such a class)
+ *      (a lambda cannot be a run-time subtype of such a class)
  *   4. Closures that implement traits which run initialization code.
  *   5. Closures that get synthesized abstract methods in the transformation pipeline. These methods can be
  *      (1) superaccessors, (2) outer references, (3) accessors for fields.
@@ -59,7 +60,7 @@ class ExpandSAMs extends MiniPhase:
           // A SAM type is allowed to have type aliases refinements (see
           // SAMType#samParent) which must be converted into type members if
           // the closure is desugared into a class.
-          val refinements = collection.mutable.ListBuffer[(TypeName, TypeAlias)]()
+          val refinements = ListBuffer.empty[(TypeName, TypeAlias)]
           def collectAndStripRefinements(tp: Type): Type = tp match
             case RefinedType(parent, name, info: TypeAlias) =>
               val res = collectAndStripRefinements(parent)
@@ -81,34 +82,40 @@ class ExpandSAMs extends MiniPhase:
       tree
   }
 
-  /** A partial function literal:
+  /** A pattern-matching anonymous function:
    *
    *  ```
    *  val x: PartialFunction[A, B] = { case C1 => E1; ...; case Cn => En }
    *  ```
+   *  or
+   *  ```
+   *  x => e(x) { case C1 => E1; ...; case Cn => En }
+   *  ```
+   *  where the expression `e(x)` may be trivially `x`
    *
    *  which desugars to:
    *
    *  ```
    *  val x: PartialFunction[A, B] = {
-   *    def $anonfun(x: A): B = x match { case C1 => E1; ...; case Cn => En }
+   *    def $anonfun(x: A): B = e(x) match { case C1 => E1; ...; case Cn => En }
    *    closure($anonfun: PartialFunction[A, B])
    *  }
    *  ```
+   *  where the expression `e(x)` defaults to `x` for a simple block of cases
    *
    *  is expanded to an anonymous class:
    *
    *  ```
    *  val x: PartialFunction[A, B] = {
    *    class $anon extends AbstractPartialFunction[A, B] {
-   *      final def isDefinedAt(x: A): Boolean = x match {
+   *      final def isDefinedAt(x: A): Boolean = e(x) match {
    *        case C1 => true
    *        ...
    *        case Cn => true
    *        case _  => false
    *      }
    *
-   *      final def applyOrElse[A1 <: A, B1 >: B](x: A1, default: A1 => B1): B1 = x match {
+   *      final def applyOrElse[A1 <: A, B1 >: B](x: A1, default: A1 => B1): B1 = e(x) match {
    *        case C1 => E1
    *        ...
    *        case Cn => En
@@ -120,7 +127,7 @@ class ExpandSAMs extends MiniPhase:
    *  }
    *  ```
    */
-  private def toPartialFunction(tree: Block, tpe: Type)(using Context): Tree = {
+  private def toPartialFunction(tree: Block, tpe: Type)(using Context): Tree =
     val closureDef(anon @ DefDef(_, List(List(param)), _, _)) = tree: @unchecked
 
     // The right hand side from which to construct the partial function. This is always a Match.
@@ -146,7 +153,7 @@ class ExpandSAMs extends MiniPhase:
       defn.AbstractPartialFunctionClass.typeRef.appliedTo(anonTpe.firstParamTypes.head, anonTpe.resultType),
       defn.SerializableType)
 
-    AnonClass(anonSym.owner, parents, tree.span) { pfSym =>
+    AnonClass(anonSym.owner, parents, tree.span): pfSym =>
       def overrideSym(sym: Symbol) = sym.copy(
         owner = pfSym,
         flags = Synthetic | Method | Final | Override,
@@ -155,7 +162,8 @@ class ExpandSAMs extends MiniPhase:
       val isDefinedAtFn = overrideSym(defn.PartialFunction_isDefinedAt)
       val applyOrElseFn = overrideSym(defn.PartialFunction_applyOrElse)
 
-      def translateMatch(tree: Match, pfParam: Symbol, cases: List[CaseDef], defaultValue: Tree)(using Context) = {
+      def translateMatch(owner: Symbol)(pfParam: Symbol, cases: List[CaseDef], defaultValue: Tree)(using Context) =
+        val tree: Match = pfRHS
         val selector = tree.selector
         val cases1 = if cases.exists(isDefaultCase) then cases
         else
@@ -165,31 +173,27 @@ class ExpandSAMs extends MiniPhase:
           cases :+ defaultCase
         cpy.Match(tree)(selector, cases1)
           .subst(param.symbol :: Nil, pfParam :: Nil)
-            // Needed because  a partial function can be written as:
+            // Needed because a partial function can be written as:
             // param => param match { case "foo" if foo(param) => param }
             // And we need to update all references to 'param'
-      }
+          .changeOwner(anonSym, owner)
 
-      def isDefinedAtRhs(paramRefss: List[List[Tree]])(using Context) = {
+      def isDefinedAtRhs(paramRefss: List[List[Tree]])(using Context) =
         val tru = Literal(Constant(true))
-        def translateCase(cdef: CaseDef) =
-          cpy.CaseDef(cdef)(body = tru).changeOwner(anonSym, isDefinedAtFn)
+        def translateCase(cdef: CaseDef) = cpy.CaseDef(cdef)(body = tru)
         val paramRef = paramRefss.head.head
         val defaultValue = Literal(Constant(false))
-        translateMatch(pfRHS, paramRef.symbol, pfRHS.cases.map(translateCase), defaultValue)
-      }
+        translateMatch(isDefinedAtFn)(paramRef.symbol, pfRHS.cases.map(translateCase), defaultValue)
 
-      def applyOrElseRhs(paramRefss: List[List[Tree]])(using Context) = {
+      def applyOrElseRhs(paramRefss: List[List[Tree]])(using Context) =
         val List(paramRef, defaultRef) = paramRefss(1)
-        def translateCase(cdef: CaseDef) =
-          cdef.changeOwner(anonSym, applyOrElseFn)
         val defaultValue = defaultRef.select(nme.apply).appliedTo(paramRef)
-        translateMatch(pfRHS, paramRef.symbol, pfRHS.cases.map(translateCase), defaultValue)
-      }
+        translateMatch(applyOrElseFn)(paramRef.symbol, pfRHS.cases, defaultValue)
 
-      val isDefinedAtDef = transformFollowingDeep(DefDef(isDefinedAtFn, isDefinedAtRhs(_)(using ctx.withOwner(isDefinedAtFn))))
-      val applyOrElseDef = transformFollowingDeep(DefDef(applyOrElseFn, applyOrElseRhs(_)(using ctx.withOwner(applyOrElseFn))))
+      val isDefinedAtDef = transformFollowingDeep:
+        DefDef(isDefinedAtFn, isDefinedAtRhs(_)(using ctx.withOwner(isDefinedAtFn)))
+      val applyOrElseDef = transformFollowingDeep:
+        DefDef(applyOrElseFn, applyOrElseRhs(_)(using ctx.withOwner(applyOrElseFn)))
       List(isDefinedAtDef, applyOrElseDef)
-    }
-  }
+  end toPartialFunction
 end ExpandSAMs

docs/_spec/08-pattern-matching.md

@@ -616,7 +616,7 @@ new scala.PartialFunction[´S´, ´T´] {
   def apply(´x´: ´S´): ´T´ = x match {
     case ´p_1´ => ´b_1´ ... case ´p_n´ => ´b_n´
   }
-  def isDefinedAt(´x´: ´S´): Boolean = {
+  def isDefinedAt(´x´: ´S´): Boolean = x match {
     case ´p_1´ => true ... case ´p_n´ => true
     case _ => false
   }
@@ -626,6 +626,22 @@ new scala.PartialFunction[´S´, ´T´] {
 Here, ´x´ is a fresh name and ´T´ is the least upper bound of the types of all ´b_i´.
 The final default case in the `isDefinedAt` method is omitted if one of the patterns ´p_1, ..., p_n´ is already a variable or wildcard pattern.
 
+As a convenience, the partial function may be written using function literal notation:
+
+```scala
+(´x: S´) => e(´x´) match {
+  case ´p_1´ => ´b_1´ ... case ´p_n´ => ´b_n´
+}
+```
+where the selector expression is used for matches in the expansion.
+The body of the function must consist solely of the match expression.
+
+This syntax permits annotating the selector:
+
+```scala
+(´x: S´) => (e(´x´): @unchecked) match { ... }
+```
+
 ###### Example
 Here's an example which uses `foldLeft` to compute the scalar product of two vectors:
 

tests/pos/i23025.scala

@@ -0,0 +1,5 @@
+
+class A {
+  def f: PartialFunction[Int, Int] =
+    a => { (try a catch { case e : Throwable => throw e}) match { case n => n } }
+}

tests/pos/i23054.scala

@@ -0,0 +1,15 @@
+
+object Bug:
+
+  def m0(f: PartialFunction[Char, Unit]): Unit = ()
+
+  def m1(): Unit =
+    m0: x =>
+      "abc".filter(_ == x) match
+        case _ => ()
+
+  def m2(): Unit =
+    m0: x =>
+      x match
+        case _ => ()
+

tests/pos/i23310.scala

@@ -0,0 +1,16 @@
+
+object Example {
+    val pf: PartialFunction[Unit, Unit] = s => (s match {
+      case a => a
+    }) match {
+      case a => ()
+    }
+}
+
+object ExampleB:
+  def test =
+    List(42).collect:
+      _.match
+        case x => x
+      .match
+        case y => y + 27