record pattern path

Author: Linyxus

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

@@ -73,6 +73,12 @@ sealed abstract class GadtConstraint extends Showable {
   /** Set the scrutinee path. */
   def withScrutineePath[T](path: TermRef | Null)(op: => T): T
 
+  /** Supply the real pattern path. */
+  def supplyPatternPath(path: TermRef)(using Context): Unit
+
+  /** Create a skolem type for pattern. */
+  def createPatternSkolem(pat: Type): SkolemType
+
   /** Is the symbol registered in the constraint?
    *
    * @note this is true even if the symbol is constrained to be equal to another type, unlike [[Constraint.contains]].
@@ -114,7 +120,8 @@ final class ProperGadtConstraint private(
   private var pathDepReverseMapping: SimpleIdentityMap[TypeParamRef, TypeRef],
   private var wasConstrained: Boolean,
   private var myScrutineePath: TermRef | Null,
-  private var myUnionFind: SimpleIdentityMap[PathType, PathType]
+  private var myUnionFind: SimpleIdentityMap[PathType, PathType],
+  private var myPatternSkolem: SkolemType | Null,
 ) extends GadtConstraint with ConstraintHandling {
   import dotty.tools.dotc.config.Printers.{gadts, gadtsConstr}
 
@@ -126,7 +133,8 @@ final class ProperGadtConstraint private(
     pathDepReverseMapping = SimpleIdentityMap.empty,
     wasConstrained = false,
     myScrutineePath = null,
-    myUnionFind = SimpleIdentityMap.empty
+    myUnionFind = SimpleIdentityMap.empty,
+    myPatternSkolem = null,
   )
 
   // /** Exposes ConstraintHandling.subsumes */
@@ -672,7 +680,8 @@ final class ProperGadtConstraint private(
     pathDepReverseMapping,
     wasConstrained,
     myScrutineePath,
-    myUnionFind
+    myUnionFind,
+    myPatternSkolem,
   )
 
   def restore(other: GadtConstraint): Unit = other match {
@@ -685,17 +694,40 @@ final class ProperGadtConstraint private(
       this.wasConstrained = other.wasConstrained
       this.myScrutineePath = other.myScrutineePath
       this.myUnionFind = other.myUnionFind
+      this.myPatternSkolem = other.myPatternSkolem
     case _ => ;
   }
 
   override def scrutineePath: TermRef | Null = myScrutineePath
 
   override def resetScrutineePath(): Unit = myScrutineePath = null
 
+  override def supplyPatternPath(path: TermRef)(using Context): Unit =
+    if myPatternSkolem eq null then
+      ()
+    else
+      pathDepMapping(myPatternSkolem.nn) match {
+        case null =>
+        case m: SimpleIdentityMap[Symbol, TypeVar] =>
+          pathDepMapping = pathDepMapping.updated(path, m)
+          m foreachBinding { (sym, tvar) =>
+            val tpr = tvar.origin
+            pathDepReverseMapping = pathDepReverseMapping.updated(tpr, TypeRef(path, sym))
+          }
+      }
+  end supplyPatternPath
+
+  override def createPatternSkolem(pat: Type): SkolemType =
+    myPatternSkolem = SkolemType(pat)
+    myPatternSkolem.nn
+  end createPatternSkolem
+
   override def withScrutineePath[T](path: TermRef | Null)(op: => T): T =
     val saved = this.myScrutineePath
     this.myScrutineePath = path
+
     val result = op
+
     this.myScrutineePath = saved
     result
 
@@ -827,6 +859,10 @@ final class ProperGadtConstraint private(
 
   override def withScrutineePath[T](path: TermRef | Null)(op: => T): T = op
 
+  override def supplyPatternPath(path: TermRef)(using Context): Unit = ()
+
+  override def createPatternSkolem(pat: Type): SkolemType = unsupported("EmptyGadtConstraint.createPatternSkolem")
+
   override def fresh = new ProperGadtConstraint
   override def restore(other: GadtConstraint): Unit =
     assert(!other.isNarrowing, "cannot restore a non-empty GADTMap")

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

@@ -184,7 +184,7 @@ trait PatternTypeConstrainer { self: TypeComparer =>
       val scrutineePath: TermRef | SkolemType = realScrutineePath match
         case null => SkolemType(scrut)
         case _ => realScrutineePath
-      val patternPath: SkolemType = SkolemType(pat)
+      val patternPath: SkolemType = ctx.gadt.createPatternSkolem(pat)
 
       val saved = state.nn.constraint
       val savedGadt = ctx.gadt.fresh

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1777,6 +1777,10 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     val pat1 = gadtCtx.gadt.withScrutineePath(scrutineePath) {
       typedPattern(tree.pat, wideSelType)(using gadtCtx)
     }
+
+    if scrutineePath.ne(null) && pat1.symbol.isPatternBound then
+      gadtCtx.gadt.supplyPatternPath(pat1.symbol.termRef)
+
     caseRest(pat1)(
       using Nullables.caseContext(sel, pat1)(
         using gadtCtx))