Use unapply tree fun as prefix

Author: nicolasstucki

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

@@ -1259,7 +1259,7 @@ class Typer extends Namer
           val constr = ctx.newConstructor(cls, Synthetic, Nil, Nil, coord = sym.coord).entered
           val unappplySym = ctx.newSymbol(cls, sym.name.toTermName, Synthetic | Method, sym.info, coord = sym.coord).entered
           val unapply = polyDefDef(unappplySym, targs => argss =>
-            Inliner.inlineCall(ref(sym).appliedToTypes(targs).appliedToArgss(argss).withSpan(t.span))
+            Inliner.inlineCall(t.fun.appliedToTypes(targs).appliedToArgss(argss).withSpan(t.span))(ctx.withOwner(unappplySym))
           )
           val cdef = ClassDef(cls, DefDef(constr), List(unapply))
           val newUnapply = Block(cdef :: Nil, New(cls.typeRef, Nil))

tests/run/i8530-b.scala

@@ -0,0 +1,18 @@
+import scala.compiletime.erasedValue
+
+class MyRegex[Pattern <: String & Singleton/*Literal constant*/]:
+  inline def unapplySeq(s: CharSequence): Option[List[String]] =
+    inline erasedValue[Pattern] match
+      case "foo" => if s == "foo" then Some(Nil) else None
+      case _ => valueOf[Pattern].r.unapplySeq(s)
+
+@main def Test: Unit =
+  val myRegexp1 = new MyRegex["foo"]
+  val myRegexp2 = new MyRegex["f(o+)"]
+  "foo" match
+    case myRegexp1() => // Match ok
+    case myRegexp2(x) => ???
+  "foooo" match
+    case myRegexp1() => ???
+    case myRegexp2(x) =>
+      assert(x == "oooo")