Retract SynthesizeExtMethodReceiver mode when going deeper in overloa…

…ding resolution

The SynthesizeExtMethodReceiver mode is supposed to be turned on only for the
direct application of of a synthesized receiver to the qualifier of an
extension method selection. previously its lifetime was accidentally extended
when overloading resolution looking at subsequent parameter lists because the
first one was not enough to disambiguate.

Fixes #18745
Fixes #18744

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

@@ -2219,7 +2219,8 @@ trait Applications extends Compatibility {
     }
     val mapped = reverseMapping.map(_._1)
     overload.println(i"resolve mapped: ${mapped.map(_.widen)}%, % with $pt")
-    resolveOverloaded(mapped, pt).map(reverseMapping.toMap)
+    resolveOverloaded(mapped, pt)(using ctx.retractMode(Mode.SynthesizeExtMethodReceiver))
+      .map(reverseMapping.toMap)
 
   /** Try to typecheck any arguments in `pt` that are function values missing a
    *  parameter type. If the formal parameter types corresponding to a closure argument

tests/pos/i18744.scala

@@ -0,0 +1,13 @@
+package dotty.tools.dotc.typer
+
+object Color:
+  def apply(): Int = ???
+
+extension (u: Unit)
+  def foo(that: String, f: Int => Int): Int = ???
+  def foo(that: Long, f: Int => Int): Int = ???
+
+def test =
+  val c = Color()
+  ().foo("", (_: Int) => c)
+  ().foo("", (_: Int) => Color())

tests/pos/i18745.scala

@@ -0,0 +1,14 @@
+object Color:
+  def apply(i: Int): Int = i
+
+type Plane
+
+object Plane:
+  extension (plane: Plane)
+    def zipWith(that: String, f: Int => Int): Int = ???
+    def zipWith(that: Int, f: Int => Int): Int = ???
+
+import Plane.zipWith
+
+def test(p: Plane) =
+  p.zipWith("", (_: Int) => Color(25))