From 68127fd777e22dd6f81e49a467f4d81a5aeef18d Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Mon, 23 Oct 2023 14:57:14 +0200
Subject: [PATCH] Retract SynthesizeExtMethodReceiver mode when going deeper in
 overloading 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

[Cherry-picked edc4bc88a4214f1353c292cc9931ac3b0cd5d147]
---
 .../src/dotty/tools/dotc/typer/Applications.scala  |  3 ++-
 tests/pos/i18744.scala                             | 13 +++++++++++++
 tests/pos/i18745.scala                             | 14 ++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i18744.scala
 create mode 100644 tests/pos/i18745.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index d5983da30d56..a14c2d119258 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Applications.scala
@@ -2212,7 +2212,8 @@ 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
diff --git a/tests/pos/i18744.scala b/tests/pos/i18744.scala
new file mode 100644
index 000000000000..6e2d630c52b8
--- /dev/null
+++ b/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())
\ No newline at end of file
diff --git a/tests/pos/i18745.scala b/tests/pos/i18745.scala
new file mode 100644
index 000000000000..2184acc4770f
--- /dev/null
+++ b/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))
\ No newline at end of file