From bd6ac1cd711efff5842c695b4052b827add0d5d8 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Thu, 19 Oct 2023 14:47:57 +0100
Subject: [PATCH] Tweak convertible implicits fix

Rather than widen in viewExists, widen earlier, past type lambda
parameters.  This allows `foo2` in `i16453b2` from being listed as a
possible implicit, as appropriate.

[Cherry-picked a17552564ab467b25a90e6b6405683d4b03ddec7]
---
 compiler/src/dotty/tools/dotc/typer/Implicits.scala |  4 ++--
 tests/neg/i16453b1.check                            |  8 ++++++++
 tests/neg/i16453b1.scala                            | 12 ++++++++++++
 tests/neg/i16453b2.check                            |  8 ++++++++
 tests/neg/i16453b2.scala                            | 12 ++++++++++++
 5 files changed, 42 insertions(+), 2 deletions(-)
 create mode 100644 tests/neg/i16453b1.check
 create mode 100644 tests/neg/i16453b1.scala
 create mode 100644 tests/neg/i16453b2.check
 create mode 100644 tests/neg/i16453b2.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Implicits.scala b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
index 3872d0dd79d0..5ecddd6f4af0 100644
--- a/compiler/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
@@ -826,7 +826,7 @@ trait Implicits:
     && !to.isError
     && !ctx.isAfterTyper
     && ctx.mode.is(Mode.ImplicitsEnabled)
-    && from.widen.isValueType
+    && from.isValueType
     && (  from.isValueSubType(to)
        || inferView(dummyTreeOfType(from), to)
             (using ctx.fresh.addMode(Mode.ImplicitExploration).setExploreTyperState()).isSuccess
@@ -958,7 +958,7 @@ trait Implicits:
             .filter { imp =>
               !isImplicitDefConversion(imp.underlying)
                 && imp.symbol != defn.Predef_conforms
-                && viewExists(imp, fail.expectedType)
+                && viewExists(imp.underlying.resultType, fail.expectedType)
             }
         else
           Nil
diff --git a/tests/neg/i16453b1.check b/tests/neg/i16453b1.check
new file mode 100644
index 000000000000..07f23c95d9ad
--- /dev/null
+++ b/tests/neg/i16453b1.check
@@ -0,0 +1,8 @@
+-- [E172] Type Error: tests/neg/i16453b1.scala:11:19 -------------------------------------------------------------------
+11 |  val ko = get[Int] // error
+   |                   ^
+   |No given instance of type Ctx => Option[Int] was found for parameter fn of method get
+   |
+   |Note: implicit conversions are not automatically applied to arguments of using clauses. You will have to pass the argument explicitly.
+   |The following implicits in scope can be implicitly converted to Ctx => Option[Int]:
+   |- final lazy given val foo: Ctx => Int
diff --git a/tests/neg/i16453b1.scala b/tests/neg/i16453b1.scala
new file mode 100644
index 000000000000..4a99321a9421
--- /dev/null
+++ b/tests/neg/i16453b1.scala
@@ -0,0 +1,12 @@
+import scala.language.implicitConversions
+
+sealed trait Ctx
+given ct[T]: Conversion[Ctx => T, Ctx => Option[T]] = fn => fn.andThen(Option.apply)
+
+def get[T](using fn: Ctx => Option[T]): Option[T] = ???
+
+def Test = {
+  given foo: (Ctx => Int) = _ => 42
+  val ok = get[Int](using summon[Ctx => Int])
+  val ko = get[Int] // error
+}
diff --git a/tests/neg/i16453b2.check b/tests/neg/i16453b2.check
new file mode 100644
index 000000000000..fc0a1fa37b82
--- /dev/null
+++ b/tests/neg/i16453b2.check
@@ -0,0 +1,8 @@
+-- [E172] Type Error: tests/neg/i16453b2.scala:11:19 -------------------------------------------------------------------
+11 |  val ko = get[Int] // error
+   |                   ^
+   |No given instance of type Ctx => Option[Int] was found for parameter fn of method get
+   |
+   |Note: implicit conversions are not automatically applied to arguments of using clauses. You will have to pass the argument explicitly.
+   |The following implicits in scope can be implicitly converted to Ctx => Option[Int]:
+   |- final given def foo2[A]: Ctx => Int
diff --git a/tests/neg/i16453b2.scala b/tests/neg/i16453b2.scala
new file mode 100644
index 000000000000..6cafeb54b540
--- /dev/null
+++ b/tests/neg/i16453b2.scala
@@ -0,0 +1,12 @@
+import scala.language.implicitConversions
+
+sealed trait Ctx
+given ct[T]: Conversion[Ctx => T, Ctx => Option[T]] = fn => fn.andThen(Option.apply)
+
+def get[T](using fn: Ctx => Option[T]): Option[T] = ???
+
+def Test = {
+  given foo2[A]: (Ctx => Int) = _ => 42
+  val ok = get[Int](using summon[Ctx => Int])
+  val ko = get[Int] // error
+}