From 68bc2d5f9cdac65cc80ca9a39e7b3871b77a2311 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Mon, 26 Apr 2021 22:50:48 +0200
Subject: [PATCH] Show tvar bounds in "no implicit argument" message

Otherwise it's not clear why no implicit of that type was found.

Fixes #12232.
---
 .../tools/dotc/typer/ErrorReporting.scala     |  2 +-
 tests/neg/i12232.check                        | 12 +++++++++++
 tests/neg/i12232.scala                        | 20 +++++++++++++++++++
 tests/neg/i9568.check                         |  5 ++++-
 4 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 tests/neg/i12232.check
 create mode 100644 tests/neg/i12232.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala b/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala
index 2c5eaca1a4c5..7770824478f5 100644
--- a/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala
+++ b/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala
@@ -315,7 +315,7 @@ class ImplicitSearchError(
   }
 
   private def defaultImplicitNotFoundMessage = {
-    em"no implicit argument of type $pt was found${location("for")}"
+    ex"no implicit argument of type $pt was found${location("for")}"
   }
 
   /** Construct a custom error message given an ambiguous implicit
diff --git a/tests/neg/i12232.check b/tests/neg/i12232.check
new file mode 100644
index 000000000000..2dd7adc02a16
--- /dev/null
+++ b/tests/neg/i12232.check
@@ -0,0 +1,12 @@
+-- Error: tests/neg/i12232.scala:17:15 ---------------------------------------------------------------------------------
+17 |  foo(min(3, 4)) // error: works in Scala 2, not in 3
+   |               ^
+   |             no implicit argument of type Op[Int, Int, V] was found for parameter op of method min in object Foo
+   |
+   |             where:    V is a type variable with constraint <: Double
+-- Error: tests/neg/i12232.scala:19:16 ---------------------------------------------------------------------------------
+19 |  foo(minR(3, 4)) // error: works in Scala 2, not in 3
+   |                ^
+   |            no implicit argument of type Op[Int, Int, R] was found for parameter op of method minR in object Foo
+   |
+   |            where:    R is a type variable with constraint <: Double
diff --git a/tests/neg/i12232.scala b/tests/neg/i12232.scala
new file mode 100644
index 000000000000..3ca080a6fe56
--- /dev/null
+++ b/tests/neg/i12232.scala
@@ -0,0 +1,20 @@
+trait Op[T1, T2, +R] {
+  def apply(t1: T1, t2: T2): R
+}
+
+object Op {
+  implicit val compInt: Op[Int, Int, Int] = new Op[Int, Int, Int] {
+    def apply(x: Int, y: Int) = scala.math.min(x, y)
+  }
+}
+
+object Foo {
+  def foo(x: Double) = x + 1.0
+  def min[T, U, V](x: T, y: U)(implicit op: Op[T, U, V]): V = op(x, y)
+  def minInt(x: Int, y: Int)(implicit op: Op[Int, Int, Int]): Int = op(x, y)
+  def minR[R](x: Int, y: Int)(implicit op: Op[Int, Int, R]): R = op(x, y)
+  min(3, 4) // works in both
+  foo(min(3, 4)) // error: works in Scala 2, not in 3
+  foo(minInt(3, 4)) // works in both
+  foo(minR(3, 4)) // error: works in Scala 2, not in 3
+}
diff --git a/tests/neg/i9568.check b/tests/neg/i9568.check
index 737abcf21d41..11aab7e9ec56 100644
--- a/tests/neg/i9568.check
+++ b/tests/neg/i9568.check
@@ -1,7 +1,10 @@
 -- Error: tests/neg/i9568.scala:13:10 ----------------------------------------------------------------------------------
 13 |  blaMonad.foo(bla) // error: diverges
    |          ^
-   |          no implicit argument of type => Monad[F] was found for parameter ev of method blaMonad in object Test.
+   |          no implicit argument of type => Monad[F] was found for parameter ev of method blaMonad in object Test
+   |
+   |          where:    F is a type variable with constraint <: [_] =>> Any
+   |          .
    |          I found:
    |
    |              Test.blaMonad[Nothing, S](Test.blaMonad[F, S])