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diff --git a/src/library/scala/annotation/implicitAmbiguous.scala b/src/library/scala/annotation/implicitAmbiguous.scala
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+++ b/src/library/scala/annotation/implicitAmbiguous.scala
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+package scala.annotation
+
+/**
+  * To customize the error message that's emitted when an implicit search finds
+  * multiple ambiguous values, annotate at least one of the implicit values
+  * `@implicitAmbiguous`. Assuming the implicit value is a method with type
+  * parameters `X1,..., XN`, the error message will be the result of replacing
+  * all occurrences of `${Xi}` in the string `msg` with the string representation
+  * of the corresponding type argument `Ti`.
+  *
+  * If more than one `@implicitAmbiguous` annotation is collected, the compiler is
+  * free to pick any of them to display.
+  *
+  * Nice errors can direct users to fix imports or even tell them why code
+  * intentionally doesn't compile.
+  *
+  * {{{
+  * trait =!=[C, D]
+  *
+  * implicit def neq[E, F] : E =!= F = null
+  *
+  * @annotation.implicitAmbiguous("Could not prove ${J} =!= ${J}")
+  * implicit def neqAmbig1[G, H, J] : J =!= J = null
+  * implicit def neqAmbig2[I] : I =!= I = null
+  *
+  * implicitly[Int =!= Int]
+  * }}}
+  *
+  * @author Brian McKenna
+  * @since 2.12.0
+  */
+final class implicitAmbiguous(msg: String) extends scala.annotation.StaticAnnotation