Don't mention evidence$n parameters in error message

Author: odersky

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

@@ -14,7 +14,7 @@ import Flags._
 import TypeErasure.{erasure, hasStableErasure}
 import Mode.ImplicitsEnabled
 import NameOps._
-import NameKinds.LazyImplicitName
+import NameKinds.{LazyImplicitName, EvidenceParamName}
 import Symbols._
 import Denotations._
 import Types._
@@ -1265,7 +1265,8 @@ trait Implicits { self: Typer =>
         def addendum = if (qt1 eq qt) "" else (i"\nwhich is an alias of: $qt1")
         em"parameter of ${qual.tpe.widen}$addendum"
       case _ =>
-        em"parameter ${paramName} of $methodStr"
+        em"${ if paramName.is(EvidenceParamName) then "an implicit parameter"
+              else s"parameter $paramName" } of $methodStr"
     }
 
   private def strictEquality(implicit ctx: Context): Boolean =

tests/neg/missing-implicit1.check

@@ -19,7 +19,7 @@
 -- Error: tests/neg/missing-implicit1.scala:23:42 ----------------------------------------------------------------------
 23 |    List(1, 2, 3).traverse(x => Option(x)) // error
    |                                          ^
-   |no implicit argument of type testObjectInstance.Zip[Option] was found for parameter evidence$1 of method traverse in trait Traverse
+   |no implicit argument of type testObjectInstance.Zip[Option] was found for an implicit parameter of method traverse in trait Traverse
    |
    |The following import might fix the problem:
    |
@@ -68,7 +68,7 @@
 -- Error: tests/neg/missing-implicit1.scala:50:42 ----------------------------------------------------------------------
 50 |    List(1, 2, 3).traverse(x => Option(x)) // error
    |                                          ^
-   |no implicit argument of type Zip[Option] was found for parameter evidence$2 of method traverse in trait Traverse
+   |no implicit argument of type Zip[Option] was found for an implicit parameter of method traverse in trait Traverse
    |
    |The following import might fix the problem:
    |