SI-9231 Don't attempt implicit search for erroneous parameter

If the instantiated type of an implicit parameter is erroneous,
we should not attempt the implicit search. This avoids the following
useless error message in the enclosed test:

    error: ambiguous implicit values: ... match expected type M[<error>]

Author: retronym

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -151,7 +151,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           for(ar <- argResultsBuff)
             paramTp = paramTp.subst(ar.subst.from, ar.subst.to)
 
-          val res = if (paramFailed || (paramTp.isError && {paramFailed = true; true})) SearchFailure else inferImplicit(fun, paramTp, context.reportErrors, isView = false, context)
+          val res = if (paramFailed || (paramTp.isErroneous && {paramFailed = true; true})) SearchFailure else inferImplicit(fun, paramTp, context.reportErrors, isView = false, context)
           argResultsBuff += res
 
           if (res.isSuccess) {

test/files/neg/t9231.check

@@ -0,0 +1,4 @@
+t9231.scala:8: error: not found: type DoesNotExist
+  foo[DoesNotExist]
+      ^
+one error found

test/files/neg/t9231.scala

@@ -0,0 +1,9 @@
+class M[A]
+class C {
+  implicit def M1: M[Int] = null
+  implicit def M2: M[String] = null
+
+  def foo[A](implicit M: M[A]) = null
+
+  foo[DoesNotExist]
+}