From 26aebfac0c6db18483d0db67bcd7f8faf7684f0d Mon Sep 17 00:00:00 2001
From: Paul Phillips <paulp@improving.org>
Date: Tue, 23 Jul 2013 13:38:33 -0700
Subject: SI-7690 ghost error message fails compile

I won't even try to explain the error reporting code, because
it would have no basis in reality. However this change appears
to fix the symptom reported.
---
 src/compiler/scala/tools/nsc/typechecker/Contexts.scala |  2 +-
 .../scala/tools/nsc/typechecker/Implicits.scala         | 12 ++++++++++--
 test/files/pos/t7690.scala                              | 17 +++++++++++++++++
 3 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 test/files/pos/t7690.scala

diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
index 60641d6752..1b6443a4cb 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -1194,7 +1194,7 @@ trait Contexts { self: Analyzer =>
     override final def imports      = impInfo :: super.imports
     override final def firstImport  = Some(impInfo)
     override final def isRootImport = !tree.pos.isDefined
-    override final def toString     = s"ImportContext { $impInfo; outer.owner = ${outer.owner} }"
+    override final def toString     = super.toString + " with " + s"ImportContext { $impInfo; outer.owner = ${outer.owner} }"
   }
 
   /** A buffer for warnings and errors that are accumulated during speculative type checking. */
diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index 100112fec1..c87de8839f 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -60,6 +60,8 @@ trait Implicits {
    *  @return                        A search result
    */
   def inferImplicit(tree: Tree, pt: Type, reportAmbiguous: Boolean, isView: Boolean, context: Context, saveAmbiguousDivergent: Boolean, pos: Position): SearchResult = {
+    // Note that the isInvalidConversionTarget seems to make a lot more sense right here, before all the
+    // work is performed, than at the point where it presently exists.
     val shouldPrint     = printTypings && !context.undetparams.isEmpty
     val rawTypeStart    = if (Statistics.canEnable) Statistics.startCounter(rawTypeImpl) else null
     val findMemberStart = if (Statistics.canEnable) Statistics.startCounter(findMemberImpl) else null
@@ -1335,12 +1337,18 @@ trait Implicits {
         }
       }
       if (result.isSuccess && isView) {
+        def maybeInvalidConversionError(msg: String) {
+          // We have to check context.ambiguousErrors even though we are calling "issueAmbiguousError"
+          // which ostensibly does exactly that before issuing the error. Why? I have no idea. Test is pos/t7690.
+          if (context.ambiguousErrors)
+            context.issueAmbiguousError(AmbiguousImplicitTypeError(tree, msg))
+        }
         if (isInvalidConversionTarget(pt)) {
-          context.issueAmbiguousError(AmbiguousImplicitTypeError(tree, "the result type of an implicit conversion must be more specific than AnyRef"))
+          maybeInvalidConversionError("the result type of an implicit conversion must be more specific than AnyRef")
           result = SearchFailure
         }
         else if (isInvalidConversionSource(pt)) {
-          context.issueAmbiguousError(AmbiguousImplicitTypeError(tree, "an expression of type Null is ineligible for implicit conversion"))
+          maybeInvalidConversionError("an expression of type Null is ineligible for implicit conversion")
           result = SearchFailure
         }
       }
diff --git a/test/files/pos/t7690.scala b/test/files/pos/t7690.scala
new file mode 100644
index 0000000000..e8911a93e8
--- /dev/null
+++ b/test/files/pos/t7690.scala
@@ -0,0 +1,17 @@
+object A
+trait B[T]
+
+object C {
+  implicit def notUsed[L[x]](in: L[Int]): B[L[Int]] = ???
+
+  class E(val ls: Int) {
+    def x(f: Int => Boolean): Boolean = f(ls)
+  }
+  implicit def isUsed(ls: Int): E = new E(ls)
+
+  def amethod(in: Int): Boolean =
+    in.x { i =>
+      import A._
+      "asdf" == i.toString
+    }
+}
\ No newline at end of file
-- 
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