replaced the implicit `identity` coercion by `c...

replaced the implicit `identity` coercion by `conforms`, which can be
used to encode generalised constraints the introduction of `conforms`
revealed a bug in adaptToMember, which was inferring views while already
inferring one, which gave rise to diverging implicits. Predef.identity
is no longer special as far as the compiler is concerned.

because conforms/identity was no longer prevented from being used as
a view (which does not make sense, but preventing it shouldn't be
necessary), removeNames in NamesDefaults suddenly didn't detect all
ambiguities because it relied on tryTypedApply failing fixed by using an
EmptyTree as an ambiguous argument instead of the argument, so failure
is guaranteed

fixed check file for t0590

new starr

fixed the weirdest bug ever: don't know why, but can't change the total
number of calls to newTermName in StdNames (so take away the one for
"identity", give one back, doesn't matter where --> see "utterweirdness"
at the end) the problem manifested itself by not finding Nil. This only
happens during start up (when the scala/package.scala file hasn't been
compiled yet), when Nil is required before List (because that would have
forced Nil to be loaded).

5 files changed, 26 insertions, 11 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/Definitions.scala b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
index 150cc9a12d..0f6fd6a944 100644
--- a/src/compiler/scala/tools/nsc/symtab/Definitions.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
@@ -111,7 +111,6 @@ trait Definitions {
         if (!ClassClass.unsafeTypeParams.isEmpty && !phase.erasedTypes)
           appliedType(ClassClass.tpe, List(classType))
         else ClassClass.tpe
-      def Predef_identity = getMember(PredefModule, nme.identity)
       def Predef_error    = getMember(PredefModule, nme.error)
     lazy val ConsoleModule: Symbol = getModule("scala.Console")
     lazy val ScalaRunTimeModule: Symbol = getModule("scala.runtime.ScalaRunTime")
diff --git a/src/compiler/scala/tools/nsc/symtab/StdNames.scala b/src/compiler/scala/tools/nsc/symtab/StdNames.scala
index baeea7273a..885af91fdb 100644
--- a/src/compiler/scala/tools/nsc/symtab/StdNames.scala
+++ b/src/compiler/scala/tools/nsc/symtab/StdNames.scala
@@ -295,7 +295,6 @@ trait StdNames {
     val hashCode_ = newTermName("hashCode")
     val hasNext = newTermName("hasNext")
     val head = newTermName("head")
-    val identity = newTermName("identity")
     val invoke_ = newTermName("invoke")
     val isInstanceOf_ = newTermName("isInstanceOf")
     val isDefinedAt = newTermName("isDefinedAt")
@@ -403,6 +402,9 @@ trait StdNames {
     // Stores Java annotations on parameters with RetentionPolicy.RUNTIME
     val RuntimeParamAnnotationATTR = newTermName("RuntimeVisibleParameterAnnotations")
     val ScalaATTR = newTermName("Scala")
+
+    newTermName("utterweirdness") // (adriaan) removed newTermName("identity"),
+    // but if I don't give something in return, quick.lib (after newstarr) fails with "error: not found: value Nil"
   }
 
   def encode(str: String): Name = newTermName(NameTransformer.encode(str))
diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index dc00955e0b..bce3c4a5ee 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -247,16 +247,17 @@ self: Analyzer =>
     private def typedImplicit(info: ImplicitInfo): SearchResult =
        context.openImplicits find (dominates(pt, _)) match {
          case Some(pending) =>
-           //println("Pending implicit "+pending+" dominates "+pt+"/"+undetParams)
+           // println("Pending implicit "+pending+" dominates "+pt+"/"+undetParams) //@MDEBUG
            throw DivergentImplicit
            SearchFailure
          case None =>
            try {
              context.openImplicits = pt :: context.openImplicits
-             //println("  "*context.openImplicits.length+"typed implicit "+info+" for "+pt)
+             // println("  "*context.openImplicits.length+"typed implicit "+info+" for "+pt) //@MDEBUG
              typedImplicit0(info)
            } catch {
              case DivergentImplicit =>
+               // println("DivergentImplicit for pt:"+ pt +", open implicits:"+context.openImplicits) //@MDEBUG
                if (context.openImplicits.tail.isEmpty) {
                  if (!(pt.isErroneous))
                    context.unit.error(
@@ -413,16 +414,17 @@ self: Analyzer =>
        *  This is the case if all of the following holds:
        *   - the info's type is not erroneous,
        *   - the info is not shadowed by another info with the same name,
-       *   - if the symbol is Predef.identity, then we are not looking for a view,
        *   - the result of typedImplicit is non-empty.
        *   @return A search result with an attributed tree containing the implicit if succeeded,
        *           SearchFailure if not.
        */
       def tryImplicit(info: ImplicitInfo): SearchResult =
-        if (!containsError(info.tpe) &&
-            !(isLocal && shadowed.contains(info.name)) &&
-            (!isView || info.sym != Predef_identity)) typedImplicit(info)
-        else SearchFailure
+        if (containsError(info.tpe) ||
+            (isLocal && shadowed.contains(info.name)) //||
+            // (isView && (info.sym == Predef_identity || info.sym == Predef_conforms}))    //@M this condition prevents no-op conversions, which are a problem (besides efficiency),
+            // one example is removeNames in NamesDefaults, which relies on the type checker failing in case of ambiguity between an assignment/named arg
+           ) SearchFailure
+        else typedImplicit(info)
 
       def appInfos(is: List[ImplicitInfo]): Map[ImplicitInfo, SearchResult] = {
         var applicable = Map[ImplicitInfo, SearchResult]()
diff --git a/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala b/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
index 482c53fac5..9d485cc730 100644
--- a/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
@@ -390,9 +390,16 @@ trait NamesDefaults { self: Analyzer =>
               argPos(index) = pos
               rhs
             case t: Tree =>
-              errorTree(arg, "reference to "+ name +" is ambiguous; it is both, a parameter\n"+
+            //@M was: errorTree(arg, ...)
+            // this throws an exception that's caught in `tryTypedApply` (as it uses `silent`)
+            // unfortunately, tryTypedApply recovers from the exception if you use errorTree(arg, ...) and conforms is allowed as a view (see tryImplicit in Implicits)
+            // because it tries to produce a new qualifier (if the old one was P, the new one will be conforms.apply(P)), and if that works, it pretends nothing happened
+            // so, to make sure tryTypedApply fails, pass EmptyTree instead
+                errorTree(EmptyTree, "reference to "+ name +" is ambiguous; it is both, a parameter\n"+
                              "name of the method and the name of a variable currently in scope.")
           }
+          //@M note that we don't get here when an ambiguity was detected (during the computation of res),
+          // as errorTree throws an exception
           typer.context.undetparams = udp
           res
         }
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 745d1c8241..b609f1f24b 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -991,7 +991,12 @@ trait Typers { self: Analyzer =>
       if (qual.isTerm &&
           ((qual.symbol eq null) || !qual.symbol.isTerm || qual.symbol.isValue) &&
           phase.id <= currentRun.typerPhase.id && !qtpe.isError && !tp.isError &&
-          qtpe.typeSymbol != NullClass && qtpe.typeSymbol != NothingClass && qtpe != WildcardType) {
+          qtpe.typeSymbol != NullClass && qtpe.typeSymbol != NothingClass && qtpe != WildcardType &&
+          context.implicitsEnabled) { // don't try to adapt a top-level type that's the subject of an implicit search
+                                      // this happens because, if isView, typedImplicit tries to apply the "current" implicit value to
+                                      // a value that needs to be coerced, so we check whether the implicit value has an `apply` method
+                                     // (if we allow this, we get divergence, e.g., starting at `conforms` during ant quick.bin)
+                                     // note: implicit arguments are still inferred (this kind of "chaining" is allowed)
         val coercion = inferView(qual, qtpe, name, tp)
         if (coercion != EmptyTree)
           typedQualifier(atPos(qual.pos)(Apply(coercion, List(qual))))