blackbox restriction #3: can't affect implicit search

When an application of a blackbox macro is used as an implicit candidate,
no expansion is performed until the macro is selected as the result of
the implicit search.

This makes it impossible to dynamically calculate availability of
implicit macros.

1 files changed, 21 insertions, 20 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index c9dbdb93ff..01acbb8cc2 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -596,7 +596,7 @@ trait Implicits {
       // workaround for deficient context provided by ModelFactoryImplicitSupport#makeImplicitConstraints
       val isScalaDoc = context.tree == EmptyTree
 
-      val itree = atPos(pos.focus) {
+      val itree0 = atPos(pos.focus) {
         if (isLocal && !isScalaDoc) {
           // SI-4270 SI-5376 Always use an unattributed Ident for implicits in the local scope,
           // rather than an attributed Select, to detect shadowing.
@@ -608,15 +608,16 @@ trait Implicits {
           Select(gen.mkAttributedQualifier(info.pre), implicitMemberName)
         }
       }
-      typingLog("considering", typeDebug.ptTree(itree))
+      val itree1 = if (isBlackbox(info.sym)) suppressMacroExpansion(itree0) else itree0
+      typingLog("considering", typeDebug.ptTree(itree1))
 
-      def fail(reason: String): SearchResult = failure(itree, reason)
-      def fallback = typed1(itree, EXPRmode, wildPt)
+      def fail(reason: String): SearchResult = failure(itree0, reason)
+      def fallback = typed1(itree1, EXPRmode, wildPt)
       try {
-        val itree1 = if (!isView) fallback else pt match {
+        val itree2 = if (!isView) fallback else pt match {
           case Function1(arg1, arg2) =>
             typed1(
-              atPos(itree.pos)(Apply(itree, List(Ident("<argument>") setType approximate(arg1)))),
+              atPos(itree0.pos)(Apply(itree1, List(Ident("<argument>") setType approximate(arg1)))),
               EXPRmode,
               approximate(arg2)
             ) match {
@@ -647,10 +648,10 @@ trait Implicits {
 
         if (Statistics.canEnable) Statistics.incCounter(typedImplicits)
 
-        val itree2 = if (isView) treeInfo.dissectApplied(itree1).callee
-                     else adapt(itree1, EXPRmode, wildPt)
+        val itree3 = if (isView) treeInfo.dissectApplied(itree2).callee
+                     else adapt(itree2, EXPRmode, wildPt)
 
-        typingStack.showAdapt(itree, itree2, pt, context)
+        typingStack.showAdapt(itree0, itree3, pt, context)
 
         def hasMatchingSymbol(tree: Tree): Boolean = (tree.symbol == info.sym) || {
           tree match {
@@ -663,21 +664,21 @@ trait Implicits {
 
         if (context.hasErrors)
           fail("hasMatchingSymbol reported error: " + context.firstError.get.errMsg)
-        else if (isLocal && !hasMatchingSymbol(itree1))
+        else if (isLocal && !hasMatchingSymbol(itree2))
           fail("candidate implicit %s is shadowed by %s".format(
-            info.sym.fullLocationString, itree1.symbol.fullLocationString))
+            info.sym.fullLocationString, itree2.symbol.fullLocationString))
         else {
           val tvars = undetParams map freshVar
           def ptInstantiated = pt.instantiateTypeParams(undetParams, tvars)
 
-          if (matchesPt(itree2.tpe, ptInstantiated, undetParams)) {
+          if (matchesPt(itree3.tpe, ptInstantiated, undetParams)) {
             if (tvars.nonEmpty)
               typingLog("solve", ptLine("tvars" -> tvars, "tvars.constr" -> tvars.map(_.constr)))
 
-            val targs = solvedTypes(tvars, undetParams, undetParams map varianceInType(pt), upper = false, lubDepth(itree2.tpe :: pt :: Nil))
+            val targs = solvedTypes(tvars, undetParams, undetParams map varianceInType(pt), upper = false, lubDepth(itree3.tpe :: pt :: Nil))
 
             // #2421: check that we correctly instantiated type parameters outside of the implicit tree:
-            checkBounds(itree2, NoPrefix, NoSymbol, undetParams, targs, "inferred ")
+            checkBounds(itree3, NoPrefix, NoSymbol, undetParams, targs, "inferred ")
             context.firstError match {
               case Some(err) =>
                 return fail("type parameters weren't correctly instantiated outside of the implicit tree: " + err.errMsg)
@@ -693,7 +694,7 @@ trait Implicits {
               if (okParams.isEmpty) EmptyTreeTypeSubstituter
               else {
                 val subst = new TreeTypeSubstituter(okParams, okArgs)
-                subst traverse itree2
+                subst traverse itree3
                 notifyUndetparamsInferred(okParams, okArgs)
                 subst
               }
@@ -711,9 +712,9 @@ trait Implicits {
             // This is just called for the side effect of error detection,
             // see SI-6966 to see what goes wrong if we use the result of this
             // as the SearchResult.
-            itree2 match {
-              case TypeApply(fun, args)           => typedTypeApply(itree2, EXPRmode, fun, args)
-              case Apply(TypeApply(fun, args), _) => typedTypeApply(itree2, EXPRmode, fun, args) // t2421c
+            itree3 match {
+              case TypeApply(fun, args)           => typedTypeApply(itree3, EXPRmode, fun, args)
+              case Apply(TypeApply(fun, args), _) => typedTypeApply(itree3, EXPRmode, fun, args) // t2421c
               case t                              => t
             }
 
@@ -721,13 +722,13 @@ trait Implicits {
               case Some(err) =>
                 fail("typing TypeApply reported errors for the implicit tree: " + err.errMsg)
               case None      =>
-                val result = new SearchResult(itree2, subst)
+                val result = new SearchResult(unsuppressMacroExpansion(itree3), subst)
                 if (Statistics.canEnable) Statistics.incCounter(foundImplicits)
                 typingLog("success", s"inferred value of type $ptInstantiated is $result")
                 result
             }
           }
-          else fail("incompatible: %s does not match expected type %s".format(itree2.tpe, ptInstantiated))
+          else fail("incompatible: %s does not match expected type %s".format(itree3.tpe, ptInstantiated))
         }
       }
       catch {