The new reflection

A must read: "SIP: Scala Reflection":
https://docs.google.com/document/d/1Z1VhhNPplbUpaZPIYdc0_EUv5RiGQ2X4oqp0i-vz1qw/edit

Highlights:
* Architecture has undergone a dramatic rehash.
* Universes and mirrors are now separate entities:
universes host reflection artifacts (trees, symbols, types, etc),
mirrors abstract loading of those artifacts (e.g. JavaMirror loads stuff
using a classloader and annotation unpickler, while GlobalMirror uses
internal compiler classreader to achieve the same goal).
* No static reflection mirror is imposed on the user.
One is free to choose between lightweight mirrors and full-blown
classloader-based mirror (read below).
* Public reflection API is split into scala.reflect.base and scala.reflect.api.
The former represents a minimalistic snapshot that is exactly enough to
build reified trees and types. To build, but not to analyze - everything smart
(for example, getting a type signature) is implemented in scala.reflect.api.
* Both reflection domains have their own universe: scala.reflect.basis and
scala.reflect.runtime.universe. The former is super lightweight and doesn't
involve any classloaders, while the latter represents a stripped down compiler.
* Classloader problems from 2.10.0-M3 are solved.
* Exprs and type tags are now bound to a mirror upon creation.
* However there is an easy way to migrate exprs and type tags between mirrors
and even between universes.
* This means that no classloader is imposed on the user of type tags and exprs.
If one doesn't like a classloader that's there (associated with tag's mirror),
one can create a custom mirror and migrate the tag or the expr to it.
* There is a shortcut that works in most cases. Requesting a type tag from
a full-blown universe will create that tag in a mirror that corresponds to
the callsite classloader aka `getClass.getClassLoader`. This imposes no
obligations on the programmer, since Type construction is lazy, so one
can always migrate a tag into a different mirror.

Migration notes for 2.10.0-M3 users:
* Incantations in Predef are gone, some of them have moved to scala.reflect.
* Everything path-dependent requires implicit prefix (for example, to refer
to a type tag, you need to explicitly specify the universe it belongs to,
e.g. reflect.basis.TypeTag or reflect.runtime.universe.TypeTag).
* ArrayTags have been removed, ConcreteTypeTag have been renamed to TypeTags,
TypeTags have been renamed to AbsTypeTags. Look for the reasoning in the
nearby children of this commit. Why not in this commit? Scroll this message
to the very bottom to find out the reason.
* Some of the functions have been renamed or moved around.
The rule of thumb is to look for anything non-trivial in scala.reflect.api.
Some of tree build utils have been moved to Universe.build.
* staticModule and staticClass have been moved from universes to mirrors
* ClassTag.erasure => ClassTag.runtimeClass
* For the sake of purity, type tags no longer have erasures.
Use multiple context bounds (e.g. def foo[T: ru.TypeTag : ClassTag](...) = ...)
if you're interested in having both erasures and types for type parameters.
* reify now rolls back macro applications.
* Runtime evaluation is now explicit, requires import scala.tools.reflect.Eval
and scala-compiler.jar on the classpath.
* Macro context now has separate universe and mirror fields.
* Most of the useful stuff is declared in c.universe,
so be sure to change your "import c.universe._" to "import c.mirror._".
* Due to the changes in expressions and type tags, their regular factories
are now really difficult to use. We acknowledge that macro users need to
frequently create exprs and tags, so we added old-style factories to context.
Bottom line: almost always prepend Expr(...)/TypeTag(...) with "c.".
* Expr.eval has been renamed to Expr.splice.
* Expr.value no longer splices (it can still be used to express cross-stage
path-dependent types as specified in SIP-16).
* c.reifyTree now has a mirror parameter that lets one customize the initial
mirror the resulting Expr will be bound to. If you provide EmptyTree, then
the reifier will automatically pick a reasonable mirror (callsite classloader
mirror for a full-blown universe and rootMirror for a basis universe).
Bottom line: this parameter should be EmptyTree in 99% of cases.
* c.reifyErasure => c.reifyRuntimeClass.

Known issues:
* API is really raw, need your feedback.
* All reflection artifacts are now represented by abstract types.
This means that pattern matching against them will emit unchecked warnings.
Adriaan is working on a patch that will fix that.

WARNING, FELLOW CODE EXPLORER! You have entered a turbulence zone.
For this commit and its nearby parents and children
tests are not guaranteed to work. Things get back to normal only after
the "repairs the tests after the refactoring spree" commit.

Why so weird? These twentish changesets were once parts of a humongous blob,
which spanned 1200 files and 15 kLOC. I did my best to split up the blob,
so that the individual parts of the code compile and make sense in isolation.
However doing the same for tests would be too much work.

1 files changed, 10 insertions, 16 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Macros.scala b/src/compiler/scala/tools/nsc/typechecker/Macros.scala
index 8895642893..ed3f372cb2 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Macros.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Macros.scala
@@ -4,7 +4,7 @@ package typechecker
 import symtab.Flags._
 import scala.tools.nsc.util._
 import scala.tools.nsc.util.ClassPath._
-import scala.reflect.ReflectionUtils
+import scala.reflect.runtime.ReflectionUtils
 import scala.collection.mutable.ListBuffer
 import scala.compat.Platform.EOL
 import util.Statistics._
@@ -796,7 +796,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
     def collectMacroArgs(tree: Tree): Unit = tree match {
       case Apply(fn, args) =>
         // todo. infer precise typetag for this Expr, namely the declared type of the corresponding macro impl argument
-        exprArgs.prepend(args map (Expr(_)(TypeTag.Nothing)))
+        exprArgs.prepend(args map (arg => Expr(rootMirror, FixedMirrorTreeCreator(rootMirror, arg))(TypeTag.Nothing)))
         collectMacroArgs(fn)
       case TypeApply(fn, args) =>
         typeArgs = args
@@ -806,7 +806,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
       case _ =>
     }
     collectMacroArgs(expandee)
-    val context = expandee.attachmentOpt[MacroAttachment].flatMap(_.macroContext).getOrElse(macroContext(typer, prefixTree, expandee))
+    val context = expandee.attachments.get[MacroAttachment].flatMap(_.macroContext).getOrElse(macroContext(typer, prefixTree, expandee))
     var argss: List[List[Any]] = List(context) :: exprArgs.toList
     macroTraceVerbose("argss: ")(argss)
     val rawArgss =
@@ -897,13 +897,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
           }
           Some(tparam)
         })
-        val tags = paramss.last takeWhile (_.isType) map (resolved(_)) map (tpe => {
-          // generally speaking, it's impossible to calculate erasure from a tpe here
-          // the tpe might be compiled by this run, so its jClass might not exist yet
-          // hence I just pass `null` instead and leave this puzzle to macro programmers
-          val ttag = TypeTag(tpe, null)
-          if (ttag.isConcrete) ttag.toConcrete else ttag
-        })
+        val tags = paramss.last takeWhile (_.isType) map (resolved(_)) map (tpe => if (tpe.isConcrete) context.ConcreteTypeTag(tpe) else context.TypeTag(tpe))
         if (paramss.lastOption map (params => !params.isEmpty && params.forall(_.isType)) getOrElse false) argss = argss :+ Nil
         argss = argss.dropRight(1) :+ (tags ++ argss.last) // todo. add support for context bounds in argss
 
@@ -1059,7 +1053,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
         + "If you have troubles tracking free @kind@ variables, consider using -Xlog-free-@kind@s"
       )
       val forgotten = (
-        if (sym.isTerm) "eval when splicing this variable into a reifee"
+        if (sym.isTerm) "splice when splicing this variable into a reifee"
         else "c.TypeTag annotation for this type parameter"
       )
       typer.context.error(expandee.pos,
@@ -1086,8 +1080,8 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
             macroLogVerbose("original:")
             macroLogLite("" + expanded.tree + "\n" + showRaw(expanded.tree))
 
-            freeTerms(expanded.tree) foreach issueFreeError
-            freeTypes(expanded.tree) foreach issueFreeError
+            expanded.tree.freeTerms foreach issueFreeError
+            expanded.tree.freeTypes foreach issueFreeError
             if (hasNewErrors) failExpansion()
 
             // inherit the position from the first position-ful expandee in macro callstack
@@ -1121,7 +1115,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
               delayed += expandee -> undetparams
               // need to save typer context for `macroExpandAll`
               // need to save macro context to preserve enclosures
-              expandee attach MacroAttachment(delayed = true, typerContext = typer.context, macroContext = Some(context))
+              expandee addAttachment MacroAttachment(delayed = true, typerContext = typer.context, macroContext = Some(context.asInstanceOf[MacroContext]))
               Delay(expandee)
             }
             else {
@@ -1136,7 +1130,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
                 case x          => x
               }
               finally {
-                expandee.detach(classOf[MacroAttachment])
+                expandee.removeAttachment[MacroAttachment]
                 if (!isSuccess) openMacros = openMacros.tail
               }
             }
@@ -1287,7 +1281,7 @@ trait Macros extends scala.tools.reflect.FastTrack with Traces {
       override def transform(tree: Tree) = super.transform(tree match {
         // todo. expansion should work from the inside out
         case wannabe if (delayed contains wannabe) && calculateUndetparams(wannabe).isEmpty =>
-          val context = wannabe.attachment[MacroAttachment].typerContext
+          val context = wannabe.attachments.get[MacroAttachment].get.typerContext
           delayed -= wannabe
           context.implicitsEnabled = typer.context.implicitsEnabled
           context.enrichmentEnabled = typer.context.enrichmentEnabled