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Improved custom builder lookup (solves #6) #7

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Sep 30, 2014
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Improved custom builder lookup (solves #6) #7

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29 changes: 29 additions & 0 deletions macros/src/main/scala/com/softwaremill/macmemo/BuilderResolver.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
package com.softwaremill.macmemo

import scala.language.experimental.macros

object BuilderResolver {

def resolve(methodFullName: String): MemoCacheBuilder = macro builderResolverMacro_impl

def builderResolverMacro_impl(c: scala.reflect.macros.whitebox.Context)(methodFullName: c.Expr[String]): c.Expr[MemoCacheBuilder] = {
import c.universe._

def bringDefaultBuilder: Tree = {
val Literal(Constant(mfn: String)) = methodFullName.tree
val msg = s"Cannot find custom memo builder for '$mfn' - default builder will be used"
c.info(c.enclosingPosition, msg, false)
reify {
MemoCacheBuilder.guavaMemoCacheBuilder
}.tree
}

val builderTree = c.inferImplicitValue(typeOf[MemoCacheBuilder]) match {
case EmptyTree => bringDefaultBuilder
case foundBuilderTree => foundBuilderTree
}

c.Expr[MemoCacheBuilder](Block(List(), builderTree))
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So it seems that putting an auxiliary macro call inside a quasiquote makes c.inferImplicitValue() work well, where calling this from an annotation macro context doesn't work in all cases? That's really meta-meta :) But it looks kinda like a bug to me, or at least some weird incosistency I cannot understand...

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I'm going to do some investigation about this behaviour.
My Current clues:

  • I can't use auxilary macro directly, I need to weave a call to it in expanded code, because both macros live in the same compilation unit.
  • annotation macro can't infer implicits vals from enclosing class scope (implicit val members), but we are able to traverse them manually. This means that problem does not lie in lack of enclosure members visibility. Maybe this behaviour is intended? From @ macros we not only can add new members but even whole companion objects. But then c.inferImplicitVal should not lookup any implicits, for the same reasons..
  • based on previous clue - maybe compiler collect informations about implicits and scopes incrementally, during some typechecks or something like that? And static annotation expansions is done before phase in which compiler scan implicit vals within enclosure?

Edit:
AFAIK def macros are an (experimental) part of scala compiler, while annotation macros are still available via macroparadise plugin. Maybe this is the reason?

@xeno-by could you elaborate on this?

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@kciesielski The issue with c.typecheck (and c.inferImplicitValue that's essentially based on c.typecheck) in macro annotations is a yet unsolved problem in the design of macro annotations. That's indeed a bug.

@mkubala Your high-level hypothesis about the reason for this limitation is spot-on (if you're interested in details, scalamacros/paradise#14 provides a lot of information on the nature of the issue).

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Thanks for explanation 👍

}

}
35 changes: 3 additions & 32 deletions macros/src/main/scala/com/softwaremill/macmemo/memoizeMacro.scala
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Expand Up @@ -37,34 +37,6 @@ object memoizeMacro {

val enclosure = c.enclosingClass

def resolveMemoBuilder: Tree = {

def inferImplicitBuilderVal: Tree = {

def findImplicitBuilderVal(body: List[Tree]): Tree =
body.collect {
case v @ ValDef(m, name, _, rhs)
if (m.hasFlag(Flag.IMPLICIT) && c.typecheck(rhs).tpe <:< typeOf[MemoCacheBuilder]) =>
Ident(name)
}.lastOption.getOrElse(EmptyTree)

enclosure match {
case ClassDef(_, _, _, Template(_, _, body)) => findImplicitBuilderVal(body)
case ModuleDef(_, _, Template(_, _, body)) => findImplicitBuilderVal(body)
case oth => EmptyTree
}
}

def bringDefaultBuilder: Tree = {
c.info(c.enclosingPosition, s"Cannot find custom memo builder for method '${cachedMethodId.methodName}' - default builder will be used", false)
reify {
MemoCacheBuilder.guavaMemoCacheBuilder
}.tree
}

c.inferImplicitValue(typeOf[MemoCacheBuilder]) orElse inferImplicitBuilderVal orElse bringDefaultBuilder
}

def buildCacheBucketId: Tree = {
val enclosingClassSymbol = enclosure.symbol
val enclosureFullName = enclosingClassSymbol.fullName + (if (enclosingClassSymbol.isModule) "$." else ".")
Expand All @@ -79,10 +51,9 @@ object memoizeMacro {
q"""com.softwaremill.macmemo.MemoizeParams($maxSize, ${ttl.toMillis}, $concurrencyLevelOpt)"""
}

val t = appliedType(weakTypeOf[Cache[Any]].typeConstructor, typeOf[List[Any]] :: Nil)
ValDef(Modifiers(Flag.LAZY), cachedMethodId.generatedMemoValName, TypeTree(t),
Apply(Select(resolveMemoBuilder, TermName("build")), List(buildCacheBucketId, buildParams))
)
q"""lazy val ${cachedMethodId.generatedMemoValName}: com.softwaremill.macmemo.Cache[List[Any]] =
com.softwaremill.macmemo.BuilderResolver.resolve($buildCacheBucketId).build($buildCacheBucketId, $buildParams)"""

}

def injectCacheUsage(cachedMethodId: MemoIdentifier, function: DefDef) = {
Expand Down