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Fix #876: Allow implicit conversions from singleton types #4738

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Merged
merged 7 commits into from
Jun 29, 2018
Merged

Fix #876: Allow implicit conversions from singleton types #4738

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bd04177
Fix #876: Allow implicit conversions from singleton types
odersky Jun 28, 2018
4721da5
Add test case
odersky Jun 28, 2018
d3cd401
Fix neg test
odersky Jun 28, 2018
69bfb34
Fix #3781: Eligibility checks should ignore SingletonType
odersky Jun 28, 2018
5728b19
Some tweaks to improve performance
odersky Jun 29, 2018
c8d9b0d
Slightly reformulate comment
smarter Jun 29, 2018
673af1f
Add neg test
smarter Jun 29, 2018
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1 change: 1 addition & 0 deletions compiler/src/dotty/tools/dotc/core/Mode.scala
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Expand Up @@ -37,6 +37,7 @@ object Mode {
* that TypeParamRefs can be sub- and supertypes of anything. See TypeComparer.
*/
val TypevarsMissContext = newMode(4, "TypevarsMissContext")

val CheckCyclic = newMode(5, "CheckCyclic")

/** We are looking at the arguments of a supercall */
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17 changes: 10 additions & 7 deletions compiler/src/dotty/tools/dotc/typer/Implicits.scala
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Expand Up @@ -71,17 +71,20 @@ object Implicits {
/** The implicit references */
def refs: List[ImplicitRef]

private var SingletonClass: ClassSymbol = null
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@allanrenucci allanrenucci Jun 29, 2018

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private[this] to avoid generating accessors?

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@smarter smarter Jun 29, 2018

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Why add a cache for SingletonClass?

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@odersky odersky Jun 29, 2018

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Same reason as for the caches in TypeComparer. It's used a lot and as a lazy val access is not super fast. It was one of the performance tweaks I applied after we saw a slip. Not sure it was the one that made the difference.


/** Widen type so that it is neither a singleton type nor it inherits from scala.Singleton. */
private def widenSingleton(tp: Type)(implicit ctx: Context): Type = {
if (SingletonClass == null) SingletonClass = defn.SingletonClass
val wtp = tp.widenSingleton
if (wtp.derivesFrom(SingletonClass)) defn.AnyType else wtp
}

/** Return those references in `refs` that are compatible with type `pt`. */
protected def filterMatching(pt: Type)(implicit ctx: Context): List[Candidate] = track("filterMatching") {

def refMatches(ref: TermRef)(implicit ctx: Context) = /*trace(i"refMatches $ref $pt")*/ {

/** Widen type so that it is neither a singleton type nor it inherits from scala.Singleton. */
def widenSingleton(tp: Type): Type = {
val wtp = tp.widenSingleton
if (wtp.derivesFrom(defn.SingletonClass)) defn.AnyType else wtp
}

def discardForView(tpw: Type, argType: Type): Boolean = tpw match {
case mt: MethodType =>
mt.isImplicitMethod ||
Expand Down Expand Up @@ -150,7 +153,7 @@ object Implicits {
val res = adjustSingletonArg(tp.resType)
if (res `eq` tp.resType) tp else tp.derivedLambdaType(resType = res)
case tp: MethodType =>
tp.derivedLambdaType(paramInfos = tp.paramInfos.map(widenSingleton))
tp.derivedLambdaType(paramInfos = tp.paramInfos.mapConserve(widenSingleton))
case _ => tp
}

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