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Erase constant value type [ci: last-only] #9431

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517d057
Minor refactor in constructors
som-snytt Jan 12, 2021
c383bf0
Erase constant type
som-snytt Apr 28, 2025
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85 changes: 49 additions & 36 deletions src/compiler/scala/tools/nsc/transform/Constructors.scala
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Expand Up @@ -81,10 +81,10 @@ abstract class Constructors extends Statics with Transform with TypingTransforme

override def transform(tree: Tree): Tree = {
tree match {
case cd @ ClassDef(mods0, name0, tparams0, impl0) if !isPrimitiveValueClass(cd.symbol) && cd.symbol.primaryConstructor != NoSymbol =>
if(cd.symbol eq AnyValClass) {
case cd @ ClassDef(mods0, name0, tparams0, impl0)
if !isPrimitiveValueClass(cd.symbol) && cd.symbol.primaryConstructor != NoSymbol =>
if (cd.symbol eq AnyValClass)
cd
}
else {
checkUninitializedReads(cd)
val tplTransformer = new TemplateTransformer(unit, impl0)
Expand Down Expand Up @@ -250,7 +250,7 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
*
* @return the DefDef for (c) above
*
* */
*/
private trait DelayedInitHelper extends ConstructorTransformerBase {
private def delayedEndpointDef(stats: List[Tree]): DefDef = {
val methodName = currentUnit.freshTermName("delayedEndpoint$" + clazz.fullNameAsName('$').toString + "$")
Expand Down Expand Up @@ -458,11 +458,9 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
{
protected def typedPos(pos: Position)(tree: Tree): Tree = localTyper.typedPos(pos)(tree)

val clazz = impl.symbol.owner // the transformed class

val isDelayedInitSubclass = clazz isSubClass DelayedInitClass

private val stats = impl.body // the transformed template body
override val clazz = impl.symbol.owner // the transformed class
private val stats = impl.body // the transformed template body
private val isDelayedInitSubclass = clazz isSubClass DelayedInitClass

// find and dissect primary constructor
private val (primaryConstr, _primaryConstrParams, primaryConstrBody) =
Expand All @@ -481,7 +479,7 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
// The constructor parameter corresponding to an accessor
def parameter(acc: Symbol): Symbol = {
//works around the edge case where unexpandedName over-unexpands shenanigans like literal $$ or `$#`
def unexpanded = parameterNamed(acc.unexpandedName.getterName)
val unexpanded = parameterNamed(acc.unexpandedName.getterName)
def expanded = parameterNamed(acc.getterName)
unexpanded.orElse(expanded).swap.map(abort).merge
}
Expand All @@ -497,15 +495,14 @@ abstract class Constructors extends Statics with Transform with TypingTransforme

// A transformer for expressions that go into the constructor
object intoConstructor extends AstTransformer {
/*
* `usesSpecializedField` makes a difference in deciding whether constructor-statements
* should be guarded in a `guardSpecializedFieldInit` class, ie in a class that's the generic super-class of
* one or more specialized sub-classes.
*
* Given that `usesSpecializedField` isn't read for any other purpose than the one described above,
* we skip setting `usesSpecializedField` in case the current class isn't `guardSpecializedFieldInit` to start with.
* That way, trips to a map in `specializeTypes` are saved.
*/
/* `usesSpecializedField` makes a difference in deciding whether constructor-statements
* should be guarded in a `guardSpecializedFieldInit` class, ie in a class that's the generic super-class of
* one or more specialized sub-classes.
*
* Given that `usesSpecializedField` isn't read for any other purpose than the one described above,
* we skip setting `usesSpecializedField` in case the current class isn't `guardSpecializedFieldInit`
* to start with. That way, trips to a map in `specializeTypes` are saved.
*/
var usesSpecializedField: Boolean = false

private def isParamRef(sym: Symbol) = sym.isParamAccessor && sym.owner == clazz
Expand All @@ -518,8 +515,9 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
!sym.isVariable
)

/*
* whether `sym` denotes a param-accessor (ie in a class a PARAMACCESSOR field, or in a trait a method with same flag)
/* whether `sym` denotes a param-accessor
* (ie in a class a PARAMACCESSOR field, or in a trait a method with same flag)
*
* that fulfills all of:
* (a) has stationary value, ie the same value provided via the corresponding ctor-arg; and
* (b) isn't subject to specialization. We might be processing statements for:
Expand All @@ -534,7 +532,7 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
// references to parameter accessor methods of own class become references to parameters
// outer accessors become references to $outer parameter
// println(s"to param ref in $clazz for ${tree.symbol} ${tree.symbol.debugFlagString} / ${tree.symbol.outerSource} / ${canBeSupplanted(tree.symbol)}")
if (clazz.isTrait && !(tree.symbol hasAllFlags (ACCESSOR | PARAMACCESSOR)))
if (clazz.isTrait && !tree.symbol.hasAllFlags(ACCESSOR | PARAMACCESSOR))
super.transform(tree)
else if (canBeSupplanted(tree.symbol))
gen.mkAttributedIdent(parameter(tree.symbol)) setPos tree.pos
Expand Down Expand Up @@ -609,7 +607,7 @@ abstract class Constructors extends Statics with Transform with TypingTransforme

private def triage() = {
// Constant typed vals are not memoized.
def memoizeValue(sym: Symbol) = !sym.info.resultType.isInstanceOf[FoldableConstantType]
def memoizeValue(sym: Symbol) = enteringErasure(!sym.info.resultType.isInstanceOf[FoldableConstantType])
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Why it's important to study history.


// The early initialized field definitions of the class (these are the class members)
val presupers = treeInfo.preSuperFields(stats)
Expand Down Expand Up @@ -679,7 +677,8 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
// - the constructor, before the super call (early initialized or a parameter accessor),
// - the constructor, after the super call (regular val).
case vd: ValDef =>
if (vd.rhs eq EmptyTree) { defBuf += vd }
if (vd.rhs eq EmptyTree)
defBuf += vd
else {
val emitField = memoizeValue(statSym)

Expand All @@ -691,14 +690,22 @@ abstract class Constructors extends Statics with Transform with TypingTransforme

case dd: DefDef =>
// either move the RHS to ctor (for getter of stored field) or just drop it (for corresponding setter)
def shouldMoveRHS =
clazz.isTrait && statSym.isAccessor && !statSym.isLazy && !statSym.isSpecialized && (statSym.isSetter || memoizeValue(statSym))

if ((dd.rhs eq EmptyTree) || !shouldMoveRHS) { defBuf += dd }
else {
if (statSym.isGetter) moveEffectToCtor(dd.mods, dd.rhs, statSym.asTerm.referenced orElse statSym.setterIn(clazz))
defBuf += deriveDefDef(stat)(_ => EmptyTree)
}
def shouldMoveRHS = (
(dd.rhs ne EmptyTree)
&& clazz.isTrait
&& statSym.isAccessor
&& !statSym.isLazy
&& !statSym.isSpecialized
&& (statSym.isSetter || memoizeValue(statSym))
)
val toMove =
if (shouldMoveRHS) {
if (statSym.isGetter)
moveEffectToCtor(dd.mods, dd.rhs, statSym.asTerm.referenced.orElse(statSym.setterIn(clazz)))
deriveDefDef(stat)(_ => EmptyTree)
}
else dd
defBuf += toMove
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I used to think vertical boolean exprs (wrapped in parens) were too much style just to have leading infix operators, but after using actual leading infix (without parens), I find it much easier to read. I only preferred the one-liner because mentally I would skip it and that's why it felt easier to read.

note that under -Xsource:3 we could be using leading infix.


// all other statements go into the constructor
case _ =>
Expand Down Expand Up @@ -727,19 +734,22 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
else clazz.constrParamAccessors

// Initialize all parameters fields that must be kept.
val paramInits = paramAccessors filterNot omittableSym map { acc =>
val paramInits = paramAccessors.filterNot(omittableSym).map { acc =>
// Check for conflicting field mixed in for a val/var defined in a parent trait (neg/t1960.scala).
// Since the fields phase has already mixed in fields, we can just look for
// an existing decl with the local variant of our paramaccessor's name.
//
// TODO: mangle the constructor parameter name (it can only be used internally), though we probably first need more robust name mangling
// TODO: mangle the constructor parameter name (it can only be used internally),
// though we probably first need more robust name mangling

// sometimes acc is a field with a local name (when it's a val/var constructor param) --> exclude the `acc` itself when looking for conflicting decl
// sometimes it's not (just a constructor param) --> any conflicting decl is a problem
val conflict = clazz.info.decl(acc.name.localName).filter(sym => sym ne acc)
if (conflict ne NoSymbol) {
val orig = exitingTyper(clazz.info.nonPrivateMember(acc.name).filter(_ hasFlag ACCESSOR))
reporter.error(acc.pos, s"parameter '${acc.name}' requires field but conflicts with ${(orig orElse conflict).fullLocationString}")
reporter.error(acc.pos, s"parameter '${acc.name}' requires field but conflicts with ${
orig.orElse(conflict).fullLocationString
}")
}

val accSetter =
Expand Down Expand Up @@ -787,7 +797,10 @@ abstract class Constructors extends Statics with Transform with TypingTransforme
)
}

if ((exitingPickler(clazz.isAnonymousClass) || clazz.originalOwner.isTerm) && omittableAccessor.exists(_.isOuterField) && !constructorStats.exists(_.exists { case i: Ident if i.symbol.isOuterParam => true; case _ => false}))
if ((exitingPickler(clazz.isAnonymousClass) || clazz.originalOwner.isTerm)
&& omittableAccessor.exists(_.isOuterField)
&& !constructorStats.exists(_.exists { case i: Ident if i.symbol.isOuterParam => true case _ => false })
)
primaryConstructor.symbol.updateAttachment(OuterArgCanBeElided)

val constructors = primaryConstructor :: auxConstructors
Expand Down
48 changes: 27 additions & 21 deletions src/compiler/scala/tools/nsc/transform/Erasure.scala
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Expand Up @@ -42,7 +42,7 @@ abstract class Erasure extends InfoTransform

// -------- erasure on types --------------------------------------------------------

// convert a numeric with a toXXX method
// convert a numeric with a toNNN method
def numericConversion(tree: Tree, numericSym: Symbol): Tree = {
val mname = newTermName("to" + numericSym.name)
val conversion = tree.tpe member mname
Expand Down Expand Up @@ -90,8 +90,13 @@ abstract class Erasure extends InfoTransform
}
}
@tailrec
private[this] def untilApply(ts: List[Type]): Unit =
if (! ts.isEmpty && ! result) { apply(ts.head) ; untilApply(ts.tail) }
private def untilApply(ts: List[Type]): Unit =
ts match {
case t :: ts if !result =>
apply(t)
untilApply(ts)
case _ =>
}
}

override protected def verifyJavaErasure = settings.Xverify.value || settings.isDebug
Expand Down Expand Up @@ -795,9 +800,10 @@ abstract class Erasure extends InfoTransform
/** A replacement for the standard typer's `typed1` method.
*/
override def typed1(tree: Tree, mode: Mode, pt: Type): Tree = {
val tree1 = try {
val tree1 = try
tree match {
case DefDef(_,_,_,_,_,_) if tree.symbol.isClassConstructor && tree.symbol.isPrimaryConstructor && tree.symbol.owner != ArrayClass =>
case tree: DefDef
if tree.symbol.isClassConstructor && tree.symbol.isPrimaryConstructor && tree.symbol.owner != ArrayClass =>
super.typed1(deriveDefDef(tree)(addMixinConstructorCalls(_, tree.symbol.owner)), mode, pt) // (3)
case Template(parents, self, body) =>
val parents1 = tree.symbol.owner.info.parents map (t => TypeTree(t) setPos tree.pos)
Expand All @@ -820,16 +826,14 @@ abstract class Erasure extends InfoTransform
case _ =>
super.typed1(adaptMember(tree), mode, pt)
}
} catch {
catch {
case er: TypeError =>
Console.println("exception when typing " + tree+"/"+tree.getClass)
Console.println(er.msg + " in file " + context.owner.sourceFile)
er.printStackTrace
abort("unrecoverable error")
case ex: Exception =>
//if (settings.debug.value)
try Console.println("exception when typing " + tree)
finally throw ex
try Console.println(s"exception when typing $tree") catch identity: @nowarn
throw ex
}

Expand All @@ -846,7 +850,6 @@ abstract class Erasure extends InfoTransform
case Some(SAMFunction(samTp, _, _)) => fun setType specialScalaErasure(samTp)
case _ => fun
}

case If(cond, thenp, elsep) =>
treeCopy.If(tree1, cond, adaptBranch(thenp), adaptBranch(elsep))
case Match(selector, cases) =>
Expand All @@ -858,7 +861,7 @@ abstract class Erasure extends InfoTransform
val first = tree1.symbol.alternatives.head
val firstTpe = first.tpe
val sym1 = tree1.symbol.filter {
alt => alt == first || !(firstTpe looselyMatches alt.tpe)
alt => alt == first || !firstTpe.looselyMatches(alt.tpe)
}
if (tree.symbol ne sym1) {
tree1 setSymbol sym1 setType sym1.tpe
Expand All @@ -884,13 +887,15 @@ abstract class Erasure extends InfoTransform
else if (low.owner == base) "name clash between defined and inherited member"
else "name clash between inherited members"
)
val when = if (exitingRefchecks(lowType matches highType)) "" else " after erasure: " + exitingPostErasure(highType)
val when =
if (exitingRefchecks(lowType matches highType)) ""
else s" after erasure: ${exitingPostErasure(highType)}"

reporter.error(pos,
s"""|$what:
|${exitingRefchecks(highString)} and
|${exitingRefchecks(lowString)}
|have same type$when""".trim.stripMargin
sm"""|$what:
|${exitingRefchecks(highString)} and
|${exitingRefchecks(lowString)}
|have same type$when"""
)
}
low setInfo ErrorType
Expand Down Expand Up @@ -1195,7 +1200,7 @@ abstract class Erasure extends InfoTransform
global.typer.typed(gen.mkRuntimeCall(nme.anyValClass, List(qual, typer.resolveClassTag(tree.pos, qual.tpe.widen))))
} else if (primitiveGetClassMethods.contains(fn.symbol)) {
// if we got here then we're trying to send a primitive getClass method to either
// a) an Any, in which cage Object_getClass works because Any erases to object. Or
// a) an Any, in which case Object_getClass works because Any erases to object. Or
//
// b) a non-primitive, e.g. because the qualifier's type is a refinement type where one parent
// of the refinement is a primitive and another is AnyRef. In that case
Expand Down Expand Up @@ -1226,10 +1231,11 @@ abstract class Erasure extends InfoTransform
case tree: Apply =>
preEraseApply(tree)

case TypeApply(fun, args) if (fun.symbol.owner != AnyClass &&
fun.symbol != Object_asInstanceOf &&
fun.symbol != Object_isInstanceOf &&
fun.symbol != Object_synchronized) =>
case TypeApply(fun, args)
if fun.symbol.owner != AnyClass
&& fun.symbol != Object_asInstanceOf
&& fun.symbol != Object_isInstanceOf
&& fun.symbol != Object_synchronized =>
// leave all other type tests/type casts, remove all other type applications
preErase(fun)

Expand Down
2 changes: 1 addition & 1 deletion src/compiler/scala/tools/nsc/transform/Mixin.scala
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Expand Up @@ -404,7 +404,7 @@ abstract class Mixin extends Transform with ast.TreeDSL with AccessorSynthesis {
// first complete the superclass with mixed in members
addMixedinMembers(clazz.superClass, unit)

for (mc <- clazz.mixinClasses ; if mc.isTrait) {
for (mc <- clazz.mixinClasses if mc.isTrait) {
// @SEAN: adding trait tracking so we don't have to recompile transitive closures
unit.registerDependency(mc)
publicizeTraitMethods(mc)
Expand Down
8 changes: 2 additions & 6 deletions src/reflect/scala/reflect/internal/Symbols.scala
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Expand Up @@ -2469,12 +2469,8 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
*
* @param ofclazz is a subclass of this symbol's owner
*/
final def overridingSymbol(ofclazz: Symbol): Symbol = (
if (canMatchInheritedSymbols)
matchingSymbol(ofclazz, ofclazz.thisType)
else
NoSymbol
)
final def overridingSymbol(ofclazz: Symbol): Symbol =
if (canMatchInheritedSymbols) matchingSymbol(ofclazz, ofclazz.thisType) else NoSymbol
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One-liner has the same form as previous method; this works well because the else alternative is trivial.


/** If false, this symbol cannot possibly participate in an override,
* either as overrider or overridee. For internal use; you should consult
Expand Down
19 changes: 9 additions & 10 deletions src/reflect/scala/reflect/internal/transform/Erasure.scala
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Expand Up @@ -134,8 +134,10 @@ trait Erasure {
def apply(tp: Type): Type = tp match {
case FoldableConstantType(ct) =>
// erase classOf[List[_]] to classOf[List]. special case for classOf[Unit], avoid erasing to classOf[BoxedUnit].
if (ct.tag == ClazzTag && ct.typeValue.typeSymbol != UnitClass) ConstantType(Constant(apply(ct.typeValue)))
else tp
if (ct.tag == ClazzTag)
if (ct.typeValue.typeSymbol == UnitClass) tp
else ConstantType(Constant(apply(ct.typeValue)))
else ct.tpe
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The fix for erasure. There are really 2 special cases under Class constant. Presumably the Unit case is handled specially later, but from this perspective, the encoding doesn't look regular.

case st: ThisType if st.sym.isPackageClass =>
tp
case st: SubType =>
Expand Down Expand Up @@ -253,7 +255,7 @@ trait Erasure {
else scalaErasure
}

/** This is used as the Scala erasure during the erasure phase itself
/** This is used as the Scala erasure during the erasure phase itself.
* It differs from normal erasure in that value classes are erased to ErasedValueTypes which
* are then later converted to the underlying parameter type in phase posterasure.
*/
Expand All @@ -262,11 +264,10 @@ trait Erasure {
erasure(sym)(tp)
else if (sym.isClassConstructor)
specialConstructorErasure(sym.owner, tp)
else {
else
specialScalaErasureFor(sym)(tp)
}

def specialConstructorErasure(clazz: Symbol, tpe: Type): Type = {
def specialConstructorErasure(clazz: Symbol, tpe: Type): Type =
tpe match {
case PolyType(tparams, restpe) =>
specialConstructorErasure(clazz, restpe)
Expand All @@ -282,7 +283,6 @@ trait Erasure {
assert(clazz == ArrayClass || tp.isError, s"unexpected constructor erasure $tp for $clazz")
specialScalaErasureFor(clazz)(tp)
}
}

/** Scala's more precise erasure than java's is problematic as follows:
*
Expand Down Expand Up @@ -530,7 +530,7 @@ trait Erasure {
ErasedValueType(tref.sym, erasedValueClassArg(tref))
}

/** This is used as the Scala erasure during the erasure phase itself
/** This is used as the Scala erasure during the erasure phase itself.
* It differs from normal erasure in that value classes are erased to ErasedValueTypes which
* are then later unwrapped to the underlying parameter type in phase posterasure.
*/
Expand All @@ -541,10 +541,9 @@ trait Erasure {
*/
object specialScala3Erasure extends Scala3ErasureMap with SpecialScalaErasure

def specialScalaErasureFor(sym: Symbol): ErasureMap = {
def specialScalaErasureFor(sym: Symbol): ErasureMap =
if (sym.isScala3Defined) specialScala3Erasure
else specialScalaErasure
}

object javaErasure extends JavaErasureMap

Expand Down
2 changes: 1 addition & 1 deletion test/files/run/patmat-seq.check
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Expand Up @@ -264,7 +264,7 @@ package <empty> {
()
};
def t(): Object = {
case <synthetic> val x1: Int(2) = 2;
case <synthetic> val x1: Int = 2;
case16(){
<synthetic> val o18: scala.collection.SeqOps = A.unapplySeq(x1);
if (scala.collection.SeqFactory.UnapplySeqWrapper.isEmpty$extension(o18).unary_!())
Expand Down
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