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Update documentation
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‎compiler/src/dotty/tools/dotc/transform/init/Objects.scala

Lines changed: 27 additions & 91 deletions
Original file line numberDiff line numberDiff line change
@@ -56,16 +56,9 @@ import dotty.tools.dotc.util.SrcPos
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* This principle not only put initialization of static objects on a solid foundation, but also
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* avoids whole-program analysis.
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*
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* 2. The design is based on the concept of "Top" --- a Top value may not be actively
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* used during initialization, i.e., it's forbidden to call methods or access fields of a Top.
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* Method arguments are widened to Top by default unless specified to be sensitive.
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* Method parameters captured in lambdas or inner classes are always widened to Top.
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* 2. It is inter-procedural and flow-sensitive.
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*
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* 3. It is inter-procedural and flow-sensitive.
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*
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* 4. It is object-sensitive by default and parameter-sensitive on-demand.
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*
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* 5. The check is modular in the sense that each object is checked separately and there is no
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* 3. The check is modular in the sense that each object is checked separately and there is no
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* whole-program analysis. However, the check is not modular in terms of project boundaries.
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*
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*/
@@ -91,30 +84,24 @@ class Objects(using Context @constructorOnly):
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/** Syntax for the data structure abstraction used in abstract domain:
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*
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* ve ::= ObjectRef(class) // global object
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* | OfClass(class, vs[outer], ctor, args, env) // instance of a class
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* | OfArray(object[owner], regions)
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* | Fun(..., env) // value elements that can be contained in ValueSet
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* | OfClass(class, ownerObject, ctor) // instance of a class
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* | OfArray(ownerObject, regions) // represents values of native array class in Array.scala
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* | Fun(code, env) // value elements that can be contained in ValueSet
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* | SafeValue // values on which method calls and field accesses won't cause warnings. Int, String, etc.
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10000 * | UnknownValue // values whose source are unknown at compile time
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* | Package // represets a package
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* vs ::= ValueSet(ve) // set of abstract values
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* Bottom ::= ValueSet(Empty)
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* val ::= ve | Top | UnknownValue | vs | Package // all possible abstract values in domain
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* Ref ::= ObjectRef | OfClass // values that represent a reference to some (global or instance) object
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* ThisValue ::= Ref | Top // possible values for 'this'
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*
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* refMap = Ref -> ( valsMap, varsMap, outersMap ) // refMap stores field informations of an object or instance
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* valsMap = valsym -> val // maps immutable fields to their values
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* varsMap = valsym -> addr // each mutable field has an abstract address
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* outersMap = class -> val // maps outer objects to their values
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*
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* arrayMap = OfArray -> addr // an array has one address that stores the join value of every element
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* val ::= ve | vs
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* Ref ::= ObjectRef | OfClass | OfArray // values that represent a reference to some (global or instance) object
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* ThisValue ::= Ref | vs // possible values for 'this'
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* LocalEnv(meth, ownerObject) // represents environments for methods or functions
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* Scope ::= Ref | LocalEnv
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* ScopeSet ::= Set(Scope)
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*
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* heap = addr -> val // heap is mutable
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*
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* env = (valsMap, Option[env]) // stores local variables in the residing method, and possibly outer environments
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*
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* addr ::= localVarAddr(regions, valsym, owner)
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* | fieldVarAddr(regions, valsym, owner) // independent of OfClass/ObjectRef
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* | arrayAddr(regions, owner) // independent of array element type
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* valsMap = sym -> val // maps variables to their values
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* outersMap = classSym -> ScopeSEt // maps the possible outer scopes for a corresponding (parent) class
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* heap.MutableData = Scope -> (valsMap, outersMap) // heap is mutable
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*
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* regions ::= List(sourcePosition)
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*/
@@ -289,6 +276,13 @@ class Objects(using Context @constructorOnly):
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assert(typeSymbol.isDefined, "Invalid creation of SafeValue with type " + tpe)
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new SafeValue(typeSymbol.get)
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279+
/** Represents values unknown to the checker, such as values loaded without source
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* UnknownValue is not ValueElement since RefSet containing UnknownValue
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* is equivalent to UnknownValue
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*/
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case object UnknownValue extends ValueElement:
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def show(using Context): String = "UnknownValue"
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/**
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* Represents a set of values
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*
@@ -310,29 +304,10 @@ class Objects(using Context @constructorOnly):
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assert(packageSym.is(Flags.Package), "Invalid symbol to create Package!")
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Package(packageSym.moduleClass.asClass)
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/** Represents values unknown to the checker, such as values loaded without source
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* UnknownValue is not ValueElement since RefSet containing UnknownValue
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* is equivalent to UnknownValue
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*/
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case object UnknownValue extends Value:
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def show(using Context): String = "UnknownValue"
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/** Represents values lost due to widening
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*
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* This is the top of the abstract domain lattice, which should not
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* be used during initialization.
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*
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* Top is not ValueElement since RefSet containing Top
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* is equivalent to Top
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*/
328-
329-
case object Top extends Value:
330-
def show(using Context): String = "Top"
331-
332307
val Bottom = ValueSet(ListSet.empty)
333308

334309
/** Possible types for 'this' */
335-
type ThisValue = Ref | Top.type | ValueSet
310+
type ThisValue = Ref | ValueSet
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337312
/** Checking state */
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object State:
@@ -572,18 +547,6 @@ class Objects(using Context @constructorOnly):
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/** Abstract heap for mutable fields
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*/
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object Heap:
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abstract class Addr:
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/** The static object which owns the mutable slot */
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def owner: ClassSymbol
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def getTrace: Trace = Trace.empty
579-
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/** The address for mutable fields of objects. */
581-
private case class FieldAddr(regions: Regions.Data, field: Symbol, owner: ClassSymbol)(trace: Trace) extends Addr:
582-
override def getTrace: Trace = trace
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584-
/** The address for mutable local variables . */
585-
private case class LocalVarAddr(regions: Regions.Data, sym: Symbol, owner: ClassSymbol) extends Addr
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587550
private case class ScopeBody(
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paramsMap: Map[Symbol, Value],
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valsMap: Map[Symbol, Value],
@@ -690,15 +653,6 @@ class Objects(using Context @constructorOnly):
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def writeJoinOuter(scope: Scope, outer: Symbol, outerScope: ScopeSet)(using mutable: MutableData): Unit =
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mutable.writeJoinOuter(scope, outer, outerScope)
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def localVarAddr(regions: Regions.Data, sym: Symbol, owner: ClassSymbol): Addr =
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LocalVarAddr(regions, sym, owner)
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def fieldVarAddr(regions: Regions.Data, sym: Symbol, owner: ClassSymbol)(using Trace): Addr =
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FieldAddr(regions, sym, owner)(summon[Trace])
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def arrayAddr(regions: Regions.Data, owner: ClassSymbol)(using Trace, Context): Addr =
700-
FieldAddr(regions, defn.ArrayClass, owner)(summon[Trace])
701-
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def getHeapData()(using mutable: MutableData): Data = mutable.heap
703657

704658
def setHeap(newHeap: Data)(using mutable: MutableData): Unit = mutable.heap = newHeap
@@ -777,10 +731,6 @@ class Objects(using Context @constructorOnly):
777731
def join(b: Value): Value =
778732
assert(!a.isInstanceOf[Package] && !b.isInstanceOf[Package], "Unexpected join between " + a + " and " + b)
779733
(a, b) match
780-
case (Top, _) => Top
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case (_, Top) => Top
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case (UnknownValue, _) => UnknownValue
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case (_, UnknownValue) => UnknownValue
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case (Bottom, b) => b
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case (a, Bottom) => a
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case (ValueSet(values1), ValueSet(values2)) => ValueSet(values1 ++ values2)
@@ -813,7 +763,7 @@ class Objects(using Context @constructorOnly):
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else
814764
val klass = sym.asClass
815765
a match
816-
case UnknownValue | Top => a
766+
case UnknownValue => a
817767
case Package(packageModuleClass) =>
818768
// the typer might mistakenly set the receiver to be a package instead of package object.
819769
// See pos/packageObjectStringInterpolator.scala
@@ -844,8 +794,6 @@ class Objects(using Context @constructorOnly):
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else
845795
scopes.reduce { (s1, s2) => s1.join(s2) }
846796

847-
// def widen(height: Int): Contextual[List[V]] = values.map(_.widen(height)).toList
848-
849797
extension [V : Join](map: Map[Symbol, V])
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def join(sym: Symbol, value: V): Map[Symbol, V] =
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if !map.contains(sym) then map.updated(sym, value)
@@ -873,9 +821,6 @@ class Objects(using Context @constructorOnly):
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*/
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def call(value: Value, meth: Symbol, args: List[ArgInfo], receiver: Type, superType: Type, needResolve: Boolean = true): Contextual[Value] = log("call " + meth.show + ", this = " + value.show + ", args = " + args.map(_.value.show), printer, (_: Value).show) {
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value.filterClass(meth.owner) match
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case Top =>
877-
report.warning("Value is unknown to the checker due to widening. " + Trace.show, Trace.position)
878-
Bottom
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case UnknownValue =>
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reportWarningForUnknownValue("Using unknown value. " + Trace.show, Trace.position)
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@@ -1084,9 +1029,6 @@ class Objects(using Context @constructorOnly):
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*/
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def select(value: Value, field: Symbol, receiver: Type, needResolve: Boolean = true): Contextual[Value] = log("select " + field.show + ", this = " + value.show, printer, (_: Value).show) {
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value.filterClass(field.owner) match
1087-
case Top =>
1088-
report.warning("Value is unknown to the checker due to widening. " + Trace.show, Trace.position)
1089-
Bottom
10901032
case UnknownValue =>
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reportWarningForUnknownValue("Using unknown value. " + Trace.show, Trace.position)
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@@ -1171,8 +1113,6 @@ class Objects(using Context @constructorOnly):
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*/
11721114
def assign(lhs: Value, field: Symbol, rhs: Value, rhsTyp: Type): Contextual[Value] = log("Assign" + field.show + " of " + lhs.show + ", rhs = " + rhs.show, printer, (_: Value).show) {
11731115
lhs.filterClass(field.owner) match
1174-
case Top =>
1175-
report.warning("Value is unknown to the checker due to widening. " + Trace.show, Trace.position)
11761116
case UnknownValue =>
11771117
val _ = reportWarningForUnknownValue("Assigning to unknown value. " + Trace.show, Trace.position)
11781118
case p: Package =>
@@ -1220,7 +1160,7 @@ class Objects(using Context @constructorOnly):
12201160
case UnknownValue =>
12211161
reportWarningForUnknownValue("Instantiating when outer is unknown. " + Trace.show, Trace.position)
12221162

1223-
case outer: (Ref | Top.type | Package) =>
1163+
case outer: (Ref | Package) =>
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if klass == defn.ArrayClass then
12251165
args.head.tree.tpe match
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case ConstantType(Constants.Constant(0)) =>
@@ -1246,7 +1186,7 @@ class Objects(using Context @constructorOnly):
12461186
if enclosingMethod == outerCls.primaryConstructor then
12471187
ScopeSet(Set(thisV.asInstanceOf[Ref]))
12481188
else
1249-
Env.resolveEnvByMethod(klass.owner.enclosingMethod, thisV, summon[Scope]).getOrElse(Top -> Env.NoEnv)._2
1189+
Env.resolveEnvByMethod(klass.owner.enclosingMethod, thisV, summon[Scope]).getOrElse(UnknownValue -> Env.NoEnv)._2
12501190

12511191
val instance = OfClass(klass, envWidened, ctor)
12521192
callConstructor(instance, ctor, args)
@@ -1280,9 +1220,6 @@ class Objects(using Context @constructorOnly):
12801220
eval(fun.code, fun.thisV, fun.klass)
12811221
case UnknownValue =>
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reportWarningForUnknownValue("Calling on unknown value. " + Trace.show, Trace.position)
1283-
case Top =>
1284-
report.warning("Calling on value lost due to widening. " + Trace.show, Trace.position)
1285-
Bottom
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case Bottom => Bottom
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case ValueSet(values) if values.size == 1 =>
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evalByNameParam(values.head)
@@ -2073,7 +2010,6 @@ class Objects(using Context @constructorOnly):
20732010
else accessObject(target)
20742011
else
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thisV match
2076-
case Top => Top
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case Bottom => Bottom
20782014
case ref: Ref =>
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recur(ScopeSet(Set(ref)))

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