Check method arguments with parametricity when static

When a global static is called, allow for a cold argument if the corresponding parameter is not `Matchable`.

Author: Xavientois

compiler/src/dotty/tools/dotc/transform/init/Semantic.scala

@@ -410,8 +410,8 @@ object Semantic {
     def select(f: Symbol, source: Tree): Contextual[Result] =
       value.select(f, source) ++ errors
 
-    def call(meth: Symbol, args: List[ArgInfo], superType: Type, source: Tree): Contextual[Result] =
-      value.call(meth, args, superType, source) ++ errors
+    def call(meth: Symbol, args: List[ArgInfo], receiver: Type, superType: Type, source: Tree): Contextual[Result] =
+      value.call(meth, args, receiver, superType, source) ++ errors
 
     def callConstructor(ctor: Symbol, args: List[ArgInfo], source: Tree): Contextual[Result] =
       value.callConstructor(ctor, args, source) ++ errors
@@ -587,7 +587,7 @@ object Semantic {
       }
     }
 
-    def call(meth: Symbol, args: List[ArgInfo], superType: Type, source: Tree, needResolve: Boolean = true): Contextual[Result] = log("call " + meth.show + ", args = " + args, printer, (_: Result).show) {
+    def call(meth: Symbol, args: List[ArgInfo], receiver: Type, superType: Type, source: Tree, needResolve: Boolean = true): Contextual[Result] = log("call " + meth.show + ", args = " + args, printer, (_: Result).show) {
       def checkArgs = args.flatMap(_.promote)
 
       def isSyntheticApply(meth: Symbol) =
@@ -600,6 +600,24 @@ object Semantic {
         || (meth eq defn.Object_ne)
         || (meth eq defn.Any_isInstanceOf)
 
+      def checkArgsWithParametricity() =
+        val methodType = atPhaseBeforeTransforms { meth.info.stripPoly }
+        var allArgsPromote = true
+        var allParamTypes = methodType.paramInfoss.flatten.map(_.repeatedToSingle)
+        val errors = allParamTypes.zip(args).flatMap { (info, arg) =>
+          val isTypeParam = info.isInstanceOf[TypeParamRef]
+          val isWithinBounds = info.bounds.lo <:< defn.NothingType && defn.AnyType <:< info.bounds.hi
+          def otherParamContains = allParamTypes.exists( param => { param != info && param.typeSymbol != defn.ClassTagClass && info.occursIn(param) } )
+          val errors = arg.promote
+          allArgsPromote = allArgsPromote && errors.isEmpty
+          // A non-hot method argument is allowed if the corresponding parameter type is a
+          // type parameter T with Any as its upper bound and Nothing as its lower bound.
+          // the other arguments should either correspond to a parameter type that is T
+          // or that does not contain T as a component.
+          if isTypeParam && !isWithinBounds && !otherParamContains then Nil else errors
+        }
+        (errors, allArgsPromote)
+
       // fast track if the current object is already initialized
       if promoted.isCurrentObjectPromoted then Result(Hot, Nil)
       else if isAlwaysSafe(meth) then Result(Hot, Nil)
@@ -610,7 +628,14 @@ object Semantic {
             val klass = meth.owner.companionClass.asClass
             instantiate(klass, klass.primaryConstructor, args, source)
           else
-            Result(Hot, checkArgs)
+            if receiver.typeSymbol.isStaticOwner then
+              val (errors, allArgsPromote) = checkArgsWithParametricity()
+              if allArgsPromote || errors.nonEmpty then
+                Result(Hot, errors)
+              else
+                Result(Cold, errors)
+            else
+              Result(Hot, checkArgs)
 
         case Cold =>
           val error = CallCold(meth, source, trace.toVector)
@@ -666,7 +691,7 @@ object Semantic {
             }
 
         case RefSet(refs) =>
-          val resList = refs.map(_.call(meth, args, superType, source))
+          val resList = refs.map(_.call(meth, args, receiver, superType, source))
           val value2 = resList.map(_.value).join
           val errors = resList.flatMap(_.errors)
           Result(value2, errors)
@@ -946,7 +971,7 @@ object Semantic {
               locally {
                 given Trace = trace2
                 val args = member.info.paramInfoss.flatten.map(_ => ArgInfo(Hot, EmptyTree))
-                val res = warm.call(member, args, superType = NoType, source = member.defTree)
+                val res = warm.call(member, args, receiver = NoType, superType = NoType, source = member.defTree)
                 buffer ++= res.ensureHot(msg, source).errors
               }
             else
@@ -1126,14 +1151,14 @@ object Semantic {
         case Select(supert: Super, _) =>
           val SuperType(thisTp, superTp) = supert.tpe
           val thisValue2 = resolveThis(thisTp.classSymbol.asClass, thisV, klass, ref)
-          Result(thisValue2, errors).call(ref.symbol, args, superTp, expr)
+          Result(thisValue2, errors).call(ref.symbol, args, thisTp, superTp, expr)
 
         case Select(qual, _) =>
           val res = eval(qual, thisV, klass) ++ errors
           if ref.symbol.isConstructor then
             res.callConstructor(ref.symbol, args, source = expr)
           else
-            res.call(ref.symbol, args, superType = NoType, source = expr)
+            res.call(ref.symbol, args, receiver = qual.tpe, superType = NoType, source = expr)
 
         case id: Ident =>
           id.tpe match
@@ -1142,13 +1167,13 @@ object Semantic {
             val enclosingClass = id.symbol.owner.enclosingClass.asClass
             val thisValue2 = resolveThis(enclosingClass, thisV, klass, id)
             // local methods are not a member, but we can reuse the method `call`
-            thisValue2.call(id.symbol, args, superType = NoType, expr, needResolve = false)
+            thisValue2.call(id.symbol, args, receiver = NoType, superType = NoType, expr, needResolve = false)
           case TermRef(prefix, _) =>
             val res = cases(prefix, thisV, klass, id) ++ errors
             if id.symbol.isConstructor then
               res.callConstructor(id.symbol, args, source = expr)
             else
-              res.call(id.symbol, args, superType = NoType, source = expr)
+              res.call(id.symbol, args, receiver = prefix, superType = NoType, source = expr)
 
       case Select(qualifier, name) =>
         val qualRes = eval(qualifier, thisV, klass)

tests/init/neg/early-promote.scala

@@ -10,7 +10,7 @@ class Y {
 
  val n = 10
  val x = new X
- List(x.b)      // unsafe promotion
+ println(x.b)      // unsafe promotion
 
 }
 
@@ -24,7 +24,7 @@ class A { // checking A
     def c = new C
   }
   val b = new B()
-  List(b) // error: the checker simply issue warnings for objects that contain inner classes
+  println(b) // error: the checker simply issue warnings for objects that contain inner classes
   val af = 42
 }
 

tests/init/neg/enum-desugared.check

@@ -4,8 +4,8 @@ class Foo {
   }
 
   val a = Inner(5)    // ok
-  println(a)           // error
+  println(a)          // error
 
   var count = 0
-  println(a)           // ok
+  println(a)          // ok
 }

tests/init/neg/enum.check

@@ -3,9 +3,9 @@ class Foo {
     def f() = count + 1
   }
 
-  val a = new Inner    // ok
-  println(a)           // error
+  val a = new Inner   // ok
+  println(a)          // error
 
   var count = 0
-  println(a)           // ok
+  println(a)          // ok
 }

tests/init/neg/inner-case.scala

@@ -1,4 +1,9 @@
--- Error: tests/init/neg/leak-warm.scala:18:26 -------------------------------------------------------------------------
-18 |    val l: List[A] = List(c, d) // error
-   |                          ^^^^
-   |             Cannot prove that the value is fully initialized. Only initialized values may be used as arguments.
+-- Error: tests/init/neg/leak-warm.scala:19:18 -------------------------------------------------------------------------
+19 |    val l2 = l.map(_.m()) // error
+   |             ^^^^^^^^^^^^
+   |             Call method leakWarm.l.map[leakWarm.A#B](
+   |               {
+   |                 def $anonfun(_$1: leakWarm.A): leakWarm.A#B = _$1.m()
+   |                 closure($anonfun)
+   |               }
+   |             ) on a value with an unknown initialization.

tests/init/neg/inner-new.scala

@@ -15,6 +15,6 @@ object leakWarm {
     }
     val c = new C(1, 2)
     val d = new D(3, 4)
-    val l: List[A] = List(c, d) // error
-    val l2 = l.map(_.m())
+    val l: List[A] = List(c, d)
+    val l2 = l.map(_.m()) // error
 }

tests/init/neg/leak-warm.check

@@ -0,0 +1,2 @@
+class X:
+  val some = Some(this) // error

tests/init/neg/leak-warm.scala

@@ -14,7 +14,7 @@ object ErrorMessageID {
   final val NoExplanationID = $new(1, "NoExplanationID")
 
   private[this] val $values: Array[ErrorMessageID] =
-    Array(this.LazyErrorId, this.NoExplanationID) // error
+    Array(this.LazyErrorId, this.NoExplanationID)
 
   def values: Array[ErrorMessageID] = $values.clone()
 

tests/init/neg/some-this.scala

@@ -0,0 +1,3 @@
+class Outer:
+  enum Color:
+    case Red, Blue

tests/init/neg/enum-desugared.scala renamed to tests/init/pos/enum-desugared.scala

@@ -0,0 +1,4 @@
+class Outer:
+  enum MyEnum {
+    case Case
+  }