Fix crash by using special resolveEnv function for local read and write

Author: q-ata

Diff for: compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -436,6 +436,39 @@ class Objects(using Context @constructorOnly):
       case _ =>
         throw new RuntimeException("Incorrect local environment for initializing " + x.show)
 
+    /**
+     * Resolve the environment by searching for a given symbol.
+     *
+     * Searches for the environment that owns `target`, starting from `env` as the innermost.
+     *
+     * Due to widening, the corresponding environment might not exist. As a result reading the local
+     * variable will return `Cold` and it's forbidden to write to the local variable.
+     *
+     * @param target  The symbol to search for.
+     * @param thisV The value for `this` of the enclosing class where the local variable is referenced.
+     * @param env   The local environment where the local variable is referenced.
+     *
+     * @return the environment that owns the `target` and value for `this` owned by the given method.
+     */
+    def resolveEnvByValue(target: Symbol, thisV: ThisValue, env: Data)(using Context): Option[(ThisValue, Data)] = log("Resolving env by value for " + target.show + ", this = " + thisV.show + ", env = " + env.show, printer) {
+      env match
+      case localEnv: LocalEnv =>
+        if localEnv.getVal(target).isDefined then Some(thisV -> localEnv)
+        else if localEnv.getVar(target).isDefined then Some(thisV -> localEnv)
+        else resolveEnvByValue(target, thisV, localEnv.outer)
+      case NoEnv =>
+        thisV match
+        case ref: OfClass =>
+          ref.outer match
+          case outer : ThisValue =>
+            resolveEnvByValue(target, outer, ref.env)
+          case _ =>
+            // TODO: properly handle the case where ref.outer is ValueSet
+            None
+        case _ =>
+          None
+    }
+
     /**
      * Resolve the environment owned by the given method.
      *
@@ -451,17 +484,17 @@ class Objects(using Context @constructorOnly):
      *
      * @return the environment and value for `this` owned by the given method.
      */
-    def resolveEnv(meth: Symbol, thisV: ThisValue, env: Data)(using Context): Option[(ThisValue, Data)] = log("Resolving env for " + meth.show + ", this = " + thisV.show + ", env = " + env.show, printer) {
+    def resolveEnvByOwner(meth: Symbol, thisV: ThisValue, env: Data)(using Context): Option[(ThisValue, Data)] = log("Resolving env by owner for " + meth.show + ", this = " + thisV.show + ", env = " + env.show, printer) {
       env match
       case localEnv: LocalEnv =>
         if localEnv.meth == meth then Some(thisV -> env)
-        else resolveEnv(meth, thisV, localEnv.outer)
+        else resolveEnvByOwner(meth, thisV, localEnv.outer)
       case NoEnv =>
         thisV match
         case ref: OfClass =>
           ref.outer match
           case outer : ThisValue =>
-            resolveEnv(meth, outer, ref.env)
+            resolveEnvByOwner(meth, outer, ref.env)
           case _ =>
             // TODO: properly handle the case where ref.outer is ValueSet
             None
@@ -724,7 +757,7 @@ class Objects(using Context @constructorOnly):
             if meth.owner.isClass then
               (ref, Env.NoEnv)
             else
-              Env.resolveEnv(meth.owner.enclosingMethod, ref, summon[Env.Data]).getOrElse(Cold -> Env.NoEnv)
+              Env.resolveEnvByOwner(meth.owner.enclosingMethod, ref, summon[Env.Data]).getOrElse(Cold -> Env.NoEnv)
 
           val env2 = Env.ofDefDef(ddef, args.map(_.value), outerEnv)
           extendTrace(ddef) {
@@ -771,9 +804,9 @@ class Objects(using Context @constructorOnly):
           end if
 
         case _ =>
-          // by-name closure
-          given Env.Data = env
-          extendTrace(code) { eval(code, thisV, klass, cacheResult = true) }
+          // Should be unreachable, by-name closures are handled by readLocal
+          report.warning("[Internal error] Only DefDef should be possible here, but found " + code.show + ". " + Trace.show, Trace.position)
+          Bottom
 
     case ValueSet(vs) =>
       vs.map(v => call(v, meth, args, receiver, superType)).join
@@ -962,7 +995,7 @@ class Objects(using Context @constructorOnly):
                   (thisV.widenRefOrCold(1), Env.NoEnv)
               else
                 // klass.enclosingMethod returns its primary constructor
-                Env.resolveEnv(klass.owner.enclosingMethod, thisV, summon[Env.Data]).getOrElse(Cold -> Env.NoEnv)
+                Env.resolveEnvByOwner(klass.owner.enclosingMethod, thisV, summon[Env.Data]).getOrElse(Cold -> Env.NoEnv)
 
         val instance = OfClass(klass, outerWidened, ctor, args.map(_.value), envWidened)
         callConstructor(instance, ctor, args)
@@ -992,7 +1025,9 @@ class Objects(using Context @constructorOnly):
    */
   def readLocal(thisV: ThisValue, sym: Symbol): Contextual[Value] = log("reading local " + sym.show, printer, (_: Value).show) {
     def isByNameParam(sym: Symbol) = sym.is(Flags.Param) && sym.info.isInstanceOf[ExprType]
-    Env.resolveEnv(sym.enclosingMethod, thisV, summon[Env.Data]) match
+    // Can't use enclosingMethod here because values defined in a by-name closure will have the wrong enclosingMethod,
+    // since our phase is before elimByName.
+    Env.resolveEnvByValue(sym, thisV, summon[Env.Data]) match
     case Some(thisV -> env) =>
       if sym.is(Flags.Mutable) then
         // Assume forward reference check is doing a good job
@@ -1047,8 +1082,9 @@ class Objects(using Context @constructorOnly):
    */
   def writeLocal(thisV: ThisValue, sym: Symbol, value: Value): Contextual[Value] = log("write local " + sym.show + " with " + value.show, printer, (_: Value).show) {
     assert(sym.is(Flags.Mutable), "Writing to immutable variable " + sym.show)
-
-    Env.resolveEnv(sym.enclosingMethod, thisV, summon[Env.Data]) match
+    // Can't use enclosingMethod here because values defined in a by-name closure will have the wrong enclosingMethod,
+    // since our phase is before elimByName.
+    Env.resolveEnvByValue(sym, thisV, summon[Env.Data]) match
     case Some(thisV -> env) =>
       given Env.Data = env
       Env.getVar(sym) match

Diff for: tests/init/pos/byname.scala renamed to tests/init-global/pos/byname.scala

@@ -5,12 +5,12 @@ class A extends T:
   override def bar(i: => Int): Int = i + 1
 
 class B extends T:
-  override def bar(i: => Int): Int = i + 2
+  override def bar(i: => Int): Int = i
 
 object A:
   val a: T = if ??? then new A else new B
-  def foo(b: List[Int]) = a.bar(b match {
-    case x :: xs => 1
+  def foo(b: List[Int]): Int = a.bar(b match {
+    case head :: rest => head + foo(rest) + a.bar(head)
     case Nil => 0
   })
 

Diff for: tests/init-global/warn/lazy-local-val.scala

@@ -15,5 +15,5 @@ object B:
     lazy val b = a
     Box(b)
 
-  val box = f(n)   // warn
+  val box = f(n)
   val n = 10