FIR DFA: add a union node for property delegates

The delegate is resolved in context-dependent mode and thus can be an
incomplete call; if there is no `provideDelegate` method to complete it,
the result is effectively `val x$delegate = y.id()` where `id` is
`fun <T> id(x: T) = x`, except we don't get a real node for `id` so the
DFA edges from lambdas in `y` go who knows where.

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/CFGNode.kt

@@ -362,6 +362,14 @@ class PropertyInitializerExitNode(owner: ControlFlowGraph, override val fir: Fir
     }
 }
 
+
+class DelegateExpressionExitNode(owner: ControlFlowGraph, override val fir: FirExpression, level: Int, id: Int)
+    : CFGNode<FirExpression>(owner, level, id), UnionNodeMarker {
+    override fun <R, D> accept(visitor: ControlFlowGraphVisitor<R, D>, data: D): R {
+        return visitor.visitDelegateExpressionExitNode(this, data)
+    }
+}
+
 // ----------------------------------- Field -----------------------------------
 
 @OptIn(CfgInternals::class)

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/CFGNodeRenderer.kt

@@ -85,6 +85,7 @@ fun CFGNode<*>.render(): String =
                 is PartOfClassInitializationNode -> "Part of class initialization"
                 is PropertyInitializerEnterNode -> "Enter property"
                 is PropertyInitializerExitNode -> "Exit property"
+                is DelegateExpressionExitNode -> "Exit property delegate"
                 is FieldInitializerEnterNode -> "Enter field"
                 is FieldInitializerExitNode -> "Exit field"
                 is InitBlockEnterNode -> "Enter init block"

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/ControlFlowGraphVisitor.kt

@@ -104,6 +104,10 @@ abstract class ControlFlowGraphVisitor<out R, in D> {
         return visitNode(node, data)
     }
 
+    open fun visitDelegateExpressionExitNode(node: DelegateExpressionExitNode, data: D): R {
+        return visitUnionNode(node, data)
+    }
+
     // ----------------------------------- Field -----------------------------------
 
     open fun visitFieldInitializerEnterNode(node: FieldInitializerEnterNode, data: D): R {

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/ControlFlowGraphVisitorVoid.kt

@@ -50,6 +50,10 @@ abstract class ControlFlowGraphVisitorVoid : ControlFlowGraphVisitor<Unit, Nothi
         visitNode(node)
     }
 
+    open fun visitDelegateExpressionExitNode(node: DelegateExpressionExitNode) {
+        visitUnionNode(node)
+    }
+
     // ----------------------------------- Init -----------------------------------
 
     open fun visitInitBlockEnterNode(node: InitBlockEnterNode) {
@@ -339,6 +343,10 @@ abstract class ControlFlowGraphVisitorVoid : ControlFlowGraphVisitor<Unit, Nothi
         visitPropertyInitializerExitNode(node)
     }
 
+    final override fun visitDelegateExpressionExitNode(node: DelegateExpressionExitNode, data: Nothing?) {
+        visitDelegateExpressionExitNode(node)
+    }
+
     // ----------------------------------- Init -----------------------------------
 
     final override fun visitInitBlockEnterNode(node: InitBlockEnterNode, data: Nothing?) {