FIR CFA: do not remove provideDelegate subgraphs when rolling back

The receiver of the provideDelegate call is the same FirExpression as
the delegate itself, so there's only one copy of the nodes in the first
place; trying to remove subgraphs completely detaches objects inside it
from the parent graph, which is not great for checkers.

Note that currently if provideDelegate is not selected, there will be a
stray FunctionCallExit node in the control flow graph. This commit *does
not change that*. It has been there for a while. Don't @ me. I'll try to
fix that. No promises.

compiler/fir/analysis-tests/testData/resolveWithStdlib/delegates/delegateWithAnonymousObject.dot

@@ -83,38 +83,6 @@ digraph delegateWithAnonymousObject_kt {
     24 -> {25};
 
     subgraph cluster_9 {
-        color=red
-        26 [label="Enter function anonymousFunction" style="filled" fillcolor=red];
-        subgraph cluster_10 {
-            color=blue
-            27 [label="Enter block"];
-            28 [label="Enter anonymous object"];
-            subgraph cluster_11 {
-                color=blue
-                33 [label="Enter class <anonymous object>" style="filled" fillcolor=red];
-                34 [label="Exit class <anonymous object>" style="filled" fillcolor=red];
-            }
-            29 [label="Exit anonymous object"];
-            30 [label="Exit anonymous object expression"];
-            31 [label="Exit block"];
-        }
-        32 [label="Exit function anonymousFunction" style="filled" fillcolor=red];
-    }
-    26 -> {27};
-    27 -> {28};
-    27 -> {35 38 45} [color=red];
-    28 -> {33} [color=green];
-    28 -> {29} [color=red];
-    28 -> {33} [style=dashed];
-    29 -> {30};
-    29 -> {35 38 45} [color=green];
-    29 -> {35 38 45} [style=dashed];
-    30 -> {31};
-    31 -> {32};
-    33 -> {34} [color=green];
-    34 -> {29} [color=green];
-
-    subgraph cluster_12 {
         color=red
         35 [label="Enter function <init>" style="filled" fillcolor=red];
         36 [label="Delegated constructor call: super<R|kotlin/Any|>()" style="filled" fillcolor=yellow];
@@ -123,10 +91,10 @@ digraph delegateWithAnonymousObject_kt {
     35 -> {36};
     36 -> {37};
 
-    subgraph cluster_13 {
+    subgraph cluster_10 {
         color=red
         38 [label="Enter function getValue" style="filled" fillcolor=red];
-        subgraph cluster_14 {
+        subgraph cluster_11 {
             color=blue
             39 [label="Enter block"];
             40 [label="Function call: R|/IssueListView.IssueListView|()" style="filled" fillcolor=yellow];
@@ -144,10 +112,10 @@ digraph delegateWithAnonymousObject_kt {
     42 -> {43} [style=dotted];
     43 -> {44} [style=dotted];
 
-    subgraph cluster_15 {
+    subgraph cluster_12 {
         color=red
         45 [label="Enter function setValue" style="filled" fillcolor=red];
-        subgraph cluster_16 {
+        subgraph cluster_13 {
             color=blue
             46 [label="Enter block"];
             47 [label="Function call: R|/IssueListView.IssueListView|()" style="filled" fillcolor=yellow];
@@ -169,10 +137,10 @@ digraph delegateWithAnonymousObject_kt {
     51 -> {52} [style=dotted];
     52 -> {53} [style=dotted];
 
-    subgraph cluster_17 {
+    subgraph cluster_14 {
         color=red
         54 [label="Enter function getter" style="filled" fillcolor=red];
-        subgraph cluster_18 {
+        subgraph cluster_15 {
             color=blue
             55 [label="Enter block"];
             56 [label="Access variable D|/IssuesListUserProfile.issueListView|"];
@@ -194,10 +162,10 @@ digraph delegateWithAnonymousObject_kt {
     60 -> {61} [style=dotted];
     61 -> {62} [style=dotted];
 
-    subgraph cluster_19 {
+    subgraph cluster_16 {
         color=red
         63 [label="Enter function setter" style="filled" fillcolor=red];
-        subgraph cluster_20 {
+        subgraph cluster_17 {
             color=blue
             64 [label="Enter block"];
             65 [label="Access variable D|/IssuesListUserProfile.issueListView|"];
@@ -216,10 +184,28 @@ digraph delegateWithAnonymousObject_kt {
     68 -> {69};
     69 -> {70};
 
-    subgraph cluster_21 {
+    subgraph cluster_18 {
         color=red
         71 [label="Enter property" style="filled" fillcolor=red];
         72 [label="Postponed enter to lambda"];
+        subgraph cluster_19 {
+            color=blue
+            26 [label="Enter function anonymousFunction" style="filled" fillcolor=red];
+            subgraph cluster_20 {
+                color=blue
+                27 [label="Enter block"];
+                28 [label="Enter anonymous object"];
+                subgraph cluster_21 {
+                    color=blue
+                    33 [label="Enter class <anonymous object>" style="filled" fillcolor=red];
+                    34 [label="Exit class <anonymous object>" style="filled" fillcolor=red];
+                }
+                29 [label="Exit anonymous object"];
+                30 [label="Exit anonymous object expression"];
+                31 [label="Exit block"];
+            }
+            32 [label="Exit function anonymousFunction" style="filled" fillcolor=red];
+        }
         73 [label="Postponed exit from lambda"];
         74 [label="Function call: this@R|/IssuesListUserProfile|.R|/delegate|<R|IssuesListUserProfile|, R|IssuesListUserProfile|, R|IssueListView|>(...)" style="filled" fillcolor=yellow];
         75 [label="Access variable this@R|/IssuesListUserProfile|"];
@@ -228,7 +214,7 @@ digraph delegateWithAnonymousObject_kt {
         78 [label="Exit property" style="filled" fillcolor=red];
     }
     71 -> {72};
-    72 -> {73 74};
+    72 -> {26 73 74};
     72 -> {26} [style=dashed];
     73 -> {74} [color=green];
     73 -> {77} [color=red];
@@ -237,6 +223,19 @@ digraph delegateWithAnonymousObject_kt {
     76 -> {77};
     77 -> {78};
     78 -> {81} [color=green];
+    26 -> {27};
+    27 -> {28};
+    27 -> {35 38 45} [color=red];
+    28 -> {33} [color=green];
+    28 -> {29} [color=red];
+    28 -> {33} [style=dashed];
+    29 -> {30};
+    29 -> {35 38 45} [color=green];
+    29 -> {35 38 45} [style=dashed];
+    30 -> {31};
+    31 -> {32};
+    33 -> {34} [color=green];
+    34 -> {29} [color=green];
 
     subgraph cluster_22 {
         color=red

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/dfa/FirDataFlowAnalyzer.kt

@@ -143,10 +143,6 @@ abstract class FirDataFlowAnalyzer(
         returnExpressionsOfAnonymousFunctionOrNull(function)
             ?: error("anonymous function ${function.render()} not analyzed")
 
-    fun dropSubgraphFromCall(call: FirFunctionCall) {
-        graphBuilder.dropSubgraphFromCall(call)
-    }
-
     // ----------------------------------- Named function -----------------------------------
 
     fun enterFunction(function: FirFunction) {

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

@@ -1381,34 +1381,6 @@ class ControlFlowGraphBuilder {
         lastNodes.reset()
     }
 
-    fun dropSubgraphFromCall(call: FirFunctionCall) {
-        val graphs = mutableListOf<ControlFlowGraph>()
-
-        call.acceptChildren(object : FirDefaultVisitor<Unit, Any?>() {
-            override fun visitElement(element: FirElement, data: Any?) {
-                element.acceptChildren(this, null)
-            }
-
-            override fun visitAnonymousFunction(anonymousFunction: FirAnonymousFunction, data: Any?) {
-                anonymousFunction.controlFlowGraphReference?.accept(this, null)
-            }
-
-            override fun visitAnonymousObject(anonymousObject: FirAnonymousObject, data: Any?) {
-                anonymousObject.controlFlowGraphReference?.accept(this, null)
-            }
-
-            override fun visitControlFlowGraphReference(controlFlowGraphReference: FirControlFlowGraphReference, data: Any?) {
-                val graph = controlFlowGraphReference.controlFlowGraph ?: return
-                if (graph.owner == null) return
-                graphs += graph
-            }
-        }, null)
-
-        for (graph in graphs) {
-            currentGraph.removeSubGraph(graph)
-        }
-    }
-
     // ----------------------------------- Edge utils -----------------------------------
 
     private fun addNewSimpleNode(node: CFGNode<*>, isDead: Boolean = false) {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirDeclarationsResolveTransformer.kt

@@ -336,6 +336,8 @@ open class FirDeclarationsResolveTransformer(transformer: FirAbstractBodyResolve
         val provideDelegateCall = wrappedDelegateExpression.delegateProvider as FirFunctionCall
 
         // Resolve call for provideDelegate, without completion
+        // TODO: this generates some nodes in the control flow graph which we don't want if we
+        //  end up not selecting this option.
         provideDelegateCall.transformSingle(this, ResolutionMode.ContextIndependent)
 
         // If we got successful candidate for provideDelegate, let's select it
@@ -365,9 +367,6 @@ open class FirDeclarationsResolveTransformer(transformer: FirAbstractBodyResolve
             return provideDelegateCall
         }
 
-        // Otherwise, rollback
-        (provideDelegateCall as? FirFunctionCall)?.let { dataFlowAnalyzer.dropSubgraphFromCall(it) }
-
         // Select delegate expression otherwise
         return delegateExpression
     }

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

@@ -55,15 +55,6 @@ sealed class CFGNode<out E : FirElement>(val owner: ControlFlowGraph, val level:
             return true
         }
 
-        @CfgInternals
-        fun removeAllIncomingEdges(to: CFGNode<*>) {
-            for (from in to._previousNodes) {
-                from._followingNodes.remove(to)
-            }
-            to._incomingEdges = null
-            to._previousNodes.clear()
-        }
-
         @CfgInternals
         fun removeAllOutgoingEdges(from: CFGNode<*>) {
             for (to in from._followingNodes) {

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

@@ -59,16 +59,6 @@ class ControlFlowGraph(val declaration: FirDeclaration?, val name: String, val k
         _subGraphs += graph
     }
 
-    @CfgInternals
-    fun removeSubGraph(graph: ControlFlowGraph) {
-        assert(graph.owner == this)
-        _subGraphs.remove(graph)
-        graph.owner = null
-
-        CFGNode.removeAllIncomingEdges(graph.enterNode)
-        CFGNode.removeAllOutgoingEdges(graph.exitNode)
-    }
-
     private fun assertState(state: State) {
         assert(this.state == state) {
             "This action can not be performed at $this state"