[LL] Avoid exceptions when analyzing inconsistent PSI in LLFirDeclarationModificationService

- The exceptions in KT-63130 occur because PSI tree change events may be
  published when parts of the PSI under modification are inconsistent.
  Such inconsistent elements are then analyzed by
  `LLFirDeclarationModificationService` to check if the modification
  occurs in a contract statement.
- The solution adds `*OrNull` functions to `KtQualifiedExpression` which
  return `null` instead of failing with an exception when the receiver
  or selector cannot be found.

^KT-63130 fixed

analysis/low-level-api-fir/testData/declarationModificationService/psiResilience/dotQualifiedExpression/contractCall.kt

@@ -1,5 +1,3 @@
-// IGNORE_FIR
-
 import kotlin.contracts.InvocationKind
 
 inline fun foo(block: () -> Unit) {

analysis/low-level-api-fir/testData/declarationModificationService/psiResilience/dotQualifiedExpression/stringLengthFirstStatement.kt

@@ -1,5 +1,3 @@
-// IGNORE_FIR
-
 fun foo(string: String) {
     <expr>string.length</expr>
 }

compiler/psi/src/org/jetbrains/kotlin/psi/KtDotQualifiedExpression.kt

@@ -34,15 +34,15 @@ class KtDotQualifiedExpression : KtExpressionImplStub<KotlinPlaceHolderStub<KtDo
     }
 
     override val receiverExpression: KtExpression
-        get() {
-            val stub = stub
-            if (stub != null) {
-                val childExpressionsByStub = getChildExpressionsByStub(stub)
-                if (childExpressionsByStub != null) {
-                    return childExpressionsByStub[0]
-                }
-            }
-            return super.receiverExpression
+        get() = stubReceiverExpression ?: super.receiverExpression
+
+    @KtPsiInconsistencyHandling
+    override val receiverExpressionOrNull: KtExpression?
+        get() = stubReceiverExpression ?: super.receiverExpressionOrNull
+
+    private val stubReceiverExpression: KtExpression?
+        get() = stub?.let { stub ->
+            getChildExpressionsByStub(stub)?.getOrNull(0)
         }
 
     override val selectorExpression: KtExpression?

compiler/psi/src/org/jetbrains/kotlin/psi/KtQualifiedExpression.kt

@@ -26,20 +26,33 @@ import java.util.*
 
 interface KtQualifiedExpression : KtExpression {
     val receiverExpression: KtExpression
-        get() = getExpression(false) ?: throw AssertionError("No receiver found: ${getElementTextWithContext()}")
+        @OptIn(KtPsiInconsistencyHandling::class)
+        get() = receiverExpressionOrNull ?: throw AssertionError("No receiver found: ${getElementTextWithContext()}")
+
+    /**
+     * A consistent [KtQualifiedExpression] should always have a receiver, so [receiverExpression] should be preferred if possible. Only use
+     * [receiverExpressionOrNull] if you suspect that the PSI might be inconsistent (e.g. due to ongoing modification) and need a `null`
+     * value instead of an error.
+     */
+    @KtPsiInconsistencyHandling
+    val receiverExpressionOrNull: KtExpression?
+        get() = getExpression(false)
 
     val selectorExpression: KtExpression?
         get() = getExpression(true)
 
     val operationTokenNode: ASTNode
-        get() = node.findChildByType(KtTokens.OPERATIONS) ?: error(
+        get() = operationTokenNodeOrNull ?: error(
             "No operation node for ${node.elementType}. Children: ${Arrays.toString(children)}"
         )
 
+    private val operationTokenNodeOrNull: ASTNode?
+        get() = node.findChildByType(KtTokens.OPERATIONS)
+
     val operationSign: KtSingleValueToken
         get() = operationTokenNode.elementType as KtSingleValueToken
 
     private fun getExpression(afterOperation: Boolean): KtExpression? {
-        return operationTokenNode.psi?.siblings(afterOperation, false)?.firstIsInstanceOrNull<KtExpression>()
+        return operationTokenNodeOrNull?.psi?.siblings(afterOperation, false)?.firstIsInstanceOrNull<KtExpression>()
     }
 }

compiler/psi/src/org/jetbrains/kotlin/psi/annotations.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.psi
+
+/**
+ * Functions and classes annotated with [KtPsiInconsistencyHandling] are not intended for general-purpose use, but for working with possibly
+ * inconsistent PSI. The specific circumstances need to be described in the documentation of the annotated function/class.
+ *
+ * Inconsistent PSI cannot be produced by the Kotlin parser. It occurs rarely, for example during modification of the PSI by the IDE. In
+ * general, it can be assumed that all PSI is consistent. Inconsistent PSI should only be assumed when there is sufficient proof.
+ */
+@RequiresOptIn
+annotation class KtPsiInconsistencyHandling

compiler/psi/src/org/jetbrains/kotlin/psi/psiUtil/ktPsiUtil.kt

@@ -297,9 +297,10 @@ fun KtNamedFunction.isContractPresentPsiCheck(isAllowedOnMembers: Boolean): Bool
 fun KtExpression.isContractDescriptionCallPsiCheck(): Boolean =
     (this is KtCallExpression && calleeExpression?.text == "contract") || (this is KtQualifiedExpression && isContractDescriptionCallPsiCheck())
 
+@OptIn(KtPsiInconsistencyHandling::class)
 fun KtQualifiedExpression.isContractDescriptionCallPsiCheck(): Boolean {
     val expression = selectorExpression ?: return false
-    return receiverExpression.text == "kotlin.contracts" && expression.isContractDescriptionCallPsiCheck()
+    return receiverExpressionOrNull?.text == "kotlin.contracts" && expression.isContractDescriptionCallPsiCheck()
 }
 
 fun KtElement.isFirstStatement(): Boolean {