[FE] Use indexed loop to prevent CME in incorporation

#KT-60225 Fixed

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/inference/components/ConstraintIncorporator.kt

@@ -27,7 +27,7 @@ class ConstraintIncorporator(
         // if such type variable is fixed then it is error
         fun getTypeVariable(typeConstructor: TypeConstructorMarker): TypeVariableMarker?
 
-        fun getConstraintsForVariable(typeVariable: TypeVariableMarker): Collection<Constraint>
+        fun getConstraintsForVariable(typeVariable: TypeVariableMarker): List<Constraint>
 
         fun addNewIncorporatedConstraint(
             lowerType: KotlinTypeMarker,
@@ -67,7 +67,7 @@ class ConstraintIncorporator(
 
         // \alpha <: constraint.type
         if (constraint.kind != ConstraintKind.LOWER) {
-            getConstraintsForVariable(typeVariable).forEach {
+            forEachConstraint(typeVariable) {
                 if (it.kind != ConstraintKind.UPPER) {
                     addNewIncorporatedConstraint(it.type, constraint.type, shouldBeTypeVariableFlexible, it.isNullabilityConstraint)
                 }
@@ -76,7 +76,7 @@ class ConstraintIncorporator(
 
         // constraint.type <: \alpha
         if (constraint.kind != ConstraintKind.UPPER) {
-            getConstraintsForVariable(typeVariable).forEach {
+            forEachConstraint(typeVariable) {
                 if (it.kind != ConstraintKind.LOWER) {
                     val isFromDeclaredUpperBound =
                         it.position.from is DeclaredUpperBoundConstraintPosition<*> && !it.type.typeConstructor().isTypeVariable()
@@ -92,6 +92,16 @@ class ConstraintIncorporator(
         }
     }
 
+    private inline fun Context.forEachConstraint(typeVariable: TypeVariableMarker, action: (Constraint) -> Unit) {
+        // We use an indexed loop because the collection might be modified during the iteration.
+        // However, the only modification is appending, so we should be fine.
+        val constraints = getConstraintsForVariable(typeVariable)
+        var i = 0
+        while (i < constraints.size) {
+            action(constraints[i++])
+        }
+    }
+
     // \alpha <: Number, \beta <: Inv<\alpha> => \beta <: Inv<out Number>
     private fun Context.insideOtherConstraint(
         typeVariable: TypeVariableMarker,

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/inference/model/MutableConstraintStorage.kt

@@ -46,6 +46,14 @@ class MutableVariableWithConstraints private constructor(
 
     private val mutableConstraints = if (constraints == null) SmartList() else SmartList(constraints)
 
+    /**
+     * The contract for mutating this list is that the only allowed mutation is appending items.
+     * In any other case, it must be set to `null`, so that it will be recomputed when [constraints] is called.
+     *
+     * The reason is that the list might be mutated while it's being iterated.
+     * For this reason, we use an index loop in
+     * [org.jetbrains.kotlin.resolve.calls.inference.components.ConstraintIncorporator.forEachConstraint].
+     */
     private var simplifiedConstraints: SmartList<Constraint>? = mutableConstraints
 
     val rawConstraintsCount get() = mutableConstraints.size