Minor. Fix potential deadlock

core/descriptors/src/org/jetbrains/kotlin/types/flexibleTypes.kt

@@ -129,6 +129,26 @@ public open class DelegatingFlexibleType protected constructor(
         }
     }
 
+     // These assertions are needed for checking invariants of flexible types.
+     //
+     // Unfortunately isSubtypeOf is running resolve for lazy types.
+     // Because of this we can't run these assertions when we are creating this type. See EA-74904
+     //
+     // Also isSubtypeOf is not a very fast operation, so we are running assertions only if ASSERTIONS_ENABLED. See KT-7540
+    private var assertionsDone = false
+
+    private fun runAssertions() {
+        if (assertionsDone || !ASSERTIONS_ENABLED) return
+        assertionsDone = true
+
+        assert (!lowerBound.isFlexible()) { "Lower bound of a flexible type can not be flexible: $lowerBound" }
+        assert (!upperBound.isFlexible()) { "Upper bound of a flexible type can not be flexible: $upperBound" }
+        assert (lowerBound != upperBound) { "Lower and upper bounds are equal: $lowerBound == $upperBound" }
+        assert (KotlinTypeChecker.DEFAULT.isSubtypeOf(lowerBound, upperBound)) {
+            "Lower bound $lowerBound of a flexible type must be a subtype of the upper bound $upperBound"
+        }
+    }
+
     override fun <T : TypeCapability> getCapability(capabilityClass: Class<T>): T? {
         val extra = extraCapabilities.getCapability(capabilityClass, this, this)
         if (extra != null) return extra
@@ -150,17 +170,10 @@ public open class DelegatingFlexibleType protected constructor(
 
     override fun isMarkedNullable(): Boolean = getCapability(javaClass<NullAwareness>())!!.computeIsNullable()
 
-    override val delegateType: KotlinType by lazy {
+    override val delegateType: KotlinType
-            // we can't check this in init block, because lowerBound & upperBound can be LazyType. see EA-74904
+        get() {
-            if (ASSERTIONS_ENABLED) { // workaround for KT-7540
+            runAssertions()
-                assert (!lowerBound.isFlexible()) { "Lower bound of a flexible type can not be flexible: $lowerBound" }
+            return lowerBound
-                assert (!upperBound.isFlexible()) { "Upper bound of a flexible type can not be flexible: $upperBound" }
-                assert (lowerBound != upperBound) { "Lower and upper bounds are equal: $lowerBound == $upperBound" }
-                assert (KotlinTypeChecker.DEFAULT.isSubtypeOf(lowerBound, upperBound)) {
-                    "Lower bound $lowerBound of a flexible type must be a subtype of the upper bound $upperBound"
-                }
-            }
-            lowerBound
         }
 
     override fun getDelegate() = getCapability(javaClass<FlexibleTypeDelegation>())!!.delegateType