[Invariant Fix] Use structural descriptor equivalence in JsNamesClashChecker

It's needed for situation when we have JS module with expect declaration,
so we refine member scope for that expect declaration and try to
compare to function descriptors (e.g. of `equals` function) from
different class descriptors (expect and actual) and report diagnostic
about name clash. So, since we can earn descriptors from type refinement,
they can be not identical but still equals, so with should use structural
equality to comparing them

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsNameClashChecker.kt

@@ -16,6 +16,8 @@
 
 package org.jetbrains.kotlin.js.resolve.diagnostics
 
+import org.jetbrains.kotlin.config.LanguageVersionSettings
+import org.jetbrains.kotlin.config.isTypeRefinementEnabled
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
 import org.jetbrains.kotlin.diagnostics.Errors
@@ -24,14 +26,20 @@ import org.jetbrains.kotlin.js.naming.SuggestedName
 import org.jetbrains.kotlin.js.translate.utils.AnnotationsUtils
 import org.jetbrains.kotlin.psi.KtDeclaration
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.DescriptorEquivalenceForOverrides
 import org.jetbrains.kotlin.resolve.DescriptorUtils
-import org.jetbrains.kotlin.resolve.checkers.DeclarationCheckerContext
 import org.jetbrains.kotlin.resolve.checkers.DeclarationChecker
+import org.jetbrains.kotlin.resolve.checkers.DeclarationCheckerContext
 import org.jetbrains.kotlin.resolve.descriptorUtil.isExtension
 import org.jetbrains.kotlin.resolve.descriptorUtil.isExtensionProperty
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
+import org.jetbrains.kotlin.types.checker.KotlinTypeRefiner
+import org.jetbrains.kotlin.types.refinement.TypeRefinement
 
-class JsNameClashChecker(private val nameSuggestion: NameSuggestion) : DeclarationChecker {
+class JsNameClashChecker(
+    private val nameSuggestion: NameSuggestion,
+    private val languageVersionSettings: LanguageVersionSettings
+) : DeclarationChecker {
     companion object {
         private val COMMON_DIAGNOSTICS = setOf(
                 Errors.REDECLARATION,
@@ -87,7 +95,12 @@ class JsNameClashChecker(private val nameSuggestion: NameSuggestion) : Declarati
                 val scope = getScope(overrideFqn.scope)
                 val name = overrideFqn.names.last()
                 val existing = scope[name] as? CallableMemberDescriptor
-                if (existing != null && existing != overrideFqn.descriptor && !isFakeOverridingNative(existing)) {
+                val overrideDescriptor = overrideFqn.descriptor as? CallableMemberDescriptor
+                if (existing != null &&
+                    overrideDescriptor != null &&
+                    !areDescriptorsEquivalent(existing, overrideDescriptor) &&
+                    !isFakeOverridingNative(existing)
+                ) {
                     diagnosticHolder.report(ErrorsJs.JS_FAKE_NAME_CLASH.on(declaration, name, override, existing))
                     break
                 }
@@ -102,6 +115,20 @@ class JsNameClashChecker(private val nameSuggestion: NameSuggestion) : Declarati
         }
     }
 
+    private fun areDescriptorsEquivalent(
+        existing: CallableMemberDescriptor,
+        overrideDescriptor: CallableMemberDescriptor
+    ): Boolean {
+        return if (!languageVersionSettings.isTypeRefinementEnabled) {
+            // Fast-path
+            existing == overrideDescriptor
+        } else {
+            // If refinement is enabled, we can get duplicate descriptors for one and the same members (as refinement re-creates
+            // descriptors), so, in this case, we have to compare descriptors structurally
+            DescriptorEquivalenceForOverrides.areCallableDescriptorsEquivalent(existing, overrideDescriptor)
+        }
+    }
+
     private fun NameSuggestion.suggestAllPossibleNames(descriptor: DeclarationDescriptor): Collection<SuggestedName> =
             if (descriptor is CallableMemberDescriptor) {
                 val primary = suggest(descriptor)