KT-36808 Sink down member function Flow.collect in the completion

- This method is never supposed to be called, so we try to lower its
presence in the completion list by puting it on the last possible
position
- ^KT-36808 Fixed

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt

@@ -284,6 +284,8 @@ abstract class CompletionSession(
 
         sorter = sorter.weighAfter("kotlin.proximity", ByNameAlphabeticalWeigher, PreferLessParametersWeigher)
 
+        sorter = sorter.weighBefore("prefix", KotlinUnwantedLookupElementWeigher)
+
         sorter = if (expectedInfos.all { it.fuzzyType?.type?.isUnit() == true }) {
             sorter.weighBefore("prefix", PreferDslMembers)
         } else {

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/Weighers.kt

@@ -22,7 +22,9 @@ import org.jetbrains.kotlin.idea.resolve.ResolutionFacade
 import org.jetbrains.kotlin.idea.util.CallType
 import org.jetbrains.kotlin.idea.util.CallTypeAndReceiver
 import org.jetbrains.kotlin.idea.util.toFuzzyType
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
 import org.jetbrains.kotlin.resolve.descriptorUtil.parentsWithSelf
 import org.jetbrains.kotlin.resolve.findOriginalTopMostOverriddenDescriptors
 import org.jetbrains.kotlin.types.typeUtil.isNothing
@@ -222,6 +224,20 @@ object DeprecatedWeigher : LookupElementWeigher("kotlin.deprecated") {
     }
 }
 
+/**
+ * This weigher is designed to "sink down" specific elements in completion.
+ *
+ * For now it only works on "Flow.collect" member method (see [https://youtrack.jetbrains.com/issue/KT-36808] for details).
+ */
+object KotlinUnwantedLookupElementWeigher : LookupElementWeigher("kotlin.unwantedElement") {
+    private val flowCollectFqName = FqName("kotlinx.coroutines.flow.Flow.collect")
+
+    override fun weigh(element: LookupElement): Int {
+        val descriptor = (element.`object` as? DeclarationLookupObject)?.descriptor ?: return 0
+        return if (descriptor.fqNameSafe == flowCollectFqName) 1 else 0
+    }
+}
+
 object PreferMatchingItemWeigher : LookupElementWeigher("kotlin.preferMatching", false, true) {
     private enum class Weight {
         keywordExactMatch,