KT-29926: Get rid of filterFunctionExpected

- `filterFunctionExpected` does not provide meaningful concept, and will be a problem in the next steps on this issue.
- Refactor `SmartCompletionSession::descriptorKindFilter` to more precisely tell why we include references to constructors if we are completion functions

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/smart/LambdaItems.kt

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.idea.completion.smart
 import com.intellij.codeInsight.lookup.LookupElement
 import com.intellij.codeInsight.lookup.LookupElementBuilder
 import com.intellij.openapi.util.TextRange
+import org.jetbrains.kotlin.builtins.isFunctionType
 import org.jetbrains.kotlin.idea.completion.LambdaSignatureTemplates
 import org.jetbrains.kotlin.idea.completion.suppressAutoInsertion
 import org.jetbrains.kotlin.idea.core.ExpectedInfo
@@ -35,7 +36,7 @@ object LambdaItems {
     }
 
     fun addToCollection(collection: MutableCollection<LookupElement>, expectedInfos: Collection<ExpectedInfo>) {
-        val functionExpectedInfos = expectedInfos.filterFunctionExpected()
+        val functionExpectedInfos = expectedInfos.filter { it.fuzzyType?.type?.isFunctionType == true }
         if (functionExpectedInfos.isEmpty()) return
 
         val functionTypes = functionExpectedInfos

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/smart/SmartCompletionSession.kt

@@ -21,12 +21,14 @@ import com.intellij.codeInsight.completion.CompletionResultSet
 import com.intellij.codeInsight.completion.CompletionSorter
 import com.intellij.codeInsight.lookup.LookupElement
 import com.intellij.psi.impl.source.tree.LeafPsiElement
+import org.jetbrains.kotlin.builtins.isFunctionType
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
 import org.jetbrains.kotlin.idea.completion.*
 import org.jetbrains.kotlin.idea.core.ExpectedInfo
 import org.jetbrains.kotlin.idea.core.ExpectedInfos
 import org.jetbrains.kotlin.idea.core.completion.DeclarationLookupObject
+import org.jetbrains.kotlin.idea.core.fuzzyType
 import org.jetbrains.kotlin.idea.util.CallTypeAndReceiver
 import org.jetbrains.kotlin.load.java.sam.SamConstructorDescriptorKindExclude
 import org.jetbrains.kotlin.psi.LambdaArgument
@@ -45,14 +47,17 @@ class SmartCompletionSession(
 
     override val descriptorKindFilter: DescriptorKindFilter by lazy {
         // we do not include SAM-constructors because they are handled separately and adding them requires iterating of java classes
-        var filter = DescriptorKindFilter.VALUES exclude SamConstructorDescriptorKindExclude
+        val filter = DescriptorKindFilter.VALUES exclude SamConstructorDescriptorKindExclude
 
-        if (smartCompletion?.expectedInfos?.filterFunctionExpected()?.isNotEmpty() ?: false) {
+        val referenceToConstructorIsApplicable = smartCompletion?.expectedInfos.orEmpty().any {
-            // if function type is expected we need classes to obtain their constructors
+            it.fuzzyType?.type?.isFunctionType == true
-            filter = filter.withKinds(DescriptorKindFilter.NON_SINGLETON_CLASSIFIERS_MASK)
         }
 
-        filter
+        if (referenceToConstructorIsApplicable) {
+            filter.withKinds(DescriptorKindFilter.NON_SINGLETON_CLASSIFIERS_MASK)
+        } else {
+            filter
+        }
     }
 
     private val smartCompletion by lazy(LazyThreadSafetyMode.NONE) {

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/smart/Utils.kt

@@ -335,8 +335,5 @@ fun DeclarationDescriptor.fuzzyTypesForSmartCompletion(
     }
 }
 
-fun Collection<ExpectedInfo>.filterFunctionExpected()
-        = filter { it.fuzzyType != null && it.fuzzyType!!.type.isFunctionType }
-
 fun Collection<ExpectedInfo>.filterCallableExpected()
         = filter { it.fuzzyType != null && ReflectionTypes.isCallableType(it.fuzzyType!!.type) }