KT-12138 Do not show "::error" in smart completion when any function type accepting one argument is expected

(actually made them lowest priority)

 #KT-12138 Fixed

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

@@ -129,7 +129,10 @@ class BasicCompletionSession(
 
         if (smartCompletion != null) {
             val smartCompletionInBasicWeigher = SmartCompletionInBasicWeigher(smartCompletion, callTypeAndReceiver.callType, resolutionFacade)
-            sorter = sorter.weighBefore(KindWeigher.toString(), smartCompletionInBasicWeigher, SmartCompletionPriorityWeigher)
+            sorter = sorter.weighBefore(KindWeigher.toString(),
+                                        smartCompletionInBasicWeigher,
+                                        SmartCompletionPriorityWeigher,
+                                        CallableReferenceWeigher(callTypeAndReceiver.callType))
         }
 
         sorter = completionKind.addWeighers(sorter)

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

@@ -31,10 +31,10 @@ import org.jetbrains.kotlin.idea.core.completion.DeclarationLookupObject
 import org.jetbrains.kotlin.idea.core.completion.PackageLookupObject
 import org.jetbrains.kotlin.idea.resolve.ResolutionFacade
 import org.jetbrains.kotlin.idea.util.CallType
-import org.jetbrains.kotlin.idea.util.FuzzyType
 import org.jetbrains.kotlin.idea.util.toFuzzyType
 import org.jetbrains.kotlin.resolve.descriptorUtil.parentsWithSelf
 import org.jetbrains.kotlin.resolve.findOriginalTopMostOverriddenDescriptors
+import org.jetbrains.kotlin.types.typeUtil.isNothing
 
 object PriorityWeigher : LookupElementWeigher("kotlin.priority") {
     override fun weigh(element: LookupElement, context: WeighingContext)
@@ -298,4 +298,14 @@ object PreferLessParametersWeigher : LookupElementWeigher("kotlin.preferLessPara
         val function = lookupObject.descriptor as? FunctionDescriptor ?: return null
         return function.valueParameters.size
     }
-}
+}
+
+class CallableReferenceWeigher(private val callType: CallType<*>) : LookupElementWeigher("kotlin.callableReference") {
+    override fun weigh(element: LookupElement): Int? {
+        if (callType == CallType.CALLABLE_REFERENCE || element.getUserData(SMART_COMPLETION_ITEM_PRIORITY_KEY) == SmartCompletionItemPriority.CALLABLE_REFERENCE) {
+            val descriptor = (element.`object` as? DeclarationLookupObject)?.descriptor as? CallableDescriptor
+            return if (descriptor?.returnType?.isNothing() == true) 1 else 0
+        }
+        return null
+    }
+}

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

@@ -30,7 +30,6 @@ import org.jetbrains.kotlin.idea.completion.handlers.WithTailInsertHandler
 import org.jetbrains.kotlin.idea.core.*
 import org.jetbrains.kotlin.idea.resolve.ResolutionFacade
 import org.jetbrains.kotlin.idea.util.CallTypeAndReceiver
-import org.jetbrains.kotlin.idea.util.FuzzyType
 import org.jetbrains.kotlin.idea.util.isAlmostEverything
 import org.jetbrains.kotlin.idea.util.toFuzzyType
 import org.jetbrains.kotlin.lexer.KtTokens
@@ -351,7 +350,7 @@ class SmartCompletion(
             }
 
             return lookupElement
-                    .assignSmartCompletionPriority(SmartCompletionItemPriority.FUNCTION_REFERENCE)
+                    .assignSmartCompletionPriority(SmartCompletionItemPriority.CALLABLE_REFERENCE)
                     .addTailAndNameSimilarity(matchedExpectedInfos)
         }
 

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

@@ -201,7 +201,7 @@ class SmartCompletionSession(
 
     override fun createSorter(): CompletionSorter {
         return super.createSorter()
-                .weighBefore(KindWeigher.toString(), NameSimilarityWeigher, SmartCompletionPriorityWeigher)
+                .weighBefore(KindWeigher.toString(), NameSimilarityWeigher, SmartCompletionPriorityWeigher, CallableReferenceWeigher(callTypeAndReceiver.callType))
     }
 
     override fun createLookupElementFactory(contextVariablesProvider: ContextVariablesProvider): LookupElementFactory {

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

@@ -268,7 +268,7 @@ enum class SmartCompletionItemPriority {
     ANONYMOUS_OBJECT,
     LAMBDA_NO_PARAMS,
     LAMBDA,
-    FUNCTION_REFERENCE,
+    CALLABLE_REFERENCE,
     NULL,
     INHERITOR_INSTANTIATION
 }

idea/idea-completion/testData/weighers/basic/CallableReference_NothingLast.kt

@@ -0,0 +1,11 @@
+fun foo(p: (Int) -> Unit) { }
+
+fun fff1(p: Int): Nothing{}
+fun fff2(p: Int): Unit{}
+
+fun f() {
+    foo(::fff<caret>)
+}
+
+// ORDER: fff2
+// ORDER: fff1

idea/idea-completion/testData/weighers/smart/CallableReference_NothingLast.kt

@@ -0,0 +1,12 @@
+fun foo(p: (Int) -> Unit) { }
+
+fun fff1(p: Int): Nothing{}
+fun fff2(p: Int): Unit{}
+
+fun f() {
+    foo(<caret>)
+}
+
+// ORDER: {...}
+// ORDER: { Int -> ... }
+// ORDER: ::fff2

idea/idea-completion/testData/weighers/smart/CallableReference_NothingLast2.kt

@@ -0,0 +1,11 @@
+fun foo(p: (Int) -> Unit) { }
+
+fun fff1(p: Int): Nothing{}
+fun fff2(p: Int): Unit{}
+
+fun f() {
+    foo(::fff<caret>)
+}
+
+// ORDER: fff2
+// ORDER: fff1

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/weighers/BasicCompletionWeigherTestGenerated.java

@@ -41,6 +41,12 @@ public class BasicCompletionWeigherTestGenerated extends AbstractBasicCompletion
         KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/idea-completion/testData/weighers/basic"), Pattern.compile("^([^\\.]+)\\.kt$"), true);
     }
 
+    @TestMetadata("CallableReference_NothingLast.kt")
+    public void testCallableReference_NothingLast() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/weighers/basic/CallableReference_NothingLast.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("Callables.kt")
     public void testCallables() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/weighers/basic/Callables.kt");

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/weighers/SmartCompletionWeigherTestGenerated.java

@@ -41,6 +41,18 @@ public class SmartCompletionWeigherTestGenerated extends AbstractSmartCompletion
         doTest(fileName);
     }
 
+    @TestMetadata("CallableReference_NothingLast.kt")
+    public void testCallableReference_NothingLast() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/weighers/smart/CallableReference_NothingLast.kt");
+        doTest(fileName);
+    }
+
+    @TestMetadata("CallableReference_NothingLast2.kt")
+    public void testCallableReference_NothingLast2() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/weighers/smart/CallableReference_NothingLast2.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("FunctionExpected.kt")
     public void testFunctionExpected() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/weighers/smart/FunctionExpected.kt");