KT-12150 Smart completion suggests to compare non-nullable with null

#KT-12150 Fixed

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

@@ -26,10 +26,7 @@ import org.jetbrains.kotlin.idea.caches.resolve.resolveImportReference
 import org.jetbrains.kotlin.idea.completion.smart.ExpectedInfoMatch
 import org.jetbrains.kotlin.idea.completion.smart.SmartCompletionItemPriority
 import org.jetbrains.kotlin.idea.completion.smart.matchExpectedInfo
-import org.jetbrains.kotlin.idea.core.ExpectedInfo
-import org.jetbrains.kotlin.idea.core.IfConditionAdditionalData
-import org.jetbrains.kotlin.idea.core.WhenEntryAdditionalData
-import org.jetbrains.kotlin.idea.core.fuzzyType
+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.toFuzzyType
@@ -83,10 +80,13 @@ object KeywordValues {
             }
 
             val nullMatcher = { info: ExpectedInfo ->
-                if (info.fuzzyType != null && info.fuzzyType!!.type.isMarkedNullable)
-                    ExpectedInfoMatch.match(TypeSubstitutor.EMPTY)
-                else
-                    ExpectedInfoMatch.noMatch
+                when {
+                    (info.additionalData as? ComparisonOperandAdditionalData)?.suppressNullLiteral == true -> ExpectedInfoMatch.noMatch
+
+                    info.fuzzyType?.type?.isMarkedNullable == true -> ExpectedInfoMatch.match(TypeSubstitutor.EMPTY)
+
+                    else -> ExpectedInfoMatch.noMatch
+                }
             }
             consumer.consume("null", nullMatcher, SmartCompletionItemPriority.NULL) {
                 LookupElementBuilder.create(KeywordLookupObject(), "null").bold()

idea/idea-completion/testData/smart/EqOperator.kt

@@ -11,7 +11,7 @@ fun f(e1: E, e2: E?, x: Any) {
 // EXIST: { itemText:"e2" }
 // EXIST: { lookupString:"A", itemText:"E.A", typeText:"E" }
 // EXIST: { lookupString:"B", itemText:"E.B", typeText:"E" }
-// EXIST: null
+// ABSENT: null
 // ABSENT: { itemText:"!! e2" }
 // ABSENT: e1
 // ABSENT: x

idea/idea-completion/testData/smart/EqOperatorPlatformType.kt

@@ -0,0 +1,7 @@
+import java.io.File
+
+fun foo(file: File) {
+    if (file.name == <caret>)
+}
+
+// EXIST: null

idea/idea-completion/testData/smart/NotEqOperator.kt

@@ -3,12 +3,13 @@ enum class E {
     B
 }
 
-fun f(e1: E, e2: E?, x: Any) {
+fun f(e1: E?, e2: E, x: Any) {
     if (e1 != <caret>
 }
 
 // EXIST: { lookupString:"A", itemText:"E.A" }
 // EXIST: { lookupString:"B", itemText:"E.B" }
 // EXIST: e2
+// EXIST: null
 // ABSENT: e1
 // ABSENT: x

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JvmSmartCompletionTestGenerated.java

@@ -137,6 +137,12 @@ public class JvmSmartCompletionTestGenerated extends AbstractJvmSmartCompletionT
         doTest(fileName);
     }
 
+    @TestMetadata("EqOperatorPlatformType.kt")
+    public void testEqOperatorPlatformType() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/smart/EqOperatorPlatformType.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("ExtensionFunctionTypeVariables.kt")
     public void testExtensionFunctionTypeVariables() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/smart/ExtensionFunctionTypeVariables.kt");

idea/idea-core/src/org/jetbrains/kotlin/idea/core/ExpectedInfos.kt

@@ -148,6 +148,8 @@ object IfConditionAdditionalData : ExpectedInfo.AdditionalData
 
 object PropertyDelegateAdditionalData : ExpectedInfo.AdditionalData
 
+class ComparisonOperandAdditionalData(val suppressNullLiteral: Boolean) : ExpectedInfo.AdditionalData
+
 class ExpectedInfos(
         private val bindingContext: BindingContext,
         private val resolutionFacade: ResolutionFacade,
@@ -414,12 +416,14 @@ class ExpectedInfos(
                         return listOf(ExpectedInfo(NullableTypesFilter, expectedName, null))
                     }
 
-                    // if we complete argument of == or !=, make types in expected info's nullable to allow nullable items too
+                    var additionalData: ExpectedInfo.AdditionalData? = null
                     if (operationToken in COMPARISON_TOKENS) {
+                        // if we complete argument of == or !=, make types in expected info's nullable to allow items of nullable type too
+                        additionalData = ComparisonOperandAdditionalData(suppressNullLiteral = expectedType.nullability() == TypeNullability.NOT_NULL)
                         expectedType = expectedType.makeNullable()
                     }
 
-                    return listOf(ExpectedInfo(expectedType, expectedName, null))
+                    return listOf(ExpectedInfo(expectedType, expectedName, null, additionalData = additionalData))
                 }
             }
         }