Introduce call checker for Unit-conversions

compiler/frontend/src/org/jetbrains/kotlin/resolve/PlatformConfiguratorBase.kt

@@ -49,7 +49,8 @@ private val DEFAULT_CALL_CHECKERS = listOf(
     PrimitiveNumericComparisonCallChecker, LambdaWithSuspendModifierCallChecker,
     UselessElvisCallChecker(), ResultTypeWithNullableOperatorsChecker(), NullableVarargArgumentCallChecker,
     NamedFunAsExpressionChecker, ContractNotAllowedCallChecker, ReifiedTypeParameterSubstitutionChecker(),
-    MissingDependencySupertypeChecker.ForCalls, AbstractClassInstantiationChecker, SuspendConversionCallChecker
+    MissingDependencySupertypeChecker.ForCalls, AbstractClassInstantiationChecker, SuspendConversionCallChecker,
+    UnitConversionCallChecker
 )
 private val DEFAULT_TYPE_CHECKERS = emptyList<AdditionalTypeChecker>()
 private val DEFAULT_CLASSIFIER_USAGE_CHECKERS = listOf(

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/UnitConversionCallChecker.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.resolve.calls.checkers
+
+import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
+import org.jetbrains.kotlin.resolve.calls.tower.NewResolvedCallImpl
+import org.jetbrains.kotlin.resolve.calls.tower.psiCallArgument
+
+object UnitConversionCallChecker : CallChecker {
+    override fun check(resolvedCall: ResolvedCall<*>, reportOn: PsiElement, context: CallCheckerContext) {
+        if (resolvedCall !is NewResolvedCallImpl<*>) return
+
+        if (context.languageVersionSettings.supportsFeature(LanguageFeature.UnitConversion)) return
+
+        // lambdas are working since 1.0, callable references are handled as part of reference adaptation
+        // => here we're checking only simple argument
+        val argumentsWithUnitConversion = resolvedCall.resolvedCallAtom.argumentsWithUnitConversion
+
+        for (argumentWithUnitConversion in argumentsWithUnitConversion.keys) {
+            context.trace.report(
+                Errors.UNSUPPORTED_FEATURE.on(
+                    argumentWithUnitConversion.psiCallArgument.valueArgument.asElement(),
+                    LanguageFeature.UnitConversion to context.languageVersionSettings
+                )
+            )
+        }
+    }
+}