Introduce warning about forbidden referencing to underscore named parameter of the catch block in a future release (KT-31567)

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -889,6 +889,7 @@ public interface Errors {
     DiagnosticFactory1<PsiElement, String> YIELD_IS_RESERVED = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory0<PsiElement> UNDERSCORE_IS_RESERVED = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> UNDERSCORE_USAGE_WITHOUT_BACKTICKS = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> RESOLVED_TO_UNDERSCORE_NAMED_CATCH_PARAMETER = DiagnosticFactory0.create(WARNING);
     DiagnosticFactory1<PsiElement, String> INVALID_CHARACTERS = DiagnosticFactory1.create(ERROR);
 
     DiagnosticFactory1<PsiElement, String> INAPPLICABLE_OPERATOR_MODIFIER = DiagnosticFactory1.create(ERROR);

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -509,6 +509,7 @@ public class DefaultErrorMessages {
 
         MAP.put(UNDERSCORE_IS_RESERVED, "Names _, __, ___, ..., are reserved in Kotlin");
         MAP.put(UNDERSCORE_USAGE_WITHOUT_BACKTICKS, "Names _, __, ___, ... can be used only in back-ticks (`_`, `__`, `___`, ...)");
+        MAP.put(RESOLVED_TO_UNDERSCORE_NAMED_CATCH_PARAMETER, "Referencing to an underscore-named parameter is deprecated. It will be an error in a future release.");
         MAP.put(YIELD_IS_RESERVED, "{0}", STRING);
         MAP.put(INVALID_CHARACTERS, "Name {0}", STRING);
 

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

@@ -54,7 +54,8 @@ private val DEFAULT_CALL_CHECKERS = listOf(
     UselessElvisCallChecker(), ResultTypeWithNullableOperatorsChecker(), NullableVarargArgumentCallChecker,
     NamedFunAsExpressionChecker, ContractNotAllowedCallChecker, ReifiedTypeParameterSubstitutionChecker(),
     MissingDependencySupertypeChecker.ForCalls, AbstractClassInstantiationChecker, SuspendConversionCallChecker,
-    UnitConversionCallChecker, FunInterfaceConstructorReferenceChecker, NullableExtensionOperatorWithSafeCallChecker
+    UnitConversionCallChecker, FunInterfaceConstructorReferenceChecker, NullableExtensionOperatorWithSafeCallChecker,
+    ReferencingToUnderscoreNamedParameterOfCatchBlockChecker
 )
 private val DEFAULT_TYPE_CHECKERS = emptyList<AdditionalTypeChecker>()
 private val DEFAULT_CLASSIFIER_USAGE_CHECKERS = listOf(

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

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2010-2019 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.builtins.isBuiltinFunctionalType
+import org.jetbrains.kotlin.builtins.isFunctionOrSuspendFunctionType
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.descriptors.impl.LocalVariableDescriptor
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.diagnostics.reportDiagnosticOnce
+import org.jetbrains.kotlin.diagnostics.reportDiagnosticOnceWrtDiagnosticFactoryList
+import org.jetbrains.kotlin.psi.KtNameReferenceExpression
+import org.jetbrains.kotlin.psi.KtParameter
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.calls.SPECIAL_FUNCTION_NAMES
+import org.jetbrains.kotlin.resolve.calls.callUtil.getParameterForArgument
+import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
+import org.jetbrains.kotlin.resolve.calls.model.*
+import org.jetbrains.kotlin.resolve.calls.tower.NewResolvedCallImpl
+import org.jetbrains.kotlin.resolve.calls.tower.psiCallArgument
+import org.jetbrains.kotlin.resolve.calls.tower.psiExpression
+import org.jetbrains.kotlin.resolve.calls.tower.psiKotlinCall
+import org.jetbrains.kotlin.resolve.descriptorUtil.isUnderscoreNamed
+import org.jetbrains.kotlin.resolve.source.KotlinSourceElement
+import org.jetbrains.kotlin.types.DeferredType
+import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.TypeUtils
+import org.jetbrains.kotlin.types.typeUtil.isNothing
+import org.jetbrains.kotlin.types.typeUtil.isNothingOrNullableNothing
+import org.jetbrains.kotlin.types.typeUtil.isTypeParameter
+
+object ReferencingToUnderscoreNamedParameterOfCatchBlockChecker : CallChecker {
+    override fun check(resolvedCall: ResolvedCall<*>, reportOn: PsiElement, context: CallCheckerContext) {
+        val descriptor = resolvedCall.resultingDescriptor
+
+        if (descriptor !is LocalVariableDescriptor || !descriptor.isUnderscoreNamed) return
+
+        val sourceElement = descriptor.source as? KotlinSourceElement ?: return
+        val ktParameter = sourceElement.psi as? KtParameter ?: return
+
+        if (ktParameter.isCatchParameter) {
+            context.trace.reportDiagnosticOnce(Errors.RESOLVED_TO_UNDERSCORE_NAMED_CATCH_PARAMETER.on(reportOn))
+        }
+    }
+}

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tower/PSICallResolver.kt

@@ -40,6 +40,7 @@ import org.jetbrains.kotlin.resolve.calls.util.CallMaker
 import org.jetbrains.kotlin.resolve.constants.evaluate.ConstantExpressionEvaluator
 import org.jetbrains.kotlin.resolve.deprecation.DeprecationResolver
 import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
+import org.jetbrains.kotlin.resolve.descriptorUtil.isUnderscoreNamed
 import org.jetbrains.kotlin.resolve.scopes.*
 import org.jetbrains.kotlin.resolve.scopes.receivers.*
 import org.jetbrains.kotlin.types.*
@@ -837,7 +838,11 @@ class PSICallResolver(
         val catchScope = with(scope) {
             LexicalWritableScope(this, ownerDescriptor, false, redeclarationChecker, LexicalScopeKind.CATCH)
         }
-        catchScope.addVariableDescriptor(variableDescriptor)
+        val isReferencingToUnderscoreNamedParameterForbidden =
+            languageVersionSettings.getFeatureSupport(LanguageFeature.ForbidReferencingToUnderscoreNamedParameterOfCatchBlock) == LanguageFeature.State.ENABLED
+        if (!variableDescriptor.isUnderscoreNamed || !isReferencingToUnderscoreNamedParameterForbidden) {
+            catchScope.addVariableDescriptor(variableDescriptor)
+        }
         return replaceScope(catchScope)
     }
 }