Underscore names are now forbidden

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

@@ -558,7 +558,7 @@ public interface Errors {
 
     DiagnosticFactory1<JetSimpleNameExpression, JetType> COMPARE_TO_TYPE_MISMATCH = DiagnosticFactory1.create(ERROR);
 
-    DiagnosticFactory0<PsiElement> UNDERSCORE_IS_DEPRECATED = DiagnosticFactory0.create(WARNING);
+    DiagnosticFactory0<PsiElement> UNDERSCORE_IS_RESERVED = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory1<PsiElement, String> INVALID_CHARACTERS = DiagnosticFactory1.create(ERROR);
 
     DiagnosticFactory0<PsiElement> INAPPLICABLE_OPERATOR_MODIFIER = DiagnosticFactory0.create(WARNING);

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

@@ -365,7 +365,7 @@ public class DefaultErrorMessages {
 
         MAP.put(COMPARE_TO_TYPE_MISMATCH, "''compareTo()'' must return kotlin.Int, but returns {0}", RENDER_TYPE);
 
-        MAP.put(UNDERSCORE_IS_DEPRECATED, "Names _, __, ___, ..., are deprecated");
+        MAP.put(UNDERSCORE_IS_RESERVED, "Names _, __, ___, ..., are reserved in Kotlin");
         MAP.put(INVALID_CHARACTERS, "Name {0}", STRING);
 
         MAP.put(INAPPLICABLE_OPERATOR_MODIFIER, "'operator' modifier is inapplicable on this function");

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

@@ -30,7 +30,7 @@ object UnderscoreChecker : DeclarationChecker {
     fun checkIdentifier(identifier: PsiElement?, diagnosticHolder: DiagnosticSink) {
         if (identifier == null || identifier.text.isEmpty()) return
         if (identifier.text.all { it == '_' }) {
-            diagnosticHolder.report(Errors.UNDERSCORE_IS_DEPRECATED.on(identifier))
+            diagnosticHolder.report(Errors.UNDERSCORE_IS_RESERVED.on(identifier))
         }
     }
 

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyImportScope.kt

@@ -102,7 +102,7 @@ class LazyImportResolver(
         }
         for ((alias, import) in explicitClassImports.entries()) {
             if (alias.all { it == '_' }) {
-                traceForImportResolve.report(Errors.UNDERSCORE_IS_DEPRECATED.on(import))
+                traceForImportResolve.report(Errors.UNDERSCORE_IS_RESERVED.on(import))
             }
         }
         for (alias in explicitClassImports.keySet()) {

compiler/testData/codegen/box/classes/kt508.kt

@@ -4,9 +4,9 @@ public open class Identifier() {
     private var myNullable : Boolean = true
     companion object {
         open public fun init(isNullable : Boolean) : Identifier {
-            val __ = Identifier()
-            __.myNullable = isNullable
-            return __
+            val id = Identifier()
+            id.myNullable = isNullable
+            return id
         }
     }
 }

compiler/testData/codegen/box/objects/kt535.kt

@@ -5,8 +5,8 @@ class Identifier<T>(t : T?, myHasDollar : Boolean) {
 
     companion object {
         open public fun <T> init(name : T?) : Identifier<T> {
-            val __ = Identifier<T>(name, false)
-            return __
+            val id = Identifier<T>(name, false)
+            return id
         }
     }
     init {

compiler/testData/diagnostics/tests/Underscore.kt

@@ -1,20 +1,20 @@
 // !DIAGNOSTICS: -DEPRECATION
 
-<!UNDERSCORE_IS_DEPRECATED!>import kotlin.Deprecated as ___<!>
+<!UNDERSCORE_IS_RESERVED!>import kotlin.Deprecated as ___<!>
 
 @___("") data class Pair(val x: Int, val y: Int)
 
-class <!UNDERSCORE_IS_DEPRECATED!>_<!><<!UNDERSCORE_IS_DEPRECATED!>________<!>>
-val <!UNDERSCORE_IS_DEPRECATED!>______<!> = _<Int>()
+class <!UNDERSCORE_IS_RESERVED!>_<!><<!UNDERSCORE_IS_RESERVED!>________<!>>
+val <!UNDERSCORE_IS_RESERVED!>______<!> = _<Int>()
 
-fun <!UNDERSCORE_IS_DEPRECATED!>__<!>(<!UNDERSCORE_IS_DEPRECATED!>___<!>: Int, y: _<Int>?): Int {
-    val (x, <!UNDERSCORE_IS_DEPRECATED!>__________<!>) = Pair(___ - 1, 42)
-    val <!UNDERSCORE_IS_DEPRECATED!>____<!> = x
+fun <!UNDERSCORE_IS_RESERVED!>__<!>(<!UNDERSCORE_IS_RESERVED!>___<!>: Int, y: _<Int>?): Int {
+    val (x, <!UNDERSCORE_IS_RESERVED!>__________<!>) = Pair(___ - 1, 42)
+    val <!UNDERSCORE_IS_RESERVED!>____<!> = x
     // in backquotes: allowed
     val `_` = __________
-    <!UNDERSCORE_IS_DEPRECATED!>__<!>@ return if (y != null) __(____, y) else __(`_`, ______)
+    <!UNDERSCORE_IS_RESERVED!>__<!>@ return if (y != null) __(____, y) else __(`_`, ______)
 }
 
 fun doIt(f: (Any?) -> Any?) = f(null)
 
-val something = doIt { <!UNDERSCORE_IS_DEPRECATED!>__<!> -> __ }
+val something = doIt { <!UNDERSCORE_IS_RESERVED!>__<!> -> __ }

idea/src/org/jetbrains/kotlin/idea/quickfix/QuickFixRegistrar.kt

@@ -330,7 +330,7 @@ public class QuickFixRegistrar : QuickFixContributor {
         OPERATOR_MODIFIER_REQUIRED.registerFactory(AddModifierFixFactory(JetTokens.OPERATOR_KEYWORD))
         INFIX_MODIFIER_REQUIRED.registerFactory(AddModifierFixFactory(JetTokens.INFIX_KEYWORD))
 
-        UNDERSCORE_IS_DEPRECATED.registerFactory(RenameUnderscoreFix)
+        UNDERSCORE_IS_RESERVED.registerFactory(RenameUnderscoreFix)
 
         CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS.registerFactory(AddTypeToLHSOfCallableReferenceFix)