Revert "'async' reserved in front of function literals"

This reverts commit 6155d836a5.

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/FunctionsTypingVisitor.kt

@@ -17,7 +17,6 @@
 package org.jetbrains.kotlin.types.expressions
 
 import com.google.common.collect.Lists
-import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.builtins.getReturnTypeFromFunctionType
 import org.jetbrains.kotlin.builtins.isFunctionType
@@ -28,9 +27,7 @@ import org.jetbrains.kotlin.descriptors.impl.AnonymousFunctionDescriptor
 import org.jetbrains.kotlin.descriptors.impl.SimpleFunctionDescriptorImpl
 import org.jetbrains.kotlin.diagnostics.DiagnosticUtils
 import org.jetbrains.kotlin.diagnostics.Errors.*
-import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
-import org.jetbrains.kotlin.psi.psiUtil.checkReservedPrefixWord
 import org.jetbrains.kotlin.psi.psiUtil.getAnnotationEntries
 import org.jetbrains.kotlin.resolve.*
 import org.jetbrains.kotlin.resolve.BindingContext.EXPECTED_RETURN_TYPE
@@ -58,7 +55,6 @@ internal class FunctionsTypingVisitor(facade: ExpressionTypingInternals) : Expre
             isDeclaration: Boolean,
             statementScope: LexicalWritableScope? // must be not null if isDeclaration
     ): KotlinTypeInfo {
-        checkReservedAsync(context, function)
         if (!isDeclaration) {
             // function expression
             if (!function.getTypeParameters().isEmpty()) {
@@ -135,8 +131,6 @@ internal class FunctionsTypingVisitor(facade: ExpressionTypingInternals) : Expre
     }
 
     override fun visitLambdaExpression(expression: KtLambdaExpression, context: ExpressionTypingContext): KotlinTypeInfo? {
-        checkReservedAsync(context, expression)
-
         if (!expression.functionLiteral.hasBody()) return null
 
         val expectedType = context.expectedType
@@ -159,10 +153,6 @@ internal class FunctionsTypingVisitor(facade: ExpressionTypingInternals) : Expre
         return components.dataFlowAnalyzer.createCheckedTypeInfo(resultType, context, expression)
     }
 
-    private fun checkReservedAsync(context: ExpressionTypingContext, expression: PsiElement) {
-        checkReservedPrefixWord(context.trace, expression, "async", "async block/lambda. Use 'async() { ... }' or 'async(fun...)'")
-    }
-
     private fun createFunctionLiteralDescriptor(
             expression: KtLambdaExpression,
             context: ExpressionTypingContext

compiler/testData/diagnostics/tests/ReservedAsync.kt

@@ -1,23 +0,0 @@
-fun async(f: () -> Unit) {
-    f()
-}
-
-infix fun Any.async(f: () -> Unit) = f()
-
-fun test(foo: Any) {
-    <!UNSUPPORTED!>async<!> {  }
-    `async` {  }
-    <!UNSUPPORTED!>async<!> /**/ {  }
-    foo <!UNSUPPORTED!>async<!> {  }
-
-    async() { }
-
-    async({ })
-    foo async ({ })
-
-    foo <!UNSUPPORTED!>async<!> fun () {}
-    foo `async` fun () {}
-    foo async (fun () {})
-
-    async (fun () {})
-}

compiler/testData/diagnostics/tests/ReservedAsync.txt

@@ -1,5 +0,0 @@
-package
-
-public fun async(/*0*/ f: () -> kotlin.Unit): kotlin.Unit
-public fun test(/*0*/ foo: kotlin.Any): kotlin.Unit
-public infix fun kotlin.Any.async(/*0*/ f: () -> kotlin.Unit): kotlin.Unit

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -571,12 +571,6 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
             doTest(fileName);
         }
 
-        @TestMetadata("ReservedAsync.kt")
-        public void testReservedAsync() throws Exception {
-            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/ReservedAsync.kt");
-            doTest(fileName);
-        }
-
         @TestMetadata("ResolveOfJavaGenerics.kt")
         public void testResolveOfJavaGenerics() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/ResolveOfJavaGenerics.kt");