'async' reserved in front of function literals

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

@@ -17,6 +17,7 @@
 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.descriptors.CallableMemberDescriptor
 import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
@@ -27,6 +28,7 @@ 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
@@ -53,6 +55,7 @@ internal class FunctionsTypingVisitor(facade: ExpressionTypingInternals) : Expre
             isStatement: Boolean,
             statementScope: LexicalWritableScope? // must be not null if isStatement
     ): KotlinTypeInfo {
+        checkReservedAsync(context, function)
         if (!isStatement) {
             // function expression
             if (!function.getTypeParameters().isEmpty()) {
@@ -131,6 +134,8 @@ internal class FunctionsTypingVisitor(facade: ExpressionTypingInternals) : Expre
     }
 
     override fun visitLambdaExpression(expression: KtLambdaExpression, context: ExpressionTypingContext): KotlinTypeInfo? {
+        checkReservedAsync(context, expression)
+
         if (!expression.getFunctionLiteral().hasBody()) return null
 
         val expectedType = context.expectedType
@@ -153,6 +158,10 @@ 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

@@ -0,0 +1,21 @@
+fun async(f: () -> Unit) {
+    f()
+}
+
+infix fun Any.async(f: () -> Unit) = f()
+
+fun test(foo: Any) {
+    <!UNSUPPORTED!>async<!> {  }
+    <!UNSUPPORTED!>async<!> /**/ {  }
+    foo <!UNSUPPORTED!>async<!> {  }
+
+    async() { }
+
+    async({ })
+    foo async ({ })
+
+    foo <!UNSUPPORTED!>async<!> fun () {}
+    foo async (fun () {})
+
+    async (fun () {})
+}

compiler/testData/diagnostics/tests/ReservedAsync.txt

@@ -0,0 +1,5 @@
+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

@@ -547,6 +547,12 @@ 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");