Do not allow await in catch/finally un language version 5

Fixes #2725

src/Compilers/CSharp/Portable/Binder/Binder_Await.cs

@@ -118,32 +118,42 @@ private bool ReportBadAwaitWithoutAsync(CSharpSyntaxNode node, DiagnosticBag dia
         }
 
         /// <summary>
-        /// Report diagnostics if the await expression occurs in an unsafe context.
-        /// Errors for await in lock statement, finally block, or catch clause are detected
-        /// and reported in the warnings pass.
+        /// Report diagnostics if the await expression occurs in a context where it is not allowed.
         /// </summary>
         /// <returns>True if errors were found.</returns>
         private bool ReportBadAwaitContext(CSharpSyntaxNode node, DiagnosticBag diagnostics)
         {
-            bool hasErrors = false;
-
             if (this.InUnsafeRegion && !this.Flags.Includes(BinderFlags.AllowAwaitInUnsafeContext))
             {
                 Error(diagnostics, ErrorCode.ERR_AwaitInUnsafeContext, node);
-                hasErrors = true;
+                return true;
             }
             else if (this.Flags.Includes(BinderFlags.InLockBody))
             {
                 Error(diagnostics, ErrorCode.ERR_BadAwaitInLock, node);
-                hasErrors = true;
+                return true;
             }
             else if (this.Flags.Includes(BinderFlags.InCatchFilter))
             {
                 Error(diagnostics, ErrorCode.ERR_BadAwaitInCatchFilter, node);
-                hasErrors = true;
+                return true;
+            }
+            else if (this.Flags.Includes(BinderFlags.InFinallyBlock) &&
+                (node.SyntaxTree as CSharpSyntaxTree)?.Options?.IsFeatureEnabled(MessageID.IDS_AwaitInCatchAndFinally) == false)
+            {
+                Error(diagnostics, ErrorCode.ERR_BadAwaitInFinally, node);
+                return true;
+            }
+            else if (this.Flags.Includes(BinderFlags.InCatchBlock) &&
+                (node.SyntaxTree as CSharpSyntaxTree)?.Options?.IsFeatureEnabled(MessageID.IDS_AwaitInCatchAndFinally) == false)
+            {
+                Error(diagnostics, ErrorCode.ERR_BadAwaitInCatch, node);
+                return true;
+            }
+            else
+            {
+                return false;
             }
-
-            return hasErrors;
         }
 
         /// <summary>

src/Compilers/CSharp/Portable/CSharpParseOptions.cs

@@ -196,6 +196,13 @@ public new CSharpParseOptions WithFeatures(IEnumerable<KeyValuePair<string, stri
             }
         }
 
+        internal bool IsFeatureEnabled(MessageID feature)
+        {
+            LanguageVersion availableVersion = LanguageVersion;
+            LanguageVersion requiredVersion = feature.RequiredVersion();
+            return availableVersion >= requiredVersion;
+        }
+
         public override bool Equals(object obj)
         {
             return this.Equals(obj as CSharpParseOptions);

src/Compilers/CSharp/Portable/CSharpResources.Designer.cs

 //------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by a tool.
-//     Runtime Version:4.0.30319.0
+//     Runtime Version:4.0.30319.42000
 //
 //     Changes to this file may cause incorrect behavior and will be lost if
 //     the code is regenerated.
@@ -8692,6 +8692,15 @@ internal class CSharpResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to await in catch blocks and finally blocks.
+        /// </summary>
+        internal static string IDS_AwaitInCatchAndFinally {
+            get {
+                return ResourceManager.GetString("IDS_AwaitInCatchAndFinally", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to collection.
         /// </summary>

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -4594,6 +4594,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="IDS_FeatureInterpolatedStrings" xml:space="preserve">
     <value>interpolated strings</value>
   </data>
+  <data name="IDS_AwaitInCatchAndFinally" xml:space="preserve">
+    <value>await in catch blocks and finally blocks</value>
+  </data>
   <data name="ERR_UnescapedCurly" xml:space="preserve">
     <value>A '{0}' character must be escaped (by doubling) in an interpolated string.</value>
   </data>

src/Compilers/CSharp/Portable/Errors/MessageID.cs

@@ -110,6 +110,7 @@ internal enum MessageID
         IDS_FeatureUsingStatic = MessageBase + 12701,
         IDS_FeatureInterpolatedStrings = MessageBase + 12702,
         IDS_OperationCausedStackOverflow = MessageBase + 12703,
+        IDS_AwaitInCatchAndFinally = MessageBase + 12704,
 
     }
 
@@ -161,6 +162,7 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
                 case MessageID.IDS_FeatureDictionaryInitializer:
                 case MessageID.IDS_FeatureUsingStatic:
                 case MessageID.IDS_FeatureInterpolatedStrings:
+                case MessageID.IDS_AwaitInCatchAndFinally:
                     return LanguageVersion.CSharp6;
 
                 // C# 5 features.

src/Compilers/CSharp/Portable/Parser/SyntaxParser.cs

@@ -1056,9 +1056,7 @@ protected TNode CheckFeatureAvailability<TNode>(TNode node, MessageID feature, b
 
         protected bool IsFeatureEnabled(MessageID feature)
         {
-            LanguageVersion availableVersion = this.Options.LanguageVersion;
-            LanguageVersion requiredVersion = feature.RequiredVersion();
-            return availableVersion >= requiredVersion;
+            return this.Options.IsFeatureEnabled(feature);
         }
     }
 }

src/Compilers/CSharp/Test/Semantic/Semantics/BindingAsyncTests.cs

@@ -890,7 +890,15 @@ class Test
         }
     }
 }";
-            CreateCompilationWithMscorlib45(source).VerifyDiagnostics();
+            CreateCompilationWithMscorlib45(source, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp5)).VerifyDiagnostics(
+                // (20,17): error CS1984: Cannot await in the body of a finally clause
+                //                 await Task.Factory.StartNew(() => { });
+                Diagnostic(ErrorCode.ERR_BadAwaitInFinally, "await Task.Factory.StartNew(() => { })").WithLocation(20, 17),
+                // (30,17): error CS1984: Cannot await in the body of a finally clause
+                //                 await Task.Factory.StartNew(() => { });
+                Diagnostic(ErrorCode.ERR_BadAwaitInFinally, "await Task.Factory.StartNew(() => { })").WithLocation(30, 17)
+                );
+            CreateCompilationWithMscorlib45(source, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp6)).VerifyDiagnostics();
         }
 
         [Fact]
@@ -914,7 +922,12 @@ class Test
         }
     }
 }";
-            CreateCompilationWithMscorlib45(source).VerifyDiagnostics();
+            CreateCompilationWithMscorlib45(source, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp5)).VerifyDiagnostics(
+                // (12,13): error CS1985: Cannot await in a catch clause
+                //             await Task.Factory.StartNew(() => { });
+                Diagnostic(ErrorCode.ERR_BadAwaitInCatch, "await Task.Factory.StartNew(() => { })").WithLocation(12, 13)
+                );
+            CreateCompilationWithMscorlib45(source, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp6)).VerifyDiagnostics();
         }
 
         [Fact]