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enable main methods to be asynchronous #18157

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merged 13 commits into from
Mar 31, 2017
Merged

enable main methods to be asynchronous #18157

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88542e5
enable main methods to be asynchronous
TyOverby Mar 21, 2017
909560f
add cref to documentation
TyOverby Mar 24, 2017
b90d121
fix doc comment syntax
TyOverby Mar 27, 2017
2868b64
remove message from resx
TyOverby Mar 27, 2017
d7e9e7f
move comments
TyOverby Mar 27, 2017
2678fbe
add async int test
TyOverby Mar 27, 2017
3228961
add more test
TyOverby Mar 27, 2017
3d4363a
re-add errors for pre-71 compilers
TyOverby Mar 28, 2017
c3f2482
add tests for previous versions of csharp
TyOverby Mar 29, 2017
d88c6e4
add feature detection
TyOverby Mar 30, 2017
c113421
Disallow ref returning Main method
jaredpar Mar 30, 2017
c6c641c
add ref tests, add prototype comment
TyOverby Mar 30, 2017
c96708b
change prototype comment
TyOverby Mar 31, 2017
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9 changes: 9 additions & 0 deletions src/Compilers/CSharp/Portable/CSharpResources.Designer.cs
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3 changes: 3 additions & 0 deletions src/Compilers/CSharp/Portable/CSharpResources.resx
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Original file line number Diff line number Diff line change
Expand Up @@ -5041,4 +5041,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
<data name="ERR_VoidAssignment" xml:space="preserve">
<value>A value of type 'void' may not be assigned.</value>
</data>
<data name="IDS_FeatureAsyncMain" xml:space="preserve">
<value>async main</value>
</data>
</root>
5 changes: 3 additions & 2 deletions src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Emit;
using Microsoft.CodeAnalysis.Symbols;
using static Microsoft.CodeAnalysis.CSharp.Binder;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;

Expand Down Expand Up @@ -1470,9 +1471,9 @@ private MethodSymbol FindEntryPoint(CancellationToken cancellationToken, out Imm
continue;
}

if (candidate.IsAsync && LanguageVersion < LanguageVersion.CSharp7_1)
if (candidate.IsAsync)
{
diagnostics.Add(ErrorCode.ERR_MainCantBeAsync, candidate.Locations.First(), candidate);
CheckFeatureAvailability(candidate.DeclaringSyntaxReferences.Single().GetSyntax(), MessageID.IDS_FeatureAsyncMain, diagnostics);
}

viableEntryPoints.Add(candidate);
Expand Down
2 changes: 1 addition & 1 deletion src/Compilers/CSharp/Portable/Errors/ErrorCode.cs
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Expand Up @@ -1104,7 +1104,7 @@ internal enum ErrorCode
ERR_VarargsAsync = 4006,
ERR_ByRefTypeAndAwait = 4007,
ERR_BadAwaitArgVoidCall = 4008,
ERR_MainCantBeAsync = 4009,
// ERR_MainCantBeAsync = 4009,
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Should we delete the corresponding resource string?

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Done

ERR_CantConvAsyncAnonFuncReturns = 4010,
ERR_BadAwaiterPattern = 4011,
ERR_BadSpecialByRefLocal = 4012,
Expand Down
5 changes: 5 additions & 0 deletions src/Compilers/CSharp/Portable/Errors/MessageID.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,7 @@ internal enum MessageID
IDS_FeatureExpressionBodiedAccessor = MessageBase + 12715,
IDS_FeatureExpressionBodiedDeOrConstructor = MessageBase + 12716,
IDS_ThrowExpression = MessageBase + 12717,
IDS_FeatureAsyncMain = MessageBase + 12718,
}

// Message IDs may refer to strings that need to be localized.
Expand Down Expand Up @@ -183,6 +184,10 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
// Checks are in the LanguageParser unless otherwise noted.
switch (feature)
{
// C# 7.1 features.
case MessageID.IDS_FeatureAsyncMain:
return LanguageVersion.CSharp7_1;

// C# 7 features.
case MessageID.IDS_FeatureBinaryLiteral:
case MessageID.IDS_FeatureDigitSeparator:
Expand Down
56 changes: 39 additions & 17 deletions src/Compilers/CSharp/Test/Semantic/Semantics/BindingAsyncTests.cs
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Expand Up @@ -1259,7 +1259,13 @@ async static Task Main(string[] args)
}
}";
var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugExe, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp7));
compilation.VerifyDiagnostics(Diagnostic(ErrorCode.ERR_MainCantBeAsync, "Main").WithArguments("A.Main(string[])").WithLocation(6, 23));
compilation.VerifyDiagnostics(
// (6,5): error CS8107: Feature 'async main' is not available in C# 7. Please use language version 7.1 or greater.
// async static Task Main(string[] args)
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, @"async static Task Main(string[] args)
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Would it be possible for the diagnostic to point to a narrow piece of syntax? For example "Main" or maybe "async"?

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I've added a comment and will get back to this shortly

{
await Task.Factory.StartNew(() => { });
}").WithArguments("async main", "7.1").WithLocation(6, 5));
}

[Fact]
Expand Down Expand Up @@ -1325,10 +1331,12 @@ async static void Main()
}";
var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugExe, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp7));
compilation.VerifyDiagnostics(
// (6,23): error CS4009: 'A.Main()': an entry point cannot be marked with the 'async' modifier
// (6,5): error CS8107: Feature 'async main' is not available in C# 7. Please use language version 7.1 or greater.
// async static void Main()
Diagnostic(ErrorCode.ERR_MainCantBeAsync, "Main").WithArguments("A.Main()").WithLocation(6, 23)
);
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, @"async static void Main()
{
await Task.Factory.StartNew(() => { });
}").WithArguments("async main", "7.1").WithLocation(6, 5));
}

[Fact]
Expand Down Expand Up @@ -1375,10 +1383,14 @@ async static int Main()
compilation.VerifyDiagnostics(
// (6,22): error CS1983: The return type of an async method must be void, Task or Task<T>
// async static int Main()
Diagnostic(ErrorCode.ERR_BadAsyncReturn, "Main").WithLocation(6, 22),
// (6,22): error CS4009: 'A.Main()': an entry point cannot be marked with the 'async' modifier
Diagnostic(ErrorCode.ERR_BadAsyncReturn, "Main"),
// (6,5): error CS8107: Feature 'async main' is not available in C# 7. Please use language version 7.1 or greater.
// async static int Main()
Diagnostic(ErrorCode.ERR_MainCantBeAsync, "Main").WithArguments("A.Main()").WithLocation(6, 22));
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, @"async static int Main()
{
return await Task.Factory.StartNew(() => 5);
}").WithArguments("async main", "7.1").WithLocation(6, 5)
);
}

[Fact]
Expand Down Expand Up @@ -1420,9 +1432,13 @@ async static Task<int> Main(string[] args)
}";
var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugExe, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp7));
compilation.VerifyDiagnostics(
// (6,28): error CS4009: 'A.Main(string[])': an entry point cannot be marked with the 'async' modifier
// async static Task<int> Main(string[] args)
Diagnostic(ErrorCode.ERR_MainCantBeAsync, "Main").WithArguments("A.Main(string[])").WithLocation(6, 28));
// (6,5): error CS8107: Feature 'async main' is not available in C# 7. Please use language version 7.1 or greater.
// async static Task<int> Main(string[] args)
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, @"async static Task<int> Main(string[] args)
{
return await Task.Factory.StartNew(() => 5);
}").WithArguments("async main", "7.1").WithLocation(6, 5)
);
}

[Fact]
Expand Down Expand Up @@ -1464,9 +1480,13 @@ async static Task<int> Main()
}";
var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugExe, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp7));
compilation.VerifyDiagnostics(
// (6,28): error CS4009: 'A.Main()': an entry point cannot be marked with the 'async' modifier
// (6,5): error CS8107: Feature 'async main' is not available in C# 7. Please use language version 7.1 or greater.
// async static Task<int> Main()
Diagnostic(ErrorCode.ERR_MainCantBeAsync, "Main").WithArguments("A.Main()").WithLocation(6, 28));
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, @"async static Task<int> Main()
{
return await Task.Factory.StartNew(() => 5);
}").WithArguments("async main", "7.1").WithLocation(6, 5)
);
}

[Fact]
Expand Down Expand Up @@ -3747,8 +3767,8 @@ async public static Task Main()
}
}";
CreateCompilationWithMscorlib45(source, options: TestOptions.ReleaseExe, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp7_1)).VerifyDiagnostics(
// (4,30): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.
// async public static void Main()
// (5,30): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.
// async public static Task Main()
Diagnostic(ErrorCode.WRN_AsyncLacksAwaits, "Main"));
}

Expand All @@ -3766,10 +3786,12 @@ async public static Task Main()
CreateCompilationWithMscorlib45(source, options: TestOptions.ReleaseExe, parseOptions: TestOptions.Regular.WithLanguageVersion(LanguageVersion.CSharp7)).VerifyDiagnostics(
// (5,30): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.
// async public static Task Main()
Diagnostic(ErrorCode.WRN_AsyncLacksAwaits, "Main").WithLocation(5, 30),
// (5,30): error CS4009: 'Test.Main()': an entry point cannot be marked with the 'async' modifier
Diagnostic(ErrorCode.WRN_AsyncLacksAwaits, "Main"),
// (5,5): error CS8107: Feature 'async main' is not available in C# 7. Please use language version 7.1 or greater.
// async public static Task Main()
Diagnostic(ErrorCode.ERR_MainCantBeAsync, "Main").WithArguments("Test.Main()").WithLocation(5, 30));
Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, @"async public static Task Main()
{
}").WithArguments("async main", "7.1").WithLocation(5, 5));
}

[Fact, WorkItem(547088, "http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/547088")]
Expand Down