Make "default" a literal and other tweaks from recent LDM #18213

jcouv · 2017-03-27T22:30:05Z

Using LiteralExpressionSyntax instead of introducing a new syntax node
Disallow in expression trees (filed Expression tree support for default literal #18212 for enabling at some point)
Attaching to C# 7.1 instead of a feature flag
disallow default is T, allow x is default, allow default as RefType (with always-null warning)

@cston @gafter @dotnet/roslyn-compiler for review.

Fixes #17478
Relates to #13602

jcouv · 2017-03-28T15:57:49Z

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenExprLambdaTests.cs

@@ -5012,49 +5012,6 @@ static void Main(string[] args)
 expectedOutput: expectedOutput);
 }

- [Fact]
- public void EnumEqualityWithDefault()


Note: This is replaced by a test in TargetTypedDefaultTests.cs below.

cston · 2017-03-28T17:49:17Z

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

+ if (operand.IsLiteralDefault())
+ {
+ var defaultLiteral = (BoundDefaultLiteral)operand;
+ Debug.Assert((object)defaultLiteral.Type == null && (object)defaultLiteral.ConstantValueOpt == null);


Consider splitting into two asserts.

cston · 2017-03-28T17:51:59Z

src/Compilers/CSharp/Portable/BoundTree/BoundExpressionExtensions.cs

@@ -16,7 +16,7 @@ public static bool IsLiteralNull(this BoundExpression node)

 public static bool IsLiteralDefault(this BoundExpression node)
 {
- return node.Kind == BoundKind.DefaultLiteral && (object)node.Type == null;
+ return node.Kind == BoundKind.DefaultLiteral && node.Syntax.Kind() == SyntaxKind.DefaultLiteralExpression;
 }


Why is the second condition needed?

BoundKind.DefaultLiteral used to be BoundKind.DefaultOperator. Maybe I will rename it back.
But to answer your question, IsLiteralDefault should return false for default(int). It should only return true for the default literal.

cston · 2017-03-28T17:54:12Z

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

@@ -1475,5 +1475,6 @@ internal enum ErrorCode

 ERR_BadDynamicMethodArgDefault = 9000,
 ERR_DefaultNotValid = 9001,
+ ERR_ExpressionTreeContainsDefaultLiteral = 9002,


Should the previous two values be renamed to use the term DefaultLiteral?

cston · 2017-03-28T17:55:44Z

src/Compilers/CSharp/Portable/BoundTree/BoundExpressionExtensions.cs

@@ -16,7 +16,7 @@ public static bool IsLiteralNull(this BoundExpression node)

 public static bool IsLiteralDefault(this BoundExpression node)


Perhaps IsDefaultLiteral.

The reason I used this seemingly strange name is because it matches IsLiteralNull (a few lines above).

cston · 2017-03-28T17:56:52Z

src/Compilers/CSharp/Portable/Lowering/DiagnosticsPass_ExpressionTrees.cs

+
+ public override BoundNode VisitDefaultLiteral(BoundDefaultLiteral node)
+ {
+ if (_inExpressionLambda && node.IsLiteralDefault())


Related to earlier question: When will node.IsLiteralDefault() return false?

Why is default not allowed in an expression lambda?

cston · 2017-03-28T18:02:21Z

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

+ string source = @"
+enum E
+{
+ Entry = default


Perhaps test Entry = default + 1 as well.

cston · 2017-03-28T18:11:06Z

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

 {
 System.Console.Write(default as long);
+ System.Console.Write(default as T);
 }
 }";


Are we testing default as T with constraints on T?

jcouv · 2017-03-28T22:54:56Z

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

+enum E
+{
+ DefaultEntry = default,
+ OneEntry = default + 1


Chuck asked why this works. I'll follow up.

I'm going to guess that overload resolution finds a most specific overload of operator + that is applicable, and the result is a constant.

Yes, overload resolution succeeds, then the left and right operands get converted, which gives default an int type.

cston · 2017-03-29T00:18:07Z

LGTM

jcouv · 2017-03-31T01:29:13Z

@gafter @dotnet/roslyn-compiler for a second review. Thanks

AlekseyTs · 2017-04-04T18:30:15Z

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

@@ -773,11 +773,6 @@ private BoundExpression BindDeclarationVariables(TypeSymbol declType, VariableDe
 }
 }

- private static BoundExpression BindDefaultLiteral(DefaultLiteralSyntax node)


private static BoundExpression BindDefaultLiteral(DefaultLiteralSyntax node) [](start = 8, length = 76)

I would keep this method.

AlekseyTs · 2017-04-04T18:57:44Z

src/Compilers/Test/Utilities/CSharp/TestOptions.cs

 public static readonly CSharpParseOptions ExperimentalParseOptions =
- new CSharpParseOptions(kind: SourceCodeKind.Regular, documentationMode: DocumentationMode.None, languageVersion: LanguageVersion.CSharp7).WithFeatures(s_experimentalFeatures);
+ new CSharpParseOptions(kind: SourceCodeKind.Regular, documentationMode: DocumentationMode.None, languageVersion: LanguageVersion.CSharp7_1).WithFeatures(s_experimentalFeatures);


CSharp7_1 [](start = 141, length = 9)

Should we simply use Latest here?

AlekseyTs · 2017-04-04T19:01:20Z

src/Compilers/CSharp/Test/Syntax/Parsing/ExpressionParsingTests.cs

@@ -3540,8 +3540,7 @@ public void TestTargetTypedDefault()
 var expr = this.ParseExpression(text, TestOptions.ExperimentalParseOptions);


ExperimentalParseOptions [](start = 62, length = 24)

This is the only test in this file that is using ExperimentalParseOptions. Consider changing it to use CSharp7 and have have a test with 7.1 next to other default tests.

I changed it to use 7.1 explicitly (instead of Experimental, which now means Latest). But I didn't move it because this parsing test relies on base type (ParsingTests) for some infrastructure.

I already had a test for diagnostics in 7.0 scenario:

[Fact] public void TestCSharp7() { string source = @" class C { static void Main() { int x = default; } } "; var comp = CreateCompilationWithMscorlib(source); comp.VerifyDiagnostics( // (6,17): error CS8107: Feature 'default literal' is not available in C# 7. Please use language version 7.1 or greater. // int x = default; Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7, "default").WithArguments("default literal", "7.1").WithLocation(6, 17) ); }

Let me know if that addresses your concern.

AlekseyTs

LGTM

AlekseyTs · 2017-04-04T19:44:37Z

Still LGTM

jcouv · 2017-04-04T19:49:14Z

Thanks :-)

Fix error for missing feature

666a273

dnfclas added the cla-already-signed label Mar 27, 2017

jcouv force-pushed the default-LDM branch 3 times, most recently from 732750c to 86928ce Compare March 28, 2017 04:42

jcouv added 3 commits March 28, 2017 07:45

Disallow default literal in expression tree

fe08789

Use syntax akin of other literals

178e5d5

Update behavior for as and is

14a504c

jcouv force-pushed the default-LDM branch from 86928ce to 14a504c Compare March 28, 2017 14:46

jcouv requested a review from gafter March 28, 2017 15:47

jcouv self-assigned this Mar 28, 2017

jcouv added the Area-Compilers label Mar 28, 2017

jcouv commented Mar 28, 2017

View reviewed changes

cston reviewed Mar 28, 2017

View reviewed changes

jcouv added 2 commits March 28, 2017 13:10

Allow default in expression tree again

61cf9ea

Addressing PR feedback

580a972

jcouv commented Mar 28, 2017

View reviewed changes

Fixing EE code to use renamed bound node

363a70e

jcouv force-pushed the default-LDM branch from fa56967 to 363a70e Compare March 29, 2017 03:07

jcouv force-pushed the default-LDM branch 2 times, most recently from 248f8a4 to 9bf3a6e Compare March 31, 2017 03:07

Add warning for "case default:"

8d5e082

jcouv force-pushed the default-LDM branch from 9bf3a6e to 8d5e082 Compare March 31, 2017 05:27

jcouv assigned gafter Apr 4, 2017

AlekseyTs reviewed Apr 4, 2017

View reviewed changes

AlekseyTs approved these changes Apr 4, 2017

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Address Aleksey's feedback

a39beb2

jcouv merged commit cc1aeba into dotnet:features/default Apr 4, 2017

jcouv deleted the default-LDM branch April 4, 2017 22:07

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Make "default" a literal and other tweaks from recent LDM #18213

Make "default" a literal and other tweaks from recent LDM #18213

jcouv commented Mar 27, 2017

jcouv Mar 28, 2017

cston Mar 28, 2017

cston Mar 28, 2017

jcouv Mar 28, 2017

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jcouv Mar 28, 2017 •

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AlekseyTs commented Apr 4, 2017

jcouv commented Apr 4, 2017

		@@ -16,7 +16,7 @@ public static bool IsLiteralNull(this BoundExpression node)

		public static bool IsLiteralDefault(this BoundExpression node)

		@@ -3540,8 +3540,7 @@ public void TestTargetTypedDefault()
		var expr = this.ParseExpression(text, TestOptions.ExperimentalParseOptions);

Make "default" a literal and other tweaks from recent LDM #18213

Make "default" a literal and other tweaks from recent LDM #18213

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jcouv commented Mar 27, 2017

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