Deconstruction-declaration parsing for local declaration, for and foreach #12104

jcouv · 2016-06-20T17:59:37Z

Adds parsing for three deconstruction-declaration contexts. Other contexts (such as let or from will be added later).

@dotnet/roslyn-compiler for review. Thanks

// All those are parsed as a LocalDeclarationStatement, except that its VariableDeclaration is extended to hold a DeconstructionDeclaration
// DeconstructionDeclaration is DeconstructionVariables + equalsToken + expression
(Int32 a, Int64 b) = foo;
((Int32 a, Int64 b), Int32 c) = foo;
var (a, b) = foo;
var ((a, b), c) = foo;
(Int32 x, var (y, z)) = foo; // var syntax inside list syntax

// This is still a method call
var(a, b);

// ForStatement with the VariableDeclaration holding a DeconstructionDeclaration
for ((Int32 x, Int64 y) = foo; ; ) { }
for (var (x, y) = foo; ; ) { }

// Foreach statement which is extended to hold DeconstructionVariables
foreach ((int x, var y) in foo) { }
foreach (var (x, y) in foo) { }

Note 1: because my VS is busted, I expect some public API errors. I will fix that before checking in.

Note 2: this change includes a copy of Aleksey's recent change in outvar branch to support Internal="true" in Syntax.xml, which will help maintain a backwards compatible public API.

Issue #11299

foreach statements

jaredpar · 2016-06-20T20:28:00Z

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

            //  foreach ( <type> <identifier> in <expr> ) <embedded-statement>
+            // or
+            //  foreach ( <deconstruction-variables> in <expr> ) <embedded-statement>


The name implies to me that it can only be variables. I assume we can have declarations here as well.

Fixed the comment.

jcouv · 2016-06-20T21:33:56Z

Hold off any reviews. From discussion with Cyrus and Aleksey, I'm going to remove the terminals I introduced (to represent "type id" or "id") and use VariableDeclaration instead.

jcouv · 2016-06-21T16:29:30Z

@dotnet/roslyn-compiler This is ready to review again.

Two examples:

var (x, (y, z)) = expression gets parsed as a VariableDeclaration with type=var, no regular declarators, and the new deconstruction declarator holding the rest.
That deconstruction declarator has two variables, each which is a VariableDeclaration where type is null.
For the first one, the x is inside the regular declarator.
For the second one, the two variables are inside the deconstruction declarator.
(int x, int y) = expression gets parsed as a VariableDeclaration with no type, no regular declarators, and the deconstruction declarator holding everything.
That deconstruction declarator has two variables, each which are held as a VariableDeclaration with type=int and the name of the variable inside the regular declarator.

To recap, VariableDeclaration is used in four ways:

type is var, declarator=null and deconstruction is set. Example: var (...) = ...
type is null, declarator=null and deconstruction is set. Example: (int x, int y)
type is set, declarator is set with one element with just a name and deconstruction is null, as before. Example: int x in (int x, int y) = ...
type is null, declarator is set with one element with just a name and deconstruction is null. Example: y in var (x, y) = ...

cston · 2016-06-21T17:23:50Z

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


-                    this.Reset(ref resetPoint);
+                    if ((object)decl == null)


Minor point: CSharpSyntaxNode does not define == so the cast to object is unnecessary.

Fixed here and other similar instances below. Thanks

jcouv · 2016-06-21T21:34:01Z

Just pushed a PR addressing Chuck and Cyrus's feedback.
It removes the new SyntaxKinds, factors ParseDeconstructionListForm and ParseDeconstructionIdentifiers, removes the Internal="true" (and supporting source generation code), and some smaller things.

cston · 2016-06-21T21:44:18Z

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

+
+                    if (this.CurrentToken.Kind != SyntaxKind.CloseParenToken)
+                    {
+                        VariableDeclarationSyntax variable;


variable declaration can be moved inside while.

AlekseyTs · 2016-06-23T17:52:14Z

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

+                return null;
+            }
+
+            return CheckFeatureAvailability(result, MessageID.IDS_FeatureTuples);


Please add tests for this check, positive and negative. #Resolved

Added CSharp6 test. Positive tests will be easier once I have some binding, so they will be added in subsequent PRs.

jcouv · 2016-06-23T21:30:31Z

This change to public API is not ready yet. I have more changes coming.

jcouv · 2016-06-23T23:52:53Z

Ok, the latest commit I pushed provides a more reasonable public API. If anything, some APIs could be added for convenience.

cston · 2016-06-24T16:18:51Z

docs/features/deconstruction.md

+    ;
+
+for_statement
+    : 'for' '(' for_initializer? ';' for_condition? ';' for_iterator? ')' embedded_statement
    ;


Has for_statement changed or is the same as without deconstruction variables?

In the grammar, I kept for_statement as before. The difference appears below, in for_initializer.

cston · 2016-06-24T17:35:05Z

What kind of parse errors do we report for contexts where deconstruct is not allowed? For instance using ((x, y) = F()) { ... }. Is it necessary to report good errors in these cases?

cston · 2016-06-24T17:35:11Z

LGTM

AlekseyTs · 2016-06-24T18:04:57Z

src/Compilers/CSharp/Portable/Syntax/Syntax.xml

@@ -1809,11 +1809,29 @@
      <Kind Name="SemicolonToken"/>
    </Field>
  </Node>
-  <Node Name="VariableDeclarationSyntax" Base="CSharpSyntaxNode">
+
+  <Node Name="VariableDeconstructionDeclaratorSyntax" Base="CSharpSyntaxNode" AvoidAutoCreation="true" InternalConstructor="true">


Should this say InternalFactory rather than constructor? #Resolved

Sure. Renamed.

jcouv · 2016-06-24T19:00:16Z

@cston, I will take a note on your question (should we report errors for un-supported contexts?).

AlekseyTs · 2016-06-24T19:36:04Z

src/Compilers/CSharp/Portable/PublicAPI.Unshipped.txt

@@ -117,6 +119,20 @@ Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax.Update(Microsoft.CodeAnalys
 Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax.WithCloseParenToken(Microsoft.CodeAnalysis.SyntaxToken closeParenToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax
 Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax.WithElements(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.TupleElementSyntax> elements) -> Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax
 Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax.WithOpenParenToken(Microsoft.CodeAnalysis.SyntaxToken openParenToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.TupleTypeSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.VariableDeclarationSyntax.Deconstruction.get -> Microsoft.CodeAnalysis.CSharp.Syntax.VariableDeconstructionDeclaratorSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.VariableDeclarationSyntax.WithDeconstruction(Microsoft.CodeAnalysis.CSharp.Syntax.VariableDeconstructionDeclaratorSyntax deconstruction) -> Microsoft.CodeAnalysis.CSharp.Syntax.VariableDeclarationSyntax


I would expect this method to remove regular variables and even type when it has an incompatible value. Does it?

Null input should probably be disallowed as well.

In reply to: 68451172 [](ancestors = 68451172)

An existing VariableDeclarationSyntax.WithVariables should probably be also adjusted accordingly.

In reply to: 68451298 [](ancestors = 68451298,68451172)

I added two work items to track this:

Add validation to factory methods (only allow creating valid combinations with reasonable-looking children)

Add validation logic or erasure to WithXYZ methods

Thanks for raising the questions.

AlekseyTs · 2016-06-24T21:32:01Z

LGTM

jcouv · 2016-06-24T21:55:33Z

Thanks both for the review and feedback. I'll go ahead with merge.

Deconstruction-declaration parsing for local declaration, for and

62d0b88

foreach statements

jcouv added Area-Compilers Feature - Tuples Tuples labels Jun 20, 2016

jcouv self-assigned this Jun 20, 2016

dnfclas added the cla-already-signed label Jun 20, 2016

jaredpar reviewed Jun 20, 2016
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jcouv added 2 commits June 20, 2016 22:22

Switching to new syntax model

219bc7c

Minor improvements

1160bc7

Improving comments

2f53b73

cston reviewed Jun 21, 2016
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PR feedback (1)

13736b8

cston reviewed Jun 21, 2016
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AlekseyTs reviewed Jun 23, 2016
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PR feedback (4)

e96585a

jcouv force-pushed the d-declaration branch from 9c7805f to b4e7107 Compare June 23, 2016 21:19

Refining public API

9ae475a

jcouv force-pushed the d-declaration branch from b4e7107 to 9ae475a Compare June 23, 2016 23:48

Removing accidentally-added files

de691fe

cston reviewed Jun 24, 2016
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AlekseyTs reviewed Jun 24, 2016
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PR feedback (5)

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AlekseyTs reviewed Jun 24, 2016
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jcouv merged commit 78cb91d into dotnet:features/tuples Jun 24, 2016

jcouv deleted the d-declaration branch June 24, 2016 21:55

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Deconstruction-declaration parsing for local declaration, for and foreach #12104

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Deconstruction-declaration parsing for local declaration, for and foreach #12104

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