Record structs: add ToString and PrintMembers #52012

jcouv · 2021-03-20T03:06:08Z

Spec: https://github.com/dotnet/csharplang/blob/main/proposals/record-structs.md (relevant section copied below for convenience)
Test plan: #51199

Printing members: PrintMembers and ToString methods

The record struct includes a synthesized method equivalent to a method declared as follows:
private bool PrintMembers(System.Text.StringBuilder builder);
The method does the following:

for each of the record struct's printable members (non-static public field and readable property members), appends that member's name followed by " = " followed by the member's value separated with ", ",

return true if the record struct has printable members.

For a member that has a value type, we will convert its value to a string representation using the most efficient method available to the target platform. At present that means calling ToString before passing to StringBuilder.Append.

The PrintMembers method can be declared explicitly.
It is an error if the explicit declaration does not match the expected signature or accessibility.

The record struct includes a synthesized method equivalent to a method declared as follows:
public override string ToString();
The method can be declared explicitly. It is an error if the explicit declaration does not match the expected signature or accessibility.

The synthesized method:

creates a StringBuilder instance,

appends the record struct name to the builder, followed by " { ",

invokes the record struct's PrintMembers method giving it the builder, followed by " " if it returned true,

appends "}",

returns the builder's contents with builder.ToString().

For example, consider the following record struct:
record struct R1(T1 P1, T2 P2);
For this record struct, the synthesized printing members would be something like:

Youssef1313 · 2021-03-20T06:50:52Z

...mpilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordEqualityOperatorBase.cs

-    ///        
+    ///
+    /// For record struct:
+    /// public static bool operator==(R r1, R r2)


Should be left and right based on #51973?

It will. That'll get picked up next time the feature branch is refreshed with changes from main branch.

jcouv · 2021-03-23T18:51:13Z

src/Compilers/CSharp/Test/Symbol/Symbols/Source/RecordTests.cs

@@ -1081,7 +1081,7 @@ record C
                "System.String! C.Y { get; init; }",
                "System.String! C.Y.get",
                "void C.Y.init",
-                "System.String C.ToString()",


📝 we were missing the annotation on record's ToString #Resolved

jcouv · 2021-03-25T16:22:11Z

@AlekseyTs @dotnet/roslyn-compiler for review. Thanks

AlekseyTs · 2021-03-25T16:49:54Z

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs

                DeclarationModifiers.Private :
                DeclarationModifiers.Protected;

-            if (virtualPrintInBase() is object)
+            if (ContainingType.IsRecord && virtualPrintInBase() is object)


virtualPrintInBase() [](start = 43, length = 20)

This logic doesn't feel right. If a record class doesn't inherit from object, the method should always have Override flag. If base doesn't contain the right method to override, an appropriate error is going to be reported about that. #Closed

AlekseyTs · 2021-03-25T16:50:49Z

            result |= ContainingType.IsSealed ? DeclarationModifiers.None : DeclarationModifiers.Virtual;

Is this true for a record struct? #Closed

Refers to: src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs:42 in 21dd0d0. [](commit_id = 21dd0d0, deletion_comment = False)

AlekseyTs · 2021-03-25T16:52:05Z

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol.cs

@@ -3671,7 +3667,7 @@ MethodSymbol addPrintMembersMethod()
                else
                {
                    printMembersMethod = (MethodSymbol)existingPrintMembersMethod;
-                    if (this.IsSealed && this.BaseTypeNoUseSiteDiagnostics.IsObjectType())
+                    if ((this.IsSealed && this.BaseTypeNoUseSiteDiagnostics.IsObjectType()) || !isRecordClass)


this.IsSealed [](start = 25, length = 13)

Is this true for a record struct? If so, consider checking !isRecordClass first. #Closed

AlekseyTs · 2021-03-25T16:58:00Z

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs

@@ -124,6 +130,14 @@ internal override void GenerateMethodBody(TypeCompilationState compilationState,
                        return;
                    }
                }
+                else if (ContainingType.IsRecordStruct)


ContainingType.IsRecordStruct [](start = 25, length = 29)

It looks like we can combine this condition with the previous if #Closed

AlekseyTs · 2021-03-25T17:01:13Z

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs

@@ -113,7 +119,7 @@ internal override void GenerateMethodBody(TypeCompilationState compilationState,
                    return;
                }

-                ArrayBuilder<BoundStatement>? block = printableMembers.IsEmpty ? null : ArrayBuilder<BoundStatement>.GetInstance();
+                ArrayBuilder<BoundStatement>? block = (printableMembers.IsEmpty && !ContainingType.IsRecordStruct) ? null : ArrayBuilder<BoundStatement>.GetInstance();


&& !ContainingType.IsRecordStruct [](start = 80, length = 33)

Addition of this condition looks suspicious. Are we going to return from the added if below without releasing the builder? #Closed

Thanks. That was indeed a problem.

In reply to: 601677092 [](ancestors = 601677092)

AlekseyTs · 2021-03-25T17:08:21Z

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs

+                        F.CloseMethod(F.Return(F.Literal(false)));
+                        return;
+                    }
+                }
                else
                {
                    MethodSymbol? printMethod = FindValidPrintMembersMethod(ContainingType.BaseTypeNoUseSiteDiagnostics, DeclaringCompilation);


FindValidPrintMembersMethod [](start = 48, length = 27)

Usage of this method here doesn't feel right. Should we simply get OverriddenMethod here? #Closed

AlekseyTs · 2021-03-25T17:16:46Z

    internal static MethodSymbol? FindValidPrintMembersMethod(TypeSymbol containingType, CSharpCompilation compilation)

It is quite possible I am missing something, but it looks to me that we shouldn't be needing this method. I already commented on the two call sites in this file and I believe we should remove the other remaining call as well. Instead we should override MethodChecks where we would verify that OverriddenMethod belongs to the immediate base. #Closed

Refers to: src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs:244 in 21dd0d0. [](commit_id = 21dd0d0, deletion_comment = False)

AlekseyTs · 2021-03-25T18:00:58Z

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

+                //     static private bool PrintMembers(System.Text.StringBuilder builder) => throw null;
+                Diagnostic(ErrorCode.ERR_StaticAPIInRecord, "PrintMembers").WithArguments("C1.PrintMembers(System.Text.StringBuilder)").WithLocation(4, 25)
+                );
+        }


} [](start = 8, length = 1)

Are we testing a scenario when synthesized PrintMembers used explicitly by user code? #Closed

Updated ToString_UserDefinedPrintMembers to cover

In reply to: 601724459 [](ancestors = 601724459)

Are we testing a scenario when synthesized PrintMembers used explicitly by user code?

Updated ToString_UserDefinedPrintMembers to cover

It looks like it doesn't call "synthesized PrintMembers".

In reply to: 601913646 [](ancestors = 601913646,601724459)

Added ToString_CallingSynthesizedPrintMembers

In reply to: 601929272 [](ancestors = 601929272,601913646,601724459)

AlekseyTs · 2021-03-25T18:02:01Z

Done with review pass (commit 1) #Closed

jcouv · 2021-03-25T21:47:49Z

            result |= ContainingType.IsSealed ? DeclarationModifiers.None : DeclarationModifiers.Virtual;

Yes. The sealed modifier is applied for all structs in MakeModifiers:

            switch (typeKind)
            {
...
                case TypeKind.Struct:
                case TypeKind.Enum:
                    mods |= DeclarationModifiers.Sealed;
                    break;
...
            }

In reply to: 807085029 [](ancestors = 807085029)

Refers to: src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs:42 in 21dd0d0. [](commit_id = 21dd0d0, deletion_comment = False)

AlekseyTs · 2021-03-26T01:03:56Z

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs

                {
                    if (printableMembers.IsEmpty)
                    {
                        // return false;
                        F.CloseMethod(F.Return(F.Literal(false)));
                        return;
                    }
+                    block = ArrayBuilder<BoundStatement>.GetInstance();


block = ArrayBuilder.GetInstance(); [](start = 20, length = 51)

Consider moving block's declaration and initialization after the entire if. #ByDesign

I'll leave this as-is. Seems fine

In reply to: 601939283 [](ancestors = 601939283)

AlekseyTs · 2021-03-26T01:11:35Z

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

@@ -6781,9 +6879,6 @@ extends A
 ";
            var comp = CreateCompilationWithIL(new[] { source, IsExternalInitTypeDefinition }, ilSource: ilSource, parseOptions: TestOptions.Regular9);
            comp.VerifyEmitDiagnostics(
-                // (2,19): error CS8864: Records may only inherit from object or another record
-                // public record C : B
-                Diagnostic(ErrorCode.ERR_BadRecordBase, "B").WithLocation(2, 19),
                // (4,29): error CS8871: 'C.PrintMembers(StringBuilder)' does not override expected method from 'B'.
                //     protected override bool PrintMembers(System.Text.StringBuilder builder) => throw null;
                Diagnostic(ErrorCode.ERR_DoesNotOverrideBaseMethod, "PrintMembers").WithArguments("C.PrintMembers(System.Text.StringBuilder)", "B").WithLocation(4, 29)


ERR_DoesNotOverrideBaseMethod [](start = 37, length = 29)

I would expect the same error reported for a record like this:

public record C : B;

Do we have a test for a scenario like this? #Closed

AlekseyTs · 2021-03-26T01:13:39Z

    internal static MethodSymbol? FindValidPrintMembersMethod(TypeSymbol containingType, CSharpCompilation compilation)

Instead we should override MethodChecks where we would verify that OverriddenMethod belongs to the immediate base.

It doesn't look like the override is added. It feels like we need it and are missing a unit-test for the error scenario when overriding skips immediate base.

In reply to: 807125057 [](ancestors = 807125057)

Refers to: src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs:244 in 21dd0d0. [](commit_id = 21dd0d0, deletion_comment = False)

AlekseyTs · 2021-03-26T01:15:51Z

Done with review pass (commit 3) #Closed

AlekseyTs · 2021-03-26T01:17:08Z

Done with review pass (commit 3), it looks like there are legitimate test failures. #Closed

jcouv · 2021-03-26T18:21:54Z

    internal static MethodSymbol? FindValidPrintMembersMethod(TypeSymbol containingType, CSharpCompilation compilation)

I thought it was covered by check in VerifyOverridesPrintMembersFromBase already. But we only apply that check when the PrintMembers method is in source.

In reply to: 807855586 [](ancestors = 807855586,807125057)

Refers to: src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs:244 in 21dd0d0. [](commit_id = 21dd0d0, deletion_comment = False)

AlekseyTs

LGTM (commit 4)

RikkiGibson · 2021-03-29T19:42:23Z

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordPrintMembers.cs

@@ -48,21 +48,14 @@ protected override DeclarationModifiers MakeDeclarationModifiers(DeclarationModi
 #endif
            return result;

-            MethodSymbol? virtualPrintInBase()
+#if DEBUG
+            bool modifiersAreValid(DeclarationModifiers modifiers)


What happens when the surrounding #if DEBUG directives are removed from here and the call site? #Resolved

We'd emit non-product code into the shipping product.

In reply to: 603564256 [](ancestors = 603564256)

jcouv added the Area-Compilers label Mar 20, 2021

jcouv self-assigned this Mar 20, 2021

jcouv added the New Language Feature - Records Records label Mar 20, 2021

jcouv added this to the C# 10 milestone Mar 20, 2021

Youssef1313 reviewed Mar 20, 2021

View reviewed changes

jcouv force-pushed the rs-symbol5 branch 2 times, most recently from 4fb75c8 to 94d781b Compare March 23, 2021 18:13

Record structs: add ToString and PrintMembers

21dd0d0

jcouv force-pushed the rs-symbol5 branch from 94d781b to 21dd0d0 Compare March 23, 2021 18:50

jcouv commented Mar 23, 2021

View reviewed changes

jcouv marked this pull request as ready for review March 23, 2021 23:54

jcouv requested a review from a team as a code owner March 23, 2021 23:54

AlekseyTs reviewed Mar 25, 2021

View reviewed changes

jcouv added 2 commits March 25, 2021 14:59

Address feedback

6aaf5aa

Remove FindValidPrintMembersMethod

00dc122

jcouv requested a review from AlekseyTs March 26, 2021 00:03

AlekseyTs reviewed Mar 26, 2021

View reviewed changes

Add MethodChecks and tests

e906957

AlekseyTs approved these changes Mar 26, 2021

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RikkiGibson self-assigned this Mar 29, 2021

RikkiGibson reviewed Mar 29, 2021

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RikkiGibson approved these changes Mar 29, 2021

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jcouv merged commit 7574293 into dotnet:features/record-structs Mar 29, 2021

jcouv deleted the rs-symbol5 branch March 29, 2021 21:43

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Record structs: add ToString and PrintMembers #52012

Record structs: add ToString and PrintMembers #52012

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Record structs: add ToString and PrintMembers #52012

Record structs: add ToString and PrintMembers #52012

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jcouv commented Mar 20, 2021

Printing members: PrintMembers and ToString methods

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