Reduce cascading errors when record inherits from non-record #81293

Copilot · 2025-11-17T11:27:45Z

Completed: Reduce cascading errors when record inherits from non-record

Summary of Changes:

This PR successfully reduces cascading errors when a record inherits from a non-record type. Previously, 5 errors were reported. Now only CS8864 is reported.

Before: When record Derived : Base { } where Base is not a record:

CS8864: Records may only inherit from object or another record (the relevant error)
CS8867: No accessible copy constructor found in base type
CS0115: No suitable method found to override (EqualityContract)
CS0115: No suitable method found to override (Equals)
CS0115: No suitable method found to override (PrintMembers)

After: Only CS8864 is reported (the relevant error)

All relevant tests pass.

Fixes Reduce cascading errors when record inherits from non-record #63270

Original prompt

This section details on the original issue you should resolve

<issue_title>Reduce cascading errors when record inherits from non-record</issue_title>
<issue_description>SharpLab
class Base { }

record Derived : Base { }
This scenario produces 5 errors (at the time this issue was filed). It seems like it would be reasonable to only produce error CS8864: Records may only inherit from object or another record in this case.

Originally posted by @RikkiGibson in #62999 (comment)</issue_description>

<agent_instructions>Copilot, the errors reported are:

CS8864: Records may only inherit from object or another record
No accessible copy constructor found in base type 'Base'.
'Derived.PrintMembers(StringBuilder)': no suitable method found to override
'Derived.Equals(Base?)': no suitable method found to override
'Derived.EqualityContract': no suitable method found to override

The first one is the relevant one. First, it means we've detected that there is a problem with the base type and have a distinct way to check for that in the future.

For the remainder, we should perform the same check. First, we should not look for a copy constructor if hte base type is not a record. Second, we should not attempt to emit these overrides if the base type is not a record.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes Reduce cascading errors when record inherits from non-record #63270

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Co-authored-by: CyrusNajmabadi <[email protected]>

CyrusNajmabadi · 2025-11-17T12:17:27Z

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

+            // Check if the base type is a valid record base first.
+            // If it's not a record (FindValidCloneMethod returns null), then ERR_BadRecordBase
+            // will have already been reported, so we should not report a copy constructor error.
+            if (SynthesizedRecordClone.FindValidCloneMethod(baseType, ref useSiteInfo) is null)


@copilot can you extract this out to a helper? Something like BaseTypeIsRecordNoUseSiteDiagnostics? IN that helper you should pass CompoundUseSiteInfo<AssemblySymbol>.Discarded as the useSiteInfo with a comment saying that use site info will already have been computed in CheckBase.

Then, use this new helper here, and in the other places you updated below.

Done. Extracted BaseTypeIsRecordNoUseSiteDiagnostics helper method in SynthesizedRecordClone and updated all call sites to use it. (5bcad2f)

CyrusNajmabadi · 2025-11-17T12:19:12Z

src/Compilers/CSharp/Test/Emit3/Semantics/RecordTests.cs

 }";
            var comp = CreateCompilationWithIL(new[] { source, IsExternalInitTypeDefinition }, ilSource: ilSource, parseOptions: TestOptions.Regular9);
            comp.VerifyEmitDiagnostics(
+                // (2,15): warning CS0114: 'B.EqualityContract' hides inherited member 'A.EqualityContract'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.


@copilot can we add the IsNew modifier in the error case so that we don't have these warnings show up?

Done. Added 'new' modifier to synthesized members (EqualityContract and PrintMembers) when base is not a record. This suppresses WRN_NewOrOverrideExpected warnings when the base class has matching members. (089652a)

CyrusNajmabadi · 2025-11-17T12:20:02Z

src/Compilers/CSharp/Test/Emit3/Semantics/TestCascadingErrors.cs

+    public class CascadingRecordErrorsTest : CSharpTestBase
+    {
+        [Fact]
+        public void RecordInheritingFromNonRecord_OnlyReportsBaseError()


@copilot move this test to RecordTests. It should also be [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/63270")]. Also, use raw string literals in the test.

Done. Moved test to RecordTests.cs, added WorkItem attribute, and converted to raw string literals. (089652a)

src/Compilers/CSharp/Test/Emit3/Semantics/TestCascadingErrors.cs

Extract the check for whether a base type is a record into a helper method as suggested by code review. This avoids repeating the pattern of creating a discarded CompoundUseSiteInfo and calling FindValidCloneMethod. Co-authored-by: CyrusNajmabadi <[email protected]>

CyrusNajmabadi · 2025-11-17T12:47:13Z

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

+                        // Base is not a record, error was reported elsewhere
+                        F.CloseMethod(F.ThrowNull());
+                        return;
+                    }


@copilot was this actually needed? why would get to the emit stage if an error was already reported. please remove this if not needed.

The check is needed because SynthesizedRecordBaseEquals is not created when the base type is not a record (see addBaseEquals() in SourceMemberContainerSymbol.cs). This is necessary because SynthesizedRecordBaseEquals always has the override modifier, which would cause ERR_OverrideNotExpected errors if we created it when there's nothing to override. During emit, when generating the body of SynthesizedRecordEquals, we need to handle the case where SynthesizedRecordBaseEquals doesn't exist - otherwise .Single() would throw an exception.

@copilot but why are we getting to emit if there's alreayd a reported error. Or, put another way. if you remove this change, does a single test fail?

Yes, removing the check causes BaseErrorTypeWithParameters and 5 other tests to fail with System.InvalidOperationException: Sequence contains no elements when .Single() is called on an empty sequence. The compiler does reach emit even with ERR_BadRecordBase reported - it needs to generate method bodies for IDE services and other scenarios. Since SynthesizedRecordBaseEquals isn't created when base is not a record (to avoid ERR_OverrideNotExpected), the null check is required to avoid the crash during emit.

@copilot what are the 5 tests that fail?

13 tests fail: Inheritance_29, Inheritance_30, Inheritance_31, BaseErrorTypeWithParameters, Clone_05_IntReturnType_UsedAsBaseType, Clone_07_Ambiguous_UsedAsBaseType, Clone_09_AmbiguousReverseOrder_UsedAsBaseType, Clone_16, Clone_17_NonOverridable, Clone_18_NonOverridable, ToString_ErrorBase, ToString_SelfReferentialBase, and CopyCtor_InaccessibleToCallerFromPE_WithIVT. All fail with InvalidOperationException: Sequence contains no elements from .Single().

- Add 'new' modifier to synthesized record members when base is not a record This suppresses WRN_NewOrOverrideExpected warnings when the base class happens to have members with matching signatures (EqualityContract, PrintMembers) - Move test from TestCascadingErrors.cs to RecordTests.cs - Add WorkItem attribute and use raw string literals in test - Update test expectations to account for new modifier behavior Co-authored-by: CyrusNajmabadi <[email protected]>

Remove System.Runtime.Intrinsics.X86 using that was accidentally added during merge. Co-authored-by: CyrusNajmabadi <[email protected]>

CyrusNajmabadi · 2025-11-22T19:25:43Z

...Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol_ImplementationChecks.cs

+                !SynthesizedRecordClone.BaseTypeIsRecordNoUseSiteDiagnostics(baseType))
+            {
+                return;
+            }


Alternate approaches include moving this into the loop below and only skipping synthesized record members, as well as wrapping the individual checks that report specific override/new warnings. I preferred this approach as it matches intuition of the check above this. If we don't have a valid base type, don't bother with new/override checks as they're just cascading from the root problem (the invalid base).

...Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol_ImplementationChecks.cs

…inerSymbol_ImplementationChecks.cs

AlekseyTs · 2025-11-24T19:00:42Z

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

+        /// <summary>
+        /// Returns true if the base type is a record (has a valid Clone method).
+        /// </summary>
+        internal static bool BaseTypeIsRecordNoUseSiteDiagnostics(NamedTypeSymbol baseType)


BaseTypeIsRecordNoUseSiteDiagnostics

It doesn't feel like this helper belongs in this class/file.

It doesn't look like we need this helper at all. Tit looks like existing IsRecord property will be sufficient, especially as we aren't interested in any use-site information from this check. #Closed

AlekseyTs · 2025-11-24T19:04:05Z

...Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol_ImplementationChecks.cs

+                !baseType.IsObjectType() &&
+                !SynthesizedRecordClone.BaseTypeIsRecordNoUseSiteDiagnostics(baseType))
+            {
+                return;


return;

I am not comfortable with this approach. I think the suppression should happen only for specific members synthesized by compiler. #Closed

works for me :)

AlekseyTs · 2025-11-24T19:10:50Z

...ers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordEqualityContractProperty.cs

-                reportAnError = true;
-            }
-            else
+            if (!baseType.IsObjectType() && SynthesizedRecordClone.BaseTypeIsRecordNoUseSiteDiagnostics(baseType))


if (!baseType.IsObjectType() && SynthesizedRecordClone.BaseTypeIsRecordNoUseSiteDiagnostics(baseType))

Please keep an early out approach that was used before. Otherwise, the local declaration and the if statement following this one should be moved inside this one. #Closed

AlekseyTs · 2025-11-24T19:14:41Z

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

-            else
+            // If the base type is not a record, ERR_BadRecordBase will already be reported.
+            // Don't cascade an override error in this case.
+            if (SynthesizedRecordClone.BaseTypeIsRecordNoUseSiteDiagnostics(baseType))


if (SynthesizedRecordClone.BaseTypeIsRecordNoUseSiteDiagnostics(baseType))

Similar comment as for VerifyOverridesEqualityContractFromBase. Either move all related code inside, or use an early out approach. #Closed

AlekseyTs · 2025-11-24T19:17:45Z

Done with review pass (commit 56) #Closed

Out of date

AlekseyTs

LGTM (commit 61)

jjonescz · 2025-11-25T09:33:33Z

...Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol_ImplementationChecks.cs

                cancellationToken.ThrowIfCancellationRequested();

+                // If we have invalid record inheritance (a record deriving from a non-record), skip checking the
+                // synthesized members for proper new/override usage as we're very likely to just report cascaded


Is it just "very likely"? I thought it better be guaranteed otherwise we could have an invalid program for which we don't report any errors.

good point. revising verbiage.

...Compilers/CSharp/Portable/Symbols/Source/SourceMemberContainerSymbol_ImplementationChecks.cs

…inerSymbol_ImplementationChecks.cs

Initial plan

cf927fc

Copilot AI assigned Copilot and CyrusNajmabadi Nov 17, 2025

Copilot started work on behalf of CyrusNajmabadi November 17, 2025 11:28 View session

Copilot AI and others added 2 commits November 17, 2025 11:53

Fix cascading errors when record inherits from non-record

fc8e091

Co-authored-by: CyrusNajmabadi <[email protected]>

Update test expectations for member hiding warnings

da2d5d0

Co-authored-by: CyrusNajmabadi <[email protected]>

Copilot AI changed the title ~~[WIP] Fix cascading errors for record inheritance~~ Reduce cascading errors when record inherits from non-record Nov 17, 2025

Copilot AI requested a review from CyrusNajmabadi November 17, 2025 12:09

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src/Compilers/CSharp/Test/Emit3/Semantics/TestCascadingErrors.cs Outdated Show resolved Hide resolved

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Update src/Compilers/CSharp/Test/Emit3/Semantics/TestCascadingErrors.cs

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Simplify

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Copilot AI and others added 2 commits November 17, 2025 12:47

Remove incorrect using statement

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Remove System.Runtime.Intrinsics.X86 using that was accidentally added during merge. Co-authored-by: CyrusNajmabadi <[email protected]>

Copilot AI requested a review from CyrusNajmabadi November 17, 2025 12:56

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CyrusNajmabadi added 2 commits November 22, 2025 20:26

Update src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberConta…

6d36f2b

…inerSymbol_ImplementationChecks.cs

Update src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberConta…

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…inerSymbol_ImplementationChecks.cs

jjonescz previously approved these changes Nov 24, 2025

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CyrusNajmabadi added 3 commits November 24, 2025 21:26

Move check into loop

0e6f6e5

Switch to directly using IsRecord

946082b

prefer early out here

8385e02

CyrusNajmabadi force-pushed the copilot/reduce-cascading-errors branch from b62e639 to 8385e02 Compare November 24, 2025 20:31

CyrusNajmabadi added 2 commits November 24, 2025 21:32

prefer early out here

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prefer early out here

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Update src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberConta…

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…inerSymbol_ImplementationChecks.cs

CyrusNajmabadi enabled auto-merge (squash) November 25, 2025 09:43

CyrusNajmabadi merged commit 411961a into main Nov 25, 2025
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[release/10.0.2xx] Source code updates from dotnet/roslyn dotnet/dotnet#3561

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[main] Source code updates from dotnet/roslyn dotnet/dotnet#3957

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Reduce cascading errors when record inherits from non-record #81293

Reduce cascading errors when record inherits from non-record #81293

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Completed: Reduce cascading errors when record inherits from non-record

Summary of Changes:

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