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Nullness issue - Compiler-generated member overrides should change nullness #17531

@kerams

Description

@kerams

Issue description

ToString on a record or union returns string | null. The method body is generated by the compiler and the result is known to be not null.

Choose one or more from the following categories of impact

  • Unexpected nullness warning (false positive in nullness checking, code uses --checknulls and langversion:preview).
  • Missing nullness warning in a case which can produce nulls (false negative, code uses --checknulls and langversion:preview).
  • Breaking change related to older null constructs in code not using the checknulls switch.
  • Breaking change related to generic code and explicit type constraints (null, not null).
  • Type inference issue (i.e. code worked without type annotations before, and applying the --checknulls enforces type annotations).
  • C#/F# interop issue related to nullness metadata.
  • Other (none of the categories above apply).

Operating System

Windows (Default)

What .NET runtime/SDK kind are you seeing the issue on

.NET SDK (.NET Core, .NET 5+)

.NET Runtime/SDK version

9.0.0-preview.7.24405.7

Reproducible code snippet and actual behavior

type X = A | B

let x: string = A.ToString ()

Possible workarounds

No response

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Area-NullnessIssues related to handling of Nullable Reference TypesBugImpact-Low(Internal MS Team use only) Describes an issue with limited impact on existing code.

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