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Nullness issue - ToString on an integer with UoM takes nullness information from ValueType #17539

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@kerams

Description

@kerams

Issue description

image

Similarly with UMX when the underlying type is a reference type, nullness is inherited from Object.ToString, rather than the underlying type, whose overriden ToString is 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

> (1).ToString();;
val it: string = "1"

> [<Measure>] type id;;
[<Measure>]
type id

> 1<id>.ToString ();;
val it: string | null = "1"

Possible workarounds

Unchecked.nonNull

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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.help wanted

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