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Nullness bug - duplicate warning for the same range #17410

Description

@T-Gro

Issue description

A single line of code produces two identical nullness warnings.

let getLength (x: string | null) = x.Length

image

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

No response

Reproducible code snippet and actual behavior

let getLength (x: string | null) = x.Length

image

Possible workarounds

Ignore the warning, use IDE which deduplicates equal warnings for equal ranges.

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Area-NullnessIssues related to handling of Nullable Reference TypesBug

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