Improve nullability ergonomics for ConditionExpression cast
#5977
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WalkthroughAdds a conditional NotNullIfNotNull return-value attribute to the implicit string-to-ConditionExpression operator in ConditionExpression, gated by target frameworks. No runtime behavior changes; enhances nullability annotations for newer targets. Changes
Estimated code review effort🎯 2 (Simple) | ⏱️ ~10 minutes Poem
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🧹 Nitpick comments (1)
src/NLog/Conditions/ConditionExpression.cs (1)
55-61: Tighten the XML docs to reflect null on null inputAdd that the operator returns null when the input is null to avoid ambiguity in generated API docs.
/// <param name="conditionExpressionText">Condition text to be converted.</param> -/// <returns>Condition expression tree.</returns> +/// <returns> +/// Condition expression tree if <paramref name="conditionExpressionText"/> is not null; +/// otherwise, null. +/// </returns>
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📒 Files selected for processing (1)
src/NLog/Conditions/ConditionExpression.cs(1 hunks)
🔇 Additional comments (1)
src/NLog/Conditions/ConditionExpression.cs (1)
56-58: Good use of NotNullIfNotNull and correct TFM gating
- Applying the return-attribute to the implicit operator precisely models the contract: non-null input → non-null result.
- The conditional compile guards look right for where the attribute is available. The OR_GREATER symbols behave as expected across SDKs.
References: Microsoft docs on nullable-analysis attributes and OR_GREATER preprocessor symbols, and NLog docs showing ParseExpression returns a non-null ConditionExpression for non-null input. (learn.microsoft.com, nlog-project.org)
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Thank you for the pull-request, a really nice improvement. Going to tickle the build-servers by closing and re-opening the pull-request. |
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Hooray your first pull request is merged! Thanks for the contribution! Looking for more? 👼 Please check the up-for-grabs issues - thanks! |
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NLog v6.0.4 have now been released: Thanks again for the help with improving NLog |
This currently produces a "Possible null reference assignment. CS8601" warning:
This is because the
ConditionExpressionimplicit cast fromstring?returns aConditionExpression?(i.e. it may be null), but theConditionBasedFilter.Conditionproperty does not allow nulls.In this case though, the warning is a false positive, because the cast only actually returns null when the original string is null - and we (and the compiler) can clearly see that the string is not null. Fortunately, we can easily resolve this using the
[NotNullIfNotNull]attribute (available in .NET Core 3+ and .NET Standard 2.1).