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FilePatternMatch.Stem changed to non-nullable

The FilePatternMatch.Stem property was previously annotated as nullable because the PatternTestResult.Stem property it gets its value from is nullable. While the PatternTestResult can indeed be null if the result isn't successful, the FilePatternMatch never is because it's only constructed when PatternTestResult is successful.

To accurately reflect nullability, the [MemberNotNullWhen()] attribute is applied to the PatternTestResult.Stem property to tell the compiler it won't be null if it's successful. Additionally, the stem argument passed into the FilePatternMatch constructor is no longer nullable, and an ArgumentNullException will be thrown if a null stem is passed in.

Version introduced

.NET 10

Previous behavior

Previously, the FilePatternMatch constructor accepted null for the stem parameter without any compile-time or runtime warnings or errors.

// Allowed in previous versions.
var match = new FilePatternMatch("path/to/file.txt", null);

The FilePatternMatch.Stem property was also annotated as being nullable.

New behavior

Starting in .NET 10, passing a null or possibly-null value to the stem argument in the FilePatternMatch constructor yields a compile-time warning. And, if null is passed in, a runtime ArgumentNullException is thrown.

The FilePatternMatch.Stem property is now annotated to indicate that the value won't be null if IsSuccessful is true.

// Generates compile-time warning.
var match = new FilePatternMatch("path/to/file.txt", null);

Type of breaking change

This change can affect source compatibility and is a behavioral change.

Reason for change

The previous nullability annotations were inaccurate, and a null value for the stem argument was unexpected but not properly guarded against. This change reflects the expected behavior of the API and guards against unpredictable behavior while also producing design-time guidance around usage.

If a possibly null value was passed in for the stem argument, review usage and update the call site to ensure stem can't be paTssed in as null.

If you applied nullability warning suppressions when consuming the FilePatternMatch.Stem property, you can remove those suppressions.

Affected APIs

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