Make FilePatternMatch.Stem non-nullable.

[MitchBodmer]

• Make FilePatternMatch.Stem non-nullable.
• Add an ArgumentNullException if stem is null in Success method.
• Add tests for null checks.

Implements #116982

[Copilot]

Pull Request Overview

This pull request makes the FilePatternMatch.Stem property non-nullable to improve type safety. The change ensures that the Stem property always has a valid string value, preventing potential null reference exceptions when consumers use this property.

Key changes:

• Converted Stem property from nullable string to non-nullable string
• Added null validation in the constructor to enforce the contract
• Added comprehensive tests to verify null argument validation

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
FilePatternMatch.cs	Changed Stem property to non-nullable and added null validation in constructor
PatternTestResult.cs	Added MemberNotNullWhen attribute to support nullable analysis when IsSuccessful is true
FilePatternMatchTests.cs	Added unit tests to verify ArgumentNullException is thrown for null path and stem parameters

Comments suppressed due to low confidence (2)

src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/FilePatternMatchTests.cs:32

• The test should verify that the exception is thrown for the correct parameter name. Consider using Assert.Throws("path", () => new FilePatternMatch(null, "sub2/bar/baz/three.txt")) to ensure the parameter name is validated.

            Assert.Throws<ArgumentNullException>(() => new FilePatternMatch(null, "sub2/bar/baz/three.txt"));

src/libraries/Microsoft.Extensions.FileSystemGlobbing/tests/FilePatternMatchTests.cs:38

• The test should verify that the exception is thrown for the correct parameter name. Consider using Assert.Throws("stem", () => new FilePatternMatch("sub2/bar/baz/three.txt", null)) to ensure the parameter name is validated.

            Assert.Throws<ArgumentNullException>(() => new FilePatternMatch("sub2/bar/baz/three.txt", null));

[MitchBodmer]

@dotnet-policy-service agree company="Microsoft"

[jeffhandley]

Looks good to me; thanks, @MitchBodmer! I will mark this as a breaking-change Issue or PR that represents a breaking API or functional change over a previous release. and create the documentation issue.

[dotnet-policy-service]

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

When you commit this breaking change:

1. Create and link to this PR and the issue a matching issue in the dotnet/docs repo using the breaking change documentation template, then remove this needs-breaking-change-doc-created label.
2. Ask a committer to mail the .NET Breaking Change Notification DL.

Tagging @dotnet/compat for awareness of the breaking change.

[MitchBodmer]

@jeffhandley it looks like the build hit some unrelated failures. Is there something I should do here?

[jeffhandley]

Thanks, @MitchBodmer. No worries; I'll review the failures further and the build analysis shortly and will update the build analysis with the justification for override, and then I'll merge this after I create the breaking-change notification. I'll let you know if I need anything further from you on it. Thanks for the contribution!

[jeffhandley]

Breaking change documentation issue created: [Breaking change]: FilePatternMatch.Stem annotated as non-nullable (dotnet/docs#47914). PR is pending review from @artl93 for .NET 10 RC1 consideration.