Make FilePatternMatch.Stem non-nullable. (#118410)

- Add an ArgumentNullException if stem is null in Success method.
- Add tests for null checks.

Author: MitchBodmer

src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/FilePatternMatch.cs

@@ -28,16 +28,17 @@ public struct FilePatternMatch : IEquatable<FilePatternMatch>
         /// If the matcher searched for "src/Project/**/*.cs" and the pattern matcher found "src/Project/Interfaces/IFile.cs",
         /// then <see cref="Stem" /> = "Interfaces/IFile.cs" and <see cref="Path" /> = "src/Project/Interfaces/IFile.cs".
         /// </remarks>
-        public string? Stem { get; }
+        public string Stem { get; }
 
         /// <summary>
         /// Initializes new instance of <see cref="FilePatternMatch" />
         /// </summary>
         /// <param name="path">The path to the file matched, relative to the beginning of the matching search pattern.</param>
         /// <param name="stem">The subpath to the file matched, relative to the first wildcard in the matching search pattern.</param>
-        public FilePatternMatch(string path, string? stem)
+        public FilePatternMatch(string path, string stem)
         {
             ArgumentNullException.ThrowIfNull(path);
+            ArgumentNullException.ThrowIfNull(stem);
 
             Path = path;
             Stem = stem;

src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Internal/PatternTestResult.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.FileSystemGlobbing.Internal
 {
     /// <summary>
@@ -11,6 +13,7 @@ public struct PatternTestResult
     {
         public static readonly PatternTestResult Failed = new(isSuccessful: false, stem: null);
 
+        [MemberNotNullWhen(returnValue: true, nameof(Stem))]
         public bool IsSuccessful { get; }
         public string? Stem { get; }
 

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

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using Xunit;
 
 namespace Microsoft.Extensions.FileSystemGlobbing.Tests
@@ -24,5 +25,17 @@ public void TestGetHashCode()
             FilePatternMatch matchCase2 = new FilePatternMatch("sub/sub2/bar/baz/three.txt", "Sub2/bar/baz/thrEE.txt");
             Assert.Equal(matchCase1.GetHashCode(), matchCase2.GetHashCode());
         }
+
+        [Fact]
+        public void TestPathArgumentNullExceptions()
+        {
+            Assert.Throws<ArgumentNullException>(() => new FilePatternMatch(null, "sub2/bar/baz/three.txt"));
+        }
+
+        [Fact]
+        public void TestStemArgumentNullExceptions()
+        {
+            Assert.Throws<ArgumentNullException>(() => new FilePatternMatch("sub2/bar/baz/three.txt", null));
+        }
     }
 }