Fix IsOSVersionAtLeast when build or revision are not provided

src/libraries/System.Private.CoreLib/src/System/Environment.OSVersion.MacCatalyst.cs

@@ -7,7 +7,16 @@ public static partial class Environment
     {
         private static OperatingSystem GetOSVersion()
         {
-            Version version = new Version(Interop.Sys.iOSSupportVersion());
+            Version version = Version.Parse(Interop.Sys.iOSSupportVersion());
+
+            // Check if build and revision are -1 and default them to 0
+            int major = version.Major;
+            int minor = version.Minor;
+            int build = version.Build < 0 ? 0 : version.Build;
+            int revision = version.Revision < 0 ? 0 : version.Revision;
+
+            version = new Version(major, minor, build, revision);
+
             return new OperatingSystem(PlatformID.Unix, version);
         }
     }

src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/OperatingSystemTests.cs

@@ -236,11 +236,18 @@ private static void TestIsOSVersionAtLeast(string currentOSName)
                     isCurrentOS = true;
                 }
 
+                // Four-parameter overload
                 AssertVersionChecks(isCurrentOS, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast(platformName, major, minor, build, revision));
                 AssertVersionChecks(isCurrentOS, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast(platformName.ToLower(), major, minor, build, revision));
                 AssertVersionChecks(isCurrentOS, (major, minor, build, revision) => OperatingSystem.IsOSPlatformVersionAtLeast(platformName.ToUpper(), major, minor, build, revision));
+
+                // Three-parameter overload
+                AssertVersionChecks(isCurrentOS, (major, minor, build) => OperatingSystem.IsOSPlatformVersionAtLeast(platformName, major, minor, build));
+
+                // Two-parameter overload
+                AssertVersionChecks(isCurrentOS, (major, minor) => OperatingSystem.IsOSPlatformVersionAtLeast(platformName, major, minor));
             }
-            
+
             AssertVersionChecks(currentOSName.Equals("Android", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsAndroidVersionAtLeast);
             AssertVersionChecks(currentOSName == "MacCatalyst" || currentOSName.Equals("iOS", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsIOSVersionAtLeast);
             AssertVersionChecks(currentOSName.Equals("macOS", StringComparison.OrdinalIgnoreCase), OperatingSystem.IsMacOSVersionAtLeast);
@@ -281,5 +288,18 @@ private static void AssertVersionChecks(bool isCurrentOS, Func<int, int, int, bo
             Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor - 1, current.Build));
             Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build - 1));
         }
+
+        private static void AssertVersionChecks(bool isCurrentOS, Func<int, int, bool> isOSVersionAtLeast)
+        {
+            Version current = Environment.OSVersion.Version;
+
+            Assert.False(isOSVersionAtLeast(current.Major + 1, current.Minor));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor + 1));
+
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor));
+
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major - 1, current.Minor));
+            Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor - 1));
+        }
     }
 }