Fix IsOSVersionAtLeast when build or revision are not provided

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

@@ -8,6 +8,16 @@ public static partial class Environment
         private static OperatingSystem GetOSVersion()
         {
             Version version = new Version(Interop.Sys.iOSSupportVersion());
+
+            int major = version.Major;
+            int minor = version.Minor;
+            // Normalize the build component to 0 if undefined
+            // to match iOS behavior
+            int build = version.Build < 0 ? 0 : version.Build;
+
+            // The revision component is always set to -1,
+            // as it is not specified on MacCatalyst or iOS
+            version = new Version(major, minor, build);
             return new OperatingSystem(PlatformID.Unix, version);
         }
     }

src/libraries/System.Private.CoreLib/src/System/OperatingSystem.cs

@@ -335,13 +335,19 @@ private static bool IsOSVersionAtLeast(int major, int minor, int build, int revi
             {
                 return current.Minor > minor;
             }
-            if (current.Build != build)
+            // Unspecified build component is to be treated as zero
+            int currentBuild = current.Build < 0 ? 0 : current.Build;
+            build = build < 0 ? 0 : build;
+            if (currentBuild != build)
             {
-                return current.Build > build;
+                return currentBuild > build;
             }
 
-            return current.Revision >= revision
-                || (current.Revision == -1 && revision == 0); // it is unavailable on OSX and Environment.OSVersion.Version.Revision returns -1
+            // Unspecified revision component is to be treated as zero
+            int currentRevision = current.Revision < 0 ? 0 : current.Revision;
+            revision = revision < 0 ? 0 : revision;
+
+            return currentRevision >= revision;
         }
     }
 }

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);
@@ -256,8 +263,8 @@ private static void AssertVersionChecks(bool isCurrentOS, Func<int, int, int, in
 
             Assert.False(isOSVersionAtLeast(current.Major + 1, current.Minor, current.Build, current.Revision));
             Assert.False(isOSVersionAtLeast(current.Major, current.Minor + 1, current.Build, current.Revision));
-            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build + 1, current.Revision));
-            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build, Math.Max(current.Revision + 1, 1))); // OSX Revision reports -1
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, Math.Max(current.Build + 1, 1), current.Revision));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build, Math.Max(current.Revision + 1, 1)));
 
             Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build, current.Revision));
 
@@ -273,13 +280,26 @@ private static void AssertVersionChecks(bool isCurrentOS, Func<int, int, int, bo
 
             Assert.False(isOSVersionAtLeast(current.Major + 1, current.Minor, current.Build));
             Assert.False(isOSVersionAtLeast(current.Major, current.Minor + 1, current.Build));
-            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, current.Build + 1));
+            Assert.False(isOSVersionAtLeast(current.Major, current.Minor, Math.Max(current.Build + 1, 1)));
 
             Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major, current.Minor, current.Build));
 
             Assert.Equal(isCurrentOS, isOSVersionAtLeast(current.Major - 1, current.Minor, current.Build));
             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));
+        }
     }
 }