Implement platform guards in OperatingSystem class

src/coreclr/clr.featuredefines.props

@@ -66,9 +66,5 @@
 
         <DefineConstants Condition="'$(ProfilingSupportedBuild)' == 'true'">$(DefineConstants);PROFILING_SUPPORTED</DefineConstants>
         <DefineConstants Condition="'$(FeatureProfAttach)' == 'true'">$(DefineConstants);FEATURE_PROFAPI_ATTACH_DETACH</DefineConstants>
-
-        <DefineConstants Condition="'$(TargetsUnix)' == 'true'">$(DefineConstants);TARGET_UNIX</DefineConstants>
-        <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);TARGET_WINDOWS</DefineConstants>
-        <DefineConstants Condition="'$(TargetsOSX)' == 'true'">$(DefineConstants);TARGET_OSX</DefineConstants>
     </PropertyGroup>
 </Project>

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -15,6 +15,17 @@
     <SupportsX86Intrinsics Condition="'$(Platform)' == 'x64' or ('$(Platform)' == 'x86' and '$(TargetsUnix)' != 'true')">true</SupportsX86Intrinsics>
     <ILLinkSharedDirectory>$(MSBuildThisFileDirectory)ILLink\</ILLinkSharedDirectory>
   </PropertyGroup>
+  <PropertyGroup>
+    <DefineConstants Condition="'$(TargetsUnix)' == 'true'">$(DefineConstants);TARGET_UNIX</DefineConstants>
+    <DefineConstants Condition="'$(TargetsWindows)' == 'true'">$(DefineConstants);TARGET_WINDOWS</DefineConstants>
+    <DefineConstants Condition="'$(TargetsOSX)' == 'true'">$(DefineConstants);TARGET_OSX</DefineConstants>
+    <DefineConstants Condition="'$(TargetsiOS)' == 'true'">$(DefineConstants);TARGET_IOS</DefineConstants>
+    <DefineConstants Condition="'$(TargetstvOS)' == 'true'">$(DefineConstants);TARGET_TVOS</DefineConstants>
+    <DefineConstants Condition="'$(TargetsBrowser)' == 'true'">$(DefineConstants);TARGET_BROWSER</DefineConstants>
+    <DefineConstants Condition="'$(TargetsAndroid)' == 'true'">$(DefineConstants);TARGET_ANDROID</DefineConstants>
+    <DefineConstants Condition="'$(TargetsLinux)' == 'true'">$(DefineConstants);TARGET_LINUX</DefineConstants>
+    <DefineConstants Condition="'$(TargetsFreeBSD)' == 'true'">$(DefineConstants);TARGET_FREEBSD</DefineConstants>
+  </PropertyGroup>
   <ItemGroup>
     <ILLinkSubstitutionsXmls Include="$(ILLinkSharedDirectory)ILLink.Substitutions.Shared.xml" />
     <!-- TODO: Enable these substitutions files for more platforms once https://github.com/mono/linker/issues/1260 is fixed -->

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

@@ -8,6 +8,10 @@ namespace System
 {
     public sealed class OperatingSystem : ISerializable, ICloneable
     {
+#if TARGET_UNIX && !TARGET_OSX
+        private static readonly string s_osPlatformName = Interop.Sys.GetUnixName();
+#endif
+
         private readonly Version _version;
         private readonly PlatformID _platform;
         private readonly string? _servicePack;
@@ -79,5 +83,193 @@ public string VersionString
                 return _versionString;
             }
         }
+
+        /// <summary>
+        /// Indicates whether the current application is running on the specified platform.
+        /// </summary>
+        /// <param name="platform">Case-insensitive platform name. Examples: Browser, Linux, FreeBSD, Android, iOS, macOS, tvOS, watchOS, Windows.</param>
+        public static bool IsOSPlatform(string platform)
+        {
+            if (platform == null)
+            {
+                throw new ArgumentNullException(nameof(platform));
+            }
+
+#if TARGET_BROWSER
+            return platform.Equals("BROWSER", StringComparison.OrdinalIgnoreCase);
+#elif TARGET_WINDOWS
+            return platform.Equals("WINDOWS", StringComparison.OrdinalIgnoreCase);
+#elif TARGET_OSX
+            return platform.Equals("OSX", StringComparison.OrdinalIgnoreCase) || platform.Equals("MACOS", StringComparison.OrdinalIgnoreCase);
+#elif TARGET_UNIX
+            return platform.Equals(s_osPlatformName, StringComparison.OrdinalIgnoreCase);
+#else
+#error Unknown OS
+#endif
+        }
+
+        /// <summary>
+        /// Check for the OS with a >= version comparison. Used to guard APIs that were added in the given OS release.
+        /// </summary>
+        /// <param name="platform">Case-insensitive platform name. Examples: Browser, Linux, FreeBSD, Android, iOS, macOS, tvOS, watchOS, Windows.</param>
+        /// <param name="major">Major OS version number.</param>
+        /// <param name="minor">Minor OS version number (optional).</param>
+        /// <param name="build">Build OS version number (optional).</param>
+        /// <param name="revision">Revision OS version number (optional).</param>
+        public static bool IsOSPlatformVersionAtLeast(string platform, int major, int minor = 0, int build = 0, int revision = 0)
+            => IsOSPlatform(platform) && IsOSVersionAtLeast(major, minor, build, revision);
+
+        /// <summary>
+        /// Indicates whether the current application is running as WASM in a Browser.
+        /// </summary>
+        public static bool IsBrowser() =>
+#if TARGET_BROWSER
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Indicates whether the current application is running on Linux.
+        /// </summary>
+        public static bool IsLinux() =>
+#if TARGET_LINUX
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Indicates whether the current application is running on FreeBSD.
+        /// </summary>
+        public static bool IsFreeBSD() =>
+#if TARGET_FREEBSD
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the FreeBSD version (returned by 'uname') with a >= version comparison. Used to guard APIs that were added in the given FreeBSD release.
+        /// </summary>
+        public static bool IsFreeBSDVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsFreeBSD() && IsOSVersionAtLeast(major, minor, build, revision);
+
+        /// <summary>
+        /// Indicates whether the current application is running on Android.
+        /// </summary>
+        public static bool IsAndroid() =>
+#if TARGET_ANDROID
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the Android version (returned by 'uname') with a >= version comparison. Used to guard APIs that were added in the given Android release.
+        /// </summary>
+        public static bool IsAndroidVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsAndroid() && IsOSVersionAtLeast(major, minor, build, revision);
+
+        /// <summary>
+        /// Indicates whether the current application is running on iOS.
+        /// </summary>
+        public static bool IsIOS() =>
+#if TARGET_IOS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the iOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given iOS release.
+        /// </summary>
+        public static bool IsIOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsIOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on macOS.
+        /// </summary>
+        public static bool IsMacOS() =>
+#if TARGET_OSX
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the macOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given macOS release.
+        /// </summary>
+        public static bool IsMacOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsMacOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on tvOS.
+        /// </summary>
+        public static bool IsTvOS() =>
+#if TARGET_TVOS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the tvOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given tvOS release.
+        /// </summary>
+        public static bool IsTvOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsTvOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on watchOS.
+        /// </summary>
+        public static bool IsWatchOS() =>
+#if TARGET_WATCHOS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the watchOS version (returned by 'libobjc.get_operatingSystemVersion') with a >= version comparison. Used to guard APIs that were added in the given watchOS release.
+        /// </summary>
+        public static bool IsWatchOSVersionAtLeast(int major, int minor = 0, int build = 0)
+            => IsWatchOS() && IsOSVersionAtLeast(major, minor, build, 0);
+
+        /// <summary>
+        /// Indicates whether the current application is running on Windows.
+        /// </summary>
+        public static bool IsWindows() =>
+#if TARGET_WINDOWS
+            true;
+#else
+            false;
+#endif
+
+        /// <summary>
+        /// Check for the Windows version (returned by 'RtlGetVersion') with a >= version comparison. Used to guard APIs that were added in the given Windows release.
+        /// </summary>
+        public static bool IsWindowsVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsWindows() && IsOSVersionAtLeast(major, minor, build, revision);
+
+        private static bool IsOSVersionAtLeast(int major, int minor, int build, int revision)
+        {
+            Version current = Environment.OSVersion.Version;
+
+            if (current.Major != major)
+            {
+                return current.Major > major;
+            }
+            if (current.Minor != minor)
+            {
+                return current.Minor > minor;
+            }
+            if (current.Build != build)
+            {
+                return current.Build > build;
+            }
+
+            return current.Revision >= revision
+                || (current.Revision == -1 && revision == 0); // it is unavailable on OSX and Environment.OSVersion.Version.Revision returns -1
+        }
     }
 }