Annotate System.Runtime.InteropServices.RuntimeInformation for nullab…

…le reference types (dotnet/corefx#41856)

Commit migrated from dotnet/corefx@fd6714a

src/libraries/System.Runtime.InteropServices.RuntimeInformation/ref/System.Runtime.InteropServices.RuntimeInformation.cs

@@ -23,7 +23,7 @@ public enum Architecture
         public static System.Runtime.InteropServices.OSPlatform OSX { get { throw null; } }
         public static System.Runtime.InteropServices.OSPlatform Windows { get { throw null; } }
         public static System.Runtime.InteropServices.OSPlatform Create(string osPlatform) { throw null; }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public bool Equals(System.Runtime.InteropServices.OSPlatform other) { throw null; }
         public override int GetHashCode() { throw null; }
         public static bool operator ==(System.Runtime.InteropServices.OSPlatform left, System.Runtime.InteropServices.OSPlatform right) { throw null; }

src/libraries/System.Runtime.InteropServices.RuntimeInformation/ref/System.Runtime.InteropServices.RuntimeInformation.csproj

@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
+    <Nullable>enable</Nullable>
     <Configurations>netcoreapp-Debug;netcoreapp-Release</Configurations>
   </PropertyGroup>
   <ItemGroup>

src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System.Runtime.InteropServices.RuntimeInformation.csproj

@@ -2,6 +2,7 @@
   <PropertyGroup>
     <RootNamespace>System.Runtime.InteropServices</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <Nullable>enable</Nullable>
     <Configurations>netcoreapp-Unix-Debug;netcoreapp-Unix-Release;netcoreapp-Windows_NT-Debug;netcoreapp-Windows_NT-Release</Configurations>
   </PropertyGroup>
   <ItemGroup>

src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/OSPlatform.cs

@@ -34,12 +34,12 @@ public bool Equals(OSPlatform other)
             return Equals(other._osPlatform);
         }
 
-        internal bool Equals(string other)
+        internal bool Equals(string? other)
         {
             return string.Equals(_osPlatform, other, StringComparison.Ordinal);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is OSPlatform && Equals((OSPlatform)obj);
         }

src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Unix.cs

@@ -10,29 +10,18 @@ public static partial class RuntimeInformation
     {
         private static readonly object s_osLock = new object();
         private static readonly object s_processLock = new object();
-        private static string s_osPlatformName;
-        private static string s_osDescription;
+        private static string? s_osPlatformName;
+        private static string? s_osDescription;
         private static Architecture? s_osArch;
         private static Architecture? s_processArch;
 
         public static bool IsOSPlatform(OSPlatform osPlatform)
         {
-            string name = s_osPlatformName ?? (s_osPlatformName = Interop.Sys.GetUnixName());
+            string name = s_osPlatformName ??= Interop.Sys.GetUnixName();
             return osPlatform.Equals(name);
         }
 
-        public static string OSDescription
-        {
-            get
-            {
-                if (null == s_osDescription)
-                {
-                    s_osDescription = Interop.Sys.GetUnixVersion();
-                }
-
-                return s_osDescription;
-            }
-        }
+        public static string OSDescription => s_osDescription ??= Interop.Sys.GetUnixVersion();
 
         public static Architecture OSArchitecture
         {

src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.Windows.cs

@@ -8,7 +8,7 @@ namespace System.Runtime.InteropServices
 {
     public static partial class RuntimeInformation
     {
-        private static string s_osDescription = null;
+        private static string? s_osDescription = null;
         private static readonly object s_osLock = new object();
         private static readonly object s_processLock = new object();
         private static Architecture? s_osArch = null;
@@ -19,18 +19,7 @@ public static bool IsOSPlatform(OSPlatform osPlatform)
             return OSPlatform.Windows == osPlatform;
         }
 
-        public static string OSDescription
-        {
-            get
-            {
-                if (null == s_osDescription)
-                {
-                    s_osDescription = Interop.NtDll.RtlGetVersion();
-                }
-
-                return s_osDescription;
-            }
-        }
+        public static string OSDescription => s_osDescription ??= Interop.NtDll.RtlGetVersion();
 
         public static Architecture OSArchitecture
         {

src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.cs

@@ -9,15 +9,15 @@ namespace System.Runtime.InteropServices
     public static partial class RuntimeInformation
     {
         private const string FrameworkName = ".NET Core";
-        private static string s_frameworkDescription;
+        private static string? s_frameworkDescription;
 
         public static string FrameworkDescription
         {
             get
             {
                 if (s_frameworkDescription == null)
                 {
-                    string versionString = (string)AppContext.GetData("FX_PRODUCT_VERSION");
+                    string? versionString = (string?)AppContext.GetData("FX_PRODUCT_VERSION");
 
                     if (versionString == null)
                     {