dotnet · stephentoub · Jul 14, 2021 · Jul 14, 2021
diff --git a/src/libraries/System.Net.WebClient/src/System/Net/WebClient.cs b/src/libraries/System.Net.WebClient/src/System/Net/WebClient.cs
@@ -143,7 +143,7 @@ public Encoding Encoding
             get { return _encoding; }
             set
             {
-                ThrowIfNull(value, nameof(value));
+                ArgumentNullException.ThrowIfNull(value, nameof(value));
                 _encoding = value;
             }
         }
@@ -280,7 +280,7 @@ public byte[] DownloadData(string address) =>
 
         public byte[] DownloadData(Uri address)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             StartOperation();
             try
@@ -320,8 +320,8 @@ public void DownloadFile(string address, string fileName) =>
 
         public void DownloadFile(Uri address, string fileName)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(fileName, nameof(fileName));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(fileName, nameof(fileName));
 
             WebRequest? request = null;
             FileStream? fs = null;
@@ -359,7 +359,7 @@ public Stream OpenRead(string address) =>
 
         public Stream OpenRead(Uri address)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             WebRequest? request = null;
             StartOperation();
@@ -392,7 +392,7 @@ public Stream OpenWrite(string address, string? method) =>
 
         public Stream OpenWrite(Uri address, string? method)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -432,8 +432,8 @@ public byte[] UploadData(string address, string? method, byte[] data) =>
 
         public byte[] UploadData(Uri address, string? method, byte[] data)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(data, nameof(data));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(data, nameof(data));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -553,8 +553,8 @@ public byte[] UploadFile(string address, string? method, string fileName) =>
 
         public byte[] UploadFile(Uri address, string? method, string fileName)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(fileName, nameof(fileName));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(fileName, nameof(fileName));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -626,8 +626,8 @@ public byte[] UploadValues(string address, string? method, NameValueCollection d
 
         public byte[] UploadValues(Uri address, string? method, NameValueCollection data)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(data, nameof(data));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(data, nameof(data));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -665,8 +665,8 @@ public string UploadString(string address, string? method, string data) =>
 
         public string UploadString(Uri address, string? method, string data)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(data, nameof(data));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(data, nameof(data));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -691,7 +691,7 @@ public string DownloadString(string address) =>
 
         public string DownloadString(Uri address)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             StartOperation();
             try
@@ -781,7 +781,7 @@ private void CopyHeadersTo(WebRequest request)
 
         private Uri GetUri(string address)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             Uri? uri;
             if (_baseAddress != null)
@@ -801,7 +801,7 @@ private Uri GetUri(string address)
 
         private Uri GetUri(Uri address)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             Uri? uri = address;
 
@@ -1297,7 +1297,7 @@ public void OpenReadAsync(Uri address) =>
 
         public void OpenReadAsync(Uri address, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             AsyncOperation asyncOp = StartAsyncOperation(userToken);
             try
@@ -1335,7 +1335,7 @@ public void OpenWriteAsync(Uri address, string? method) =>
 
         public void OpenWriteAsync(Uri address, string? method, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -1396,7 +1396,7 @@ public void DownloadStringAsync(Uri address) =>
 
         public void DownloadStringAsync(Uri address, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             AsyncOperation asyncOp = StartAsyncOperation(userToken);
             try
@@ -1422,7 +1422,7 @@ public void DownloadDataAsync(Uri address) =>
 
         public void DownloadDataAsync(Uri address, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
 
             AsyncOperation asyncOp = StartAsyncOperation(userToken);
             try
@@ -1448,8 +1448,8 @@ public void DownloadFileAsync(Uri address, string fileName) =>
 
         public void DownloadFileAsync(Uri address, string fileName, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(fileName, nameof(fileName));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(fileName, nameof(fileName));
 
             FileStream? fs = null;
             AsyncOperation asyncOp = StartAsyncOperation(userToken);
@@ -1474,8 +1474,8 @@ public void UploadStringAsync(Uri address, string? method, string data) =>
 
         public void UploadStringAsync(Uri address, string? method, string data, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(data, nameof(data));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(data, nameof(data));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -1525,8 +1525,8 @@ public void UploadDataAsync(Uri address, string? method, byte[] data) =>
 
         public void UploadDataAsync(Uri address, string? method, byte[] data, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(data, nameof(data));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(data, nameof(data));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -1566,8 +1566,8 @@ public void UploadFileAsync(Uri address, string? method, string fileName) =>
 
         public void UploadFileAsync(Uri address, string? method, string fileName, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(fileName, nameof(fileName));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(fileName, nameof(fileName));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -1605,8 +1605,8 @@ public void UploadValuesAsync(Uri address, string? method, NameValueCollection d
 
         public void UploadValuesAsync(Uri address, string? method, NameValueCollection data, object? userToken)
         {
-            ThrowIfNull(address, nameof(address));
-            ThrowIfNull(data, nameof(data));
+            ArgumentNullException.ThrowIfNull(address, nameof(address));
+            ArgumentNullException.ThrowIfNull(data, nameof(data));
             if (method == null)
             {
                 method = MapToDefaultMethod(address);
@@ -1940,14 +1940,6 @@ private void PostProgressChanged(AsyncOperation asyncOp, ProgressData progress)
             }
         }
 
-        private static void ThrowIfNull(object argument, string parameterName)
-        {
-            if (argument == null)
-            {
-                throw new ArgumentNullException(parameterName);
-            }
-        }
-
         #region Supporting Types
         private sealed class ProgressData
         {

diff --git a/src/libraries/System.Private.CoreLib/src/System/ArgumentNullException.cs b/src/libraries/System.Private.CoreLib/src/System/ArgumentNullException.cs
@@ -10,6 +10,8 @@
 **
 =============================================================================*/
 
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
 
 namespace System
@@ -50,5 +52,20 @@ public ArgumentNullException(string? paramName, string? message)
         protected ArgumentNullException(SerializationInfo info, StreamingContext context) : base(info, context)
         {
         }
+
+        /// <summary>Throws an <see cref="ArgumentNullException"/> if <paramref name="argument"/> is null.</summary>
+        /// <param name="argument">The reference type argument to validate as non-null.</param>
+        /// <param name="paramName">The name of the parameter with which <paramref name="argument"/> corresponds.</param>
+        public static void ThrowIfNull([NotNull] object? argument, [CallerArgumentExpression("argument")] string? paramName = null)
+        {
+            if (argument is null)
+            {
+                Throw(paramName);
+            }
+        }
+
+        [DoesNotReturn]
+        private static void Throw(string? paramName) =>
+            throw new ArgumentNullException(paramName);
     }
 }
diff --git a/src/libraries/System.Reflection.TypeExtensions/src/System.Reflection.TypeExtensions.csproj b/src/libraries/System.Reflection.TypeExtensions/src/System.Reflection.TypeExtensions.csproj
@@ -5,10 +5,9 @@
     <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="System\Reflection\Requires.cs" />
     <Compile Include="System\Reflection\TypeExtensions.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
   </ItemGroup>
-</Project>
+</Project>
diff --git a/src/libraries/System.Reflection.TypeExtensions/src/System/Reflection/Requires.cs b/src/libraries/System.Reflection.TypeExtensions/src/System/Reflection/Requires.cs