Annotate System.Text.Json for nullable

src/libraries/System.Text.Json/ref/System.Text.Json.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <Configurations>net461-Debug;net461-Release;$(NetCoreAppCurrent)-Debug;$(NetCoreAppCurrent)-Release;$(NetFrameworkCurrent)-Debug;$(NetFrameworkCurrent)-Release;netstandard2.0-Debug;netstandard2.0-Release</Configurations>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Text.Json.cs" />

src/libraries/System.Text.Json/src/System.Text.Json.csproj

@@ -10,6 +10,8 @@
     <!-- https://github.com/dotnet/arcade/blob/ea6addfdc65e5df1b2c036f11614a5f922e36267/src/Microsoft.DotNet.Arcade.Sdk/tools/ProjectDefaults.props#L90 -->
     <!-- For this project, we want warnings if there are public APIs/types without properly formatted XML comments (particularly CS1591). -->
     <NoWarn />
+    <NoWarn Condition="'$(TargetsNetCoreApp)' != 'true'">$(NoWarn);nullable</NoWarn>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Text\Json\BitStack.cs" />

src/libraries/System.Text.Json/src/System/Collections/Generic/StackExtensions.netstandard.cs

@@ -3,14 +3,15 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
 namespace System.Collections.Generic
 {
     /// <summary>Polyfills for <see cref="Stack{T}"/>.</summary>
     internal static class StackExtensions
     {
-        public static bool TryPeek<T>(this Stack<T> stack, out T result)
+        public static bool TryPeek<T>(this Stack<T> stack, [MaybeNullWhen(false)] out T result)
         {
             if (stack.Count > 0)
             {
@@ -22,7 +23,7 @@ public static bool TryPeek<T>(this Stack<T> stack, out T result)
             return false;
         }
 
-        public static bool TryPop<T>(this Stack<T> stack, out T result)
+        public static bool TryPop<T>(this Stack<T> stack, [MaybeNullWhen(false)] out T result)
         {
             if (stack.Count > 0)
             {

src/libraries/System.Text.Json/src/System/Text/Json/BitStack.cs

@@ -5,6 +5,7 @@
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
 
+#nullable enable
 namespace System.Text.Json
 {
     internal struct BitStack
@@ -15,7 +16,7 @@ internal struct BitStack
 
         private const int DefaultInitialArraySize = 2;
 
-        private int[] _array;
+        private int[]? _array;
 
         // This ulong container represents a tiny stack to track the state during nested transitions.
         // The first bit represents the state of the current depth (1 == object, 0 == array).
@@ -135,6 +136,7 @@ private bool PopFromArray()
 
         private void DoubleArray(int minSize)
         {
+            Debug.Assert(_array != null);
             Debug.Assert(_array.Length < int.MaxValue / 2, $"Array too large - arrayLength: {_array.Length}");
             Debug.Assert(minSize >= 0 && minSize >= _array.Length);
 

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs

@@ -149,7 +149,7 @@ internal MetadataDb(MetadataDb source, bool useArrayPools)
 
             public void Dispose()
             {
-                byte[] data = Interlocked.Exchange(ref _data, null);
+                byte[]? data = Interlocked.Exchange(ref _data, null!);
                 if (data == null)
                 {
                     return;

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.Parse.cs

@@ -4,6 +4,7 @@
 
 using System.Buffers;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
@@ -118,7 +119,7 @@ public static JsonDocument Parse(Stream utf8Json, JsonDocumentOptions options =
             }
 
             ArraySegment<byte> drained = ReadToEnd(utf8Json);
-
+            Debug.Assert(drained.Array != null);
             try
             {
                 return Parse(drained.AsMemory(), options.GetReaderOptions(), drained.Array);
@@ -167,7 +168,7 @@ private static async Task<JsonDocument> ParseAsyncCore(
             CancellationToken cancellationToken = default)
         {
             ArraySegment<byte> drained = await ReadToEndAsync(utf8Json, cancellationToken).ConfigureAwait(false);
-
+            Debug.Assert(drained.Array != null);
             try
             {
                 return Parse(drained.AsMemory(), options.GetReaderOptions(), drained.Array);
@@ -284,7 +285,7 @@ public static JsonDocument Parse(string json, JsonDocumentOptions options = defa
         /// <exception cref="JsonException">
         ///   A value could not be read from the reader.
         /// </exception>
-        public static bool TryParseValue(ref Utf8JsonReader reader, out JsonDocument document)
+        public static bool TryParseValue(ref Utf8JsonReader reader, [NotNullWhen(true)] out JsonDocument? document)
         {
             return TryParseValue(ref reader, out document, shouldThrow: false);
         }
@@ -326,12 +327,12 @@ public static bool TryParseValue(ref Utf8JsonReader reader, out JsonDocument doc
         /// </exception>
         public static JsonDocument ParseValue(ref Utf8JsonReader reader)
         {
-            bool ret = TryParseValue(ref reader, out JsonDocument document, shouldThrow: true);
+            bool ret = TryParseValue(ref reader, out JsonDocument? document, shouldThrow: true);
             Debug.Assert(ret, "TryParseValue returned false with shouldThrow: true.");
-            return document;
+            return document!;
         }
 
-        private static bool TryParseValue(ref Utf8JsonReader reader, out JsonDocument document, bool shouldThrow)
+        private static bool TryParseValue(ref Utf8JsonReader reader, [NotNullWhen(true)] out JsonDocument? document, bool shouldThrow)
         {
             JsonReaderState state = reader.CurrentState;
             CheckSupportedOptions(state.Options, nameof(reader));
@@ -551,7 +552,7 @@ private static bool TryParseValue(ref Utf8JsonReader reader, out JsonDocument do
         private static JsonDocument Parse(
             ReadOnlyMemory<byte> utf8Json,
             JsonReaderOptions readerOptions,
-            byte[] extraRentedBytes)
+            byte[]? extraRentedBytes)
         {
             ReadOnlySpan<byte> utf8JsonSpan = utf8Json.Span;
             var database = new MetadataDb(utf8Json.Length);
@@ -577,7 +578,7 @@ private static JsonDocument Parse(
         private static ArraySegment<byte> ReadToEnd(Stream stream)
         {
             int written = 0;
-            byte[] rented = null;
+            byte[]? rented = null;
 
             ReadOnlySpan<byte> utf8Bom = JsonConstants.Utf8Bom;
 
@@ -659,7 +660,7 @@ private static async
             CancellationToken cancellationToken)
         {
             int written = 0;
-            byte[] rented = null;
+            byte[]? rented = null;
 
             try
             {

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.StackRowStack.cs

@@ -24,7 +24,7 @@ internal StackRowStack(int initialSize)
             public void Dispose()
             {
                 byte[] toReturn = _rentedBuffer;
-                _rentedBuffer = null;
+                _rentedBuffer = null!;
                 _topOfStack = 0;
 
                 if (toReturn != null)

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.TryGetProperty.cs

@@ -180,7 +180,7 @@ private bool TryGetNamedPropertyValue(
                         {
                             int remaining = currentPropertyName.Length - idx;
                             int written = 0;
-                            byte[] rented = null;
+                            byte[]? rented = null;
 
                             try
                             {

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.cs

@@ -9,6 +9,7 @@
 using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
 using System.Threading;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Text.Json
 {
@@ -25,8 +26,8 @@ public sealed partial class JsonDocument : IDisposable
     {
         private ReadOnlyMemory<byte> _utf8Json;
         private MetadataDb _parsedData;
-        private byte[] _extraRentedBytes;
-        private (int, string) _lastIndexAndString = (-1, null);
+        private byte[]? _extraRentedBytes;
+        private (int, string?) _lastIndexAndString = (-1, null);
 
         internal bool IsDisposable { get; }
 
@@ -38,7 +39,7 @@ public sealed partial class JsonDocument : IDisposable
         private JsonDocument(
             ReadOnlyMemory<byte> utf8Json,
             MetadataDb parsedData,
-            byte[] extraRentedBytes,
+            byte[]? extraRentedBytes,
             bool isDisposable = true)
         {
             Debug.Assert(!utf8Json.IsEmpty);
@@ -67,7 +68,7 @@ public void Dispose()
 
             // When "extra rented bytes exist" they contain the document,
             // and thus need to be cleared before being returned.
-            byte[] extraRentedBytes = Interlocked.Exchange(ref _extraRentedBytes, null);
+            byte[]? extraRentedBytes = Interlocked.Exchange(ref _extraRentedBytes, null);
 
             if (extraRentedBytes != null)
             {
@@ -243,14 +244,15 @@ private ReadOnlyMemory<byte> GetPropertyRawValue(int valueIndex)
             return _utf8Json.Slice(start, end - start);
         }
 
-        internal string GetString(int index, JsonTokenType expectedType)
+        internal string? GetString(int index, JsonTokenType expectedType)
         {
             CheckNotDisposed();
 
-            (int lastIdx, string lastString) = _lastIndexAndString;
+            (int lastIdx, string? lastString) = _lastIndexAndString;
 
             if (lastIdx == index)
             {
+                Debug.Assert(lastString != null);
                 return lastString;
             }
 
@@ -278,6 +280,7 @@ internal string GetString(int index, JsonTokenType expectedType)
                 lastString = JsonReaderHelper.TranscodeHelper(segment);
             }
 
+            Debug.Assert(lastString != null);
             _lastIndexAndString = (index, lastString);
             return lastString;
         }
@@ -288,14 +291,14 @@ internal bool TextEquals(int index, ReadOnlySpan<char> otherText, bool isPropert
 
             int matchIndex = isPropertyName ? index - DbRow.Size : index;
 
-            (int lastIdx, string lastString) = _lastIndexAndString;
+            (int lastIdx, string? lastString) = _lastIndexAndString;
 
             if (lastIdx == matchIndex)
             {
                 return otherText.SequenceEqual(lastString.AsSpan());
             }
 
-            byte[] otherUtf8TextArray = null;
+            byte[]? otherUtf8TextArray = null;
 
             int length = checked(otherText.Length * JsonConstants.MaxExpansionFactorWhileTranscoding);
             Span<byte> otherUtf8Text = length <= JsonConstants.StackallocThreshold ?
@@ -371,10 +374,10 @@ internal bool TextEquals(int index, ReadOnlySpan<byte> otherUtf8Text, bool isPro
         internal string GetNameOfPropertyValue(int index)
         {
             // The property name is one row before the property value
-            return GetString(index - DbRow.Size, JsonTokenType.PropertyName);
+            return GetString(index - DbRow.Size, JsonTokenType.PropertyName)!;
         }
 
-        internal bool TryGetValue(int index, out byte[] value)
+        internal bool TryGetValue(int index, [NotNullWhen(true)] out byte[]? value)
         {
             CheckNotDisposed();
 

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonElement.ArrayEnumerator.cs

@@ -24,6 +24,7 @@ internal ArrayEnumerator(JsonElement target)
             {
                 _target = target;
                 _curIdx = -1;
+                Debug.Assert(target._parent != null);
 
                 if (target._parent is JsonDocument document)
                 {
@@ -128,6 +129,7 @@ public bool MoveNext()
                 }
                 else
                 {
+                    Debug.Assert(_target._parent != null);
                     var document = (JsonDocument)_target._parent;
                     _curIdx = document.GetEndIndex(_curIdx, includeEndElement: true);
                 }

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonElement.ObjectEnumerator.cs

@@ -19,13 +19,14 @@ public struct ObjectEnumerator : IEnumerable<JsonProperty>, IEnumerator<JsonProp
             private readonly JsonElement _target;
             private int _curIdx;
             private readonly int _endIdxOrVersion;
-            private JsonObjectProperty _current;
+            private JsonObjectProperty? _current;
 
             internal ObjectEnumerator(JsonElement target)
             {
                 _target = target;
                 _curIdx = -1;
                 _current = null;
+                Debug.Assert(target._parent != null);
 
                 if (target._parent is JsonDocument document)
                 {
@@ -143,6 +144,7 @@ public bool MoveNext()
                 }
                 else
                 {
+                    Debug.Assert(_target._parent != null);
                     var document = (JsonDocument)_target._parent;
                     _curIdx = document.GetEndIndex(_curIdx, includeEndElement: true);
                 }

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonElement.cs

@@ -4,6 +4,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Text.Json
 {
@@ -62,6 +63,7 @@ public JsonValueKind ValueKind
                     return TokenType.ToValueKind();
                 }
 
+                Debug.Assert(_parent != null);
                 var jsonNode = (JsonNode)_parent;
 
                 return jsonNode.ValueKind;
@@ -328,7 +330,7 @@ public bool TryGetProperty(ReadOnlySpan<char> propertyName, out JsonElement valu
 
             if (jsonNode is JsonObject jsonObject)
             {
-                if (jsonObject.TryGetPropertyValue(propertyName.ToString(), out JsonNode nodeValue))
+                if (jsonObject.TryGetPropertyValue(propertyName.ToString(), out JsonNode? nodeValue))
                 {
                     value = nodeValue.AsJsonElement();
                     return true;
@@ -383,7 +385,7 @@ public bool TryGetProperty(ReadOnlySpan<byte> utf8PropertyName, out JsonElement
 
             if (jsonNode is JsonObject jsonObject)
             {
-                if (jsonObject.TryGetPropertyValue(JsonHelpers.Utf8GetString(utf8PropertyName), out JsonNode nodeValue))
+                if (jsonObject.TryGetPropertyValue(JsonHelpers.Utf8GetString(utf8PropertyName), out JsonNode? nodeValue))
                 {
                     value = nodeValue.AsJsonElement();
                     return true;
@@ -448,7 +450,7 @@ public bool GetBoolean()
         ///   The parent <see cref="JsonDocument"/> has been disposed.
         /// </exception>
         /// <seealso cref="ToString"/>
-        public string GetString()
+        public string? GetString()
         {
             CheckValidInstance();
 
@@ -484,7 +486,7 @@ public string GetString()
         /// <exception cref="ObjectDisposedException">
         ///   The parent <see cref="JsonDocument"/> has been disposed.
         /// </exception>
-        public bool TryGetBytesFromBase64(out byte[] value)
+        public bool TryGetBytesFromBase64([NotNullWhen(true)] out byte[]? value)
         {
             CheckValidInstance();
 
@@ -522,7 +524,7 @@ public bool TryGetBytesFromBase64(out byte[] value)
         /// <seealso cref="ToString"/>
         public byte[] GetBytesFromBase64()
         {
-            if (TryGetBytesFromBase64(out byte[] value))
+            if (TryGetBytesFromBase64(out byte[]? value))
             {
                 return value;
             }
@@ -1492,7 +1494,7 @@ internal string GetPropertyRawText()
         ///   This method is functionally equal to doing an ordinal comparison of <paramref name="text" /> and
         ///   the result of calling <see cref="GetString" />, but avoids creating the string instance.
         /// </remarks>
-        public bool ValueEquals(string text)
+        public bool ValueEquals(string? text)
         {
             // CheckValidInstance is done in the helper
 
@@ -1720,7 +1722,7 @@ public ObjectEnumerator EnumerateObject()
         /// <exception cref="ObjectDisposedException">
         ///   The parent <see cref="JsonDocument"/> has been disposed.
         /// </exception>
-        public override string ToString()
+        public override string? ToString()
         {
             if (_parent is JsonNode jsonNode)
             {