Allow specifying IndentCharacter and IndentSize when writing JSON

src/libraries/System.Text.Json/Common/JsonConstants.cs

@@ -11,5 +11,7 @@ internal static partial class JsonConstants
 
         public const int StackallocByteThreshold = 256;
         public const int StackallocCharThreshold = StackallocByteThreshold / 2;
+
+        public const string DefaultIndent = "  ";
     }
 }

src/libraries/System.Text.Json/Common/JsonSourceGenerationOptionsAttribute.cs

@@ -125,6 +125,11 @@ public JsonSourceGenerationOptionsAttribute(JsonSerializerDefaults defaults)
         /// </summary>
         public bool WriteIndented { get; set; }
 
+        /// <summary>
+        /// Specifies the default value of <see cref="JsonSerializerOptions.IndentText"/> when set.
+        /// </summary>
+        public string IndentText { get; set; } = JsonConstants.DefaultIndent;
+
         /// <summary>
         /// Specifies the default source generation mode for type declarations that don't set a <see cref="JsonSerializableAttribute.GenerationMode"/>.
         /// </summary>

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -1168,6 +1168,9 @@ private static void GetLogicForDefaultSerializerOptionsInit(SourceGenerationOpti
                 if (optionsSpec.WriteIndented is bool writeIndented)
                     writer.WriteLine($"WriteIndented = {FormatBool(writeIndented)},");
 
+                if (optionsSpec.IndentText is string indentText)
+                    writer.WriteLine($"IndentText = {FormatStringLiteral(indentText)},");
+
                 writer.Indentation--;
                 writer.WriteLine("};");
 

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs

@@ -280,6 +280,7 @@ private SourceGenerationOptionsSpec ParseJsonSourceGenerationOptionsAttribute(IN
                 JsonUnmappedMemberHandling? unmappedMemberHandling = null;
                 bool? useStringEnumConverter = null;
                 bool? writeIndented = null;
+                string? indentText = null;
 
                 if (attributeData.ConstructorArguments.Length > 0)
                 {
@@ -373,6 +374,10 @@ private SourceGenerationOptionsSpec ParseJsonSourceGenerationOptionsAttribute(IN
                             writeIndented = (bool)namedArg.Value.Value!;
                             break;
 
+                        case nameof(JsonSourceGenerationOptionsAttribute.IndentText):
+                            indentText = (string)namedArg.Value.Value!;
+                            break;
+
                         case nameof(JsonSourceGenerationOptionsAttribute.GenerationMode):
                             generationMode = (JsonSourceGenerationMode)namedArg.Value.Value!;
                             break;
@@ -404,6 +409,7 @@ private SourceGenerationOptionsSpec ParseJsonSourceGenerationOptionsAttribute(IN
                     UnmappedMemberHandling = unmappedMemberHandling,
                     UseStringEnumConverter = useStringEnumConverter,
                     WriteIndented = writeIndented,
+                    IndentText = indentText,
                 };
             }
 

src/libraries/System.Text.Json/gen/Model/SourceGenerationOptionsSpec.cs

@@ -52,6 +52,8 @@ public sealed record SourceGenerationOptionsSpec
 
         public required bool? WriteIndented { get; init; }
 
+        public required string? IndentText { get; init; }
+
         public JsonKnownNamingPolicy? GetEffectivePropertyNamingPolicy()
             => PropertyNamingPolicy ?? (Defaults is JsonSerializerDefaults.Web ? JsonKnownNamingPolicy.CamelCase : null);
     }

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

@@ -394,6 +394,7 @@ public JsonSerializerOptions(System.Text.Json.JsonSerializerOptions options) { }
         public System.Text.Json.Serialization.JsonUnknownTypeHandling UnknownTypeHandling { get { throw null; } set { } }
         public System.Text.Json.Serialization.JsonUnmappedMemberHandling UnmappedMemberHandling { get { throw null; } set { } }
         public bool WriteIndented { get { throw null; } set { } }
+        public string IndentText { get { throw null; } set { } }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         [System.ObsoleteAttribute("JsonSerializerOptions.AddContext is obsolete. To register a JsonSerializerContext, use either the TypeInfoResolver or TypeInfoResolverChain properties.", DiagnosticId="SYSLIB0049", UrlFormat="https://aka.ms/dotnet-warnings/{0}")]
         public void AddContext<TContext>() where TContext : System.Text.Json.Serialization.JsonSerializerContext, new() { }
@@ -439,6 +440,7 @@ public partial struct JsonWriterOptions
         private int _dummyPrimitive;
         public System.Text.Encodings.Web.JavaScriptEncoder? Encoder { readonly get { throw null; } set { } }
         public bool Indented { get { throw null; } set { } }
+        public string IndentText { get { throw null; } set { } }
         public int MaxDepth { readonly get { throw null; } set { } }
         public bool SkipValidation { get { throw null; } set { } }
     }
@@ -1074,6 +1076,7 @@ public JsonSourceGenerationOptionsAttribute(System.Text.Json.JsonSerializerDefau
         public System.Text.Json.Serialization.JsonUnmappedMemberHandling UnmappedMemberHandling { get { throw null; } set { } }
         public bool UseStringEnumConverter { get { throw null; } set { } }
         public bool WriteIndented { get { throw null; } set { } }
+        public string IndentText { get { throw null; } set { } }
     }
     [System.Diagnostics.CodeAnalysis.RequiresDynamicCodeAttribute("JsonStringEnumConverter cannot be statically analyzed and requires runtime code generation. Applications should use the generic JsonStringEnumConverter<TEnum> instead.")]
     public partial class JsonStringEnumConverter : System.Text.Json.Serialization.JsonConverterFactory

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

@@ -47,7 +47,6 @@ internal static partial class JsonConstants
         // Explicitly skipping ReverseSolidus since that is handled separately
         public static ReadOnlySpan<byte> EscapableChars => "\"nrt/ubf"u8;
 
-        public const int SpacesPerIndent = 2;
         public const int RemoveFlagsBitMask = 0x7FFFFFFF;
 
         // In the worst case, an ASCII character represented as a single utf-8 byte could expand 6x when escaped.

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Caching.cs

@@ -511,6 +511,7 @@ public bool Equals(JsonSerializerOptions? left, JsonSerializerOptions? right)
                     left._includeFields == right._includeFields &&
                     left._propertyNameCaseInsensitive == right._propertyNameCaseInsensitive &&
                     left._writeIndented == right._writeIndented &&
+                    left._indentText == right._indentText &&
                     left._typeInfoResolver == right._typeInfoResolver &&
                     CompareLists(left._converters, right._converters);
 
@@ -565,6 +566,7 @@ public int GetHashCode(JsonSerializerOptions options)
                 AddHashCode(ref hc, options._includeFields);
                 AddHashCode(ref hc, options._propertyNameCaseInsensitive);
                 AddHashCode(ref hc, options._writeIndented);
+                AddHashCode(ref hc, options._indentText.GetHashCode());
                 AddHashCode(ref hc, options._typeInfoResolver);
                 AddListHashCode(ref hc, options._converters);
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

@@ -75,6 +75,7 @@ public static JsonSerializerOptions Default
         private bool _includeFields;
         private bool _propertyNameCaseInsensitive;
         private bool _writeIndented;
+        private string _indentText = JsonConstants.DefaultIndent;
 
         /// <summary>
         /// Constructs a new <see cref="JsonSerializerOptions"/> instance.
@@ -124,6 +125,7 @@ public JsonSerializerOptions(JsonSerializerOptions options)
             _includeFields = options._includeFields;
             _propertyNameCaseInsensitive = options._propertyNameCaseInsensitive;
             _writeIndented = options._writeIndented;
+            _indentText = options._indentText;
             _typeInfoResolver = options._typeInfoResolver;
             EffectiveMaxDepth = options.EffectiveMaxDepth;
             ReferenceHandlingStrategy = options.ReferenceHandlingStrategy;
@@ -645,6 +647,30 @@ public bool WriteIndented
             }
         }
 
+        /// <summary>
+        /// Defines the text used as indent when <see cref="WriteIndented" /> is enabled
+        /// By default, the JSON is indented with 2 white spaces.
+        /// </summary>
+        /// <exception cref="InvalidOperationException">
+        /// Thrown if this property is set after serialization or deserialization has occurred.
+        /// </exception>
+        public string IndentText
+        {
+            get
+            {
+                return _indentText;
+            }
+            set
+            {
+                if (value is null)
+                {
+                    ThrowHelper.ThrowArgumentNullException(nameof(value));
+                }
+                VerifyMutable();
+                _indentText = value;
+            }
+        }
+
         /// <summary>
         /// Configures how object references are handled when reading and writing JSON.
         /// </summary>
@@ -876,6 +902,7 @@ internal JsonWriterOptions GetWriterOptions()
             {
                 Encoder = Encoder,
                 Indented = WriteIndented,
+                IndentText = IndentText,
                 MaxDepth = EffectiveMaxDepth,
 #if !DEBUG
                 SkipValidation = true

src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs

@@ -10,25 +10,36 @@ namespace System.Text.Json
 {
     internal static partial class JsonWriterHelper
     {
-        public static void WriteIndentation(Span<byte> buffer, int indent)
+        public static void WriteIndentation(Span<byte> buffer, int indent, byte indentByte)
         {
-            Debug.Assert(indent % JsonConstants.SpacesPerIndent == 0);
             Debug.Assert(buffer.Length >= indent);
 
             // Based on perf tests, the break-even point where vectorized Fill is faster
             // than explicitly writing the space in a loop is 8.
-            if (indent < 8)
+            if (indent < 8 && indent % 2 == 0)
             {
                 int i = 0;
                 while (i < indent)
                 {
-                    buffer[i++] = JsonConstants.Space;
-                    buffer[i++] = JsonConstants.Space;
+                    buffer[i++] = indentByte;
+                    buffer[i++] = indentByte;
                 }
             }
             else
             {
-                buffer.Slice(0, indent).Fill(JsonConstants.Space);
+                buffer.Slice(0, indent).Fill(indentByte);
+            }
+        }
+
+        public static void WriteIndentation(Span<byte> buffer, int indentation, Span<byte> indent)
+        {
+            Debug.Assert(buffer.Length >= indentation);
+
+            int offset = 0;
+            while (offset < indentation)
+            {
+                indent.CopyTo(buffer.Slice(offset));
+                offset += indent.Length;
             }
         }
 

src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterOptions.cs

@@ -17,6 +17,7 @@ public struct JsonWriterOptions
 
         private int _maxDepth;
         private int _optionsMask;
+        private string _indentText;
 
         /// <summary>
         /// The encoder to use when escaping strings, or <see langword="null" /> to use the default encoder.
@@ -43,6 +44,23 @@ public bool Indented
             }
         }
 
+        /// <summary>
+        /// Defines the text used as indent by the <see cref="Utf8JsonWriter"/> when <see cref="Indented"/> is enabled
+        /// By default, the JSON is written with 2 white spaces.
+        /// </summary>
+        public string IndentText
+        {
+            get => _indentText ?? JsonConstants.DefaultIndent;
+            set
+            {
+                if (value is null)
+                {
+                    ThrowHelper.ThrowArgumentNullException(nameof(value));
+                }
+                _indentText = value;
+            }
+        }
+
         /// <summary>
         /// Gets or sets the maximum depth allowed when writing JSON, with the default (i.e. 0) indicating a max depth of 1000.
         /// </summary>

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Bytes.cs

@@ -309,7 +309,7 @@ private void WriteBase64Indented(ReadOnlySpan<char> escapedPropertyName, ReadOnl
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -359,7 +359,7 @@ private void WriteBase64Indented(ReadOnlySpan<byte> escapedPropertyName, ReadOnl
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTime.cs

@@ -311,7 +311,7 @@ private void WriteStringIndented(ReadOnlySpan<char> escapedPropertyName, DateTim
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -359,7 +359,7 @@ private void WriteStringIndented(ReadOnlySpan<byte> escapedPropertyName, DateTim
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTimeOffset.cs

@@ -310,7 +310,7 @@ private void WriteStringIndented(ReadOnlySpan<char> escapedPropertyName, DateTim
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -358,7 +358,7 @@ private void WriteStringIndented(ReadOnlySpan<byte> escapedPropertyName, DateTim
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Decimal.cs

@@ -304,7 +304,7 @@ private void WriteNumberIndented(ReadOnlySpan<char> escapedPropertyName, decimal
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -349,7 +349,7 @@ private void WriteNumberIndented(ReadOnlySpan<byte> escapedPropertyName, decimal
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Double.cs

@@ -308,7 +308,7 @@ private void WriteNumberIndented(ReadOnlySpan<char> escapedPropertyName, double
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -353,7 +353,7 @@ private void WriteNumberIndented(ReadOnlySpan<byte> escapedPropertyName, double
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Float.cs

@@ -308,7 +308,7 @@ private void WriteNumberIndented(ReadOnlySpan<char> escapedPropertyName, float v
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -353,7 +353,7 @@ private void WriteNumberIndented(ReadOnlySpan<byte> escapedPropertyName, float v
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;

src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Guid.cs

@@ -312,7 +312,7 @@ private void WriteStringIndented(ReadOnlySpan<char> escapedPropertyName, Guid va
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;
@@ -361,7 +361,7 @@ private void WriteStringIndented(ReadOnlySpan<byte> escapedPropertyName, Guid va
                 WriteNewLine(output);
             }
 
-            JsonWriterHelper.WriteIndentation(output.Slice(BytesPending), indent);
+            WriteIndentation(output.Slice(BytesPending), indent);
             BytesPending += indent;
 
             output[BytesPending++] = JsonConstants.Quote;