Allow Utf8String package to work on netstandard 2.0

eng/referenceFromRuntime.targets

@@ -106,7 +106,7 @@
       <ReferencePath Include="@(_filteredReferencePathFromRuntimeByFileName->'%(ReferencePath)')" Condition="'%(_filteredReferencePathFromRuntimeByFileName.Aliases)' != ''" Aliases="" />
     </ItemGroup>
 
-    <Error Condition="'@(_missingReferenceFromRuntime)' != ''"
+    <Error Condition="'@(_missingReferenceFromRuntime)' != '' and '$(DesignTimeBuild)' != 'true'"
            Text="Could not resolve ReferenceFromRuntime item(s) '%(_missingReferenceFromRuntime.OriginalReferenceFromRuntime)' from '$(RuntimeProjectFile)'." />
   </Target>
 </Project>

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

@@ -861,7 +861,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\Unicode\Utf8Utility.Helpers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\Unicode\Utf8Utility.Transcoding.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\Unicode\Utf8Utility.Validation.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Text\Unicode\Utf8Utility.WhiteSpace.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Text\Unicode\Utf8Utility.WhiteSpace.CoreLib.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\UnicodeDebug.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\UnicodeEncoding.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\UnicodeUtility.cs" />
@@ -1811,6 +1811,7 @@
   <ItemGroup Condition="'$(FeatureUtf8String)' == 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Char8.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Utf8Extensions.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Utf8Extensions.CoreLib.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Utf8String.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Utf8String.Comparison.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Utf8String.Construction.cs" />
@@ -1827,4 +1828,4 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\Utf8Span.Searching.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Text\Utf8StringComparer.cs" />
   </ItemGroup>
-</Project>
+</Project>

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

@@ -4,6 +4,7 @@
 
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
+using System.Text;
 
 namespace System
 {
@@ -140,11 +141,15 @@ public override string ToString()
 
         private string ToStringFromEnd()
         {
+#if !NETSTANDARD2_0
             Span<char> span = stackalloc char[11]; // 1 for ^ and 10 for longest possible uint value
             bool formatted = ((uint)Value).TryFormat(span.Slice(1), out int charsWritten);
             Debug.Assert(formatted);
             span[0] = '^';
             return new string(span.Slice(0, charsWritten + 1));
+#else
+            return '^' + Value.ToString();
+#endif
         }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Numerics/BitOperations.cs

@@ -6,7 +6,9 @@
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics.X86;
 
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 // Some routines inspired by the Stanford Bit Twiddling Hacks by Sean Eron Anderson:
 // http://graphics.stanford.edu/~seander/bithacks.html
@@ -18,7 +20,12 @@ namespace System.Numerics
     /// The methods use hardware intrinsics when available on the underlying platform,
     /// otherwise they use optimized software fallbacks.
     /// </summary>
-    public static class BitOperations
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+        static class BitOperations
     {
         // C# no-alloc optimization that directly wraps the data section of the dll (similar to string constants)
         // https://github.com/dotnet/roslyn/pull/24621

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

@@ -4,6 +4,11 @@
 
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
+using System.Text;
+
+#if NETSTANDARD2_0
+using System.Numerics.Hashing;
+#endif
 
 namespace System
 {
@@ -47,12 +52,17 @@ value is Range r &&
         /// <summary>Returns the hash code for this instance.</summary>
         public override int GetHashCode()
         {
+#if !NETSTANDARD2_0
             return HashCode.Combine(Start.GetHashCode(), End.GetHashCode());
+#else
+            return HashHelpers.Combine(Start.GetHashCode(), End.GetHashCode());
+#endif
         }
 
         /// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
         public override string ToString()
         {
+#if !NETSTANDARD2_0
             Span<char> span = stackalloc char[2 + (2 * 11)]; // 2 for "..", then for each index 1 for '^' and 10 for longest possible uint
             int pos = 0;
 
@@ -77,6 +87,10 @@ public override string ToString()
             pos += charsWritten;
 
             return new string(span.Slice(0, pos));
+#else
+            return Start.ToString() + ".." + End.ToString();
+#endif
+
         }
 
         /// <summary>Create a Range object starting from start index to the end of the collection.</summary>

src/libraries/System.Private.CoreLib/src/System/Text/ASCIIUtility.cs

@@ -7,7 +7,10 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.X86;
+
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 #pragma warning disable SA1121 // explicitly using type aliases instead of built-in types
 #if TARGET_64BIT

src/libraries/System.Private.CoreLib/src/System/Text/Rune.cs

@@ -20,6 +20,10 @@ namespace System.Text
     [DebuggerDisplay("{DebuggerDisplay,nq}")]
     public readonly struct Rune : IComparable<Rune>, IEquatable<Rune>
     {
+        private const char HIGH_SURROGATE_START = '\ud800';
+        private const char LOW_SURROGATE_START = '\udc00';
+        private const int HIGH_SURROGATE_RANGE = 0x3FF;
+
         private const byte IsWhiteSpaceFlag = 0x80;
         private const byte IsLetterOrDigitFlag = 0x40;
         private const byte UnicodeCategoryMask = 0x1F;
@@ -175,10 +179,10 @@ private Rune(uint scalarValue, bool unused)
         /// </summary>
         public int Value => (int)_value;
 
-        private static Rune ChangeCaseCultureAware(Rune rune, TextInfo textInfo, bool toUpper)
+        private static Rune ChangeCaseCultureAware(Rune rune, CultureInfo culture, bool toUpper)
         {
             Debug.Assert(!GlobalizationMode.Invariant, "This should've been checked by the caller.");
-            Debug.Assert(textInfo != null, "This should've been checked by the caller.");
+            Debug.Assert(culture != null, "This should've been checked by the caller.");
 
             Span<char> original = stackalloc char[2]; // worst case scenario = 2 code units (for a surrogate pair)
             Span<char> modified = stackalloc char[2]; // case change should preserve UTF-16 code unit count
@@ -187,14 +191,25 @@ private static Rune ChangeCaseCultureAware(Rune rune, TextInfo textInfo, bool to
             original = original.Slice(0, charCount);
             modified = modified.Slice(0, charCount);
 
+#if SYSTEM_PRIVATE_CORELIB
+            if (toUpper)
+            {
+                culture!.TextInfo.ChangeCaseToUpper(original, modified);
+            }
+            else
+            {
+                culture!.TextInfo.ChangeCaseToLower(original, modified);
+            }
+#else
             if (toUpper)
             {
-                textInfo.ChangeCaseToUpper(original, modified);
+                MemoryExtensions.ToUpper(original, modified, culture);
             }
             else
             {
-                textInfo.ChangeCaseToLower(original, modified);
+                MemoryExtensions.ToLower(original, modified, culture);
             }
+#endif
 
             // We use simple case folding rules, which disallows moving between the BMP and supplementary
             // planes when performing a case conversion. The helper methods which reconstruct a Rune
@@ -827,6 +842,7 @@ private static int ReadRuneFromString(string input, int index)
         /// </summary>
         public override string ToString()
         {
+#if SYSTEM_PRIVATE_CORELIB
             if (IsBmp)
             {
                 return string.CreateFromChar((char)_value);
@@ -836,6 +852,19 @@ public override string ToString()
                 UnicodeUtility.GetUtf16SurrogatesFromSupplementaryPlaneScalar(_value, out char high, out char low);
                 return string.CreateFromChar(high, low);
             }
+#else
+            if (IsBmp)
+            {
+
+                return ((char)_value).ToString();
+            }
+            else
+            {
+                Span<char> buffer = stackalloc char[2];
+                UnicodeUtility.GetUtf16SurrogatesFromSupplementaryPlaneScalar(_value, out buffer[0], out buffer[1]);
+                return buffer.ToString();
+            }
+#endif
         }
 
         /// <summary>
@@ -865,17 +894,17 @@ public static bool TryCreate(char highSurrogate, char lowSurrogate, out Rune res
             // First, extend both to 32 bits, then calculate the offset of
             // each candidate surrogate char from the start of its range.
 
-            uint highSurrogateOffset = (uint)highSurrogate - CharUnicodeInfo.HIGH_SURROGATE_START;
-            uint lowSurrogateOffset = (uint)lowSurrogate - CharUnicodeInfo.LOW_SURROGATE_START;
+            uint highSurrogateOffset = (uint)highSurrogate - HIGH_SURROGATE_START;
+            uint lowSurrogateOffset = (uint)lowSurrogate - LOW_SURROGATE_START;
 
             // This is a single comparison which allows us to check both for validity at once since
             // both the high surrogate range and the low surrogate range are the same length.
             // If the comparison fails, we call to a helper method to throw the correct exception message.
 
-            if ((highSurrogateOffset | lowSurrogateOffset) <= CharUnicodeInfo.HIGH_SURROGATE_RANGE)
+            if ((highSurrogateOffset | lowSurrogateOffset) <= HIGH_SURROGATE_RANGE)
             {
                 // The 0x40u << 10 below is to account for uuuuu = wwww + 1 in the surrogate encoding.
-                result = UnsafeCreate((highSurrogateOffset << 10) + ((uint)lowSurrogate - CharUnicodeInfo.LOW_SURROGATE_START) + (0x40u << 10));
+                result = UnsafeCreate((highSurrogateOffset << 10) + ((uint)lowSurrogate - LOW_SURROGATE_START) + (0x40u << 10));
                 return true;
             }
             else
@@ -1070,7 +1099,11 @@ public static double GetNumericValue(Rune value)
             else
             {
                 // not an ASCII char; fall back to globalization table
+#if SYSTEM_PRIVATE_CORELIB
                 return CharUnicodeInfo.GetNumericValue(value.Value);
+#else
+                return CharUnicodeInfo.GetNumericValue(value.ToString(), 0);
+#endif
             }
         }
 
@@ -1089,7 +1122,11 @@ public static UnicodeCategory GetUnicodeCategory(Rune value)
         private static UnicodeCategory GetUnicodeCategoryNonAscii(Rune value)
         {
             Debug.Assert(!value.IsAscii, "Shouldn't use this non-optimized code path for ASCII characters.");
+#if !NETSTANDARD2_0
             return CharUnicodeInfo.GetUnicodeCategory(value.Value);
+#else
+            return CharUnicodeInfo.GetUnicodeCategory(value.ToString(), 0);
+#endif
         }
 
         // Returns true iff this Unicode category represents a letter
@@ -1240,7 +1277,12 @@ public static bool IsWhiteSpace(Rune value)
             // Only BMP code points can be white space, so only call into CharUnicodeInfo
             // if the incoming value is within the BMP.
 
-            return value.IsBmp && CharUnicodeInfo.GetIsWhiteSpace((char)value._value);
+            return value.IsBmp &&
+#if SYSTEM_PRIVATE_CORELIB
+                CharUnicodeInfo.GetIsWhiteSpace((char)value._value);
+#else
+                char.IsWhiteSpace((char)value._value);
+#endif
         }
 
         public static Rune ToLower(Rune value, CultureInfo culture)
@@ -1259,7 +1301,7 @@ public static Rune ToLower(Rune value, CultureInfo culture)
                 return ToLowerInvariant(value);
             }
 
-            return ChangeCaseCultureAware(value, culture!.TextInfo, toUpper: false);
+            return ChangeCaseCultureAware(value, culture, toUpper: false);
         }
 
         public static Rune ToLowerInvariant(Rune value)
@@ -1283,7 +1325,7 @@ public static Rune ToLowerInvariant(Rune value)
 
             // Non-ASCII data requires going through the case folding tables.
 
-            return ChangeCaseCultureAware(value, TextInfo.Invariant, toUpper: false);
+            return ChangeCaseCultureAware(value, CultureInfo.InvariantCulture, toUpper: false);
         }
 
         public static Rune ToUpper(Rune value, CultureInfo culture)
@@ -1302,7 +1344,7 @@ public static Rune ToUpper(Rune value, CultureInfo culture)
                 return ToUpperInvariant(value);
             }
 
-            return ChangeCaseCultureAware(value, culture!.TextInfo, toUpper: true);
+            return ChangeCaseCultureAware(value, culture, toUpper: true);
         }
 
         public static Rune ToUpperInvariant(Rune value)
@@ -1326,7 +1368,7 @@ public static Rune ToUpperInvariant(Rune value)
 
             // Non-ASCII data requires going through the case folding tables.
 
-            return ChangeCaseCultureAware(value, TextInfo.Invariant, toUpper: true);
+            return ChangeCaseCultureAware(value, CultureInfo.InvariantCulture, toUpper: true);
         }
     }
 }

src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf16Utility.Validation.cs

@@ -5,8 +5,12 @@
 using System.Diagnostics;
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.X86;
+using System.Runtime.CompilerServices;
 using System.Numerics;
+
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 #pragma warning disable SA1121 // explicitly using type aliases instead of built-in types
 #if TARGET_64BIT

src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8.cs

@@ -4,12 +4,21 @@
 
 using System.Buffers;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 namespace System.Text.Unicode
 {
-    public static class Utf8
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+        static class Utf8
     {
         /*
          * OperationStatus-based APIs for transcoding of chunked data.

src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Helpers.cs

@@ -6,7 +6,10 @@
 using System.Diagnostics;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 namespace System.Text.Unicode
 {

src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs

@@ -6,9 +6,13 @@
 using System.Buffers.Binary;
 using System.Diagnostics;
 using System.Numerics;
+using System.Runtime.CompilerServices;
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.X86;
+
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 #pragma warning disable SA1121 // explicitly using type aliases instead of built-in types
 #if TARGET_64BIT

src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Validation.cs

@@ -5,7 +5,11 @@
 using System.Diagnostics;
 using System.Numerics;
 using System.Runtime.Intrinsics.X86;
+using System.Runtime.CompilerServices;
+
+#if SYSTEM_PRIVATE_CORELIB
 using Internal.Runtime.CompilerServices;
+#endif
 
 #pragma warning disable SA1121 // explicitly using type aliases instead of built-in types
 #if TARGET_64BIT