Repository: dotnet/roslyn
File: src/Compilers/Core/Portable/WellKnownTypes.cs (C#)

Code before:
        System_Linq_Expressions_TypeBinaryExpression,
        System_Linq_Expressions_ConditionalExpression,
        System_Linq_Expressions_InvocationExpression,
        System_Linq_Expressions_NewArrayExpression,
        System_Linq_Expressions_DefaultExpression,

        System_Text_Encoding,

        System_Runtime_CompilerServices_InlineArray2,
        System_Runtime_CompilerServices_InlineArray3,
        System_Runtime_CompilerServices_InlineArray4,
        System_Runtime_CompilerServices_InlineArray5,
        System_Runtime_CompilerServices_InlineArray6,
        System_Runtime_CompilerServices_InlineArray7,
        System_Runtime_CompilerServices_InlineArray8,
        System_Runtime_CompilerServices_InlineArray9,
        System_Runtime_CompilerServices_InlineArray10,
        System_Runtime_CompilerServices_InlineArray11,
        System_Runtime_CompilerServices_InlineArray12,
        System_Runtime_CompilerServices_InlineArray13,
        System_Runtime_CompilerServices_InlineArray14,
        System_Runtime_CompilerServices_InlineArray15,
        System_Runtime_CompilerServices_InlineArray16,

        NextAvailable,
        // Remember to update the AllWellKnownTypes tests when making changes here
    }

    internal static class WellKnownTypes
    {
        /// <summary>
        /// Number of well known types in WellKnownType enum
        /// </summary>
        internal const int Count = WellKnownType.NextAvailable - WellKnownType.First;

        /// <summary>
        /// Array of names for types.
        /// The names should correspond to ids from WellKnownType enum so
        /// that we could use ids to index into the array
        /// </summary>
        /// <remarks></remarks>
        private static readonly string[] s_metadataNames = new string[Count]
        {
            "System.Math",
            "System.Attribute",
            "System.CLSCompliantAttribute",
            "System.Convert",
            "System.Exception",
            "System.FlagsAttribute",
            "System.FormattableString",
            "System.Guid",

Review comment (suggestion):
> Remember to update the AllWellKnownTypes tests when making changes here

You seem to have forgot this ;)

Code after:
        System_Linq_Expressions_TypeBinaryExpression,
        System_Linq_Expressions_ConditionalExpression,
        System_Linq_Expressions_InvocationExpression,
        System_Linq_Expressions_NewArrayExpression,
        System_Linq_Expressions_DefaultExpression,

        System_Text_Encoding,

        // The InlineArray types must be sequential, as we do arithmetic on them.
        System_Runtime_CompilerServices_InlineArray2,
        System_Runtime_CompilerServices_InlineArray3,
        System_Runtime_CompilerServices_InlineArray4,
        System_Runtime_CompilerServices_InlineArray5,
        System_Runtime_CompilerServices_InlineArray6,
        System_Runtime_CompilerServices_InlineArray7,
        System_Runtime_CompilerServices_InlineArray8,
        System_Runtime_CompilerServices_InlineArray9,
        System_Runtime_CompilerServices_InlineArray10,
        System_Runtime_CompilerServices_InlineArray11,
        System_Runtime_CompilerServices_InlineArray12,
        System_Runtime_CompilerServices_InlineArray13,
        System_Runtime_CompilerServices_InlineArray14,
        System_Runtime_CompilerServices_InlineArray15,
        System_Runtime_CompilerServices_InlineArray16,

        NextAvailable,
        // Remember to update MissingSpecialMember.AllWellKnownTypes and WellKnownTypeValidationTests.AllWellKnownTypes tests when making changes here
    }

    internal static class WellKnownTypes
    {
        /// <summary>
        /// Number of well known types in WellKnownType enum
        /// </summary>
        internal const int Count = WellKnownType.NextAvailable - WellKnownType.First;

        /// <summary>
        /// Array of names for types.
        /// The names should correspond to ids from WellKnownType enum so
        /// that we could use ids to index into the array
        /// </summary>
        /// <remarks></remarks>
        private static readonly string[] s_metadataNames = new string[Count]
        {
            "System.Math",
            "System.Attribute",
            "System.CLSCompliantAttribute",
            "System.Convert",
            "System.Exception",
            "System.FlagsAttribute",
            "System.FormattableString",