RoslynExtensions.cs

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace DotnetAutomaticInterface;

/// <summary>
/// Source: https://github.com/dominikjeske/Samples/blob/main/SourceGenerators/HomeCenter.SourceGenerators/Extensions/RoslynExtensions.cs
/// </summary>
/// <remarks>
/// Enhancements or additional Roslyn-related extension methods should be placed in <see cref="RoslynExtensionsAutomaticInterface"/>
/// </remarks>
public static class RoslynExtensions
{
    private static IEnumerable<ITypeSymbol> GetBaseTypesAndThis(this ITypeSymbol type)
    {
        var current = type;
        while (current != null)
        {
            yield return current;
            current = current.BaseType;
        }
    }

    public static IEnumerable<ISymbol> GetAllMembers(this ITypeSymbol type)
    {
        return type.GetBaseTypesAndThis().SelectMany(n => n.GetMembers());
    }

    public static string GetClassName(this ClassDeclarationSyntax proxy)
    {
        return proxy.Identifier.Text;
    }

    /// <summary>
    /// Thanks to https://www.codeproject.com/Articles/871704/Roslyn-Code-Analysis-in-Easy-Samples-Part-2
    /// </summary>
    public static string GetWhereStatement(
        this ITypeParameterSymbol typeParameterSymbol,
        SymbolDisplayFormat typeDisplayFormat
    )
    {
        var result = $"where {typeParameterSymbol.Name} : ";

        var constraints = new List<string>();

        if (typeParameterSymbol.HasReferenceTypeConstraint)
        {
            constraints.Add("class");
        }

        if (typeParameterSymbol.HasValueTypeConstraint)
        {
            constraints.Add("struct");
        }

        if (typeParameterSymbol.HasNotNullConstraint)
        {
            constraints.Add("notnull");
        }

        constraints.AddRange(
            typeParameterSymbol.ConstraintTypes.Select(t => t.ToDisplayString(typeDisplayFormat))
        );

        // The new() constraint must be last
        if (typeParameterSymbol.HasConstructorConstraint)
        {
            constraints.Add("new()");
        }

        if (constraints.Count == 0)
        {
            return "";
        }

        result += string.Join(", ", constraints);

        return result;
    }
}