A small class to add JSON files to the Visual Studio project that Unity auto-generates.

VisualStudioProjectCustomisation.cs

#if ENABLE_VSTU
using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml.Linq;

using UnityEditor;

using SyntaxTree.VisualStudio.Unity.Bridge;

[InitializeOnLoad]
public class VisualStudioProjectCustomisation
{
    // necessary for XLinq to save the xml project file in utf8
    class Utf8StringWriter : StringWriter
    {
        public override Encoding Encoding
        {
            get { return Encoding.UTF8; }
        }
    }

    static VisualStudioProjectCustomisation()
    {
        ProjectFilesGenerator.ProjectFileGeneration += OnGenerateProjectFile;
    }

    private static string OnGenerateProjectFile(string name, string content)
    {
        var filename = Path.GetFileNameWithoutExtension(name);

        // parse the document and make some changes
        var document = XDocument.Parse(content);

        if (filename == "Assembly-CSharp")
        {
            // Find the <ItemGroup> that contains the files. We search for the first ItemGroup that has any "Compile" entries.
            var itemGroups = document.Root.Elements().Where(element => element.Name.LocalName == "ItemGroup");
            var compileItemGroup = itemGroups.Where(itemGroup => itemGroup.Elements().Any(child => child.Name.LocalName == "Compile")).FirstOrDefault();
            if (compileItemGroup != null)
            {
                // Get all json files under the Assets directory. Note that this will also include json files under Editor directories.
                var assetsDir = Directory.GetCurrentDirectory();
                assetsDir = Path.Combine(assetsDir, "Assets");
                var jsonFiles = Directory.GetFiles(assetsDir, "*.json", SearchOption.AllDirectories);

                // Construct a Uri instance for the Assets root.
                var root = new Uri(assetsDir, UriKind.Absolute);

                // Add each json file to the project.
                foreach (var file in jsonFiles)
                {
                    // Make the path relative to the Assets directory.
                    var uri = new Uri(file, UriKind.Absolute);
                    var relativePath = root.MakeRelativeUri(uri).ToString();

                    // VS requires the path separator to be backslash, otherwise it uses the full path of the file as the filename.
                    relativePath = relativePath.Replace("/", "\\");

                    // Make a new XML node.
                    // Nodes for files that aren't compiled look like this: <None Include="Assets\TextMesh Pro\Resources\Shaders\TMP_SDF.shader" />
                    var element = new XElement("None");
                    element.SetAttributeValue("Include", relativePath);
                    compileItemGroup.Add(element);
                }
            }
        }

        // Save the changes using the Utf8StringWriter
        var str = new Utf8StringWriter();
        document.Save(str);

        return str.ToString();
    }
}
#endif