Optimize Roslyn analyzers usage

Author: bdovaz

src/UnityNuGet/RegistryCache.cs

@@ -633,6 +633,7 @@ RegistryEntry packageEntry
                             string? meta;
 
                             string fileExtension = Path.GetExtension(fileInUnityPackage);
+
                             if (fileExtension == ".dll")
                             {
                                 meta = UnityMeta.GetMetaForDll(
@@ -664,6 +665,20 @@ RegistryEntry packageEntry
                             // write meta file
                             await WriteTextFileToTar(tarArchive, $"{fileInUnityPackage}.meta", meta);
                         }
+
+                        // Write analyzer asmdef
+                        // Check Analyzer Scope section: https://docs.unity3d.com/Manual/roslyn-analyzers.html
+                        var analyzerAsmdef = CreateAnalyzerAmsdef(identity);
+                        var analyzerAsmdefAsJson = analyzerAsmdef.ToJson();
+                        string analyzerAsmdefFileName = $"{identity.Id}.asmdef";
+                        await WriteTextFileToTar(tarArchive, analyzerAsmdefFileName, analyzerAsmdefAsJson);
+                        await WriteTextFileToTar(tarArchive, $"{analyzerAsmdefFileName}.meta", UnityMeta.GetMetaForExtension(GetStableGuid(identity, analyzerAsmdefFileName), ".asmdef")!);
+
+                        // Write empty script (Necessary to compile the asmdef file)
+                        var emptyScriptContent = UnityScript.GetEmptyScript();
+                        const string emptyScriptFileName = "EmptyScript.cs";
+                        await WriteTextFileToTar(tarArchive, emptyScriptFileName, emptyScriptContent);
+                        await WriteTextFileToTar(tarArchive, $"{emptyScriptFileName}.meta", UnityMeta.GetMetaForExtension(GetStableGuid(identity, emptyScriptFileName), ".cs")!);
                     }
 
                     // Get all known platform definitions
@@ -1067,6 +1082,15 @@ private static UnityPackage CreateUnityPackage(NpmPackageInfo npmPackageInfo, Np
             return unityPackage;
         }
 
+        private static UnityAsmdef CreateAnalyzerAmsdef(PackageIdentity packageIdentity)
+        {
+            return new()
+            {
+                Name = $"{packageIdentity.Id}_Unity", // Add _Unity suffix because Unity has a validation so that assemblies names do not collide with asmdefs assembly names
+                IncludePlatforms = new string[] { "Editor" }
+            };
+        }
+
         private static Guid StringToGuid(string text)
         {
             var guid = new byte[16];

src/UnityNuGet/UnityAsmdef.cs

@@ -0,0 +1,14 @@
+using Newtonsoft.Json;
+
+namespace UnityNuGet
+{
+    public class UnityAsmdef : JsonObjectBase
+    {
+        [JsonProperty("name")]
+        public string? Name { get; set; }
+
+        // The values come from: https://docs.unity3d.com/ScriptReference/BuildTarget.html
+        [JsonProperty("includePlatforms")]
+        public string[]? IncludePlatforms { get; set; }
+    }
+}

src/UnityNuGet/UnityMeta.cs

@@ -17,6 +17,7 @@ internal static class UnityMeta
                 case ".pdb":
                     break;
                 case ".asmdef":
+                case ".cs":
                 case ".json":
                 case ".md":
                 case ".txt":

src/UnityNuGet/UnityScript.cs

@@ -0,0 +1,7 @@
+namespace UnityNuGet
+{
+    internal static class UnityScript
+    {
+        public static string GetEmptyScript() => string.Empty;
+    }
+}