Make it an Incremental Source Generator

.gitignore

@@ -1,3 +1,4 @@
+artifacts/
 bin/
 obj/
 /packages/

BepInEx.AutoPlugin.sln

@@ -1,7 +1,10 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
+# 
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BepInEx.AutoPlugin", "BepInEx.AutoPlugin\BepInEx.AutoPlugin.csproj", "{DF01D949-82F0-4CCA-A094-903C8F30E691}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestPlugin", "TestPlugin\TestPlugin.csproj", "{6C291C8C-CC69-45BE-9235-421F7B12B0B2}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -12,5 +15,12 @@ Global
 		{DF01D949-82F0-4CCA-A094-903C8F30E691}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{DF01D949-82F0-4CCA-A094-903C8F30E691}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{DF01D949-82F0-4CCA-A094-903C8F30E691}.Release|Any CPU.Build.0 = Release|Any CPU
+		{6C291C8C-CC69-45BE-9235-421F7B12B0B2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{6C291C8C-CC69-45BE-9235-421F7B12B0B2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{6C291C8C-CC69-45BE-9235-421F7B12B0B2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{6C291C8C-CC69-45BE-9235-421F7B12B0B2}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
 	EndGlobalSection
 EndGlobal

BepInEx.AutoPlugin/AnalyzerReleases.Shipped.md

@@ -0,0 +1,3 @@
+; Shipped analyzer releases
+; https://github.com/dotnet/roslyn-analyzers/blob/main/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md
+

BepInEx.AutoPlugin/AnalyzerReleases.Unshipped.md

@@ -0,0 +1,8 @@
+; Unshipped analyzer release
+; https://github.com/dotnet/roslyn-analyzers/blob/main/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md
+
+### New Rules
+
+Rule ID | Category | Severity | Notes
+--------|----------|----------|-------
+AutoPlugin0001 | BepInEx.AutoPlugin | Warning | AutoPluginAnalyzer

BepInEx.AutoPlugin/Analyzers/PluginClassAnalyzer.cs

@@ -0,0 +1,104 @@
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace BepInEx.AutoPlugin.Analyzers;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class PluginClassAnalyzer : DiagnosticAnalyzer
+{
+    const string Category = "BepInEx.AutoPlugin";
+
+    public static readonly DiagnosticDescriptor PluginClassMustBeMarkedPartial = new(
+        "AutoPlugin0001",
+        "Plugin class must be marked partial",
+        "Plugin class '{0}' must be marked partial for use with AutoPlugin",
+        Category,
+        DiagnosticSeverity.Warning,
+        isEnabledByDefault: true
+    );
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } =
+        ImmutableArray.Create(PluginClassMustBeMarkedPartial);
+
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+        context.EnableConcurrentExecution();
+
+        context.RegisterSymbolAction(AnalyzeClassSymbol, SymbolKind.NamedType);
+    }
+
+    static void AnalyzeClassSymbol(SymbolAnalysisContext context)
+    {
+        var typeSymbol = (INamedTypeSymbol)context.Symbol;
+
+        bool isNotClassOrIsPartialClass = typeSymbol.DeclaringSyntaxReferences.All(
+            static syntaxReference =>
+                syntaxReference.GetSyntax() is not ClassDeclarationSyntax classSyntax
+                || classSyntax.Modifiers.Any(SyntaxKind.PartialKeyword)
+        );
+
+        if (isNotClassOrIsPartialClass)
+        {
+            return;
+        }
+
+        foreach (AttributeData attribute in typeSymbol.GetAttributes())
+        {
+            var attributeClass = attribute.AttributeClass;
+            if (attributeClass is null)
+            {
+                continue;
+            }
+
+            switch (attributeClass.Name)
+            {
+                case AutoPluginGenerator.BepInAutoPluginAttributeName:
+                    string attributeFullName = attributeClass.ToDisplayString();
+                    if (attributeFullName != AutoPluginGenerator.BepInAutoPluginAttributeFullName)
+                    {
+                        continue;
+                    }
+                    break;
+
+                case AutoPluginGenerator.PatcherAutoPluginAttributeName:
+                    attributeFullName = attributeClass.ToDisplayString();
+                    if (attributeFullName != AutoPluginGenerator.PatcherAutoPluginAttributeFullName)
+                    {
+                        continue;
+                    }
+                    break;
+
+                default:
+                    continue;
+            }
+
+            if (
+                attribute.ApplicationSyntaxReference?.GetSyntax()
+                is not AttributeSyntax attributeSyntax
+            )
+            {
+                continue;
+            }
+
+            if (
+                attributeSyntax.Parent is not AttributeListSyntax attributeList
+                || attributeList.Parent is not ClassDeclarationSyntax classDeclaration
+            )
+            {
+                continue;
+            }
+
+            var diagnostic = Diagnostic.Create(
+                PluginClassMustBeMarkedPartial,
+                classDeclaration.Identifier.GetLocation(),
+                classDeclaration.Identifier.ToString()
+            );
+
+            context.ReportDiagnostic(diagnostic);
+        }
+    }
+}