add experimental analyzer

src/UniTask.Analyzer/UniTaskAnalyzer.cs

@@ -0,0 +1,54 @@
+#pragma warning disable RS2008
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+using System.Collections.Immutable;
+using System.Threading;
+
+namespace UniTask.Analyzer
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class UniTaskAnalyzer : DiagnosticAnalyzer
+    {
+        private static readonly DiagnosticDescriptor Rule = new DiagnosticDescriptor(
+            id: "UNITASK001",
+            title: "UniTaskAnalyzer001: Must pass CancellationToken",
+            messageFormat: "Must pass CancellationToken",
+            category: "Usage",
+            defaultSeverity: DiagnosticSeverity.Error,
+            isEnabledByDefault: true,
+            description: "Pass CancellationToken or CancellationToken.None.");
+
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get { return ImmutableArray.Create(Rule); } }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+            context.EnableConcurrentExecution();
+
+            context.RegisterOperationAction(AnalyzeSymbol, OperationKind.Invocation);
+        }
+
+        private static void AnalyzeSymbol(OperationAnalysisContext context)
+        {
+            var token = context.Compilation.GetTypeByMetadataName(typeof(CancellationToken).FullName);
+            if (token == null) return;
+
+            if (context.Operation is IInvocationOperation invocation)
+            {
+                foreach (var arg in invocation.Arguments)
+                {
+                    if (arg.ArgumentKind == ArgumentKind.DefaultValue)
+                    {
+                        if (SymbolEqualityComparer.Default.Equals(arg.Parameter.Type, token))
+                        {
+                            var diagnostic = Diagnostic.Create(Rule, arg.Syntax.GetLocation());
+                            context.ReportDiagnostic(diagnostic);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}