New rule MA0129: Await task in using statements (#459)

README.md

@@ -144,5 +144,6 @@ If you are already using other analyzers, you can check [which rules are duplica
 |[MA0126](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0126.md)|Design|The list of log parameter types contains a duplicate|⚠️|✔️|❌|
 |[MA0127](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0127.md)|Usage|Use String.Equals instead of is pattern|⚠️|❌|❌|
 |[MA0128](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0128.md)|Usage|Use 'is' operator instead of SequenceEqual|ℹ️|✔️|✔️|
+|[MA0129](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0129.md)|Usage|Await task in using statement|⚠️|✔️|❌|
 
 <!-- rules -->

docs/README.md

@@ -128,6 +128,7 @@
 |[MA0126](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0126.md)|Design|The list of log parameter types contains a duplicate|<span title='Warning'>⚠️</span>|✔️|❌|
 |[MA0127](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0127.md)|Usage|Use String.Equals instead of is pattern|<span title='Warning'>⚠️</span>|❌|❌|
 |[MA0128](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0128.md)|Usage|Use 'is' operator instead of SequenceEqual|<span title='Info'>ℹ️</span>|✔️|✔️|
+|[MA0129](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0129.md)|Usage|Await task in using statement|<span title='Warning'>⚠️</span>|✔️|❌|
 
 # .editorconfig - default values
 
@@ -512,6 +513,9 @@ dotnet_diagnostic.MA0127.severity = none
 
 # MA0128: Use 'is' operator instead of SequenceEqual
 dotnet_diagnostic.MA0128.severity = suggestion
+
+# MA0129: Await task in using statement
+dotnet_diagnostic.MA0129.severity = warning
 ```
 
 # .editorconfig - all rules disabled
@@ -897,4 +901,7 @@ dotnet_diagnostic.MA0127.severity = none
 
 # MA0128: Use 'is' operator instead of SequenceEqual
 dotnet_diagnostic.MA0128.severity = none
+
+# MA0129: Await task in using statement
+dotnet_diagnostic.MA0129.severity = none
 ```

docs/Rules/MA0129.md

@@ -0,0 +1,10 @@
+# MA0129 - Await task in using statement
+
+A `Task` doesn't need to be disposed. When used in a `using` statement, most of the time, developers forgot to await it.
+
+````
+Task<IDiposable> t = ...;
+using(t) { } // non-compliant
+
+using(await t) { } // ok
+````

src/Meziantou.Analyzer/RuleIdentifiers.cs

@@ -131,6 +131,7 @@ internal static class RuleIdentifiers
     public const string LoggerParameterType_DuplicateRule = "MA0126";
     public const string UseStringEqualsInsteadOfIsPattern = "MA0127";
     public const string UseIsPatternInsteadOfSequenceEqual = "MA0128";
+    public const string TaskInUsing = "MA0129";
 
     public static string GetHelpUri(string identifier)
     {

src/Meziantou.Analyzer/Rules/TaskInUsingAnalyzer.cs

@@ -0,0 +1,93 @@
+using System;
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+namespace Meziantou.Analyzer.Rules;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class TaskInUsingAnalyzer : DiagnosticAnalyzer
+{
+    private static readonly DiagnosticDescriptor s_rule = new(
+        RuleIdentifiers.TaskInUsing,
+        title: "Await task in using statement",
+        messageFormat: "Await task in using statement",
+        RuleCategories.Usage,
+        DiagnosticSeverity.Warning,
+        isEnabledByDefault: true,
+        description: "",
+        helpLinkUri: RuleIdentifiers.GetHelpUri(RuleIdentifiers.TaskInUsing));
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(s_rule);
+
+    public override void Initialize(AnalysisContext context)
+    {
+        context.EnableConcurrentExecution();
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.Analyze);
+
+        context.RegisterCompilationStartAction(ctx =>
+        {
+            var taskSymbol = ctx.Compilation.GetBestTypeByMetadataName("System.Threading.Tasks.Task");
+            if (taskSymbol == null)
+                return;
+
+            var analyzerContext = new AnalyzerContext(taskSymbol);
+            ctx.RegisterOperationAction(analyzerContext.AnalyzeUsing, OperationKind.Using);
+            ctx.RegisterOperationAction(analyzerContext.AnalyzeUsingDeclaration, OperationKind.UsingDeclaration);
+        });
+    }
+
+    private sealed class AnalyzerContext
+    {
+        private INamedTypeSymbol _taskSymbol;
+
+        public AnalyzerContext(INamedTypeSymbol taskSymbol)
+        {
+            _taskSymbol = taskSymbol;
+        }
+
+        public void AnalyzeUsing(OperationAnalysisContext context)
+        {
+            var operation = (IUsingOperation)context.Operation;
+            AnalyzeResource(context, operation.Resources);
+        }
+
+        internal void AnalyzeUsingDeclaration(OperationAnalysisContext context)
+        {
+            var operation = (IUsingDeclarationOperation)context.Operation;
+            AnalyzeResource(context, operation.DeclarationGroup);
+        }
+
+        private void AnalyzeResource(OperationAnalysisContext context, IOperation? operation)
+        {
+            if (operation == null)
+                return;
+
+            if (operation is IVariableDeclarationGroupOperation variableDeclarationGroupOperation)
+            {
+                foreach (var declaration in variableDeclarationGroupOperation.Declarations)
+                {
+                    AnalyzeResource(context, declaration);
+                }
+
+                return;
+            }
+
+            if (operation is IVariableDeclarationOperation variableDeclarationOperation)
+            {
+                foreach (var declarator in variableDeclarationOperation.Declarators)
+                {
+                    AnalyzeResource(context, declarator.Initializer?.Value);
+                }
+                return;
+            }
+
+            operation = operation.UnwrapImplicitConversionOperations();
+            if (operation.Type != null && operation.Type.IsOrInheritFrom(_taskSymbol))
+            {
+                context.ReportDiagnostic(s_rule, operation);
+            }
+        }
+    }
+}

tests/Meziantou.Analyzer.Test/Rules/TaskInUsingAnalyzerTests.cs

@@ -0,0 +1,92 @@
+using System.Threading.Tasks;
+using Meziantou.Analyzer.Rules;
+using Microsoft.CodeAnalysis;
+using TestHelper;
+using Xunit;
+
+namespace Meziantou.Analyzer.Test.Rules;
+public sealed class TaskInUsingAnalyzerTests
+{
+    private static ProjectBuilder CreateProjectBuilder()
+    {
+        return new ProjectBuilder()
+            .WithOutputKind(OutputKind.ConsoleApplication)
+            .WithAnalyzer<TaskInUsingAnalyzer>();
+    }
+
+    [Fact]
+    public async Task SingleTaskInUsing()
+    {
+        const string SourceCode = """
+            using System.Threading.Tasks;
+            
+            Task t = null;
+            using ([|t|]) { }
+            """;
+
+        await CreateProjectBuilder()
+              .WithSourceCode(SourceCode)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task SingleTaskAssignedInUsing()
+    {
+        const string SourceCode = """
+            using System.Threading.Tasks;
+            
+            Task t = null;
+            using (var a = [|t|]) { }
+            """;
+
+        await CreateProjectBuilder()
+              .WithSourceCode(SourceCode)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task MultipleTasksInUsing()
+    {
+        const string SourceCode = """
+            using System.Threading.Tasks;
+            
+            Task t1 = null;
+            Task t2 = null;
+            using (Task a = [|t1|], b = [|t2|]) { }
+            """;
+
+        await CreateProjectBuilder()
+              .WithSourceCode(SourceCode)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task TaskOfTInUsing()
+    {
+        const string SourceCode = """
+            using System.Threading.Tasks;
+
+            Task<System.IDisposable> t1 = null;
+            using ([|t1|]) { }
+            """;
+
+        await CreateProjectBuilder()
+              .WithSourceCode(SourceCode)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task TaskOfTInUsingStatement()
+    {
+        const string SourceCode = """
+            using System.Threading.Tasks;
+
+            Task<System.IDisposable> t1 = null;
+            using var a = [|t1|];
+            """;
+
+        await CreateProjectBuilder()
+              .WithSourceCode(SourceCode)
+              .ValidateAsync();
+    }
+}