Annotate rule docs with violation markers and fix EPC20 category (#310)

Added explicit ❌ and ✅ markers to code examples in rule documentation files to clarify violations and correct usage. Also changed the category for EPC20 in DiagnosticDescriptors.cs from AsyncCategory to CodeSmellCategory for accuracy.

Author: SergeyTeplyakov

docs/Rules/EPC11.md

@@ -14,7 +14,7 @@ public class MyClass
     public override bool Equals(object obj)
     {
         // Suspicious: only using static members or not using 'this' instance
-        return SomeStaticProperty == 42;
+        return SomeStaticProperty == 42; // ❌ EPC11
     }
 }
 ```
@@ -27,7 +27,7 @@ public class Person
     public override bool Equals(object obj)
     {
         // Suspicious: parameter 'obj' is never used
-        return this.Name == "test";
+        return this.Name == "test"; // ❌ EPC11
     }
 }
 ```
@@ -49,7 +49,7 @@ public class Person
     {
         if (obj is Person other)
         {
-            return this.Name == other.Name;
+            return this.Name == other.Name; // ✅ Correct
         }
         return false;
     }

docs/Rules/EPC12.md

@@ -17,7 +17,7 @@ try
 catch (Exception ex)
 {
     // Only using ex.Message - this triggers the warning
-    Console.WriteLine(ex.Message);
+    Console.WriteLine(ex.Message); // ❌ EPC12
 }
 ```
 
@@ -34,8 +34,8 @@ try
 catch (Exception ex)
 {
     // Log the full exception object
-    Console.WriteLine(ex.ToString());
+    Console.WriteLine(ex.ToString()); // ✅ Correct
     // Or access the exception object directly
-    LogException(ex);
+    LogException(ex); // ✅ Correct
 }
 ```

docs/Rules/EPC13.md

@@ -14,13 +14,13 @@ public class Example
     public void ProcessData()
     {
         // Return value is ignored - this triggers the warning
-        GetImportantValue();
+        GetImportantValue(); // ❌ EPC13
         
         // String methods return new strings but result is ignored
-        "hello".ToUpper();
+        "hello".ToUpper(); // ❌ EPC13
         
         // Collection methods that return new collections
-        list.Where(x => x > 0);
+        list.Where(x => x > 0); // ❌ EPC13
     }
 
     public string GetImportantValue()
@@ -40,14 +40,14 @@ public class Example
     public void ProcessData()
     {
         // Store the result in a variable
-        var importantValue = GetImportantValue();
+        var importantValue = GetImportantValue(); // ✅ Correct
         
         // Use the result directly
-        var upperText = "hello".ToUpper();
+        var upperText = "hello".ToUpper(); // ✅ Correct
         Console.WriteLine(upperText);
 
         // Chain operations or store result
-        var filteredList = list.Where(x => x > 0).ToList();
+        var filteredList = list.Where(x => x > 0).ToList(); // ✅ Correct
     }
 
     public string GetImportantValue()

docs/Rules/EPC15.md

@@ -12,10 +12,10 @@ The analyzer warns when `ConfigureAwait(false)` should be used but is missing. T
 public async Task ProcessAsync()
 {
     // Missing ConfigureAwait(false) - this triggers the warning
-    await SomeAsyncMethod();
+    await SomeAsyncMethod(); // ❌ EPC15
     
     // Also missing ConfigureAwait(false)
-    var result = await GetDataAsync();
+    var result = await GetDataAsync(); // ❌ EPC15
 }
 ```
 
@@ -27,9 +27,9 @@ Add `ConfigureAwait(false)` to all await expressions:
 public async Task ProcessAsync()
 {
     // Add ConfigureAwait(false) to avoid capturing sync context
-    await SomeAsyncMethod().ConfigureAwait(false);
+    await SomeAsyncMethod().ConfigureAwait(false); // ✅ Correct
     
-    var result = await GetDataAsync().ConfigureAwait(false);
+    var result = await GetDataAsync().ConfigureAwait(false); // ✅ Correct
 }
 ```
 

docs/Rules/EPC16.md

@@ -14,7 +14,7 @@ public async Task ProcessAsync()
     SomeService service = GetService(); // might return null
     
     // Dangerous: if service is null, this returns null, and awaiting null throws NRE
-    await service?.ProcessAsync();
+    await service?.ProcessAsync(); // ❌ EPC16
 }
 ```
 
@@ -24,7 +24,7 @@ public async Task<string> GetDataAsync()
     var client = GetHttpClient(); // might return null
     
     // This will throw NRE if client is null
-    return await client?.GetStringAsync("http://example.com");
+    return await client?.GetStringAsync("http://example.com"); // ❌ EPC16
 }
 ```
 
@@ -40,11 +40,11 @@ public async Task ProcessAsync()
     // Option 1: Check for null first
     if (service != null)
     {
-        await service.ProcessAsync();
+        await service.ProcessAsync(); // ✅ Correct
     }
 
     // Option 2: Use null-coalescing with Task.CompletedTask
-    await (service?.ProcessAsync() ?? Task.CompletedTask);
+    await (service?.ProcessAsync() ?? Task.CompletedTask); // ✅ Correct
 }
 ```
 
@@ -59,6 +59,6 @@ public async Task<string> GetDataAsync()
         return null; // or throw, or return default value
     }
 
-    return await client.GetStringAsync("http://example.com");
+    return await client.GetStringAsync("http://example.com"); // ✅ Correct
 }
 ```

docs/Rules/EPC17.md

@@ -12,14 +12,14 @@ The analyzer warns against using async void delegates. Unlike async void methods
 public void SetupHandlers()
 {
     // Dangerous: async void delegate
-    SomeEvent += async () =>
+    SomeEvent += async () => // ❌ EPC17
     {
         await SomeAsyncMethod();
         // If this throws, it will crash the app
     };
 
     // Another dangerous pattern
-    Task.Run(async () =>
+    Task.Run(async () => // ❌ EPC17
     {
         await ProcessAsync();
         // Exceptions here are unhandled
@@ -31,7 +31,7 @@ public void SetupHandlers()
 public void RegisterCallback()
 {
     // Async void delegate in callback
-    RegisterCallback(async () =>
+    RegisterCallback(async () => // ❌ EPC17
     {
         await DoWorkAsync();
     });

docs/Rules/EPC18.md

@@ -17,13 +17,13 @@ public async Task<string> GetDataAsync()
 public void ProcessData()
 {
     // Missing await - Task<string> converted to string
-    string result = GetDataAsync(); // This will be "System.Threading.Tasks.Task`1[System.String]"
+    string result = GetDataAsync(); // ❌ EPC18 - This will be "System.Threading.Tasks.Task`1[System.String]"
     
     // In string interpolation
-    Console.WriteLine($"Result: {GetDataAsync()}"); // Prints task type, not result
+    Console.WriteLine($"Result: {GetDataAsync()}"); // ❌ EPC18 - Prints task type, not result
     
     // In concatenation
-    string message = "Data: " + GetDataAsync(); // Concatenates with task type
+    string message = "Data: " + GetDataAsync(); // ❌ EPC18 - Concatenates with task type
 }
 ```
 
@@ -40,12 +40,12 @@ public async Task<string> GetDataAsync()
 public async Task ProcessData()
 {
     // Properly await the task
-    string result = await GetDataAsync(); // Now gets "Hello World"
+    string result = await GetDataAsync(); // ✅ Correct - Now gets "Hello World"
     
     // In string interpolation
-    Console.WriteLine($"Result: {await GetDataAsync()}"); // Prints actual result
+    Console.WriteLine($"Result: {await GetDataAsync()}"); // ✅ Correct - Prints actual result
     
     // In concatenation
-    string message = "Data: " + await GetDataAsync(); // Concatenates with actual result
+    string message = "Data: " + await GetDataAsync(); // ✅ Correct - Concatenates with actual result
 }
 ```

docs/Rules/EPC19.md

@@ -14,7 +14,7 @@ public class MyService
     public void StartOperation(CancellationToken cancellationToken)
     {
         // Registration is not stored - potential memory leak
-        cancellationToken.Register(() => 
+        cancellationToken.Register(() =>  // ❌ EPC19
         {
             Console.WriteLine("Operation cancelled");
         });
@@ -26,7 +26,7 @@ public class MyService
 public async Task ProcessAsync(CancellationToken token)
 {
     // Registration result is ignored
-    token.Register(OnCancellation);
+    token.Register(OnCancellation); // ❌ EPC19
     
     await DoWorkAsync();
 }
@@ -49,7 +49,7 @@ public class MyService : IDisposable
     public void StartOperation(CancellationToken cancellationToken)
     {
         // Store the registration
-        _registration = cancellationToken.Register(() => 
+        _registration = cancellationToken.Register(() =>  // ✅ Correct
         {
             Console.WriteLine("Operation cancelled");
         });
@@ -58,7 +58,7 @@ public class MyService : IDisposable
     public void Dispose()
     {
         // Dispose the registration to prevent memory leaks
-        _registration.Dispose();
+        _registration.Dispose(); // ✅ Correct
     }
 }
 ```
@@ -67,21 +67,21 @@ public class MyService : IDisposable
 public async Task ProcessAsync(CancellationToken token)
 {
     // Store registration and dispose in finally block
-    var registration = token.Register(OnCancellation);
+    var registration = token.Register(OnCancellation); // ✅ Correct
     try
     {
         await DoWorkAsync();
     }
     finally
     {
-        registration.Dispose();
+        registration.Dispose(); // ✅ Correct
     }
 }
 
 // Or use using statement
 public async Task ProcessAsync(CancellationToken token)
 {
-    using var registration = token.Register(OnCancellation);
+    using var registration = token.Register(OnCancellation); // ✅ Correct
     await DoWorkAsync();
     // registration automatically disposed here
 }

docs/Rules/EPC20.md

@@ -21,13 +21,13 @@ public void Example()
     var person = new Person { Name = "John", Age = 30 };
 
     // Using default ToString() - outputs "Person" instead of useful info
-    Console.WriteLine(person.ToString());
+    Console.WriteLine(person.ToString()); // ❌ EPC20
     
     // Implicit ToString() call
-    string personString = person;
+    string personString = person; // ❌ EPC20
     
     // In string interpolation
-    Console.WriteLine($"Person: {person}");
+    Console.WriteLine($"Person: {person}"); // ❌ EPC20
 }
 ```
 
@@ -42,7 +42,7 @@ public class Person
     public int Age { get; set; }
 
     // Custom ToString() implementation
-    public override string ToString()
+    public override string ToString() // ✅ Correct
     {
         return $"Person(Name: {Name}, Age: {Age})";
     }

docs/Rules/EPC23.md

@@ -16,10 +16,10 @@ public void Example()
     var hashSet = new HashSet<string> { "apple", "banana", "cherry" };
 
     // Inefficient: uses Enumerable.Contains (O(n) linear search)
-    bool found = hashSet.Contains("apple", StringComparer.OrdinalIgnoreCase);
+    bool found = hashSet.Contains("apple", StringComparer.OrdinalIgnoreCase); // ❌ EPC23
     
     // Also inefficient when using Enumerable.Contains explicitly
-    bool found2 = Enumerable.Contains(hashSet, "banana");
+    bool found2 = Enumerable.Contains(hashSet, "banana"); // ❌ EPC23
 }
 ```
 
@@ -33,14 +33,14 @@ public void Example()
     var hashSet = new HashSet<string> { "apple", "banana", "cherry" };
 
     // Efficient: uses HashSet.Contains (O(1) hash lookup)
-    bool found = hashSet.Contains("apple");
+    bool found = hashSet.Contains("apple"); // ✅ Correct
     
     // If you need custom comparison, create HashSet with comparer
     var caseInsensitiveSet = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
     {
         "apple", "banana", "cherry"
     };
-    bool found2 = caseInsensitiveSet.Contains("APPLE"); // O(1) with custom comparer
+    bool found2 = caseInsensitiveSet.Contains("APPLE"); // ✅ Correct - O(1) with custom comparer
 }
 ```