Docs: defining Akka.Analyzer rules (akkadotnet#7039)

* defining Akka.Analyzer rules

These will be shown from the tooltips inside Visual Studio whenever an error is flagged.

* attempting to debug Akka.Persistence.TestKit.Tests

* Revert "attempting to debug Akka.Persistence.TestKit.Tests"

This reverts commit df57633.

* added AK1001.md page

* added `AK2000`

* added links to all rules to index

* added TOC for rules

* fixed markdown linting issues

docs/articles/actors/dependency-injection.md

@@ -1,6 +1,6 @@
 ---
 uid: dependency-injection
-title: Dependency injection
+title: Dependency Injection Support in Akka.NET
 ---
 # Dependency Injection
 

docs/articles/debugging/akka-analyzers.md

@@ -0,0 +1,18 @@
+---
+uid: akka-analyzers
+title: Akka.Analyzers - Roslyn Analyzers and Code Fixes for Akka.NET
+---
+
+# Akka.Analyzers
+
+As of Akka.NET v1.5.15 we now include [Akka.Analyzers](https://github.com/akkadotnet/akka.analyzers) as a package dependency for the core Akka library, which means any projects that reference anything depending on [`Akka`](https://www.nuget.org/packages/Akka) will automatically pull in all of Akka.Analyzer's rules and code fixes.
+
+Akka.Analyzer is a [Roslyn Analysis and Code Fix](https://learn.microsoft.com/en-us/visualstudio/extensibility/getting-started-with-roslyn-analyzers) package, which means that it leverages the .NET compiler platform ("Roslyn") to detect Akka.NET-specific anti-patterns and problems during _compilation_, rather than at run-time.
+
+## Supported Rules
+
+| Id     | Title                                                  | Severity | Category     |
+|--------|--------------------------------------------------------|----------|--------------|
+| [AK1000](xref:AK1000) | Do not use `new` to create actors.                     | Error    | Actor Design |
+| [AK1001](xref:AK1001) | Should always close over `Sender` when using `PipeTo`. | Error    | Actor Design |
+| [AK2000](xref:AK2000) | Do not use `Ask` with `TimeSpan.Zero` for timeout.     | Error    | API Usage    |

docs/articles/debugging/rules/AK1000.md

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+---
+uid: AK1000
+title: Akka.Analyzers Rule AK1000 - "Do not use `new` to create actors"
+---
+
+# AK1000 - Error
+
+Do not use the `new` keyword to create Akka.NET actors.
+
+## Cause
+
+A class inheriting from [`Akka.Actor.ActorBase`](xref:Akka.Actor.ActorBase) or one of its descendants was instantiated directly via the `new` keyword, which is illegal. Actors can only be instantiated inside a [`Props.Create` method](xref:Akka.Actor.Props) or via an [`IIndirectActorProducer`](xref:Akka.Actor.IIndirectActorProducer) implementation (such as [`Akka.DependencyInjection`](xref:dependency-injection).)
+
+An example:
+
+```csharp
+using Akka.Actor;
+
+class MyActor : ActorBase {
+    protected override bool Receive(object message) {
+        return true;
+    }
+}
+
+class Test
+{
+    void Method()
+    {
+        MyActor actorInstance = new MyActor(); // not supported by Akka.NET
+    }
+}
+```
+
+## Resolution
+
+The correct way to get a reference back to an actor is to wrap your actor's constructor call inside a `Props.Create` method and then pass that into either [`ActorSystem.ActorOf`](xref:Akka.Actor.ActorSystem) (when creating a top-level actor) or [`Context.ActorOf`](xref:Akka.Actor.IActorRefFactory#Akka_Actor_IActorRefFactory_ActorOf_Akka_Actor_Props_System_String_) (when creating a child actor.)
+
+Here's an example below:
+
+```csharp
+using Akka.Actor;
+
+class MyActor : ReceiveActor {
+    private readonly string _name;
+    private readonly int _myVar;
+
+    public MyActor(string name, int myVar){
+        _name = name;
+        _myVar = myVar;
+        ReceiveAny(_ => {
+            Sender.Tell(_name + _myVar);
+        });
+    }
+}
+
+class Test
+{
+    void Method()
+    {
+        // obviously, don't create a new ActorSystem every time - this is just an example.
+        ActorSystem sys = ActorSystem.Create("MySys");
+        Akka.Actor.Props props = Akka.Actor.Props.Create(() => new MyActor("foo", 1));
+        IActorRef realActorInstance = sys.ActorOf(props);
+    }
+}
+```

docs/articles/debugging/rules/AK1001.md

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+---
+uid: AK1001
+title: Akka.Analyzers Rule AK1001 - "Should always close over `Sender` when using `PipeTo`"
+---
+
+# AK1000 - Error
+
+You should always close over [`Context.Sender`](xref:Akka.Actor.IActorContext#Akka_Actor_IActorContext_Sender) when using [`PipeTo`](xref:Akka.Actor.PipeToSupport#Akka_Actor_PipeToSupport_PipeTo_System_Threading_Tasks_Task_Akka_Actor_ICanTell_Akka_Actor_IActorRef_System_Func_System_Object__System_Func_System_Exception_System_Object__)
+
+## Cause
+
+When using `PipeTo`, you must always close over `Sender` to ensure that the actor's `Sender` property is captured at the time you're scheduling the `PipeTo`, as this value may change asynchronously.
+
+This is a concurrent programming problem: `PipeTo` will be evaluated and executed at some point in the future because it's an asynchronous continuation, therefore the `Context.Sender` property, which is _mutable and changes each time the original actor processes a message_, may change.
+
+An example:
+
+```csharp
+using Akka.Actor;
+using System.Threading.Tasks;
+using System;
+
+public sealed class MyActor : UntypedActor{
+
+    protected override void OnReceive(object message){
+        async Task<int> LocalFunction(){
+            await Task.Delay(10);
+            return message.ToString().Length;
+        }
+
+        // potentially unsafe use of Context.Sender
+        LocalFunction().PipeTo(Sender); 
+    }
+}
+```
+
+## Resolution
+
+To avoid this entire category of problem, we should close over the `Context.Sender` property in a local variable.
+
+Here's an example below:
+
+```csharp
+using Akka.Actor;
+using System.Threading.Tasks;
+using System;
+
+public sealed class MyActor : UntypedActor{
+
+    protected override void OnReceive(object message){
+        async Task<int> LocalFunction(){
+            await Task.Delay(10);
+            return message.ToString().Length;
+        }
+
+        var sender = Sender;
+        LocalFunction().PipeTo(sender); 
+    }
+}
+```

docs/articles/debugging/rules/AK2000.md

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+---
+uid: AK2000
+title: Akka.Analyzers Rule AK2000 - "Do not use `Ask` with `TimeSpan.Zero` for timeout."
+---
+
+# AK2000 - Error
+
+Do not use [`Ask<T>`](xref:Akka.Actor.Futures#Akka_Actor_Futures_Ask__1_Akka_Actor_ICanTell_System_Object_System_Nullable_System_TimeSpan__) or [`Ask`](xref:Akka.Actor.Futures#Akka_Actor_Futures_Ask_Akka_Actor_ICanTell_System_Object_System_Nullable_System_TimeSpan__) with `TimeSpan.Zero` for timeout.
+
+## Cause
+
+When using `Ask`, you must always specify a timeout value greater than `TimeSpan.Zero` otherwise the process might deadlock. See [https://github.com/akkadotnet/akka.net/issues/6131](https://github.com/akkadotnet/akka.net/issues/6131) for details.
+
+> [!IMPORTANT]
+> This rule is not exhaustive - Roslyn can't scan every possible variable value at compilation time, so it's still possible to pass in a `TimeSpan.Zero` value even with this rule present.
+
+An example:
+
+```csharp
+using Akka.Actor;
+using System.Threading.Tasks;
+using System;
+
+public static class MyActorCaller{
+ public static Task<string> Call(IActorRef actor){
+     return actor.Ask<string>(""hello"", TimeSpan.Zero);
+ }
+}
+```
+
+## Resolution
+
+The right way to fix this issue is to pass in a non-zero value or to use the `Ask<T>` overload that accepts a `CancellationToken`.
+
+Here's an example below:
+
+```csharp
+using Akka.Actor;
+using System.Threading.Tasks;
+using System;
+
+public static class MyActorCaller{
+    public static Task<string> Call(IActorRef actor){
+        return actor.Ask<string>(""hello"", TimeSpan.FromSeconds(1));
+    }
+}
+```

docs/articles/debugging/rules/toc.yml

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+- name: AK1000
+  href: AK1000.md
+- name: AK1001
+  href: AK1001.md
+- name: AK2000
+  href: AK2000.md

docs/articles/debugging/toc.yml

@@ -0,0 +1,4 @@
+- name: Akka.NET Roslyn Analyzers
+  href: akka-analyzers.md
+- name: Analysis Rules
+  href: rules/toc.yml

docs/articles/toc.yml

@@ -24,5 +24,7 @@
   href: configuration/toc.yml
 - name: Serialization
   href: serialization/toc.yml
+- name: Debugging Akka.NET
+  href: debugging/toc.yml
 - name: Examples
   href: examples.md