Invoke Build Callbacks at Lifetime Scope Creation

nullabilitynotes.md

@@ -0,0 +1,105 @@
+
+# Notes on nullability
+
+ - Anywhere that we have a 'Try....' method, we now apply [NotNullWhen(returnValue: true)] on the out parameter.
+   This should probably be enforced via code review in the future.
+
+   ReflectionExtensions
+   ```
+
+    public static bool TryGetDeclaringProperty(this ParameterInfo pi, [NotNullWhen(returnValue: true)] out PropertyInfo? prop)
+
+   ```
+
+ - Null annotation attributes only inform the caller if used in a straight if declaration.
+
+    ResolutionExtensions.TryResolve
+
+ - Registration methods where we accept a 'limit' now constrain the limit to where T: notnull.
+
+   The only impact I can think of is if someone was using ``Nullable<int>`` as the limit for a service.
+
+   In addition, TryResolve is now constrained to 'class'.
+
+ - Types that overload == and != need to specify the overload parameters as nullable, otherwise we can't do null checks on those values.
+
+    Service
+    ```
+        /// <summary>
+        /// Implements the operator ==.
+        /// </summary>
+        /// <param name="left">The left operand.</param>
+        /// <param name="right">The right operand.</param>
+        /// <returns>The result of the operator.</returns>
+        public static bool operator ==(Service? left, Service? right)
+        {
+            return Equals(left, right);
+        }
+    ```
+
+ - Need to make 'optional' methods return TService? to indicate to the caller that the response may be null.
+
+ - Upgraded StyleCop analyzers to a beta version (for now), to understand nullable modifiers on arrays.
+
+ - The Roslyn compiler reports a class field as being uninitialized (and potentially null) if it can't tell it's been initialised at the end of the constructor.
+   This happens even if the constructor calls a method or property that always instantiates the field. So you can set 'default!' or 'null!' on the field to get round this (not ideal, but explainable).
+
+    ResolveOperation
+    ```
+        // _successfulActivations can never be null, but the roslyn compiler doesn't look deeper than
+        // the initial constructor methods yet.
+        private List<InstanceLookup> _successfulActivations = default!;
+    ```
+
+    DeferredCallbacks
+    ```
+        // _callback set to default! to get around initialisation detection problem in rosyln.
+        private Action<IComponentRegistry> _callback = default!;
+    ```
+
+   There are a couple of open rosyln issues that are related to this, some discussion about adding flow analysis to check that constructors
+   do in fact finish having initialised those properties.
+
+   This is also a massive pain whenever I have a class that I want to instantiate using 'Property' notation, e.g. DecoratorContext:
+
+   ```
+     private DecoratorContext()  // error on this line
+     {
+
+     }
+
+     internal static DecoratorContext Create(Type implementationType, Type serviceType, object implementationInstance)
+     {
+        var context = new DecoratorContext
+        {
+            ImplementationType = implementationType,
+            ServiceType = serviceType,
+            AppliedDecorators = new List<object>(0),
+            AppliedDecoratorTypes = new List<Type>(0),
+            CurrentInstance = implementationInstance
+        };
+        return context;
+     }
+
+
+   ```
+
+   https://github.com/dotnet/roslyn/issues/39291
+   https://github.com/dotnet/roslyn/issues/39090
+   https://github.com/dotnet/roslyn/issues/37975
+
+ - If a method is being passed as an expression for reflection only, it's better to mark the arguments as default! rather than
+   change the signature of the type:
+
+    FactoryGenerator
+    ```
+        // The explicit '!' default is ok because the code is never executed, it's just used by
+        // the expression tree.
+        private static readonly ConstructorInfo RequestConstructor
+            = ReflectionExtensions.GetConstructor(() => new ResolveRequest(default!, default!, default!));
+    ```
+
+ - In a couple of specific cases, some generic methods now need to state explicitly 'class' as a type constraint, where they didn't before; if I don't do that
+   then duplicate overloads for class and struct need to be defined to remove ambiguity.
+
+   RegistrationExtensions.RegisterDecorator

src/Autofac/Autofac.csproj

@@ -59,6 +59,11 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Compile Update="Builder\BuildCallbackServiceResources.Designer.cs">
+      <DesignTime>True</DesignTime>
+      <AutoGen>True</AutoGen>
+      <DependentUpon>BuildCallbackServiceResources.resx</DependentUpon>
+    </Compile>
     <Compile Update="Builder\RegistrationBuilderResources.Designer.cs">
       <DesignTime>True</DesignTime>
       <AutoGen>True</AutoGen>
@@ -267,6 +272,10 @@
   </ItemGroup>
 
   <ItemGroup>
+    <EmbeddedResource Update="Builder\BuildCallbackServiceResources.resx">
+      <Generator>ResXFileCodeGenerator</Generator>
+      <LastGenOutput>BuildCallbackServiceResources.Designer.cs</LastGenOutput>
+    </EmbeddedResource>
     <EmbeddedResource Update="Builder\RegistrationBuilderResources.resx">
       <Generator>ResXFileCodeGenerator</Generator>
       <LastGenOutput>RegistrationBuilderResources.Designer.cs</LastGenOutput>

src/Autofac/Builder/BuildCallbackManager.cs

@@ -0,0 +1,63 @@
+// This software is part of the Autofac IoC container
+// Copyright © 2019 Autofac Contributors
+// https://autofac.org
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+
+using System.Linq;
+using Autofac.Core;
+
+namespace Autofac.Builder
+{
+    internal static class BuildCallbackManager
+    {
+        private static readonly TypedService CallbackServiceType = new TypedService(typeof(BuildCallbackService));
+
+        private const string BuildCallbacksExecutedKey = nameof(BuildCallbacksExecutedKey);
+
+        /// <summary>
+        /// Executes the newly-registered build callbacks for a given scope/container..
+        /// </summary>
+        /// <param name="scope">The new scope/container.</param>
+        internal static void RunBuildCallbacks(ILifetimeScope scope)
+        {
+            var buildCallbackServices = scope.ComponentRegistry.RegistrationsFor(CallbackServiceType);
+
+            foreach (var srv in buildCallbackServices)
+            {
+                // Use the metadata to track whether we've executed already, to avoid issuing a resolve request.
+                if (srv.Metadata.ContainsKey(BuildCallbacksExecutedKey))
+                {
+                    continue;
+                }
+
+                var request = new ResolveRequest(CallbackServiceType, srv, Enumerable.Empty<Parameter>());
+                var component = scope.ResolveComponent(request) as BuildCallbackService;
+
+                srv.Metadata[BuildCallbacksExecutedKey] = true;
+
+                // Run the callbacks for the relevant scope.
+                component.Execute(scope);
+            }
+        }
+    }
+}

src/Autofac/Builder/BuildCallbackService.cs

@@ -0,0 +1,75 @@
+// This software is part of the Autofac IoC container
+// Copyright © 2019 Autofac Contributors
+// https://autofac.org
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Autofac.Builder
+{
+    /// <summary>
+    /// Represent a collection of callbacks that can be run after a container or scope is 'built'.
+    /// </summary>
+    internal class BuildCallbackService
+    {
+        private List<Action<ILifetimeScope>> _callbacks = new List<Action<ILifetimeScope>>();
+
+        /// <summary>
+        /// Add a callback to the set that will get executed.
+        /// </summary>
+        /// <param name="callback">The callback to run.</param>
+        public void AddCallback(Action<ILifetimeScope> callback)
+        {
+            if (callback == null) throw new ArgumentNullException(nameof(callback));
+
+            _callbacks.Add(callback);
+        }
+
+        public void Execute(ILifetimeScope scope)
+        {
+            if (scope == null) throw new ArgumentNullException(nameof(scope));
+
+            if (_callbacks == null)
+            {
+                throw new InvalidOperationException(BuildCallbackServiceResources.BuildCallbacksAlreadyRun);
+            }
+
+            try
+            {
+                foreach (var callback in _callbacks)
+                {
+                    callback(scope);
+                }
+            }
+            finally
+            {
+                // Clear the reference to the callbacks to release any held scopes (and function as a do-not-run flag)
+                // This object will be a singleton instance in the container/scope, so the initial function scopes that
+                // define the callbacks could be holding onto closure resources. We want the GC to take that back.
+                _callbacks = null;
+            }
+        }
+    }
+}