[Version 9.0] Feature support for module initializers

standard/attributes.md

@@ -496,6 +496,7 @@
 - `System.Runtime.CompilerServices.AsyncMethodBuilderAttribute` ([§23.5.5](attributes.md#2355-the-asyncmethodbuilder-attribute)), which is used to establish a task builder for an async method.
 - `System.Runtime.CompilerServices.CallerLineNumberAttribute` ([§23.5.6.2](attributes.md#23562-the-callerlinenumber-attribute)), `System.Runtime.CompilerServices.CallerFilePathAttribute` ([§23.5.6.3](attributes.md#23563-the-callerfilepath-attribute)), and `System.Runtime.CompilerServices.CallerMemberNameAttribute` ([§23.5.6.4](attributes.md#23564-the-callermembername-attribute)), which are used to supply information about the calling context to optional parameters.
 - `System.Runtime.CompilerServices.EnumeratorCancellationAttribute` ([§23.5.8](attributes.md#2358-the-enumeratorcancellation-attribute)), which is used to specify parameter for the cancellation token in an asynchronous iterator.
+- `System.Runtime.CompilerServices.ModuleInitializer` (§module-init-attr), which is used to mark a method as a module initializer.
 
 The Nullable static analysis attributes ([§23.5.7](attributes.md#2357-code-analysis-attributes)) can improve the correctness of warnings generated for nullabilities and null states ([§8.9.5](types.md#895-nullabilities-and-null-states)).
 
@@ -953,11 +954,11 @@
 > ```csharp
 > #nullable enable
 > public class X
 > {
 >     private void ThrowIfNull([DoesNotReturnIf(true)] bool isNull, string argumentName)
 >     {
 >         if (!isNull)
 >         {
 >             throw new ArgumentException(argumentName, $"argument {argumentName} can't be null");
 >         }
 >     }
@@ -1003,7 +1004,7 @@
 >
 > <!-- Example: {template:"code-in-class-lib", name:"NotNullAttribute"} -->
 > ```csharp
 > #nullable enable
 > public static void ThrowWhenNull([NotNull] object? value, string valueExpression = "") =>
 >     _ = value ?? throw new ArgumentNullException(valueExpression);
 >
@@ -1085,7 +1086,7 @@
 >         }
 >     }
 > }
 >
 > static async IAsyncEnumerable<string> GetStringsAsync([EnumeratorCancellation] CancellationToken token)
 > {
 >     for (int i = 0; i < 10; i++)
@@ -1099,6 +1100,22 @@
 >
 > *end example*
 
+### §module-init-attr The ModuleInitializer attribute
+
+The attribute `ModuleInitializer` is used to mark a method as a ***module initializer***. Such a method is called during initialization of the containing module. A module may have multiple initializers, which are called in an implementation-defined order.
+
+There are no limitations on what code is permitted in a module initializer.
+
+A module initializer shall have the following characteristics:
+
+- The *method_modifier* `static`.
+- No *parameter_list*.
+- A *return_type* of `void`.
+- No *type_parameter_list*.
+- Not be declared inside a *class_declaration* having a *type_parameter_list*.
+- Be accessible from the containing module (that is, have an access modifier `internal` or `public`).
+- Not be a local function.
+
 ## 23.6 Attributes for interoperation
 
 For interoperation with other languages, an indexer may be implemented using indexed properties. If no `IndexerName` attribute is present for an indexer, then the name `Item` is used by default. The `IndexerName` attribute enables a developer to override this default and specify a different name.

standard/portability-issues.md

@@ -44,6 +44,7 @@ A conforming implementation is required to document its choice of behavior in ea
 1. The impact of thread termination when a thread has no handler for an exception, and the thread is itself terminated. ([§13.10.6](statements.md#13106-the-throw-statement))
 1. The mechanism by which linkage to an external method is achieved. ([§15.6.8](classes.md#1568-external-methods))
 1. The impact of thread termination when no matching `catch` clause is found for an exception and the code that initially started that thread is reached. ([§22.4](exceptions.md#224-how-exceptions-are-handled)).
+1. The order of execution of module initializers in a module (§module-init-attr).
 1. An execution environment may provide additional attributes that affect the execution of a C# program. ([§23.5.1](attributes.md#2351-general))
 1. The mappings between pointers and integers. ([§24.5.1](unsafe-code.md#2451-general))
 1. The effect of applying the unary `*` operator to a `null` pointer. ([§24.6.2](unsafe-code.md#2462-pointer-indirection))

standard/standard-library.md

@@ -190,7 +190,7 @@
     public class NullReferenceException : Exception
     {
         public NullReferenceException();
         public NullReferenceException(string? message);
         public NullReferenceException(string? message, Exception? innerException);
     }
 
@@ -238,7 +238,7 @@
     public sealed class StackOverflowException : Exception
     {
         public StackOverflowException();
         public StackOverflowException(string? message);
         public StackOverflowException(string? message, Exception? innerException);
     }
 
@@ -405,7 +405,7 @@
     public class OperationCanceledException : Exception
     {
         public OperationCanceledException();
         public OperationCanceledException(string? message);
         public OperationCanceledException(string? message, Exception? innerException);
     }
 
@@ -678,7 +678,7 @@
     }
 
     public interface IAsyncEnumerable<out T>
     {
         IAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken token = default);
     }
 
@@ -816,6 +816,12 @@
         void OnCompleted(Action continuation);
     }
 
+    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
+    public sealed class ModuleInitializerAttribute : Attribute
+    {
+        public ModuleInitializerAttribute() { }
+    }
+
     public readonly struct TaskAwaiter : ICriticalNotifyCompletion,
         INotifyCompletion
     {
@@ -1367,6 +1373,7 @@
 - `global::System.Runtime.CompilerServices.ICriticalNotifyCompletion`
 - `global::System.Runtime.CompilerServices.IndexerNameAttribute`
 - `global::System.Runtime.CompilerServices.INotifyCompletion`
+- `global::System.Runtime.CompilerServices.ModuleInitializerAttribute`
 - `global::System.Runtime.CompilerServices.TaskAwaiter`
 - `global::System.Runtime.CompilerServices.TaskAwaiter<T>`
 - `global::System.Runtime.CompilerServices.ValueTaskAwaiter`