Remove restrictions on async methods

Where applicable, remove restrictions on async methods and await statements.

Author: BillWagner

docs/csharp/language-reference/builtin-types/ref-struct.md

@@ -13,7 +13,7 @@ You can use the `ref` modifier in the declaration of a [structure type](struct.m
 - A `ref struct` can't be boxed to <xref:System.ValueType?displayProperty=nameWithType> or <xref:System.Object?displayProperty=nameWithType>.
 - A `ref struct` can't be a type argument.
 - A `ref struct` variable can't be captured by a [lambda expression](../operators/lambda-expressions.md) or a [local function](../../programming-guide/classes-and-structs/local-functions.md).
-- A `ref struct` variable can't be used in an [`async`](../keywords/async.md) method. However, you can use `ref struct` variables in synchronous methods, for example, in methods that return <xref:System.Threading.Tasks.Task> or <xref:System.Threading.Tasks.Task%601>.
+- A `ref struct` variable can't be used in the same block as the [`await`](../operators/await.md) expression in an [`async`](../keywords/async.md) method. Prior to C# 13, `ref struct` variables can't be used in an `async` method. However, you can use `ref struct` variables in synchronous methods, for example, in methods that return <xref:System.Threading.Tasks.Task> or <xref:System.Threading.Tasks.Task%601>.
 - Prior to C# 13, a `ref struct` variable can't be used in [iterators](../../iterators.md). Beginning with C# 13, `ref struct` types and `ref` locals may be used in iterators, provided they are not in code segments with the `yield return` statement.
 
 You can define a disposable `ref struct`. To do that, ensure that a `ref struct` fits the [disposable pattern](~/_csharplang/proposals/csharp-8.0/using.md#pattern-based-using). That is, it has an instance `Dispose` method, which is accessible, parameterless and has a `void` return type. You can use the [using statement or declaration](../statements/using.md) with an instance of a disposable `ref struct`.

docs/csharp/language-reference/compiler-messages/cs1996.md

@@ -1,7 +1,7 @@
 ---
 description: "Compiler Error CS1996"
 title: "Compiler Error CS1996"
-ms.date: 9/12/2022
+ms.date: 7/01/2024
 f1_keywords:
   - "CS1996"
 helpviewer_keywords:
@@ -33,6 +33,8 @@ public class C
 }
 ```
 
+This code still generates this error with C# 13, as the `await` is in the `lock` statement block.
+
 ## To correct this error
 
 Asynchronous code within a `lock` statement block is hard to implement reliably and even harder to implement in a general sense.  The C# compiler doesn't support doing this to avoid emitting code that will be prone to deadlocks.  Extracting the asynchronous code from the `lock` statement block will correct this error.  For example:

docs/csharp/language-reference/compiler-messages/cs4004.md

@@ -47,6 +47,8 @@ public static class C
 }
 ```
 
+This code generates an error in C# 13 because the `await` is in the `unsafe` block.
+
 The `ReverseText` method naively uses a background task to asynchronously create a new string in reverse order of a given string.
 
 ## To correct this error

docs/csharp/language-reference/compiler-messages/cs4013.md

@@ -11,7 +11,7 @@ helpviewer_keywords:
 
 Instance of type cannot be used inside a nested function, query expression, iterator block or async method
 
-Beginning with C# 13, `ref struct` types can be used in iterator methods, provided that they are not in scope during a `yield return` statement.
+Beginning with C# 13, `ref struct` types can be used in iterator methods, provided that they are not in scope during a `yield return` statement. 
 
 ## Example
 

docs/csharp/language-reference/compiler-messages/cs8177.md

@@ -1,7 +1,7 @@
 ---
 description: "Compiler Error CS8177"
 title: "Compiler Error CS8177"
-ms.date: 9/19/2022
+ms.date: 7/01/2024
 f1_keywords:
   - "CS8177"
 helpviewer_keywords:
@@ -15,7 +15,7 @@ To manage asynchronous state, `async` methods use a state machine, capturing var
 
 ## Example
 
- The following sample generates CS8177:
+ The following sample generates CS8177 in C# prior to C# 13:
 
 ```csharp
 // CS8177.cs (20,26)
@@ -49,7 +49,7 @@ class C
 
 ## To correct this error
 
-Changing the variable declaration to remove the `ref` modifier corrects this error:
+Changing the variable declaration to remove the `ref` modifier corrects this error. Or, you can upgrade to C# 13, which ships with .NET 9.
 
 ```csharp
 class C

docs/csharp/language-reference/compiler-messages/warning-waves.md

@@ -1,7 +1,7 @@
 ---
 title: "Compiler warning waves"
 description: "C# warning waves are optional warnings that can be reported on code where previously a warning wouldn't have been reported. They represent practices that could be harmful, or potentially elements that may be breaking changes in the future."
-ms.date: 05/11/2022
+ms.date: 07/01/2024
 f1_keywords:
   - "CS7023"
   - "CS8073"
@@ -50,6 +50,8 @@ The following code produces CS9123:
 
 :::code language="csharp" source="./snippets/WarningWaves/WaveEight.cs" id="NoAmpersand":::
 
+Beginning with C# 13, this code generates a compiler error.
+
 ## CS8981 - The type name only contains lower-cased ascii characters.
 
 *Warning wave 7*

docs/csharp/language-reference/keywords/method-parameters.md

@@ -79,7 +79,7 @@ When you use these modifiers, they describe how the argument is used:
 - `ref readonly` means the method reads, but can't write the value of the argument. The argument *should* be passed by reference.
 - `in` means the method reads, but can't write the value of the argument. The argument will be passed by reference or through a temporary variable.
 
-Properties aren't variables. They're methods, and can't be passed to `ref` parameters. You can't use the previous parameter modifiers in the following kinds of methods:
+You can't use the previous parameter modifiers in the following kinds of methods:
 
 - Async methods, which you define by using the [async](async.md) modifier.
 - Iterator methods, which include a [yield return](../statements/yield.md) or `yield break` statement.
@@ -91,6 +91,8 @@ Properties aren't variables. They're methods, and can't be passed to `ref` param
 - The `ref readonly` and `in` keywords can't be used unless the first argument is a `struct`.
 - The `ref readonly` and `in` keywords can't be used on any generic type, even when constrained to be a struct.
 
+Properties aren't variables. They're methods. Properties can't be arguments for `ref` parameters.
+
 ### `ref` parameter modifier
 
 To use a `ref` parameter, both the method definition and the calling method must explicitly use the `ref` keyword, as shown in the following example. (Except that the calling method can omit `ref` when making a COM call.)