Add, update messages in dotnet/roslyn#73567

The PR for `ref struct` interfaces added new compiler error and warning messages. It also updates a few messages. This commit creates the stubs for the new messages, and updates the text for updated messages.

Author: BillWagner

docs/csharp/language-reference/compiler-messages/feature-version-errors.md

@@ -53,6 +53,7 @@ f1_keywords:
   - "CS9194"
   - "CS9202"
   - "CS9211"
+  - "CS9240"
 helpviewer_keywords:
   - "CS0171"
   - "CS0188"
@@ -105,6 +106,7 @@ helpviewer_keywords:
   - "CS9194"
   - "CS9202"
   - "CS9211"
+  - "CS9240"
 ms.date: 11/02/2023
 ---
 # Resolve warnings related to language features and versions
@@ -146,6 +148,7 @@ That's be design. The text closely matches the text of the compiler error / warn
 - **CS9194**: *Argument may not be passed with the `ref` keyword. To pass `ref` arguments to `in` parameters, upgrade to language version 12 or greater.*
 - **CS9202**: *Feature is not available in C# 12.0. Please use newer language version*
 - **CS9211**: *The diagnosticId argument to the 'Experimental' attribute must be a valid identifier.*
+- **CS9240**: *Target runtime doesn't support by-ref-like generics.*
 
 In addition, the following errors and warnings relate to struct initialization changes in recent versions:
 

docs/csharp/language-reference/compiler-messages/ref-modifiers-errors.md

@@ -183,8 +183,8 @@ That's by design. The text closely matches the text of the compiler error / warn
 - [**CS9078**](#ref-safety-violations): *Cannot return by reference a member of parameter through a `ref` parameter; it can only be returned in a return statement*
 - [**CS9079**](#ref-safety-violations): *Cannot ref-assign because source can only escape the current method through a return statement.*
 - [**CS9096**](#ref-safety-violations): *Cannot ref-assign because source has a wider value escape scope than destination allowing assignment through source of values with narrower escapes scopes than destination.*
-- [**CS9101**](#unscoped-ref-restrictions): *UnscopedRefAttribute can only be applied to struct instance methods and properties, and cannot be applied to constructors or init-only members.*
-- [**CS9102**](#unscoped-ref-restrictions): *UnscopedRefAttribute cannot be applied to an interface implementation.*
+- [**CS9101**](#unscoped-ref-restrictions): *UnscopedRefAttribute can only be applied to struct or virtual interface instance methods and properties, and cannot be applied to constructors or init-only members.*
+- [**CS9102**](#unscoped-ref-restrictions): *UnscopedRefAttribute cannot be applied to an interface implementation  because implemented member doesn't have this attribute.*
 - [**CS9104**](#reference-variable-restrictions): *A `using` statement resource of type cannot be used in async methods or async lambda expressions.*
 - [**CS9190**](#incorrect-syntax): *`readonly` modifier must be specified after `ref`.*
 - [**CS9199**](#reference-variable-restrictions): *A `ref readonly` parameter cannot have the Out attribute.*
@@ -285,8 +285,8 @@ To fix the error, remove the reference variable where it isn't allowed:
 
 The `unscoped` qualifier on `ref` parameters isn't allowed in some locations:
 
-- **CS9101**:  *UnscopedRefAttribute can only be applied to struct instance methods and properties, and cannot be applied to constructors or  or init-only members.*
-- **CS9102**:  *UnscopedRefAttribute cannot be applied to an interface implementation.*
+- **CS9101**:  *UnscopedRefAttribute can only be applied to struct instance or virtual interface methods and properties, and cannot be applied to constructors or  or init-only members.*
+- **CS9102**:  *UnscopedRefAttribute cannot be applied to an interface implementation because implemented member doesn't have this attribute..*
 
 You must remove the `unscoped` modifier on the parameter declaration that caused the error.
 

docs/csharp/language-reference/compiler-messages/ref-struct-errors.md

@@ -0,0 +1,40 @@
+---
+title: Errors and warnings associated with `ref struct` types
+description: Learn about errors and warnings related to `ref struct` types. The compiler enforces several restrictions on `ref struct` types to enforce ref safety rules
+f1_keywords:
+  - "CS8343"
+  - "CS8344"
+  - "CS9241"
+  - "CS9242"
+  - "CS9243"
+  - "CS9244"
+  - "CS9245"
+  - "CS9246"
+  - "CS9247"
+helpviewer_keywords:
+  - "CS8343"
+  - "CS8344"
+  - "CS9241"
+  - "CS9242"
+  - "CS9243"
+  - "CS9244"
+  - "CS9245"
+  - "CS9246"
+  - "CS9247"
+ms.date: 07/30/2024
+---
+# Errors and warnings associated with reference parameters, variables, and returns
+
+- [**CS8343**](#ref-struct-interface-implementations): *`ref structs` cannot implement interfaces*
+- [**CS8344**](#ref-struct-interface-implementations): *`foreach` statement cannot operate on enumerators in async or iterator methods because type is a `ref struct` or a type parameter that allows `ref struct`.*
+- [**CS9241**](#ref-struct-interface-implementations): *'ref struct' is already specified.*
+- [**CS9242**](#ref-struct-interface-implementations): *The 'allows' constraint clause must be the last constraint specified.*
+- [**CS9243**](#ref-struct-interface-implementations): *Cannot allow ref structs for a type parameter known from other constraints to be a class.*
+- [**CS9244**](#ref-struct-interface-implementations): *The type may not be a `ref struct` or a type parameter allowing ref structs in order to use it as parameter in the generic type or method.*
+- [**CS9245**](#ref-struct-interface-implementations): *Type cannot implement interface member for `ref struct` type.*
+- [**CS9246**](#ref-struct-interface-implementations): *A non-virtual instance interface member cannot be accessed on a type parameter that allows ref struct.*
+- [**CS9247**](#ref-struct-interface-implementations): *foreach statement cannot operate on enumerators of type '{0}' because it is a type parameter that allows ref struct and it is not known at compile time to implement IDisposable.*
+
+## ref struct interface implementations
+
+More content here.

docs/csharp/language-reference/toc.yml

@@ -437,7 +437,7 @@ items:
       CS0171, CS0188, CS0843, CS8904, CS1738, CS8022, CS8023, CS8024, CS8025, CS8026, CS8058, CS8059, CS8107, CS8192, CS8302,
       CS8303, CS8304, CS8305, CS8306, CS8314, CS8320, CS8370, CS8371, CS8400, CS8401, CS8511, CS8627, CS8630, CS8652, CS8703,
       CS8704, CS8706, CS8773, CS8912, CS8919, CS8929, CS8936, CS8957, CS8967, CS9014, CS9015, CS9016, CS9017, CS9058, CS9064,
-      CS9103, CS9171, CS9194, CS9202, CS9204
+      CS9103, CS9171, CS9194, CS9202, CS9204, CS9240
   - name: Assembly references
     href: ./compiler-messages/assembly-references.md
     displayName: >
@@ -464,6 +464,11 @@ items:
       CS8351, CS8373, CS8374, CS8388, CS8977, CS9072, CS9077, CS9078, CS9079, CS9085, CS9086, CS9087, CS9089, CS9091, CS9092,
       CS9093, CS9094, CS9095, CS9096, CS9097, CS9101, CS9102, CS9104, CS9190, CS9191, CS9192, CS9193, CS9195, CS9196, CS9197,
       CS9198, CS9199, CS9200, CS9201
+  - name: "`ref struct` types"
+    href: ./compiler-messages/ref-struct-errors.md
+    displayName: > 
+      ref struct,
+      CS8343, CS8344, CS9241, CS9242, CS9243, CS9244, CS9245, CS9246, CS9247
   - name: Iterator methods
     href: ./compiler-messages/iterator-yield.md
     displayName: > 

docs/csharp/misc/cs0401.md

@@ -10,7 +10,7 @@ ms.assetid: 94eac5a8-7344-44d2-9d0c-a9954993603d
 ---
 # Compiler Error CS0401
 
-The new() constraint must be the last constraint specified  
+The new() constraint must be the last restrictive constraint specified  
 
  When using multiple constraints, list all other constraints before the new() constraint.  
 

docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md

@@ -304,8 +304,6 @@ f1_keywords:
   - "CS8340"
   - "CS8341"
   - "CS8342"
-  - "CS8343"
-  - "CS8344"
   - "CS8346"
   - "CS8347"
   - "CS8348"