[Version 9.0] Feature support for function pointers

standard/expressions.md

@@ -1,15 +1,15 @@
 # 12 Expressions
 
 ## 12.1 General
 
 An expression is a sequence of operators and operands. This clause defines the syntax, order of evaluation of operands and operators, and meaning of expressions.
 
 ## 12.2 Expression classifications
 
 ### 12.2.1 General
 
 The result of an expression is classified as one of the following:
 
 - A value. Every value has an associated type.
 - A variable. Unless otherwise specified, a variable is explicitly typed and has an associated type, namely the declared type of the variable. An implicitly typed variable has no associated type.
 - A null literal. An expression with this classification can be implicitly converted to a reference type or nullable value type.
@@ -782,10 +782,18 @@
 
 If `E` is a method group or implicitly typed anonymous function and `T` is a delegate type or expression tree type then all the parameter types of `T` are *input types of* `E` *with type* `T`.
 
+If `E` is an address-of method group and `T` is a function pointer type (§function-pointers) then all the parameter types of `T` are input types of `E` with type `T`.
+
+> *Note*: This is only applicable in unsafe code. *end note*
+
 #### 12.6.3.5 Output types
 
 If `E` is a method group or an anonymous function and `T` is a delegate type or expression tree type then the return type of `T` is an *output type of* `E` *with type* `T`.
 
+If `E` is an address-of method group and `T` is a function pointer type (§function-pointers) then the return type of `T` is an output type of `E` with type `T`.
+
+> *Note*: This is only applicable in unsafe code. *end note*
+
 #### 12.6.3.6 Dependence
 
 An *unfixed* type variable `Xᵢ` *depends directly on* an *unfixed* type variable `Xₑ` if for some argument `Eᵥ` with type `Tᵥ` `Xₑ` occurs in an *input type* of `Eᵥ` with type `Tᵥ` and `Xᵢ` occurs in an *output type* of `Eᵥ` with type `Tᵥ`.
@@ -811,6 +819,8 @@
 - If `E` is a tuple literal with arity `N` and elements `Eᵢ`, and `T` is a tuple type with arity `N` with corresponding element types `Tₑ` or `T` is a nullable value type `T0?` and `T0` is a tuple type with arity `N` that has a corresponding element type `Tₑ`, then for each `Eᵢ` an output type inference is made from `Eᵢ` to `Tₑ`.
 - If `E` is an anonymous function with inferred return type `U` ([§12.6.3.14](expressions.md#126314-inferred-return-type)) and `T` is a delegate type or expression tree type with return type `Tₓ`, then a *lower-bound inference* ([§12.6.3.11](expressions.md#126311-lower-bound-inferences)) is made *from* `U` *to* `Tₓ`.
 - Otherwise, if `E` is a method group and `T` is a delegate type or expression tree type with parameter types `T₁...Tᵥ` and return type `Tₓ`, and overload resolution of `E` with the types `T₁...Tᵥ` yields a single method with return type `U`, then a *lower-bound inference* is made *from* `U` *to* `Tₓ`.
+- If `E` is an address-of method group and `T` is a function pointer type (§function-pointers) then with parameter types `T1..Tk` and return type `Tb`, and overload resolution of `E` with the types `T1..Tk` yields a single method with return type `U`, then a *lower-bound inference* is made from `U` to `Tb`.
+  > *Note*: This is only applicable in unsafe code. *end note*
 - Otherwise, if `E` is an expression with type `U`, then a *lower-bound inference* is made *from* `U` *to* `T`.
 - Otherwise, no inferences are made.
 
@@ -842,14 +852,25 @@
   - `V` is an array type `V₁[...]`and `U` is an array type `U₁[...]`of the same rank
   - `V` is one of `IEnumerable<V₁>`, `ICollection<V₁>`, `IReadOnlyList<V₁>>`, `IReadOnlyCollection<V₁>` or `IList<V₁>` and `U` is a single-dimensional array type `U₁[]`
   - `V` is a constructed `class`, `struct`, `interface` or `delegate` type `C<V₁...Vₑ>` and there is a unique type `C<U₁...Uₑ>` such that `U` (or, if `U` is a type `parameter`, its effective base class or any member of its effective interface set) is identical to, `inherits` from (directly or indirectly), or implements (directly or indirectly) `C<U₁...Uₑ>`.
+  - `V` is a function pointer type (§function-pointers) `delegate*<V2..Vk, V1>` and there is a function pointer type `delegate*<U2..Uk, U1>` such that `U` is identical to `delegate*<U2..Uk, U1>`, and the calling convention of `V` is identical to `U`, and the refness of `Vi` is identical to `Ui`.
+    > *Note*: This is only applicable in unsafe code. *end note*
   - (The “uniqueness” restriction means that in the case interface `C<T>{} class U: C<X>, C<Y>{}`, then no inference is made when inferring from `U` to `C<T>` because `U₁` could be `X` or `Y`.)  
   If any of these cases apply then an inference is made from each `Uᵢ` to the corresponding `Vᵢ` as follows:
-  - If `Uᵢ` is not known to be a reference type then an *exact inference* is made
+  - If `Uᵢ` is not known to be a reference type then an *exact inference* is made; or alternatively, if `U` is not a function pointer type and `Ui` is not known to be a reference type, or if `U` is a function pointer type and `Ui` is not known to be a function pointer type or a reference type, then an exact inference is made
+    > *Note*: This is only applicable in unsafe code. *end note*
   - Otherwise, if `U` is an array type then a *lower-bound inference* is made
   - Otherwise, if `V` is `C<V₁...Vₑ>` then inference depends on the `i-th` type parameter of `C`:
     - If it is covariant then a *lower-bound inference* is made.
     - If it is contravariant then an *upper-bound inference* is made.
     - If it is invariant then an *exact inference* is made.
+  - Otherwise, if `V` is `delegate*<V2..Vk, V1>` then inference depends on the i-th parameter of `delegate*<V2..Vk, V1>`:
+    - If V1:
+      - If the return is by value, then a lower-bound inference is made.
+      - If the return is by reference, then an exact inference is made.
+    - If V2..Vk:
+      - If the parameter is by value, then an upper-bound inference is made.
+      - If the parameter is by reference, then an exact inference is made.
+    > *Note*: This is only applicable in unsafe code. *end note*
 - Otherwise, no inferences are made.
 
 #### 12.6.3.12 Upper-bound inferences
@@ -862,14 +883,25 @@
   - `U` is one of `IEnumerable<Uₑ>`, `ICollection<Uₑ>`, `IReadOnlyList<Uₑ>`, `IReadOnlyCollection<Uₑ>` or `IList<Uₑ>` and `V` is a single-dimensional array type `Vₑ[]`
   - `U` is the type `U1?` and `V` is the type `V1?`
   - `U` is constructed class, struct, interface or delegate type `C<U₁...Uₑ>` and `V` is a `class, struct, interface` or `delegate` type which is `identical` to, `inherits` from (directly or indirectly), or implements (directly or indirectly) a unique type `C<V₁...Vₑ>`
+  - `U` is a function pointer type (§function-pointers) then `delegate*<U2..Uk, U1>` and `V` is a function pointer type which is identical to `delegate*<V2..Vk, V1>`, and the calling convention of `U` is identical to `V`, and the refness of `Ui` is identical to `Vi`.
+    > *Note*: This is only applicable in unsafe code. *end note*
   - (The “uniqueness” restriction means that given an interface `C<T>{} class V<Z>: C<X<Z>>, C<Y<Z>>{}`, then no inference is made when inferring from `C<U₁>` to `V<Q>`. Inferences are not made from `U₁` to either `X<Q>` or `Y<Q>`.)  
   If any of these cases apply then an inference is made from each `Uᵢ` to the corresponding `Vᵢ` as follows:
-  - If `Uᵢ` is not known to be a reference type then an *exact inference* is made
+  - If `U` is not a function pointer type and `Ui` is not known to be a reference type, or if `U` is a function pointer type and `Ui` is not known to be a function pointer type or a reference type, then an *exact inference* is made
+    > *Note*: Function-pointer type-related text is only applicable in unsafe code. *end note*
   - Otherwise, if `V` is an array type then an *upper-bound inference* is made
   - Otherwise, if `U` is `C<U₁...Uₑ>` then inference depends on the `i-th` type parameter of `C`:
     - If it is covariant then an *upper-bound inference* is made.
     - If it is contravariant then a *lower-bound inference* is made.
     - If it is invariant then an *exact inference* is made.
+- Otherwise, if `U` is `delegate*<U2..Uk, U1>` then inference depends on the i-th parameter of `delegate*<U2..Uk, U1>`:
+  - If `U1`:
+    - If the return is by value, then an upper-bound inference is made.
+    - If the return is by reference, then an exact inference is made.
+  - If `U2`..`Uk`:
+    - If the parameter is by value, then a lower-bound inference is made.
+    - If the parameter is by reference, then an exact inference is made.
+  > *Note*: This is only applicable in unsafe code. *end note*
 - Otherwise, no inferences are made.
 
 #### 12.6.3.13 Fixing
@@ -1095,6 +1127,10 @@
 - If for at least one parameter `Mᵥ` uses the ***better parameter-passing choice*** ([§12.6.4.4](expressions.md#12644-better-parameter-passing-mode)) than the corresponding parameter in `Mₓ` and none of the parameters in `Mₓ` use the better parameter-passing choice than `Mᵥ`, `Mᵥ` is better than `Mₓ`.
 - Otherwise, no function member is better.
 
+A `delegate*` is more specific than `void*`.
+
+> *Note*: This is only applicable in unsafe code, and permits overloading on `void*` and a `delegate*` allowing the `&` operator to distinguish between the two. *end note*
+
 #### 12.6.4.4 Better parameter-passing mode
 
 It is permitted to have corresponding parameters in two overloaded methods differ only by parameter-passing mode provided one of the two parameters has value-passing mode, as follows:
@@ -1115,6 +1151,8 @@
 
 - `E` exactly matches `T₁` and `E` does not exactly match `T₂` ([§12.6.4.6](expressions.md#12646-exactly-matching-expression))
 - `E` exactly matches both or neither of `T₁` and `T₂`, and `T₁` is a better conversion target than `T₂` ([§12.6.4.7](expressions.md#12647-better-conversion-target))
+  - `V` is a function pointer type `delegate*<V2..Vk, V1>` and `U` is a function pointer type `delegate*<U2..Uk, U1>`, and the calling convention of `V` is identical to `U`, and the refness of `Vi` is identical to `Ui`.
+    > *Note*: This is only applicable in unsafe code. *end note*
 - `E` is a method group ([§12.2](expressions.md#122-expression-classifications)), `T₁` is compatible ([§21.4](delegates.md#214-delegate-compatibility)) with the single best method from the method group for conversion `C₁`, and `T₂` is not compatible with the single best method from the method group for conversion `C₂`
 
 #### 12.6.4.6 Exactly matching expression
@@ -1976,6 +2014,25 @@
 - Otherwise, if the *invocation_expression* invokes a returns-by-ref method ([§15.6.1](classes.md#1561-general)) or a returns-by-ref delegate, the result is a variable with an associated type of the return type of the method or delegate. If the invocation is of an instance method, and the receiver is of a class type `T`, the associated type is picked from the first declaration or override of the method found when starting with `T` and searching through its base classes.
 - Otherwise, the *invocation_expression* invokes a returns-by-value method ([§15.6.1](classes.md#1561-general)) or returns-by-value delegate, and the result is a value, with an associated type of the return type of the method or delegate. If the invocation is of an instance method, and the receiver is of a class type `T`, the associated type is picked from the first declaration or override of the method found when starting with `T` and searching through its base classes.
 
+> *Note*: The following is only applicable in unsafe code. *end note*
+
+The *method_declaration* [§15.6.1](classes.md#1561-general) for an unmanaged method shall have the attribute `System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute`. The use of this attribute on a method results in the following constraints:
+
+- It is an error to directly call that method from C#. Instead, one can obtain a function pointer (§function-pointers) to that method and then invoke the method via that pointer.
+- It is an error for that method to have a parameter or return type that is not an `unmanaged_type` ([§8.8](types.md#88-unmanaged-types)).
+- It is an error for that method to have type parameters, even if those type parameters are constrained to `unmanaged`.
+- It is an error for that method to be in a generic type.
+- It is an error to convert that method to a delegate type.
+
+For a function pointer invocation, the *primary_expression* of the *invocation_expression* shall be a value of a *funcptr_type*. Furthermore, considering the method being pointed to to be a function member with the same parameter list as the *funcptr_type*, the *funcptr_type* shall be applicable ([§12.6.4.2](expressions.md#12642-applicable-function-member)) with respect to the *argument_list* of the *invocation_expression*.
+
+The run-time processing of a function pointer invocation of the form `F(A)`, where `F` is a *primary_expression* of a *funcptr_type* and `A` is an optional *argument_list*, consists of the following steps:
+
+- `F` is evaluated. If this evaluation causes an exception, no further steps are executed.
+- The argument list `A` is evaluated. If this evaluation causes an exception, no further steps are executed.
+- The value of `F` is checked to be valid. If that value is `null`, an implementation-defined exception is thrown, and no further steps are executed.
+- Otherwise, `F` points to a method. Function member invocation ([§12.6.6](expressions.md#1266-function-member-invocation)) is performed on the method to which `F` points.
+
 #### 12.8.10.2 Method invocations
 
 For a method invocation, the *primary_expression* of the *invocation_expression* shall be a method group. The method group identifies the one method to invoke or the set of overloaded methods from which to choose a specific method to invoke. In the latter case, determination of the specific method to invoke is based on the context provided by the types of the arguments in the *argument_list*.

standard/lexical-structure.md

@@ -606,12 +606,13 @@ A ***contextual keyword*** is an identifier-like sequence of characters that has
 
 ```ANTLR
 contextual_keyword
-    : 'add'     | 'alias'      | 'ascending' | 'async'     | 'await'
-    | 'by'      | 'descending' | 'dynamic'   | 'equals'    | 'from'
-    | 'get'     | 'global'     | 'group'     | 'into'      | 'join'
-    | 'let'     | 'nameof'     | 'notnull'   | 'on'        | 'orderby'
-    | 'partial' | 'remove'     | 'select'    | 'set'       | 'unmanaged'
-    | 'value'   | 'var'        | 'when'      | 'where'     | 'yield'
+    : 'add'      | 'alias'      | 'ascending'  | 'async'     | 'await'
+    | 'by'       | 'Cdecl'      | 'descending' | 'dynamic'   | 'equals'
+    | 'Fastcall' | 'from'.      | 'get'        | 'global'    | 'group'
+    | 'into'     | 'join'.      | 'let'        | 'managed'   | 'nameof'
+    | 'notnull'  | 'on'         | 'orderby'.   | 'partial'   | 'remove'
+    | 'select'   | 'set'        | 'Stdcall'.   | 'Thiscall'  | 'unmanaged'
+    | 'value'.   | 'var'.       | 'when'       | 'where'     | 'yield'
     ;
 ```
 

standard/portability-issues.md

@@ -11,10 +11,11 @@ This annex collects some information about portability that appears in this spec
 The behavior is undefined in the following circumstances:
 
 1. The behavior of the enclosing async function when an awaiter’s implementation of the interface methods `INotifyCompletion.OnCompleted` and `ICriticalNotifyCompletion.UnsafeOnCompleted` does not cause the resumption delegate to be invoked at most once ([§12.9.9.4](expressions.md#12994-run-time-evaluation-of-await-expressions)).
-1. Passing pointers as reference or output parameters ([§24.3](unsafe-code.md#243-pointer-types)).
+1. Passing pointers as `ref` or `out` parameters (§data-pointers).
 1. When dereferencing the result of converting one pointer type to another and the resulting pointer is not correctly aligned for the pointed-to type. ([§24.5.1](unsafe-code.md#2451-general)).
 1. When the unary `*` operator is applied to a pointer containing an invalid value ([§24.6.2](unsafe-code.md#2462-pointer-indirection)).
 1. When a pointer is subscripted to access an out-of-bounds element ([§24.6.4](unsafe-code.md#2464-pointer-element-access)).
+1. When comparing values of *funcptr_type*s, or `void*` copies thereof ([§24.6.8](unsafe-code.md#2468-pointer-comparison).
 1. Modifying objects of managed type through fixed pointers ([§24.7](unsafe-code.md#247-the-fixed-statement)).
 1. The content of memory newly allocated by `stackalloc` ([§12.8.22](expressions.md#12822-stack-allocation)).
 1. Attempting to allocate a negative number of items using `stackalloc`([§12.8.22](expressions.md#12822-stack-allocation)).
@@ -43,13 +44,16 @@ 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 token name mapping and semantics of unmanaged calling conventions beyond those required by this specification, and the set of valid combinations of those tokens (§function-pointers).
 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))
+1. The type of exception thrown when the *primary_expression* of an *invocation_expression* is a function pointer with value `null`, and an attempt is made to invoke the (non-existent) pointed-to method ([§12.8.10](expressions.md#12810-invocation-expressions)).
 1. The behavior when pointer arithmetic overflows the domain of the pointer type. ([§24.6.6](unsafe-code.md#2466-pointer-increment-and-decrement), [§24.6.7](unsafe-code.md#2467-pointer-arithmetic))
 1. The result of the `sizeof` operator for non-pre-defined value types. ([§24.6.9](unsafe-code.md#2469-the-sizeof-operator))
 1. The behavior of the `fixed` statement if the array expression is `null` or if the array has zero elements. ([§24.7](unsafe-code.md#247-the-fixed-statement))
 1. The behavior of the `fixed` statement if the string expression is `null`. ([§24.7](unsafe-code.md#247-the-fixed-statement))
+1. The value returned when a stack allocation of size zero is made ([§12.8.22](expressions.md#12822-stack-allocation)).
 
 ## B.4 Unspecified behavior
 

standard/standard-library.md

@@ -11,7 +11,7 @@
 The standard library is intended to be the minimum set of types and members required by a conforming C# implementation. As such, it contains only those members that are explicitly required by the C# language specification.
 
 It is expected that a conforming C# implementation will supply a significantly more extensive library that enables useful programs to be written. For example, a conforming implementation might extend this library by
 
 - Adding namespaces.
 - Adding types.
 - Adding members to non-interface types.
@@ -162,7 +162,7 @@
     {
         public InvalidCastException();
         public InvalidCastException(string? message);
         public InvalidCastException(string? message, Exception? innerException);
     }
 
     public class InvalidOperationException : Exception
@@ -210,7 +210,7 @@
         AttributeTargets.Property | AttributeTargets.Field |
         AttributeTargets.Event | AttributeTargets.Delegate, Inherited = false)]
     public sealed class ObsoleteAttribute : Attribute
     {
         public ObsoleteAttribute();
         public ObsoleteAttribute(string? message);
         public ObsoleteAttribute(string? message, bool error);
@@ -219,7 +219,7 @@
     }
 
     public class OutOfMemoryException : Exception
     {
         public OutOfMemoryException();
         public OutOfMemoryException(string? message);
         public OutOfMemoryException(string? message, Exception? innerException);
@@ -279,7 +279,7 @@
 
 namespace System.Collections
 {
     public interface ICollection : IEnumerable
     {
         int Count { get; }
         bool IsSynchronized { get; }
@@ -346,7 +346,7 @@
     }
 }
 
 namespace System.Diagnostics
 {
     [AttributeUsageAttribute(AttributeTargets.Method | AttributeTargets.Class,
                              AllowMultiple = true)]
@@ -496,7 +496,7 @@
         /// </summary>
         /// <param name="other">
         ///    The value to compare with this Index.
         /// </param>
         public bool Equals(Index other);
     }
 
@@ -843,6 +843,14 @@
         public TResult GetResult();
     }
 
+    [System.AttributeUsage(System.AttributeTargets.Method, Inherited=false)]
+    public sealed class UnmanagedCallersOnlyAttribute : Attribute
+    {
+        public UnmanagedCallersOnlyAttribute ();
+        public Type[]? CallConvs;
+        public string? EntryPoint;
+    }
+
     public readonly struct ValueTaskAwaiter : ICriticalNotifyCompletion,
         INotifyCompletion
     {
@@ -1387,6 +1395,7 @@
 - `global::System.Runtime.CompilerServices.ValueTaskAwaiter`
 - `global::System.Runtime.CompilerServices.ValueTaskAwaiter<TResult>`
 - `global::System.Runtime.CompilerServices.Unsafe`
+- `global::System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute`
 - `global::System.Threading.Monitor`
 - `global::System.Threading.Tasks.Task`
 - `global::System.Threading.Tasks.Task<TResult>`