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C# 7.x §15.15.1 must special-case Task and Task<TResult> because they lack AsyncMethodBuilderAttribute #854

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KalleOlaviNiemitalo opened this issue Jul 14, 2023 · 0 comments · Fixed by #875
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C# 7.x §15.15.1 must special-case Task and Task<TResult> because they lack AsyncMethodBuilderAttribute #854

KalleOlaviNiemitalo opened this issue Jul 14, 2023 · 0 comments · Fixed by #875
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@jskeet
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C# 7.x

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@KalleOlaviNiemitalo
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Describe the bug

In the C# 7.x draft, §15.15.1 (Async functions / General) states:

The return_type of an async method shall be either void or a task type. For an async method that returns a value, a task type shall be generic. For an async method that does not return a value, a task type shall not be generic. Such types are referred to in this specification as «TaskType»<T> and «TaskType», respectively. (The Standard library type System.Threading.Tasks.Task and types constructed from System.Threading.Tasks.Task<TResult> are task types.)
A task type shall be a class or struct type that is associated with a task builder type via the attribute System.Runtime.CompilerServices.AsyncMethodBuilderAttribute. Such types are referred to in this specification as «TaskBuilderType»<T> and «TaskBuilderType».

However, System.Threading.Tasks.Task and System.Threading.Tasks.Task<TResult> are not decorated with AsyncMethodBuilderAttribute. Not in §C.3 (Standard Library Types not defined in ISO/IEC 23271), and not in .NET Framework either.

Example

None.

Expected behavior

Special-case System.Threading.Tasks.Task and System.Threading.Tasks.Task<TResult> so that they need not be decorated with AsyncMethodBuilderAttribute.

Additional context

None.
This was referenced Jul 14, 2023
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@jskeet jskeet added this to the C# 7.x milestone Aug 7, 2023
@jskeet jskeet self-assigned this Aug 7, 2023
jskeet added a commit to jskeet/csharpstandard that referenced this issue Aug 7, 2023
@jskeet
Clarify task types
a478c5b 
- `Task` and `Task<T>` are classified as task types despite not
  specifying builder types
- Interfaces are allowed to be task types
- Enums and methods are prohibited from being decorated with
  AsyncMethodBuilderAttribute
- Task types must not be generic in more than one type parameter
  (including in terms of containing types)

Discussion required for all of this, but if merged, would fix dotnet#854,
jskeet added a commit to jskeet/csharpstandard that referenced this issue Aug 7, 2023
@jskeet
Clarify task types
20b0a62 
- `Task` and `Task<T>` are classified as task types despite not
  specifying builder types
- Interfaces are allowed to be task types
- Enums and methods are prohibited from being decorated with
  AsyncMethodBuilderAttribute
- Task types must not be generic in more than one type parameter
  (including in terms of containing types)

Discussion required for all of this, but if merged, would fix dotnet#854,
jskeet added a commit to jskeet/csharpstandard that referenced this issue Aug 7, 2023
@jskeet
Clarify task types
63d3375 
- `Task` and `Task<T>` are classified as task types despite not
  specifying builder types
- Interfaces are allowed to be task types
- Enums and methods are prohibited from being decorated with
  AsyncMethodBuilderAttribute
- Task types must not be generic in more than one type parameter
  (including in terms of containing types)

Discussion required for all of this, but if merged, would
fix dotnet#854, dotnet#856, dotnet#858 and dotnet#859.
@jskeet jskeet mentioned this issue Aug 7, 2023
Merged
BillWagner pushed a commit that referenced this issue Aug 15, 2023
@jskeet
Clarify task types (#875)
c48d041 
* Clarify task types

- `Task` and `Task<T>` are classified as task types despite not
  specifying builder types
- Interfaces are allowed to be task types
- Enums and methods are prohibited from being decorated with
  AsyncMethodBuilderAttribute
- Task types must not be generic in more than one type parameter
  (including in terms of containing types)

Discussion required for all of this, but if merged, would
fix #854, #856, #858 and #859.

* Prevent nesting within generic types, for task types.

This wording follows the wording in 15.15.2 for task builders.
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Clarify task types jskeet/csharpstandard
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@jskeet @KalleOlaviNiemitalo