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[Concurrency] Adopt typed throws in Task creation APIs #84802

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ea17a92
[Concurrency] Adopt typed throws in Task creation APIs
ktoso Oct 10, 2025
4709e23
adopt typed throw in Task.value
ktoso Oct 10, 2025
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39 changes: 26 additions & 13 deletions stdlib/public/Concurrency/Task+init.swift.gyb
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ import Swift
% [ # PARAMS
% 'name: String? = nil',
% 'priority: TaskPriority? = nil',
% '@_inheritActorContext @_implicitSelfCapture operation: sending @escaping @isolated(any) () async throws -> Success',
% '@_inheritActorContext @_implicitSelfCapture operation: sending @escaping @isolated(any) () async throws(Failure) -> Success',
% ]),
% # ==== --------------------------------------------------------------------
% ([ # METHOD_VARIANT
Expand All @@ -40,7 +40,7 @@ import Swift
% [ # PARAMS
% 'name: String? = nil',
% 'priority: TaskPriority? = nil',
% 'operation: sending @escaping @isolated(any) () async throws -> Success',
% 'operation: sending @escaping @isolated(any) () async throws(Failure) -> Success',
% ]),
% # ==== -------------------------------------------------------------------------------------------------------------
% # ==== With task executor, but available only since 6.0
Expand All @@ -56,7 +56,7 @@ import Swift
% 'name: String? = nil',
% 'executorPreference taskExecutor: (any TaskExecutor)?',
% 'priority: TaskPriority? = nil',
% 'operation: sending @escaping () async throws -> Success',
% 'operation: sending @escaping () async throws(Failure) -> Success',
% ]),
% # ==== --------------------------------------------------------------------
% ([ # METHOD_VARIANT
Expand All @@ -71,7 +71,7 @@ import Swift
% 'name: String? = nil',
% 'executorPreference taskExecutor: (any TaskExecutor)?',
% 'priority: TaskPriority? = nil',
% 'operation: sending @escaping () async throws -> Success',
% 'operation: sending @escaping () async throws(Failure) -> Success',
% ]),
% # !!!! -------------------------------------------------------------------------------------------------------------
% # !!!! Legacy / Source Compatibility "Shims"
Expand All @@ -91,6 +91,7 @@ import Swift
% ],
% [ # PARAMS
% 'priority: TaskPriority? = nil',
% # detach does not support typed throws, it's a legacy api for compat only
% '@_inheritActorContext @_implicitSelfCapture operation: __owned @Sendable @escaping @isolated(any) () async throws -> Success',
% ]),
% # ==== Legacy API: runDetached
Expand All @@ -105,6 +106,7 @@ import Swift
% ],
% [ # PARAMS
% 'priority: TaskPriority? = nil',
% # runDetached does not support typed throws, it's a legacy api for compat only
% '@_inheritActorContext @_implicitSelfCapture operation: __owned @Sendable @escaping @isolated(any) () async throws -> Success',
% ]),
% # ==== Legacy API: asyncDetached
Expand All @@ -119,6 +121,7 @@ import Swift
% ],
% [ # PARAMS
% 'priority: TaskPriority? = nil',
% # asyncDetached does not support typed throws, it's a legacy api for compat only
% '@_inheritActorContext @_implicitSelfCapture operation: __owned @Sendable @escaping @isolated(any) () async throws -> Success',
% ]),
% # ==== Legacy API: async
Expand All @@ -133,6 +136,7 @@ import Swift
% ],
% [ # PARAMS
% 'priority: TaskPriority? = nil',
% # async does not support typed throws, it's a legacy api for compat only
% '@_inheritActorContext @_implicitSelfCapture operation: __owned @Sendable @escaping @isolated(any) () async throws -> Success',
% ]),
% ]:
Expand All @@ -149,8 +153,10 @@ import Swift
% HAS_ISOLATED_ANY = any('@isolated(any)' in param for param in PARAMS)
% IS_DEPRECATED = any('deprecated' in a for a in ALL_AVAILABILITY)
%
% if IS_THROWING:
% FAILURE_TYPE = 'Error'
% if IS_THROWING and IS_TOP_LEVEL_FUNC:
% FAILURE_TYPE = 'Error' # the legacy top-level funcs don't have a generic Failure, so we keep the un-typed throw
% elif IS_THROWING:
% FAILURE_TYPE = 'Failure' # use typed throws, the thrown type is Failure of the Task<_, Failure> type
% else:
% FAILURE_TYPE = 'Never'
% end
Expand All @@ -162,6 +168,7 @@ def adjust_params_for_kind(params):
for p in params:
np = p
if not IS_THROWING:
np = np.replace("throws(Failure)", "")
np = np.replace("throws", "")
res.append(np)
return res
Expand All @@ -184,8 +191,12 @@ else:

% # ====================================================================================================================
% if not IS_TOP_LEVEL_FUNC:
% if IS_THROWING:
extension Task { // throwing Failure error type
% else:
extension Task where Failure == ${FAILURE_TYPE} {
% end
% end

% # --------------------------------------------------------------------------------------------------------------------
#if SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
Expand Down Expand Up @@ -285,8 +296,10 @@ extension Task where Failure == ${FAILURE_TYPE} {
/// - Returns: A reference to the task.
% end # IS_DEPRECATED
${"\n ".join(adjust_availability(ALL_AVAILABILITY))}
% if not IS_THROWING:
@discardableResult
public ${METHOD_VARIANT}( // Task ${METHOD_VARIANT}
% end
public ${METHOD_VARIANT}(
${",\n ".join(adjust_params_for_kind(PARAMS))}
) ${ARROW_RETURN_TYPE}{

Expand Down Expand Up @@ -323,7 +336,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
initialTaskExecutorConsuming: taskExecutor,
% end
taskName: nameBytes.baseAddress!._rawValue,
operation: operation).0
operation: operation).0 // Task ${METHOD_VARIANT}
}
#else // no $BuiltinCreateAsyncTaskOwnedTaskExecutor
// legacy branch for the non-consuming task executor
Expand All @@ -338,7 +351,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
% end
initialTaskExecutor: executorBuiltin,
taskName: nameBytes.baseAddress!._rawValue,
operation: operation).0
operation: operation).0 // Task ${METHOD_VARIANT}
}
#endif // $BuiltinCreateAsyncTaskOwnedTaskExecutor
% else: # if no TASK_EXECUTOR
Expand All @@ -350,7 +363,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
initialSerialExecutor: builtinSerialExecutor,
% end
taskName: nameBytes.baseAddress!._rawValue,
operation: operation).0
operation: operation).0 // Task ${METHOD_VARIANT}
}
% end # if no HAS_TASK_EXECUTOR
} // let name
Expand All @@ -368,7 +381,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
initialSerialExecutor: builtinSerialExecutor,
% end
initialTaskExecutorConsuming: taskExecutor,
operation: operation).0
operation: operation).0 // Task ${METHOD_VARIANT}
#else
// legacy branch for the non-consuming task executor
let executorBuiltin: Builtin.Executor =
Expand All @@ -380,7 +393,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
initialSerialExecutor: builtinSerialExecutor,
% end
initialTaskExecutor: executorBuiltin,
operation: operation).0
operation: operation).0 // Task ${METHOD_VARIANT}
#endif
}
% end # HAS_TASK_EXECUTOR
Expand All @@ -392,7 +405,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
% if HAS_ISOLATED_ANY:
initialSerialExecutor: builtinSerialExecutor,
% end
operation: operation).0
operation: operation).0 // Task ${METHOD_VARIANT}
}

% if IS_INIT:
Expand Down
10 changes: 7 additions & 3 deletions stdlib/public/Concurrency/Task.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -167,8 +167,12 @@ extension Task {
///
/// - Returns: The task's result.
public var value: Success {
get async throws {
return try await _taskFutureGetThrowing(_task)
get async throws(Failure) {
do {
return try await _taskFutureGetThrowing(_task)
} catch {
throw (error as! Failure) // as!-safe, because typed throw on the operation closure
}
}
}

Expand All @@ -189,7 +193,7 @@ extension Task {
do {
return .success(try await value)
} catch {
return .failure(error as! Failure) // as!-safe, guaranteed to be Failure
return .failure(error) // as!-safe, guaranteed to be Failure
Comment on lines -192 to +196
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Comment now refers to a force cast that has moved elsewhere.

}
}
}
Expand Down
11 changes: 10 additions & 1 deletion test/Concurrency/Runtime/task_creation.swift
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Expand Up @@ -31,6 +31,15 @@ enum SomeError: Error {
return 7
}

let t2f = Task { () throws(SomeError) -> Int in
throw SomeError.bad
}
do {
try await t2f.value
} catch {
let err: SomeError = error // confirm it was a typed throw
}

let t3 = Task.detached {
return 9
}
Expand All @@ -43,7 +52,7 @@ enum SomeError: Error {
return 11
}

let result = try! await t1.get() + t2.get() + t3.get() + t4.get()
let result = try! await t1.value + t2.value + t3.value + t4.value
assert(result == 32)
}
}
4 changes: 2 additions & 2 deletions test/Concurrency/sendable_metatype_typecheck.swift
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Expand Up @@ -190,15 +190,15 @@ func f<T: P>(_: T.Type) {
}

func sendableSequence<S: AsyncSequence & Sendable>(_ s: S) throws {
Task.detached {
_ = Task.detached {
for try await i in s {
print(i)
}
}
}

func nonSendableSequence<S: AsyncSequence>(_ s: S) throws {
Task.detached {
_ = Task.detached {
for try await i in s { // expected-warning{{capture of non-Sendable type 'S.AsyncIterator.Type' in an isolated closure}}
// expected-warning@-1{{capture of non-Sendable type 'S.Type' in an isolated closure}}
print(i)
Expand Down
8 changes: 4 additions & 4 deletions test/Concurrency/task_naming_availability.swift
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Expand Up @@ -10,9 +10,9 @@ func testName() {
@available(SwiftStdlib 6.0, *)
func taskExecutor() async {
Task(name: "name", executorPreference: nil) { }
Task(name: "name", executorPreference: nil) { throw Boom() }
_ = Task(name: "name", executorPreference: nil) { throw Boom() }

Task.detached(name: "name", executorPreference: nil) { throw Boom() }
_ = Task.detached(name: "name", executorPreference: nil) { throw Boom() }

await withTaskGroup(of: Void.self) { group in
group.addTask(name: "name", executorPreference: nil) {
Expand Down Expand Up @@ -40,10 +40,10 @@ func taskExecutor() async {
@available(SwiftStdlib 5.1, *)
func backDeployedNames() async {
Task(name: "name") { }
Task(name: "name") { throw Boom() }
_ = Task(name: "name") { throw Boom() }

Task.detached(name: "name") { }
Task.detached(name: "name") { throw Boom() }
_ = Task.detached(name: "name") { throw Boom() }

await withTaskGroup(of: Void.self) { group in
group.addTask(name: "name") {
Expand Down