Adopt @abi in the standard library

This commit enables the ABIAttribute feature in the standard library build and replaces every instance of `@_silgen_name(<mangled Swift name>)` in stdlib/public with an `@abi` attribute.

Author: beccadax

docs/ReferenceGuides/UnderscoredAttributes.md

@@ -1131,15 +1131,17 @@ ways to misuse it:
   be reliably recovered through C interfaces like `dlsym`. If you want to
   implement a plugin-style interface, use `Bundle`/`NSBundle` if available, or
   export your plugin entry points as C entry points using `@_cdecl`.
-  
+- Don't use `@_silgen_name` when you need to make a change to an ABI-stable
+  declaration's signature that would normally alter its mangled name, but you
+  need to preserve the old mangled name for ABI compatibility. We used to use it
+  for this task, but `@abi` can do it with fewer limitations, more safety, and
+  better readability. If for some reason you do need `@_silgen_name`, you will
+  need to be careful that the change doesn't materially affect the actual
+  calling convention of the function in an incompatible way.
+
 Legitimate uses may include:
 
 - Use `@_silgen_name` if you're implementing the Swift runtime.
-- Use `@_silgen_name` if you need to make a change to an ABI-stable
-  declaration's signature that would normally alter its mangled name, but you
-  need to preserve the old mangled name for ABI compatibility. You will need
-  to be careful that the change doesn't materially affect the actual calling
-  convention of the function in an incompatible way.
 - Use `@_silgen_name` if certain declarations need to have predictable symbol
   names, such as to be easily referenced by linker scripts or other highly
   customized build environments (and it's OK for those predictable symbols to

docs/StandardLibraryProgrammersManual.md

@@ -455,6 +455,8 @@ This attribute specifies the name that a declaration will have at link time. It
 1. To specify the symbol name of a Swift function so that it can be called from Swift-aware C. Such functions have bodies.
 2. To provide a Swift declaration which really represents a C declaration. Such functions do not have bodies.
 
+In the past it was sometimes used for ABI backwards compatibility hacks, but `@abi` does this job better.
+
 ##### Using `@_silgen_name` to call Swift from Swift-aware C
 
 Rather than hard-code Swift mangling into C code, `@_silgen_name` is used to provide a stable and known symbol name for linking. Note that C code still must understand and use the Swift calling convention (available in swift-clang) for such Swift functions (if they use Swift's CC). Example:

stdlib/cmake/modules/SwiftSource.cmake

@@ -633,6 +633,7 @@ function(_compile_swift_files
   list(APPEND swift_flags "-enable-experimental-feature" "NonescapableTypes")
 
   list(APPEND swift_flags "-enable-experimental-feature" "ExtensionImportVisiblity")
+  list(APPEND swift_flags "-enable-experimental-feature" "ABIAttribute")
 
   if (SWIFT_STDLIB_ENABLE_STRICT_CONCURRENCY_COMPLETE)
     list(APPEND swift_flags "-strict-concurrency=complete")

stdlib/public/Concurrency/AsyncStream.swift

@@ -330,7 +330,12 @@ public struct AsyncStream<Element> {
   ///     }
   ///
   ///
-  @_silgen_name("$sScS9unfolding8onCancelScSyxGxSgyYac_yyYbcSgtcfC")
+  @abi(
+    public init(
+      unfolding produce: @escaping /* not @Sendable*/ () async -> Element?,
+      onCancel: (@Sendable () -> Void)? = nil
+    )
+  )
   @preconcurrency // Original API had `@Sendable` only on `onCancel`
   public init(
     unfolding produce: @escaping @Sendable () async -> Element?,

stdlib/public/Concurrency/CheckedContinuation.swift

@@ -313,9 +313,14 @@ public func withCheckedContinuation<T>(
 //
 // This function also doubles as an ABI-compatibility shim predating the
 // introduction of #isolation.
+@abi(
+  public func withCheckedContinuation<T>(
+    function: String,
+    _ body: (CheckedContinuation<T, Never>) -> Void
+  ) async -> T
+)
 @available(SwiftStdlib 5.1, *)
 @_unsafeInheritExecutor // ABI compatibility with Swift 5.1
-@_silgen_name("$ss23withCheckedContinuation8function_xSS_yScCyxs5NeverOGXEtYalF")
 public func _unsafeInheritExecutor_withCheckedContinuation<T>(
   function: String = #function,
   _ body: (CheckedContinuation<T, Never>) -> Void
@@ -377,9 +382,14 @@ public func withCheckedThrowingContinuation<T>(
 //
 // This function also doubles as an ABI-compatibility shim predating the
 // introduction of #isolation.
+@abi(
+  public func withCheckedThrowingContinuation<T>(
+    function: String,
+    _ body: (CheckedContinuation<T, Error>) -> Void
+  ) async throws -> T
+)
 @available(SwiftStdlib 5.1, *)
 @_unsafeInheritExecutor // ABI compatibility with Swift 5.1
-@_silgen_name("$ss31withCheckedThrowingContinuation8function_xSS_yScCyxs5Error_pGXEtYaKlF")
 public func _unsafeInheritExecutor_withCheckedThrowingContinuation<T>(
   function: String = #function,
   _ body: (CheckedContinuation<T, Error>) -> Void

stdlib/public/Concurrency/DiscardingTaskGroup.swift

@@ -97,9 +97,14 @@ public func withDiscardingTaskGroup<GroupResult>(
 //
 // This function also doubles as an ABI-compatibility shim predating the
 // introduction of #isolation.
+@abi(
+  public func withDiscardingTaskGroup<GroupResult>(
+    returning returnType: GroupResult.Type = GroupResult.self,
+    body: (inout DiscardingTaskGroup) async -> GroupResult
+  ) async -> GroupResult
+)
 @available(SwiftStdlib 5.9, *)
 @_unsafeInheritExecutor // for ABI compatibility
-@_silgen_name("$ss23withDiscardingTaskGroup9returning4bodyxxm_xs0bcD0VzYaXEtYalF")
 public func _unsafeInheritExecutor_withDiscardingTaskGroup<GroupResult>(
   returning returnType: GroupResult.Type = GroupResult.self,
   body: (inout DiscardingTaskGroup) async -> GroupResult
@@ -513,9 +518,14 @@ public func withThrowingDiscardingTaskGroup<GroupResult>(
   return result
 }
 
+@abi(
+  public func withThrowingDiscardingTaskGroup<GroupResult>(
+      returning returnType: GroupResult.Type = GroupResult.self,
+      body: (inout ThrowingDiscardingTaskGroup<Error>) async throws -> GroupResult
+  ) async throws -> GroupResult
+)
 @available(SwiftStdlib 5.9, *)
 @_unsafeInheritExecutor // for ABI compatibility
-@_silgen_name("$ss31withThrowingDiscardingTaskGroup9returning4bodyxxm_xs0bcdE0Vys5Error_pGzYaKXEtYaKlF")
 public func _unsafeInheritExecutor_withThrowingDiscardingTaskGroup<GroupResult>(
     returning returnType: GroupResult.Type = GroupResult.self,
     body: (inout ThrowingDiscardingTaskGroup<Error>) async throws -> GroupResult

stdlib/public/Concurrency/ExecutorAssertions.swift

@@ -368,10 +368,17 @@ extension Actor {
     }
   }
 
+  @abi(
+    @usableFromInline
+    @_unavailableInEmbedded
+    internal nonisolated func assumeIsolated<T>(
+        _ operation: (isolated Self) throws -> T,
+        file: StaticString, line: UInt
+    ) rethrows -> T
+  )
   @available(SwiftStdlib 5.9, *)
   @usableFromInline
   @_unavailableInEmbedded
-  @_silgen_name("$sScAsE14assumeIsolated_4file4lineqd__qd__xYiKXE_s12StaticStringVSutKlF")
   internal nonisolated func __abi__assumeIsolated<T : Sendable>(
       _ operation: (isolated Self) throws -> T,
       _ file: StaticString, _ line: UInt

stdlib/public/Concurrency/MainActor.swift

@@ -148,9 +148,15 @@ extension MainActor {
     }
   }
 
+  @abi(
+    @usableFromInline
+    internal static func assumeIsolated<T>(
+        _ operation: @MainActor () throws -> T,
+        file: StaticString, line: UInt
+    ) rethrows -> T
+  )
   @available(SwiftStdlib 5.9, *)
   @usableFromInline
-  @_silgen_name("$sScM14assumeIsolated_4file4linexxyKScMYcXE_s12StaticStringVSutKlFZ")
   internal static func __abi__assumeIsolated<T : Sendable>(
       _ operation: @MainActor () throws -> T,
       _ file: StaticString, _ line: UInt

stdlib/public/Concurrency/Task+TaskExecutor.swift

@@ -164,10 +164,16 @@ public func withTaskExecutorPreference<T, Failure>(
 //
 // This function also doubles as an ABI-compatibility shim predating the
 // introduction of #isolation.
+@abi(
+  @_unavailableInEmbedded
+  public func withTaskExecutorPreference<T: Sendable>(
+    _ taskExecutor: (any TaskExecutor)?,
+    operation: @Sendable () async throws -> T
+  ) async rethrows -> T
+)
 @_unavailableInEmbedded
 @available(SwiftStdlib 6.0, *)
 @_unsafeInheritExecutor // for ABI compatibility
-@_silgen_name("$ss26withTaskExecutorPreference_9operationxSch_pSg_xyYaYbKXEtYaKs8SendableRzlF")
 public func _unsafeInheritExecutor_withTaskExecutorPreference<T: Sendable>(
   _ taskExecutor: (any TaskExecutor)?,
   operation: @Sendable () async throws -> T

stdlib/public/Concurrency/TaskCancellation.swift

@@ -89,9 +89,14 @@ public func withTaskCancellationHandler<T>(
 //
 // This function also doubles as an ABI-compatibility shim predating the
 // introduction of #isolation.
+@abi(
+  public func withTaskCancellationHandler<T>(
+    operation: () async throws -> T,
+    onCancel handler: @Sendable () -> Void
+  ) async rethrows -> T
+)
 @_unsafeInheritExecutor // ABI compatibility with Swift 5.1
 @available(SwiftStdlib 5.1, *)
-@_silgen_name("$ss27withTaskCancellationHandler9operation8onCancelxxyYaKXE_yyYbXEtYaKlF")
 public func _unsafeInheritExecutor_withTaskCancellationHandler<T>(
   operation: () async throws -> T,
   onCancel handler: @Sendable () -> Void