Merge pull request swiftlang#78283 from atrick/remove-trivial-feature

Remove the experimental LifetimeDependenceDiagnoseTrivial feature.

Author: atrick

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LifetimeDependenceDiagnostics.swift

@@ -101,10 +101,11 @@ let lifetimeDependenceDiagnosticsPass = FunctionPass(
 private func analyze(dependence: LifetimeDependence, _ context: FunctionPassContext) -> Bool {
   log("Dependence scope:\n\(dependence)")
 
-  // Early versions of Span in the standard library violate trivial lifetimes. Contemporary versions of the compiler
-  // simply ignored dependencies on trivial values.
-  if !context.options.hasFeature(.LifetimeDependenceDiagnoseTrivial) {
-    if dependence.parentValue.type.objectType.isTrivial(in: dependence.function) {
+  // Briefly, some versions of Span in the standard library violated trivial lifetimes; versions of the compiler built
+  // at that time simply ignored dependencies on trivial values. For now, disable trivial dependencies to allow newer
+  // compilers to build against those older standard libraries. This check is only relevant for ~6 mo (until July 2025).
+  if dependence.parentValue.type.objectType.isTrivial(in: dependence.function) {
+    if let sourceFileKind = dependence.function.sourceFileKind, sourceFileKind == .interface {
       return true
     }
   }

SwiftCompilerSources/Sources/SIL/Function.swift

@@ -256,6 +256,27 @@ final public class Function : CustomStringConvertible, HasShortDescription, Hash
         fatalError()
     }
   }
+
+  public enum SourceFileKind {
+    case library         /// A normal .swift file.
+    case main            /// A .swift file that can have top-level code.
+    case sil             /// Came from a .sil file.
+    case interface       /// Came from a .swiftinterface file, representing another module.
+    case macroExpansion  /// Came from a macro expansion.
+    case defaultArgument /// Came from default argument at caller side
+  };
+
+  public var sourceFileKind: SourceFileKind? {
+    switch bridged.getSourceFileKind() {
+    case .Library: return .library
+    case .Main: return .main
+    case .SIL: return .sil
+    case .Interface: return .interface
+    case .MacroExpansion: return .macroExpansion
+    case .DefaultArgument: return .defaultArgument
+    case .None: return nil
+    }
+  }
 }
 
 public func == (lhs: Function, rhs: Function) -> Bool { lhs === rhs }

include/swift/Basic/Features.def

@@ -362,9 +362,6 @@ EXPERIMENTAL_FEATURE(StructLetDestructuring, true)
 /// Enable returning non-escapable types from functions.
 EXPERIMENTAL_FEATURE(LifetimeDependence, true)
 
-/// Enable LifetimeDependence diagnostics for trivial types.
-EXPERIMENTAL_FEATURE(LifetimeDependenceDiagnoseTrivial, false)
-
 /// Enable the `@_staticExclusiveOnly` attribute.
 EXPERIMENTAL_FEATURE(StaticExclusiveOnly, true)
 

include/swift/SIL/SILBridging.h

@@ -477,6 +477,16 @@ struct BridgedFunction {
     IsSerializedForPackage
   };
 
+  enum class OptionalSourceFileKind {
+    Library,
+    Main,
+    SIL,
+    Interface,
+    MacroExpansion,
+    DefaultArgument, // must match swift::SourceFileKind::DefaultArgument
+    None
+  };
+
   SWIFT_NAME("init(obj:)")
   BridgedFunction(SwiftObject obj) : obj(obj) {}
   BridgedFunction() {}
@@ -529,6 +539,7 @@ struct BridgedFunction {
   bool isAutodiffVJP() const;
   SwiftInt specializationLevel() const;
   SWIFT_IMPORT_UNSAFE BridgedSubstitutionMap getMethodSubstitutions(BridgedSubstitutionMap contextSubs) const;
+  BRIDGED_INLINE OptionalSourceFileKind getSourceFileKind() const;
 
   enum class ParseEffectsMode {
     argumentEffectsFromSource,

include/swift/SIL/SILBridgingImpl.h

@@ -22,6 +22,7 @@
 #include "SILBridging.h"
 #include "swift/AST/Builtins.h"
 #include "swift/AST/Decl.h"
+#include "swift/AST/SourceFile.h"
 #include "swift/AST/SubstitutionMap.h"
 #include "swift/AST/Types.h"
 #include "swift/Basic/BasicBridging.h"
@@ -924,6 +925,14 @@ swift::SILFunction * _Nullable OptionalBridgedFunction::getFunction() const {
   return static_cast<swift::SILFunction *>(obj);
 }
 
+BridgedFunction::OptionalSourceFileKind BridgedFunction::getSourceFileKind() const {
+  if (auto *dc = getFunction()->getDeclContext()) {
+    if (auto *sourceFile = dc->getParentSourceFile())
+      return (OptionalSourceFileKind)sourceFile->Kind;
+  }
+  return OptionalSourceFileKind::None;
+}
+
 //===----------------------------------------------------------------------===//
 //                                BridgedGlobalVar
 //===----------------------------------------------------------------------===//

lib/AST/FeatureSet.cpp

@@ -263,8 +263,6 @@ static bool usesFeatureLifetimeDependence(Decl *decl) {
       ->hasLifetimeDependencies();
 }
 
-UNINTERESTING_FEATURE(LifetimeDependenceDiagnoseTrivial)
-
 UNINTERESTING_FEATURE(DynamicActorIsolation)
 UNINTERESTING_FEATURE(NonfrozenEnumExhaustivity)
 UNINTERESTING_FEATURE(ClosureIsolation)

stdlib/public/Cxx/CxxSpan.swift

@@ -18,6 +18,24 @@ internal func unsafeBitCast<T: ~Escapable, U>(
   Builtin.reinterpretCast(x)
 }
 
+/// Unsafely discard any lifetime dependency on the `dependent` argument. Return
+/// a value identical to `dependent` with a lifetime dependency on the caller's
+/// borrow scope of the `source` argument.
+@unsafe
+@_unsafeNonescapableResult
+@_alwaysEmitIntoClient
+@_transparent
+@lifetime(borrow source)
+internal func _overrideLifetime<
+  T: ~Copyable & ~Escapable, U: ~Copyable & ~Escapable
+>(
+  _ dependent: consuming T, borrowing source: borrowing U
+) -> T {
+  // TODO: Remove @_unsafeNonescapableResult. Instead, the unsafe dependence
+  // should be expressed by a builtin that is hidden within the function body.
+  dependent
+}
+
 /// A C++ type that is an object that can refer to a contiguous sequence of objects.
 ///
 /// C++ standard library type `std::span` conforms to this protocol.
@@ -62,12 +80,15 @@ extension CxxSpan {
 @available(SwiftStdlib 6.1, *)
 extension Span {
   @_alwaysEmitIntoClient
-  @lifetime(immortal)
   @unsafe
+  @lifetime(borrow span)
   public init<T: CxxSpan<Element>>(
-    _unsafeCxxSpan span: T,
+    _unsafeCxxSpan span: borrowing T,
   ) {
-    self.init(_unsafeElements: .init(start: span.__dataUnsafe(), count: Int(span.size())))
+    let buffer = UnsafeBufferPointer(start: span.__dataUnsafe(), count: Int(span.size()))
+    let newSpan = Span(_unsafeElements: buffer)
+    // 'self' is limited to the caller's scope of the variable passed to the 'span' argument.
+    self = _overrideLifetime(newSpan, borrowing: span)
   }
 }
 

test/Generics/inverse_generics.swift

@@ -1,10 +1,8 @@
 // RUN: %target-typecheck-verify-swift \
 // RUN: -enable-experimental-feature LifetimeDependence \
-// RUN: -enable-experimental-feature LifetimeDependenceDiagnoseTrivial \
 // RUN: -enable-experimental-feature SuppressedAssociatedTypes
 
 // REQUIRES: swift_feature_LifetimeDependence
-// REQUIRES: swift_feature_LifetimeDependenceDiagnoseTrivial
 // REQUIRES: swift_feature_SuppressedAssociatedTypes
 
 // expected-note@+1 {{'T' has '~Copyable' constraint preventing implicit 'Copyable' conformance}}

test/SIL/Parser/basic2_noncopyable_generics.sil

@@ -1,16 +1,13 @@
 // RUN: %target-sil-opt                                      \
 // RUN:     %s                                               \
 // RUN:     -enable-experimental-feature LifetimeDependence   \
-// RUN:     -enable-experimental-feature LifetimeDependenceDiagnoseTrivial \
 // RUN: |                                                    \
 // RUN: %target-sil-opt                                      \
 // RUN:     -enable-experimental-feature LifetimeDependence   \
-// RUN:     -enable-experimental-feature LifetimeDependenceDiagnoseTrivial \
 // RUN: |                                                    \
 // RUN: %FileCheck %s
 
 // REQUIRES: swift_feature_LifetimeDependence
-// REQUIRES: swift_feature_LifetimeDependenceDiagnoseTrivial
 
 // For -enable-experimental-feature LifetimeDependence
 

test/SIL/Parser/lifetime_dependence.sil

@@ -1,10 +1,8 @@
 // RUN: %target-sil-opt %s \
 // RUN:   -enable-experimental-feature LifetimeDependence \
-// RUN:   -enable-experimental-feature LifetimeDependenceDiagnoseTrivial \
 // RUN: | %FileCheck %s
 
 // REQUIRES: swift_feature_LifetimeDependence
-// REQUIRES: swift_feature_LifetimeDependenceDiagnoseTrivial
 
 sil_stage canonical