From 771e9b522eb9620267b10c798804759c5810ba12 Mon Sep 17 00:00:00 2001
From: Andrew Trick <atrick@apple.com>
Date: Sat, 13 Sep 2025 18:00:57 -0700
Subject: [PATCH] Lifetimes: add a diagnostic note for implicit accessors

Lifetime diagnostics may report an error within an implicit initializer or
accessor. The source location is misleading in these cases and causes much
consternation.
---
 .../LifetimeDependenceDiagnostics.swift        | 18 ++++++++++++++++++
 .../Sources/SIL/Function.swift                 | 12 ++++++++++++
 include/swift/AST/DiagnosticsSIL.def           |  2 ++
 include/swift/SIL/SILBridging.h                |  3 +++
 include/swift/SIL/SILBridgingImpl.h            | 15 +++++++++++++++
 5 files changed, 50 insertions(+)

diff --git a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LifetimeDependenceDiagnostics.swift b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LifetimeDependenceDiagnostics.swift
index ec92036c60de3..b7bd49bb7923a 100644
--- a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LifetimeDependenceDiagnostics.swift
+++ b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LifetimeDependenceDiagnostics.swift
@@ -284,6 +284,7 @@ private struct DiagnoseDependence {
         diagnose(sourceLoc, .lifetime_value_outside_thunk, thunkSelect, function.name)
       }
     }
+    diagnoseImplicitFunction()
     reportScope()
     // Identify the use point.
     if let userSourceLoc = operand.instruction.location.sourceLoc {
@@ -323,6 +324,23 @@ private struct DiagnoseDependence {
       }
     }
   }
+
+  func diagnoseImplicitFunction() {
+    guard let funcLoc = function.location.sourceLoc else {
+      return
+    }
+    if let kindName = {
+         if function.isInitializer {
+           return "init"
+         }
+         if function.isDeinitializer {
+           return "deinit"
+         }
+         return function.accessorKindName
+       }() {
+      diagnose(funcLoc, .implicit_function_note, kindName)
+    }
+  }
 }
 
 // Identify a best-effort variable declaration based on a defining SIL
diff --git a/SwiftCompilerSources/Sources/SIL/Function.swift b/SwiftCompilerSources/Sources/SIL/Function.swift
index a802984455223..45122979f77f9 100644
--- a/SwiftCompilerSources/Sources/SIL/Function.swift
+++ b/SwiftCompilerSources/Sources/SIL/Function.swift
@@ -267,6 +267,18 @@ final public class Function : CustomStringConvertible, HasShortDescription, Hash
     return StringRef(bridged: bridged.getAccessorName()).string
   }
 
+  public var isInitializer: Bool {
+    return bridged.isInitializer()
+  }
+
+  public var isDeinitializer: Bool {
+    return bridged.isDeinitializer()
+  }
+
+  public var isImplicit: Bool {
+    return bridged.isImplicit()
+  }
+
   /// True, if the function runs with a swift 5.1 runtime.
   /// Note that this is function specific, because inlinable functions are de-serialized
   /// in a client module, which might be compiled with a different deployment target.
diff --git a/include/swift/AST/DiagnosticsSIL.def b/include/swift/AST/DiagnosticsSIL.def
index b2f29be6beff1..0b744c0debd19 100644
--- a/include/swift/AST/DiagnosticsSIL.def
+++ b/include/swift/AST/DiagnosticsSIL.def
@@ -1240,6 +1240,8 @@ NOTE(lifetime_outside_scope_use, none,
 NOTE(lifetime_outside_scope_escape, none,
      "this use causes the lifetime-dependent value to escape", ())
 
+NOTE(implicit_function_note, none, "error in compiler-generated '%0'", (StringRef))
+
 ERROR(noncopyable_shared_case_block_unimplemented, none,
       "matching a non-'Copyable' value using a case label that has multiple patterns is not implemented", ())
 
diff --git a/include/swift/SIL/SILBridging.h b/include/swift/SIL/SILBridging.h
index 4384c1132fcff..7b1e63f25570c 100644
--- a/include/swift/SIL/SILBridging.h
+++ b/include/swift/SIL/SILBridging.h
@@ -509,6 +509,9 @@ struct BridgedFunction {
   BridgedOwnedString getDebugDescription() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedLocation getLocation() const;
   BRIDGED_INLINE bool isAccessor() const;
+  BRIDGED_INLINE bool isInitializer() const;
+  BRIDGED_INLINE bool isDeinitializer() const;
+  BRIDGED_INLINE bool isImplicit() const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedStringRef getAccessorName() const;
   BRIDGED_INLINE bool hasOwnership() const;
   BRIDGED_INLINE bool hasLoweredAddresses() const;
diff --git a/include/swift/SIL/SILBridgingImpl.h b/include/swift/SIL/SILBridgingImpl.h
index e5c031d7fbf45..44ed0dbf7b94c 100644
--- a/include/swift/SIL/SILBridgingImpl.h
+++ b/include/swift/SIL/SILBridgingImpl.h
@@ -701,6 +701,21 @@ BridgedStringRef BridgedFunction::getAccessorName() const {
   return accessorKindName(accessorDecl->getAccessorKind());
 }
 
+bool BridgedFunction::isInitializer() const {
+  return getFunction()->getDeclRef().isConstructor();
+}
+
+bool BridgedFunction::isDeinitializer() const {
+  return getFunction()->getDeclRef().isDestructor();
+}
+
+bool BridgedFunction::isImplicit() const {
+  if (auto *funcDecl = getFunction()->getDeclRef().getAbstractFunctionDecl()) {
+    return funcDecl->isImplicit();
+  }
+  return false;
+}
+
 bool BridgedFunction::hasOwnership() const { return getFunction()->hasOwnership(); }
 
 bool BridgedFunction::hasLoweredAddresses() const { return getFunction()->getModule().useLoweredAddresses(); }