[6.2][cxx-interop] Shared references are considered safe

Explanation: Shared references imported from C++ were not considered
safe. This is a widely used feature and this fix is blocking the users
from adopting strictly memory safe Swift.
Issue: rdar://151039766
Risk: Low, the fix only changes what declarations are considered safe.
Testing: Regression test added.
Original PR: #82203
Reviewer: @egorzhdan @fahadnayyar

Author: Xazax-hun

include/swift/ClangImporter/ClangImporterRequests.h

@@ -576,10 +576,37 @@ class ClangTypeEscapability
 void simple_display(llvm::raw_ostream &out, EscapabilityLookupDescriptor desc);
 SourceLoc extractNearestSourceLoc(EscapabilityLookupDescriptor desc);
 
+struct CxxDeclExplicitSafetyDescriptor final {
+  const clang::Decl *decl;
+  bool isClass;
+
+  CxxDeclExplicitSafetyDescriptor(const clang::Decl *decl, bool isClass)
+      : decl(decl), isClass(isClass) {}
+
+  friend llvm::hash_code
+  hash_value(const CxxDeclExplicitSafetyDescriptor &desc) {
+    return llvm::hash_combine(desc.decl, desc.isClass);
+  }
+
+  friend bool operator==(const CxxDeclExplicitSafetyDescriptor &lhs,
+                         const CxxDeclExplicitSafetyDescriptor &rhs) {
+    return lhs.decl == rhs.decl && lhs.isClass == rhs.isClass;
+  }
+
+  friend bool operator!=(const CxxDeclExplicitSafetyDescriptor &lhs,
+                         const CxxDeclExplicitSafetyDescriptor &rhs) {
+    return !(lhs == rhs);
+  }
+};
+
+void simple_display(llvm::raw_ostream &out,
+                    CxxDeclExplicitSafetyDescriptor desc);
+SourceLoc extractNearestSourceLoc(CxxDeclExplicitSafetyDescriptor desc);
+
 /// Determine the safety of the given Clang declaration.
 class ClangDeclExplicitSafety
     : public SimpleRequest<ClangDeclExplicitSafety,
-                           ExplicitSafety(SafeUseOfCxxDeclDescriptor),
+                           ExplicitSafety(CxxDeclExplicitSafetyDescriptor),
                            RequestFlags::Cached> {
 public:
   using SimpleRequest::SimpleRequest;
@@ -592,7 +619,8 @@ class ClangDeclExplicitSafety
   friend SimpleRequest;
 
   // Evaluation.
-  ExplicitSafety evaluate(Evaluator &evaluator, SafeUseOfCxxDeclDescriptor desc) const;
+  ExplicitSafety evaluate(Evaluator &evaluator,
+                          CxxDeclExplicitSafetyDescriptor desc) const;
 };
 
 #define SWIFT_TYPEID_ZONE ClangImporter

include/swift/ClangImporter/ClangImporterTypeIDZone.def

@@ -46,5 +46,5 @@ SWIFT_REQUEST(ClangImporter, ClangTypeEscapability,
               CxxEscapability(EscapabilityLookupDescriptor), Cached,
               NoLocationInfo)
 SWIFT_REQUEST(ClangImporter, ClangDeclExplicitSafety,
-              ExplicitSafety(SafeUseOfCxxDeclDescriptor), Cached,
+              ExplicitSafety(CxxDeclExplicitSafetyDescriptor), Cached,
               NoLocationInfo)

lib/AST/Decl.cpp

@@ -1240,9 +1240,10 @@ ExplicitSafety Decl::getExplicitSafety() const {
   // If this declaration is from C, ask the Clang importer.
   if (auto clangDecl = getClangDecl()) {
     ASTContext &ctx = getASTContext();
-    return evaluateOrDefault(ctx.evaluator,
-                             ClangDeclExplicitSafety({clangDecl}),
-                             ExplicitSafety::Unspecified);
+    return evaluateOrDefault(
+        ctx.evaluator,
+        ClangDeclExplicitSafety({clangDecl, isa<ClassDecl>(this)}),
+        ExplicitSafety::Unspecified);
   }
 
   // Inference: Check the enclosing context, unless this is a type.

lib/ClangImporter/ClangImporter.cpp

@@ -24,6 +24,7 @@
 #include "swift/AST/Builtins.h"
 #include "swift/AST/ClangModuleLoader.h"
 #include "swift/AST/ConcreteDeclRef.h"
+#include "swift/AST/Decl.h"
 #include "swift/AST/DiagnosticEngine.h"
 #include "swift/AST/DiagnosticsClangImporter.h"
 #include "swift/AST/DiagnosticsSema.h"
@@ -8392,6 +8393,20 @@ SourceLoc swift::extractNearestSourceLoc(SafeUseOfCxxDeclDescriptor desc) {
   return SourceLoc();
 }
 
+void swift::simple_display(llvm::raw_ostream &out,
+                           CxxDeclExplicitSafetyDescriptor desc) {
+  out << "Checking if '";
+  if (auto namedDecl = dyn_cast<clang::NamedDecl>(desc.decl))
+    out << namedDecl->getNameAsString();
+  else
+    out << "<invalid decl>";
+  out << "' is explicitly safe.\n";
+}
+
+SourceLoc swift::extractNearestSourceLoc(CxxDeclExplicitSafetyDescriptor desc) {
+  return SourceLoc();
+}
+
 CustomRefCountingOperationResult CustomRefCountingOperation::evaluate(
     Evaluator &evaluator, CustomRefCountingOperationDescriptor desc) const {
   auto swiftDecl = desc.decl;
@@ -8469,9 +8484,11 @@ static bool hasUnsafeType(Evaluator &evaluator, clang::QualType clangType) {
 
   // Handle records recursively.
   if (auto recordDecl = clangType->getAsTagDecl()) {
-    auto safety =
-        evaluateOrDefault(evaluator, ClangDeclExplicitSafety({recordDecl}),
-                          ExplicitSafety::Unspecified);
+    // If we reached this point the types is not imported as a shared reference,
+    // so we don't need to check the bases whether they are shared references.
+    auto safety = evaluateOrDefault(
+        evaluator, ClangDeclExplicitSafety({recordDecl, false}),
+        ExplicitSafety::Unspecified);
     switch (safety) {
       case ExplicitSafety::Unsafe:
         return true;
@@ -8486,10 +8503,9 @@ static bool hasUnsafeType(Evaluator &evaluator, clang::QualType clangType) {
   return false;
 }
 
-ExplicitSafety ClangDeclExplicitSafety::evaluate(
-    Evaluator &evaluator,
-    SafeUseOfCxxDeclDescriptor desc
-) const {
+ExplicitSafety
+ClangDeclExplicitSafety::evaluate(Evaluator &evaluator,
+                                  CxxDeclExplicitSafetyDescriptor desc) const {
   // FIXME: Somewhat duplicative with importAsUnsafe.
   // FIXME: Also similar to hasPointerInSubobjects
   // FIXME: should probably also subsume IsSafeUseOfCxxDecl
@@ -8502,7 +8518,11 @@ ExplicitSafety ClangDeclExplicitSafety::evaluate(
   // Explicitly safe.
   if (hasSwiftAttribute(decl, "safe"))
     return ExplicitSafety::Safe;
-  
+
+  // Shared references are considered safe.
+  if (desc.isClass)
+    return ExplicitSafety::Safe;
+
   // Enums are always safe.
   if (isa<clang::EnumDecl>(decl))
     return ExplicitSafety::Safe;

test/Interop/Cxx/class/safe-interop-mode.swift

@@ -63,6 +63,16 @@ View safeFunc(View v1 [[clang::noescape]], View v2 [[clang::lifetimebound]]);
 // Second non-escapable type is not annotated in any way.
 void unsafeFunc(View v1 [[clang::noescape]], View v2);
 
+class SharedObject {
+private:
+  int *p;
+} SWIFT_SHARED_REFERENCE(retainSharedObject, releaseSharedObject);
+
+inline void retainSharedObject(SharedObject *) {}
+inline void releaseSharedObject(SharedObject *) {}
+
+struct DerivedFromSharedObject : SharedObject {};
+
 //--- test.swift
 
 import Test
@@ -134,3 +144,13 @@ func useUnsafeLifetimeAnnotated(v: View) {
     // expected-warning@+1{{expression uses unsafe constructs but is not marked with 'unsafe'}}
     unsafeFunc(v, v) // expected-note{{reference to unsafe global function 'unsafeFunc'}}
 }
+
+@available(SwiftStdlib 5.8, *)
+func useSharedReference(frt: SharedObject) {
+  let _ = frt
+}
+
+@available(SwiftStdlib 5.8, *)
+func useSharedReference(frt: DerivedFromSharedObject) {
+  let _ = frt
+}