[SE-0302] Implement '@unchecked Sendable' syntax.

Parse and provide semantic checking for '@unchecked Sendable', for a
Sendable conformance that doesn't perform additional semantic checks
for correctness.

Part of rdar://78269000.

Author: DougGregor

include/swift/AST/ASTContext.h

@@ -1019,7 +1019,8 @@ class ASTContext final {
                  ProtocolDecl *protocol,
                  SourceLoc loc,
                  DeclContext *dc,
-                 ProtocolConformanceState state);
+                 ProtocolConformanceState state,
+                 bool isUnchecked);
 
   /// Produce a self-conformance for the given protocol.
   SelfProtocolConformance *

include/swift/AST/Attr.def

@@ -55,6 +55,7 @@ TYPE_ATTR(differentiable)
 TYPE_ATTR(noDerivative)
 TYPE_ATTR(async)
 TYPE_ATTR(Sendable)
+TYPE_ATTR(unchecked)
 
 // SIL-specific attributes
 TYPE_ATTR(block_storage)

include/swift/AST/DiagnosticsSema.def

@@ -4516,16 +4516,23 @@ ERROR(concurrent_value_class_mutable_property,none,
       (DeclName, DescriptiveDeclKind, DeclName))
 ERROR(concurrent_value_outside_source_file,none,
       "conformance to 'Sendable' must occur in the same source file as "
-      "%0 %1; use 'UnsafeSendable' for retroactive conformance",
+      "%0 %1; use '@unchecked Sendable' for retroactive conformance",
       (DescriptiveDeclKind, DeclName))
 ERROR(concurrent_value_nonfinal_class,none,
       "non-final class %0 cannot conform to `Sendable`; "
-      "use `UnsafeSendable`", (DeclName))
+      "use `@unchecked Sendable`", (DeclName))
 ERROR(concurrent_value_inherit,none,
       "`Sendable` class %1 cannot inherit from another class"
       "%select{| other than 'NSObject'}0",
       (bool, DeclName))
 
+WARNING(unchecked_conformance_not_special,none,
+      "@unchecked conformance to %0 has no meaning", (Type))
+ERROR(unchecked_not_inheritance_clause,none,
+      "'unchecked' attribute only applies in inheritance clauses", ())
+ERROR(unchecked_not_existential,none,
+      "'unchecked' attribute cannot apply to non-protocol type %0", (Type))
+
 ERROR(nonisolated_let,none,
       "'nonisolated' is meaningless on 'let' declarations because "
       "they are immutable",

include/swift/AST/NameLookup.h

@@ -503,6 +503,19 @@ void filterForDiscriminator(SmallVectorImpl<Result> &results,
 
 } // end namespace namelookup
 
+/// Describes an inherited nominal entry.
+struct InheritedNominalEntry : Located<NominalTypeDecl *> {
+  /// The location of the "unchecked" attribute, if present.
+  SourceLoc uncheckedLoc;
+
+  InheritedNominalEntry() { }
+
+  InheritedNominalEntry(
+    NominalTypeDecl *item, SourceLoc loc,
+    SourceLoc uncheckedLoc
+  ) : Located(item, loc), uncheckedLoc(uncheckedLoc) { }
+};
+
 /// Retrieve the set of nominal type declarations that are directly
 /// "inherited" by the given declaration at a particular position in the
 /// list of "inherited" types.
@@ -511,15 +524,15 @@ void filterForDiscriminator(SmallVectorImpl<Result> &results,
 /// AnyObject type, set \c anyObject true.
 void getDirectlyInheritedNominalTypeDecls(
     llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
-    unsigned i, llvm::SmallVectorImpl<Located<NominalTypeDecl *>> &result,
+    unsigned i, llvm::SmallVectorImpl<InheritedNominalEntry> &result,
     bool &anyObject);
 
 /// Retrieve the set of nominal type declarations that are directly
 /// "inherited" by the given declaration, looking through typealiases
 /// and splitting out the components of compositions.
 ///
 /// If we come across the AnyObject type, set \c anyObject true.
-SmallVector<Located<NominalTypeDecl *>, 4> getDirectlyInheritedNominalTypeDecls(
+SmallVector<InheritedNominalEntry, 4> getDirectlyInheritedNominalTypeDecls(
     llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
     bool &anyObject);
 

include/swift/AST/ProtocolConformance.h

@@ -412,11 +412,20 @@ class NormalProtocolConformance : public RootProtocolConformance,
   /// The location of this protocol conformance in the source.
   SourceLoc Loc;
 
+  // Flag bits used in ContextAndBits.
+  enum {
+    /// The conformance is invalid.
+    InvalidFlag = 0x01,
+
+    /// The conformance was labeled with @unchecked.
+    UncheckedFlag = 0x02,
+  };
+
   /// The declaration context containing the ExtensionDecl or
   /// NominalTypeDecl that declared the conformance.
   ///
-  /// Also stores the "invalid" bit.
-  llvm::PointerIntPair<DeclContext *, 1, bool> ContextAndInvalid;
+  /// Also stores the "invalid" and "unchecked" bits.
+  llvm::PointerIntPair<DeclContext *, 2, unsigned> ContextAndBits;
 
   /// The reason that this conformance exists.
   ///
@@ -457,11 +466,12 @@ class NormalProtocolConformance : public RootProtocolConformance,
 public:
   NormalProtocolConformance(Type conformingType, ProtocolDecl *protocol,
                             SourceLoc loc, DeclContext *dc,
-                            ProtocolConformanceState state)
+                            ProtocolConformanceState state,
+                            bool isUnchecked)
       : RootProtocolConformance(ProtocolConformanceKind::Normal,
                                 conformingType),
         ProtocolAndState(protocol, state), Loc(loc),
-        ContextAndInvalid(dc, false) {
+        ContextAndBits(dc, isUnchecked ? UncheckedFlag : 0) {
     assert(!conformingType->hasArchetype() &&
            "ProtocolConformances should store interface types");
   }
@@ -475,7 +485,7 @@ class NormalProtocolConformance : public RootProtocolConformance,
   /// Get the declaration context that contains the conforming extension or
   /// nominal type declaration.
   DeclContext *getDeclContext() const {
-    return ContextAndInvalid.getPointer();
+    return ContextAndBits.getPointer();
   }
 
   /// Get any additional requirements that are required for this conformance to
@@ -497,15 +507,20 @@ class NormalProtocolConformance : public RootProtocolConformance,
 
   /// Determine whether this conformance is invalid.
   bool isInvalid() const {
-    return ContextAndInvalid.getInt();
+    return ContextAndBits.getInt() & InvalidFlag;
   }
 
   /// Mark this conformance as invalid.
   void setInvalid() {
-    ContextAndInvalid.setInt(true);
+    ContextAndBits.setInt(ContextAndBits.getInt() | InvalidFlag);
     SignatureConformances = {};
   }
 
+  /// Whether this is an "unchecked" conformance.
+  bool isUnchecked() const {
+    return ContextAndBits.getInt() & UncheckedFlag;
+  }
+
   /// Get the kind of source from which this conformance comes.
   ConformanceEntryKind getSourceKind() const {
     return SourceKindAndImplyingConformance.getInt();

lib/AST/ASTContext.cpp

@@ -2188,7 +2188,8 @@ ASTContext::getConformance(Type conformingType,
                            ProtocolDecl *protocol,
                            SourceLoc loc,
                            DeclContext *dc,
-                           ProtocolConformanceState state) {
+                           ProtocolConformanceState state,
+                           bool isUnchecked) {
   assert(dc->isTypeContext());
 
   llvm::FoldingSetNodeID id;
@@ -2204,7 +2205,8 @@ ASTContext::getConformance(Type conformingType,
   // Build a new normal protocol conformance.
   auto result
     = new (*this, AllocationArena::Permanent)
-      NormalProtocolConformance(conformingType, protocol, loc, dc, state);
+        NormalProtocolConformance(
+          conformingType, protocol, loc, dc, state,isUnchecked);
   normalConformances.InsertNode(result, insertPos);
 
   return result;

lib/AST/ConformanceLookupTable.cpp

@@ -141,7 +141,17 @@ void ConformanceLookupTable::destroy() {
 }
 
 namespace {
-  using ConformanceConstructionInfo = Located<ProtocolDecl *>;
+  struct ConformanceConstructionInfo : public Located<ProtocolDecl *> {
+    /// The location of the "unchecked" attribute, if this
+    const SourceLoc uncheckedLoc;
+
+    ConformanceConstructionInfo() { }
+
+    ConformanceConstructionInfo(
+      ProtocolDecl *item, SourceLoc loc,
+      SourceLoc uncheckedLoc
+    ) : Located(item, loc), uncheckedLoc(uncheckedLoc) { }
+  };
 }
 
 template<typename NominalFunc, typename ExtensionFunc>
@@ -195,14 +205,14 @@ void ConformanceLookupTable::forEachInStage(ConformanceStage stage,
       loader.first->loadAllConformances(next, loader.second, conformances);
       loadAllConformances(next, conformances);
       for (auto conf : conformances) {
-        protocols.push_back({conf->getProtocol(), SourceLoc()});
+        protocols.push_back({conf->getProtocol(), SourceLoc(), SourceLoc()});
       }
     } else if (next->getParentSourceFile()) {
       bool anyObject = false;
       for (const auto &found :
                getDirectlyInheritedNominalTypeDecls(next, anyObject)) {
         if (auto proto = dyn_cast<ProtocolDecl>(found.Item))
-          protocols.push_back({proto, found.Loc});
+          protocols.push_back({proto, found.Loc, found.uncheckedLoc});
       }
     }
 
@@ -282,7 +292,9 @@ void ConformanceLookupTable::updateLookupTable(NominalTypeDecl *nominal,
           // its inherited protocols directly.
           auto source = ConformanceSource::forExplicit(ext);
           for (auto locAndProto : protos)
-            addProtocol(locAndProto.Item, locAndProto.Loc, source);
+            addProtocol(
+              locAndProto.Item, locAndProto.Loc,
+              source.withUncheckedLoc(locAndProto.uncheckedLoc));
         });
     break;
 
@@ -471,8 +483,10 @@ void ConformanceLookupTable::addInheritedProtocols(
   bool anyObject = false;
   for (const auto &found :
           getDirectlyInheritedNominalTypeDecls(decl, anyObject)) {
-    if (auto proto = dyn_cast<ProtocolDecl>(found.Item))
-      addProtocol(proto, found.Loc, source);
+    if (auto proto = dyn_cast<ProtocolDecl>(found.Item)) {
+      addProtocol(
+        proto, found.Loc, source.withUncheckedLoc(found.uncheckedLoc));
+    }
   }
 }
 
@@ -843,7 +857,8 @@ ConformanceLookupTable::getConformance(NominalTypeDecl *nominal,
 
     auto normalConf =
         ctx.getConformance(conformingType, protocol, conformanceLoc,
-                           conformingDC, ProtocolConformanceState::Incomplete);
+                           conformingDC, ProtocolConformanceState::Incomplete,
+                           entry->Source.getUncheckedLoc().isValid());
     // Invalid code may cause the getConformance call below to loop, so break
     // the infinite recursion by setting this eagerly to shortcircuit with the
     // early return at the start of this function.

lib/AST/ConformanceLookupTable.h

@@ -85,6 +85,9 @@ class ConformanceLookupTable {
   class ConformanceSource {
     llvm::PointerIntPair<void *, 2, ConformanceEntryKind> Storage;
 
+    /// The location of the "unchecked" attribute, if there is one.
+    SourceLoc uncheckedLoc;
+
     ConformanceSource(void *ptr, ConformanceEntryKind kind) 
       : Storage(ptr, kind) { }
 
@@ -123,6 +126,14 @@ class ConformanceLookupTable {
       return ConformanceSource(typeDecl, ConformanceEntryKind::Synthesized);
     }
 
+    /// Return a new conformance source with the given location of "@unchecked".
+    ConformanceSource withUncheckedLoc(SourceLoc uncheckedLoc) {
+      ConformanceSource result(*this);
+      if (uncheckedLoc.isValid())
+        result.uncheckedLoc = uncheckedLoc;
+      return result;
+    }
+
     /// Retrieve the kind of conformance formed from this source.
     ConformanceEntryKind getKind() const { return Storage.getInt(); }
 
@@ -149,6 +160,11 @@ class ConformanceLookupTable {
       llvm_unreachable("Unhandled ConformanceEntryKind in switch.");
     }
 
+    /// The location of the @unchecked attribute, if any.
+    SourceLoc getUncheckedLoc() const {
+      return uncheckedLoc;
+    }
+
     /// For an inherited conformance, retrieve the class declaration
     /// for the inheriting class.
     ClassDecl *getInheritingClass() const {

lib/AST/NameLookup.cpp

@@ -2662,7 +2662,7 @@ CustomAttrNominalRequest::evaluate(Evaluator &evaluator,
 
 void swift::getDirectlyInheritedNominalTypeDecls(
     llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
-    unsigned i, llvm::SmallVectorImpl<Located<NominalTypeDecl *>> &result,
+    unsigned i, llvm::SmallVectorImpl<InheritedNominalEntry> &result,
     bool &anyObject) {
   auto typeDecl = decl.dyn_cast<const TypeDecl *>();
   auto extDecl = decl.dyn_cast<const ExtensionDecl *>();
@@ -2684,18 +2684,28 @@ void swift::getDirectlyInheritedNominalTypeDecls(
   // FIXME: This is a hack. We need cooperation from
   // InheritedDeclsReferencedRequest to make this work.
   SourceLoc loc;
+  SourceLoc uncheckedLoc;
   if (TypeRepr *typeRepr = typeDecl ? typeDecl->getInherited()[i].getTypeRepr()
                                     : extDecl->getInherited()[i].getTypeRepr()){
     loc = typeRepr->getLoc();
+
+    // Dig out the @unchecked attribute, if it's present.
+    while (auto attrTypeRepr = dyn_cast<AttributedTypeRepr>(typeRepr)) {
+      if (attrTypeRepr->getAttrs().has(TAK_unchecked)) {
+        uncheckedLoc = attrTypeRepr->getAttrs().getLoc(TAK_unchecked);
+      }
+
+      typeRepr = attrTypeRepr->getTypeRepr();
+    }
   }
 
   // Form the result.
   for (auto nominal : nominalTypes) {
-    result.push_back({nominal, loc});
+    result.push_back({nominal, loc, uncheckedLoc});
   }
 }
 
-SmallVector<Located<NominalTypeDecl *>, 4>
+SmallVector<InheritedNominalEntry, 4>
 swift::getDirectlyInheritedNominalTypeDecls(
     llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
     bool &anyObject) {
@@ -2705,7 +2715,7 @@ swift::getDirectlyInheritedNominalTypeDecls(
   // Gather results from all of the inherited types.
   unsigned numInherited = typeDecl ? typeDecl->getInherited().size()
                                    : extDecl->getInherited().size();
-  SmallVector<Located<NominalTypeDecl *>, 4> result;
+  SmallVector<InheritedNominalEntry, 4> result;
   for (unsigned i : range(numInherited)) {
     getDirectlyInheritedNominalTypeDecls(decl, i, result, anyObject);
   }
@@ -2731,7 +2741,7 @@ swift::getDirectlyInheritedNominalTypeDecls(
       if (!req.getFirstType()->isEqual(protoSelfTy))
         continue;
 
-      result.emplace_back(req.getProtocolDecl(), loc);
+      result.emplace_back(req.getProtocolDecl(), loc, SourceLoc());
     }
     return result;
   }
@@ -2741,7 +2751,7 @@ swift::getDirectlyInheritedNominalTypeDecls(
   anyObject |= selfBounds.anyObject;
 
   for (auto inheritedNominal : selfBounds.decls)
-    result.emplace_back(inheritedNominal, loc);
+    result.emplace_back(inheritedNominal, loc, SourceLoc());
 
   return result;
 }

lib/ClangImporter/ImportDecl.cpp

@@ -10043,7 +10043,8 @@ void ClangImporter::Implementation::loadAllConformances(
     auto conformance = SwiftContext.getConformance(
         dc->getDeclaredInterfaceType(),
         protocol, SourceLoc(), dc,
-        ProtocolConformanceState::Incomplete);
+        ProtocolConformanceState::Incomplete,
+        protocol->isSpecificProtocol(KnownProtocolKind::Sendable));
     conformance->setLazyLoader(this, /*context*/0);
     conformance->setState(ProtocolConformanceState::Complete);
     Conformances.push_back(conformance);

lib/Sema/CSDiagnostics.cpp

@@ -3113,7 +3113,7 @@ bool ContextualFailure::tryProtocolConformanceFixIt(
     for (auto protocol : missingProtocols) {
       auto conformance = NormalProtocolConformance(
           nominal->getDeclaredType(), protocol, SourceLoc(), nominal,
-          ProtocolConformanceState::Incomplete);
+          ProtocolConformanceState::Incomplete, /*isUnchecked=*/false);
       ConformanceChecker checker(getASTContext(), &conformance,
                                  missingWitnesses);
       checker.resolveValueWitnesses();