[Sema] Enable suppression of inferred conformances.

Add the machinery to support suppression of inference of conformance to
protocols that would otherwise be derived automatically.

This commit does not enable any conformances to be suppressed.

Author: nate-chandler

include/swift/AST/Decl.h

@@ -1638,17 +1638,27 @@ struct InheritedEntry : public TypeLoc {
   /// Whether there was an @preconcurrency attribute.
   bool IsPreconcurrency : 1;
 
+  /// Whether there was a ~ indicating suppression but not inversion.
+  bool IsSuppressed : 1;
+
 public:
   InheritedEntry(const TypeLoc &typeLoc);
 
   InheritedEntry(const TypeLoc &typeLoc, bool isUnchecked, bool isRetroactive,
-                 bool isPreconcurrency)
+                 bool isPreconcurrency, bool isSuppressed = false)
       : TypeLoc(typeLoc), IsUnchecked(isUnchecked),
-        IsRetroactive(isRetroactive), IsPreconcurrency(isPreconcurrency) {}
+        IsRetroactive(isRetroactive), IsPreconcurrency(isPreconcurrency),
+        IsSuppressed(isSuppressed) {}
 
   bool isUnchecked() const { return IsUnchecked; }
   bool isRetroactive() const { return IsRetroactive; }
   bool isPreconcurrency() const { return IsPreconcurrency; }
+  bool isSuppressed() const { return IsSuppressed; }
+
+  void setSuppressed() {
+    assert(!IsSuppressed && "setting suppressed again!?");
+    IsSuppressed = true;
+  }
 };
 
 /// A wrapper for the collection of inherited types for either a `TypeDecl` or
@@ -4471,6 +4481,8 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   /// Type if it `isEscapable` instead of using this.
   CanBeInvertible::Result canBeEscapable() const;
 
+  bool suppressesConformance(KnownProtocolKind kp) const;
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) {
     return D->getKind() >= DeclKind::First_NominalTypeDecl &&

include/swift/AST/DiagnosticsSema.def

@@ -7710,6 +7710,12 @@ NOTE(add_generic_parameter_non_bitwise_copyable_conformance,none,
 ERROR(bitwise_copyable_outside_module,none,
       "conformance to 'BitwiseCopyable' must occur in the same module as %kind0",
       (const ValueDecl *))
+ERROR(suppress_inferrable_protocol_extension,none,
+      "conformance to inferrable protocol %0 cannot be suppressed in an extension", (const ProtocolDecl *))
+ERROR(suppress_nonsuppressable_protocol,none,
+      "conformance to %0 cannot be suppressed", (const ProtocolDecl *))
+WARNING(suppress_already_suppressed_protocol,none,
+      "already suppressed conformance to %0", (const ProtocolDecl *))
 
 // -- older ones below --
 ERROR(noncopyable_parameter_requires_ownership, none,

include/swift/AST/NameLookup.h

@@ -589,12 +589,16 @@ struct InheritedNominalEntry : Located<NominalTypeDecl *> {
   /// The location of the "preconcurrency" attribute if present.
   SourceLoc preconcurrencyLoc;
 
+  /// Whether this inherited entry was suppressed via "~".
+  bool isSuppressed;
+
   InheritedNominalEntry() { }
 
   InheritedNominalEntry(NominalTypeDecl *item, SourceLoc loc,
-                        SourceLoc uncheckedLoc, SourceLoc preconcurrencyLoc)
+                        SourceLoc uncheckedLoc, SourceLoc preconcurrencyLoc,
+                        bool isSuppressed)
       : Located(item, loc), uncheckedLoc(uncheckedLoc),
-        preconcurrencyLoc(preconcurrencyLoc) {}
+        preconcurrencyLoc(preconcurrencyLoc), isSuppressed(isSuppressed) {}
 };
 
 /// Retrieve the set of nominal type declarations that are directly

include/swift/AST/PrintOptions.h

@@ -388,6 +388,9 @@ struct PrintOptions {
   /// Suppress printing of `borrowing` and `consuming`.
   bool SuppressNoncopyableOwnershipModifiers = false;
 
+  /// Suppress printing of '~Proto' for suppressible, non-invertible protocols.
+  bool SuppressConformanceSuppression = false;
+
   /// List of attribute kinds that should not be printed.
   std::vector<AnyAttrKind> ExcludeAttrList = {
       DeclAttrKind::Transparent, DeclAttrKind::Effects,

include/swift/AST/TypeCheckRequests.h

@@ -16,23 +16,25 @@
 #ifndef SWIFT_TYPE_CHECK_REQUESTS_H
 #define SWIFT_TYPE_CHECK_REQUESTS_H
 
-#include "swift/AST/ActorIsolation.h"
-#include "swift/AST/AnyFunctionRef.h"
 #include "swift/AST/ASTNode.h"
 #include "swift/AST/ASTTypeIDs.h"
+#include "swift/AST/ActorIsolation.h"
+#include "swift/AST/AnyFunctionRef.h"
 #include "swift/AST/CatchNode.h"
 #include "swift/AST/Effects.h"
+#include "swift/AST/Evaluator.h"
 #include "swift/AST/GenericParamList.h"
 #include "swift/AST/GenericSignature.h"
-#include "swift/AST/Type.h"
-#include "swift/AST/Evaluator.h"
 #include "swift/AST/Pattern.h"
 #include "swift/AST/PluginRegistry.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/AST/SimpleRequest.h"
 #include "swift/AST/SourceFile.h"
+#include "swift/AST/Type.h"
 #include "swift/AST/TypeResolutionStage.h"
 #include "swift/Basic/Statistic.h"
+#include "swift/Basic/TaggedUnion.h"
+#include "swift/Basic/TypeID.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/TinyPtrVector.h"
@@ -51,6 +53,7 @@ class DoCatchStmt;
 struct ExternalMacroDefinition;
 class ClosureExpr;
 class GenericParamList;
+class InverseTypeRepr;
 class LabeledStmt;
 class MacroDefinition;
 class PrecedenceGroupDecl;
@@ -78,13 +81,75 @@ void simple_display(
 
 void simple_display(llvm::raw_ostream &out, ASTContext *ctx);
 
+/// Emulates the following enum with associated values:
+/// enum InheritedTypeResult {
+///     case inherited(Type)
+///     case suppressed(Type, InverseTypeRepr *)
+///     case `default`
+/// }
+class InheritedTypeResult {
+  struct Inherited_ {
+    Type ty;
+  };
+  struct Suppressed_ {
+    // The type which is suppressed.  Not the result of inverting a protocol.
+    Type ty;
+    InverseTypeRepr *repr;
+  };
+  struct Default_ {};
+  using Payload = TaggedUnion<Inherited_, Suppressed_, Default_>;
+  Payload payload;
+  InheritedTypeResult(Payload payload) : payload(payload) {}
+
+public:
+  enum Kind { Inherited, Suppressed, Default };
+  static InheritedTypeResult forInherited(Type ty) { return {Inherited_{ty}}; }
+  static InheritedTypeResult forSuppressed(Type ty, InverseTypeRepr *repr) {
+    return {Suppressed_{ty, repr}};
+  }
+  static InheritedTypeResult forDefault() { return {Default_{}}; }
+  operator Kind() {
+    if (payload.isa<Inherited_>()) {
+      return Kind::Inherited;
+    } else if (payload.isa<Suppressed_>()) {
+      return Kind::Suppressed;
+    }
+    return Kind::Default;
+  }
+  explicit operator bool() { return !payload.isa<Default_>(); }
+  Type getInheritedTypeOrNull(ASTContext &ctx) {
+    switch (*this) {
+    case Inherited:
+      return getInheritedType();
+    case Suppressed: {
+      auto suppressed = getSuppressed();
+      auto kp = suppressed.first->getKnownProtocol();
+      if (!kp)
+        return Type();
+      auto ipk = getInvertibleProtocolKind(*kp);
+      if (!ipk)
+        return Type();
+      return ProtocolCompositionType::getInverseOf(ctx, *ipk);
+    }
+    case Default:
+      return Type();
+    }
+  }
+  Type getInheritedType() { return payload.get<Inherited_>().ty; }
+  std::pair<Type, InverseTypeRepr *> getSuppressed() {
+    auto &suppressed = payload.get<Suppressed_>();
+    return {suppressed.ty, suppressed.repr};
+  }
+};
+
 /// Request the type from the ith entry in the inheritance clause for the
 /// given declaration.
 class InheritedTypeRequest
     : public SimpleRequest<
           InheritedTypeRequest,
-          Type(llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *>,
-               unsigned, TypeResolutionStage),
+          InheritedTypeResult(
+              llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *>,
+              unsigned, TypeResolutionStage),
           RequestFlags::SeparatelyCached> {
 public:
   using SimpleRequest::SimpleRequest;
@@ -93,21 +158,22 @@ class InheritedTypeRequest
   friend SimpleRequest;
 
   // Evaluation.
-  Type
+  InheritedTypeResult
   evaluate(Evaluator &evaluator,
            llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
            unsigned index, TypeResolutionStage stage) const;
 
-  const TypeLoc &getTypeLoc() const;
+  const InheritedEntry &getInheritedEntry() const;
+  ASTContext &getASTContext() const;
 
 public:
   // Source location
   SourceLoc getNearestLoc() const;
 
   // Caching
   bool isCached() const;
-  std::optional<Type> getCachedResult() const;
-  void cacheResult(Type value) const;
+  std::optional<InheritedTypeResult> getCachedResult() const;
+  void cacheResult(InheritedTypeResult value) const;
 };
 
 /// Request the superclass type for the given class.
@@ -4891,6 +4957,23 @@ class InheritanceClauseRequest
   void cacheResult(ArrayRef<InheritedEntry>) const;
 };
 
+class SuppressesConformanceRequest
+    : public SimpleRequest<SuppressesConformanceRequest,
+                           bool(NominalTypeDecl *decl, KnownProtocolKind kp),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  bool evaluate(Evaluator &evaluator, NominalTypeDecl *decl,
+                KnownProtocolKind kp) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
 #define SWIFT_TYPEID_ZONE TypeChecker
 #define SWIFT_TYPEID_HEADER "swift/AST/TypeCheckerTypeIDZone.def"
 #include "swift/Basic/DefineTypeIDZone.h"

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -569,3 +569,6 @@ SWIFT_REQUEST(TypeChecker, ImportDeclRequest,
               std::optional<AttributedImport<ImportedModule>>(
                   const SourceFile *sf, const ModuleDecl *mod),
               Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, SuppressesConformanceRequest,
+              bool(NominalTypeDecl *decl, KnownProtocolKind kp),
+              SeparatelyCached, NoLocationInfo)

include/swift/Basic/Features.def

@@ -342,6 +342,9 @@ EXPERIMENTAL_FEATURE(ExtractConstantsFromMembers, false)
 /// Enable bitwise-copyable feature.
 EXPERIMENTAL_FEATURE(BitwiseCopyable, true)
 
+/// Enable the suppression of inferred, non-invertible, protocols via ~.
+SUPPRESSIBLE_EXPERIMENTAL_FEATURE(ConformanceSuppression, true)
+
 /// Enables the FixedArray data type.
 EXPERIMENTAL_FEATURE(FixedArrays, true)
 

include/swift/Parse/Parser.h

@@ -163,6 +163,11 @@ class Parser {
   // to ensure there's no parsing performance regression.
   bool EnabledNoncopyableGenerics;
 
+  bool canSuppressConformancesWithTilde() const {
+    return EnabledNoncopyableGenerics ||
+           Context.LangOpts.hasFeature(Feature::ConformanceSuppression);
+  }
+
   /// Whether we should delay parsing nominal type, extension, and function
   /// bodies.
   bool isDelayedParsingEnabled() const;

lib/AST/ASTPrinter.cpp

@@ -2796,6 +2796,8 @@ void PrintAST::printInherited(const Decl *decl) {
         Printer << "@retroactive ";
       if (inherited.isPreconcurrency())
         Printer << "@preconcurrency ";
+      if (inherited.isSuppressed())
+        Printer << "~";
     });
   }, [&]() {
     Printer << ", ";
@@ -3140,6 +3142,17 @@ static void suppressingFeatureNoncopyableGenerics(
   options.ExcludeAttrList.resize(originalExcludeAttrCount);
 }
 
+static void
+suppressingFeatureConformanceSuppression(PrintOptions &options,
+                                         llvm::function_ref<void()> action) {
+  unsigned originalExcludeAttrCount = options.ExcludeAttrList.size();
+  options.ExcludeAttrList.push_back(DeclAttrKind::PreInverseGenerics);
+  llvm::SaveAndRestore<bool> scope(options.SuppressConformanceSuppression,
+                                   true);
+  action();
+  options.ExcludeAttrList.resize(originalExcludeAttrCount);
+}
+
 /// Suppress the printing of a particular feature.
 static void suppressingFeature(PrintOptions &options, Feature feature,
                                llvm::function_ref<void()> action) {
@@ -7854,6 +7867,10 @@ swift::getInheritedForPrinting(
             continue;
       }
     }
+    if (options.SuppressConformanceSuppression &&
+        inherited.getEntry(i).isSuppressed()) {
+      continue;
+    }
 
     Results.push_back(inherited.getEntry(i));
   }

lib/AST/ConformanceLookupTable.cpp

@@ -302,7 +302,14 @@ void ConformanceLookupTable::updateLookupTable(NominalTypeDecl *nominal,
           bool anyObject = false;
           for (const auto &found :
                   getDirectlyInheritedNominalTypeDecls(nominal, inverses, anyObject)) {
-            if (auto proto = dyn_cast<ProtocolDecl>(found.Item)) {
+            auto proto = dyn_cast<ProtocolDecl>(found.Item);
+            if (!proto)
+              continue;
+            auto kp = proto->getKnownProtocolKind();
+            assert(!found.isSuppressed ||
+                   kp.has_value() &&
+                       "suppressed conformance for non-known protocol!?");
+            if (!found.isSuppressed) {
               addProtocol(proto, found.Loc,
                           source.withUncheckedLoc(found.uncheckedLoc)
                                 .withPreconcurrencyLoc(found.preconcurrencyLoc));

lib/AST/Decl.cpp

@@ -1656,7 +1656,8 @@ Type InheritedTypes::getResolvedType(unsigned i,
                         ? Decl.get<const ExtensionDecl *>()->getASTContext()
                         : Decl.get<const TypeDecl *>()->getASTContext();
   return evaluateOrDefault(ctx.evaluator, InheritedTypeRequest{Decl, i, stage},
-                           Type());
+                           InheritedTypeResult::forDefault())
+      .getInheritedTypeOrNull(getASTContext());
 }
 
 ExtensionDecl::ExtensionDecl(SourceLoc extensionLoc,
@@ -5354,6 +5355,13 @@ bool NominalTypeDecl::isMainActor() const {
          getParentModule()->getName() == getASTContext().Id_Concurrency;
 }
 
+bool NominalTypeDecl::suppressesConformance(KnownProtocolKind kp) const {
+  auto mutableThis = const_cast<NominalTypeDecl *>(this);
+  return evaluateOrDefault(getASTContext().evaluator,
+                           SuppressesConformanceRequest{mutableThis, kp},
+                           false);
+}
+
 GenericTypeDecl::GenericTypeDecl(DeclKind K, DeclContext *DC,
                                  Identifier name, SourceLoc nameLoc,
                                  ArrayRef<InheritedEntry> inherited,

lib/AST/FeatureSet.cpp

@@ -674,6 +674,42 @@ UNINTERESTING_FEATURE(BorrowingSwitch)
 
 UNINTERESTING_FEATURE(ClosureIsolation)
 
+static bool usesFeatureConformanceSuppression(Decl *decl) {
+  auto *nominal = dyn_cast<NominalTypeDecl>(decl);
+  if (!nominal)
+    return false;
+
+  auto inherited = InheritedTypes(nominal);
+  for (auto index : indices(inherited.getEntries())) {
+    // Ensure that InheritedTypeRequest has set the isSuppressed bit if
+    // appropriate.
+    auto resolvedTy = inherited.getResolvedType(index);
+    (void)resolvedTy;
+
+    auto entry = inherited.getEntry(index);
+
+    if (!entry.isSuppressed())
+      continue;
+
+    auto ty = entry.getType();
+
+    if (!ty)
+      continue;
+
+    auto kp = ty->getKnownProtocol();
+    if (!kp)
+      continue;
+
+    auto rpk = getRepressibleProtocolKind(*kp);
+    if (!rpk)
+      continue;
+
+    return true;
+  }
+
+  return false;
+}
+
 static bool usesFeatureIsolatedAny(Decl *decl) {
   return usesTypeMatching(decl, [](Type type) {
     if (auto fnType = type->getAs<AnyFunctionType>()) {