Sema: Use the availability of the extended nominal as a floor for the availability of extensions

include/swift/AST/Availability.h

@@ -93,6 +93,18 @@ class VersionRange {
     return getLowerEndpoint() >= Other.getLowerEndpoint();
   }
 
+  // Returns true if all the versions in the Other range are versions in this
+  // range and the ranges are not equal.
+  bool isSupersetOf(const VersionRange &Other) const {
+    if (isEmpty() || Other.isAll())
+      return false;
+
+    if (isAll() || Other.isEmpty())
+      return true;
+
+    return getLowerEndpoint() < Other.getLowerEndpoint();
+  }
+
   /// Mutates this range to be a best-effort underapproximation of
   /// the intersection of itself and Other. This is the
   /// meet operation (greatest lower bound) in the version range lattice.
@@ -244,10 +256,17 @@ class AvailabilityContext {
   /// Returns true if \p other makes stronger guarantees than this context.
   ///
   /// That is, `a.isContainedIn(b)` implies `a.union(b) == b`.
-  bool isContainedIn(AvailabilityContext other) const {
+  bool isContainedIn(const AvailabilityContext &other) const {
     return OSVersion.isContainedIn(other.OSVersion);
   }
 
+  /// Returns true if \p other is a strict subset of this context.
+  ///
+  /// That is, `a.isSupersetOf(b)` implies `a != b` and `a.union(b) == a`.
+  bool isSupersetOf(const AvailabilityContext &other) const {
+    return OSVersion.isSupersetOf(other.OSVersion);
+  }
+
   /// Returns true if this context has constraints that make it impossible to
   /// actually occur.
   ///
@@ -272,7 +291,7 @@ class AvailabilityContext {
   ///
   /// As an example, this is used when figuring out the required availability
   /// for a type that references multiple nominal decls.
-  void intersectWith(AvailabilityContext other) {
+  void intersectWith(const AvailabilityContext &other) {
     OSVersion.intersectWith(other.getOSVersion());
   }
 
@@ -283,7 +302,7 @@ class AvailabilityContext {
   /// treating some invalid deployment environments as available.
   ///
   /// As an example, this is used for the true branch of `#available`.
-  void constrainWith(AvailabilityContext other) {
+  void constrainWith(const AvailabilityContext &other) {
     OSVersion.constrainWith(other.getOSVersion());
   }
 
@@ -295,7 +314,7 @@ class AvailabilityContext {
   ///
   /// As an example, this is used for the else branch of a conditional with
   /// multiple `#available` checks.
-  void unionWith(AvailabilityContext other) {
+  void unionWith(const AvailabilityContext &other) {
     OSVersion.unionWith(other.getOSVersion());
   }
 

include/swift/AST/TypeRefinementContext.h

@@ -54,15 +54,19 @@ class TypeRefinementContext : public ASTAllocated<TypeRefinementContext> {
     /// The root refinement context.
     Root,
 
-    /// The context was introduced by a declaration (e.g., the body of a
-    /// function declaration or the contents of a class declaration).
+    /// The context was introduced by a declaration with an explicit
+    /// availability attribute. The context contains both the signature and the
+    /// body of the declaration.
     Decl,
 
-    /// The context was introduced by an API boundary; that is, we are in
-    /// a module with library evolution enabled and the parent context's
-    /// contents can be visible to the module's clients, but this context's
-    /// contents are not.
-    APIBoundary,
+    /// The context was introduced implicitly by a declaration. The context may
+    /// cover the entire declaration or it may cover a subset of it. For
+    /// example, a public, non-inlinable function declaration in an API module
+    /// will have at least two associated contexts: one for the entire
+    /// declaration at the declared availability of the API and a nested
+    /// implicit context for the body of the function, which will always run at
+    /// the deployment target of the library.
+    DeclImplicit,
 
     /// The context was introduced for the Then branch of an IfStmt.
     IfStmtThenBranch,
@@ -131,7 +135,8 @@ class TypeRefinementContext : public ASTAllocated<TypeRefinementContext> {
     }
 
     Decl *getAsDecl() const {
-      assert(IntroReason == Reason::Decl || IntroReason == Reason::APIBoundary);
+      assert(IntroReason == Reason::Decl ||
+             IntroReason == Reason::DeclImplicit);
       return D;
     }
 
@@ -163,8 +168,8 @@ class TypeRefinementContext : public ASTAllocated<TypeRefinementContext> {
 
   SourceRange SrcRange;
 
-  /// A canonical availability info for this context, computed top-down from the root
-  /// context (compilation deployment target).
+  /// A canonical availability info for this context, computed top-down from the
+  /// root context.
   AvailabilityContext AvailabilityInfo;
 
   /// If this context was annotated with an availability attribute, this property captures that.
@@ -194,8 +199,8 @@ class TypeRefinementContext : public ASTAllocated<TypeRefinementContext> {
 
   /// Create a refinement context for the given declaration.
   static TypeRefinementContext *
-  createForAPIBoundary(ASTContext &Ctx, Decl *D, TypeRefinementContext *Parent,
-                       const AvailabilityContext &Info, SourceRange SrcRange);
+  createForDeclImplicit(ASTContext &Ctx, Decl *D, TypeRefinementContext *Parent,
+                        const AvailabilityContext &Info, SourceRange SrcRange);
 
   /// Create a refinement context for the Then branch of the given IfStmt.
   static TypeRefinementContext *

lib/AST/TypeRefinementContext.cpp

@@ -64,13 +64,13 @@ TypeRefinementContext::createForDecl(ASTContext &Ctx, Decl *D,
       TypeRefinementContext(Ctx, D, Parent, SrcRange, Info, ExplicitInfo);
 }
 
-TypeRefinementContext *TypeRefinementContext::createForAPIBoundary(
+TypeRefinementContext *TypeRefinementContext::createForDeclImplicit(
     ASTContext &Ctx, Decl *D, TypeRefinementContext *Parent,
     const AvailabilityContext &Info, SourceRange SrcRange) {
   assert(D);
   assert(Parent);
   return new (Ctx) TypeRefinementContext(
-      Ctx, IntroNode(D, Reason::APIBoundary), Parent, SrcRange, Info,
+      Ctx, IntroNode(D, Reason::DeclImplicit), Parent, SrcRange, Info,
       AvailabilityContext::alwaysAvailable());
 }
 
@@ -180,7 +180,7 @@ void TypeRefinementContext::dump(raw_ostream &OS, SourceManager &SrcMgr) const {
 SourceLoc TypeRefinementContext::getIntroductionLoc() const {
   switch (getReason()) {
   case Reason::Decl:
-  case Reason::APIBoundary:
+  case Reason::DeclImplicit:
     return Node.getAsDecl()->getLoc();
 
   case Reason::IfStmtThenBranch:
@@ -294,7 +294,7 @@ TypeRefinementContext::getAvailabilityConditionVersionSourceRange(
       Node.getAsWhileStmt()->getCond(), Platform, Version);
 
   case Reason::Root:
-  case Reason::APIBoundary:
+  case Reason::DeclImplicit:
     return SourceRange();
   }
 
@@ -308,7 +308,7 @@ void TypeRefinementContext::print(raw_ostream &OS, SourceManager &SrcMgr,
 
   OS << " versions=" << AvailabilityInfo.getOSVersion().getAsString();
 
-  if (getReason() == Reason::Decl || getReason() == Reason::APIBoundary) {
+  if (getReason() == Reason::Decl || getReason() == Reason::DeclImplicit) {
     Decl *D = Node.getAsDecl();
     OS << " decl=";
     if (auto VD = dyn_cast<ValueDecl>(D)) {
@@ -350,8 +350,8 @@ StringRef TypeRefinementContext::getReasonName(Reason R) {
   case Reason::Decl:
     return "decl";
 
-  case Reason::APIBoundary:
-    return "api_boundary";
+  case Reason::DeclImplicit:
+    return "decl_implicit";
 
   case Reason::IfStmtThenBranch:
     return "if_then";

lib/Sema/TypeCheckAccess.cpp

@@ -1850,21 +1850,8 @@ class DeclAvailabilityChecker : public DeclVisitor<DeclAvailabilityChecker> {
     });
 
     Where = wasWhere.withExported(hasExportedMembers);
-
-    // When diagnosing potential unavailability of the extended type, downgrade
-    // the diagnostics to warnings when the extension decl has no declared
-    // availability and the required availability is more than the deployment
-    // target.
-    DeclAvailabilityFlags extendedTypeFlags = None;
-    auto annotatedRange =
-        AvailabilityInference::annotatedAvailableRange(ED, ED->getASTContext());
-    if (!annotatedRange.hasValue())
-      extendedTypeFlags |= DeclAvailabilityFlag::
-          WarnForPotentialUnavailabilityBeforeDeploymentTarget;
-
     checkType(ED->getExtendedType(), ED->getExtendedTypeRepr(), ED,
-              ExportabilityReason::ExtensionWithPublicMembers,
-              extendedTypeFlags);
+              ExportabilityReason::ExtensionWithPublicMembers);
 
     // 3) If the extension contains exported members or defines conformances,
     // the 'where' clause must only name exported types.

lib/Sema/TypeCheckAvailability.cpp

@@ -460,6 +460,9 @@ class TypeRefinementContextBuilder : private ASTWalker {
     // Adds in a TRC that covers the entire declaration.
     if (auto DeclTRC = getNewContextForSignatureOfDecl(D)) {
       pushContext(DeclTRC, D);
+
+      // Possibly use this as an effective parent context later.
+      recordEffectiveParentContext(D, DeclTRC);
     }
 
     // Create TRCs that cover only the body of the declaration.
@@ -542,46 +545,63 @@ class TypeRefinementContextBuilder : private ASTWalker {
           return nullptr;
     }
 
-    // A decl only introduces a new context when it either has explicit
-    // availability or requires the deployment target.
-    bool HasExplicitAvailability = hasActiveAvailableAttribute(D, Context);
-    bool ConstrainToDeploymentTarget =
-        shouldConstrainSignatureToDeploymentTarget(D);
-    if (!HasExplicitAvailability && !ConstrainToDeploymentTarget)
-      return nullptr;
+    // Declarations with an explicit availability attribute always get a TRC.
+    if (hasActiveAvailableAttribute(D, Context)) {
+      AvailabilityContext DeclaredAvailability =
+          swift::AvailabilityInference::availableRange(D, Context);
 
-    // We require a valid range in order to be able to query for the TRC
-    // corresponding to a given SourceLoc.
-    // If this assert fires, it means we have probably synthesized an implicit
-    // declaration without location information. The appropriate fix is
-    // probably to gin up a source range for the declaration when synthesizing
-    // it.
-    assert(D->getSourceRange().isValid());
+      return TypeRefinementContext::createForDecl(
+          Context, D, getCurrentTRC(),
+          getEffectiveAvailabilityForDeclSignature(D, DeclaredAvailability),
+          DeclaredAvailability, refinementSourceRangeForDecl(D));
+    }
 
-    // The potential versions in the declaration are constrained by both
-    // the declared availability of the declaration and the potential versions
-    // of its lexical context.
-    AvailabilityContext ExplicitDeclInfo =
-        swift::AvailabilityInference::availableRange(D, Context);
-    AvailabilityContext DeclInfo = ExplicitDeclInfo;
-    DeclInfo.intersectWith(getCurrentTRC()->getAvailabilityInfo());
-
-    if (ConstrainToDeploymentTarget)
-      DeclInfo.intersectWith(AvailabilityContext::forDeploymentTarget(Context));
-
-    SourceRange Range = refinementSourceRangeForDecl(D);
-    TypeRefinementContext *NewTRC;
-    if (HasExplicitAvailability)
-      NewTRC = TypeRefinementContext::createForDecl(
-          Context, D, getCurrentTRC(), DeclInfo, ExplicitDeclInfo, Range);
-    else
-      NewTRC = TypeRefinementContext::createForAPIBoundary(
-          Context, D, getCurrentTRC(), DeclInfo, Range);
+    // Declarations without explicit availability get a TRC if they are
+    // effectively less available than the surrounding context. For example, an
+    // internal property in a public struct can be effectively less available
+    // than the containing struct decl because the internal property will only
+    // be accessed by code running at the deployment target or later.
+    AvailabilityContext CurrentAvailability =
+        getCurrentTRC()->getAvailabilityInfo();
+    AvailabilityContext EffectiveAvailability =
+        getEffectiveAvailabilityForDeclSignature(D, CurrentAvailability);
+    if (CurrentAvailability.isSupersetOf(EffectiveAvailability))
+      return TypeRefinementContext::createForDeclImplicit(
+          Context, D, getCurrentTRC(), EffectiveAvailability,
+          refinementSourceRangeForDecl(D));
+
+    return nullptr;
+  }
 
-    // Possibly use this as an effective parent context later.
-    recordEffectiveParentContext(D, NewTRC);
+  AvailabilityContext getEffectiveAvailabilityForDeclSignature(
+      Decl *D, const AvailabilityContext BaseAvailability) {
+    AvailabilityContext EffectiveAvailability = BaseAvailability;
+
+    // As a special case, extension decls are treated as effectively as
+    // available as the nominal type they extend, up to the deployment target.
+    // This rule is a convenience for library authors who have written
+    // extensions without specifying availabilty on the extension itself.
+    if (auto *ED = dyn_cast<ExtensionDecl>(D)) {
+      auto *Nominal = ED->getExtendedNominal();
+      if (Nominal && !hasActiveAvailableAttribute(D, Context)) {
+        EffectiveAvailability.intersectWith(
+            swift::AvailabilityInference::availableRange(Nominal, Context));
+
+        // We want to require availability to be specified on extensions of
+        // types that would be potentially unavailable to the module containing
+        // the extension, so limit the effective availability to the deployment
+        // target.
+        EffectiveAvailability.unionWith(
+            AvailabilityContext::forDeploymentTarget(Context));
+      }
+    }
 
-    return NewTRC;
+    EffectiveAvailability.intersectWith(getCurrentTRC()->getAvailabilityInfo());
+    if (shouldConstrainSignatureToDeploymentTarget(D))
+      EffectiveAvailability.intersectWith(
+          AvailabilityContext::forDeploymentTarget(Context));
+
+    return EffectiveAvailability;
   }
 
   /// Checks whether the entire declaration, including its signature, should be
@@ -607,6 +627,14 @@ class TypeRefinementContextBuilder : private ASTWalker {
   /// provides a convenient place to specify the refined range when it is
   /// different than the declaration's source range.
   SourceRange refinementSourceRangeForDecl(Decl *D) {
+    // We require a valid range in order to be able to query for the TRC
+    // corresponding to a given SourceLoc.
+    // If this assert fires, it means we have probably synthesized an implicit
+    // declaration without location information. The appropriate fix is
+    // probably to gin up a source range for the declaration when synthesizing
+    // it.
+    assert(D->getSourceRange().isValid());
+
     if (auto *storageDecl = dyn_cast<AbstractStorageDecl>(D)) {
       // Use the declaration's availability for the context when checking
       // the bodies of its accessors.
@@ -642,25 +670,26 @@ class TypeRefinementContextBuilder : private ASTWalker {
     return D->getSourceRange();
   }
 
-  TypeRefinementContext *createAPIBoundaryContext(Decl *D, SourceRange range) {
-    AvailabilityContext DeploymentTargetInfo =
-        AvailabilityContext::forDeploymentTarget(Context);
-    DeploymentTargetInfo.intersectWith(getCurrentTRC()->getAvailabilityInfo());
-
-    return TypeRefinementContext::createForAPIBoundary(
-        Context, D, getCurrentTRC(), DeploymentTargetInfo, range);
-  }
-
   void buildContextsForBodyOfDecl(Decl *D) {
     // Are we already constrained by the deployment target? If not, adding
     // new contexts won't change availability.
     if (isCurrentTRCContainedByDeploymentTarget())
       return;
 
+    // A lambda that creates an implicit decl TRC specifying the deployment
+    // target for `range` in decl `D`.
+    auto createContext = [this](Decl *D, SourceRange range) {
+      AvailabilityContext Availability =
+          AvailabilityContext::forDeploymentTarget(Context);
+      Availability.intersectWith(getCurrentTRC()->getAvailabilityInfo());
+
+      return TypeRefinementContext::createForDeclImplicit(
+          Context, D, getCurrentTRC(), Availability, range);
+    };
+
     // Top level code always uses the deployment target.
     if (auto tlcd = dyn_cast<TopLevelCodeDecl>(D)) {
-      auto *topLevelTRC =
-          createAPIBoundaryContext(tlcd, tlcd->getSourceRange());
+      auto *topLevelTRC = createContext(tlcd, tlcd->getSourceRange());
       pushContext(topLevelTRC, D);
       return;
     }
@@ -670,8 +699,7 @@ class TypeRefinementContextBuilder : private ASTWalker {
     if (auto afd = dyn_cast<AbstractFunctionDecl>(D)) {
       if (!afd->isImplicit() && afd->getBodySourceRange().isValid() &&
           afd->getResilienceExpansion() != ResilienceExpansion::Minimal) {
-        auto *functionBodyTRC =
-            createAPIBoundaryContext(afd, afd->getBodySourceRange());
+        auto *functionBodyTRC = createContext(afd, afd->getBodySourceRange());
         pushContext(functionBodyTRC, D);
       }
       return;
@@ -693,8 +721,7 @@ class TypeRefinementContextBuilder : private ASTWalker {
           // Create a TRC for the init written in the source. The ASTWalker
           // won't visit these expressions so instead of pushing these onto the
           // stack we build them directly.
-          auto *initTRC =
-              createAPIBoundaryContext(vd, initExpr->getSourceRange());
+          auto *initTRC = createContext(vd, initExpr->getSourceRange());
           TypeRefinementContextBuilder(initTRC, Context).build(initExpr);
         }
 
@@ -710,7 +737,7 @@ class TypeRefinementContextBuilder : private ASTWalker {
         // example, property wrapper initializers that takes block arguments
         // are not handled correctly because of this (rdar://77841331).
         for (auto *wrapper : vd->getAttachedPropertyWrappers()) {
-          createAPIBoundaryContext(vd, wrapper->getRange());
+          createContext(vd, wrapper->getRange());
         }
       }