AST: Move TypeChecker::getFragileFunctionKind() to a method on DeclContext

We had some duplicated logic between getResilienceExpansion() and
getFragileFunctionKind(). Clean this up by moving the latter into
AST, and re-implementing the former in terms of the latter.

This also fixes a crash in at least one case where these two
implementations had previously diverged.

Fixes <rdar://problem/60605117>.

Author: slavapestov

include/swift/AST/ASTTypeIDZone.def

@@ -25,6 +25,7 @@ SWIFT_TYPEID(PropertyWrapperBackingPropertyInfo)
 SWIFT_TYPEID(PropertyWrapperTypeInfo)
 SWIFT_TYPEID(Requirement)
 SWIFT_TYPEID(ResilienceExpansion)
+SWIFT_TYPEID(FragileFunctionKind)
 SWIFT_TYPEID(Type)
 SWIFT_TYPEID(TypePair)
 SWIFT_TYPEID(TypeWitnessAndDecl)

include/swift/AST/ASTTypeIDs.h

@@ -53,6 +53,7 @@ struct PropertyWrapperMutability;
 class ProtocolDecl;
 class Requirement;
 enum class ResilienceExpansion : unsigned;
+struct FragileFunctionKind;
 class SourceFile;
 class Type;
 class ValueDecl;

include/swift/AST/DeclContext.h

@@ -179,6 +179,26 @@ struct ConformanceDiagnostic {
   ProtocolDecl *ExistingExplicitProtocol;
 };
 
+/// Used in diagnostic %selects.
+struct FragileFunctionKind {
+  enum Kind : unsigned {
+    Transparent,
+    Inlinable,
+    AlwaysEmitIntoClient,
+    DefaultArgument,
+    PropertyInitializer,
+    None
+  };
+
+  Kind kind = None;
+  bool allowUsableFromInline = false;
+
+  friend bool operator==(FragileFunctionKind lhs, FragileFunctionKind rhs) {
+    return (lhs.kind == rhs.kind &&
+            lhs.allowUsableFromInline == rhs.allowUsableFromInline);
+  }
+};
+
 /// A DeclContext is an AST object which acts as a semantic container
 /// for declarations.  As a policy matter, we currently define
 /// contexts broadly: a lambda expression in a function is a new
@@ -469,6 +489,10 @@ class alignas(1 << DeclContextAlignInBits) DeclContext {
   /// are used.
   ResilienceExpansion getResilienceExpansion() const;
 
+  /// Get the fragile function kind for the code in this context, which
+  /// is used for diagnostics.
+  FragileFunctionKind getFragileFunctionKind() const;
+
   /// Returns true if this context may possibly contain members visible to
   /// AnyObject dynamic lookup.
   bool mayContainMembersAccessedByDynamicLookup() const;

include/swift/AST/TypeCheckRequests.h

@@ -672,10 +672,10 @@ class StructuralTypeRequest :
   bool isCached() const { return true; }
 };
 
-/// Request the most optimal resilience expansion for the code in the context.
-class ResilienceExpansionRequest :
-    public SimpleRequest<ResilienceExpansionRequest,
-                         ResilienceExpansion(DeclContext*),
+/// Request the fragile function kind for the context.
+class FragileFunctionKindRequest :
+    public SimpleRequest<FragileFunctionKindRequest,
+                         FragileFunctionKind(DeclContext*),
                          RequestFlags::Cached> {
 public:
   using SimpleRequest::SimpleRequest;
@@ -684,15 +684,16 @@ class ResilienceExpansionRequest :
   friend SimpleRequest;
 
   // Evaluation.
-  ResilienceExpansion evaluate(Evaluator &eval, DeclContext *context) const;
+  FragileFunctionKind evaluate(Evaluator &eval, DeclContext *context) const;
 
 public:
   // Caching.
   bool isCached() const { return true; }
 };
 
-void simple_display(llvm::raw_ostream &out,
-                    const ResilienceExpansion &value);
+void simple_display(llvm::raw_ostream &out, FragileFunctionKind value);
+
+void simple_display(llvm::raw_ostream &out, ResilienceExpansion value);
 
 /// Request the custom attribute which attaches a function builder to the
 /// given declaration.

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -168,8 +168,8 @@ SWIFT_REQUEST(TypeChecker, RequiresOpaqueAccessorsRequest, bool(VarDecl *),
               SeparatelyCached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, RequiresOpaqueModifyCoroutineRequest,
               bool(AbstractStorageDecl *), SeparatelyCached, NoLocationInfo)
-SWIFT_REQUEST(TypeChecker, ResilienceExpansionRequest,
-              ResilienceExpansion(DeclContext *), Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, FragileFunctionKindRequest,
+              FragileFunctionKind(DeclContext *), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, SelfAccessKindRequest, SelfAccessKind(FuncDecl *),
               SeparatelyCached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, StorageImplInfoRequest,

lib/AST/DeclContext.cpp

@@ -312,19 +312,31 @@ bool DeclContext::isGenericContext() const {
   return false;
 }
 
-/// Get the most optimal resilience expansion for the body of this function.
-/// If the body is able to be inlined into functions in other resilience
-/// domains, this ensures that only sufficiently-conservative access patterns
-/// are used.
 ResilienceExpansion DeclContext::getResilienceExpansion() const {
+  auto fragileKind = getFragileFunctionKind();
+  switch (fragileKind.kind) {
+  case FragileFunctionKind::Transparent:
+  case FragileFunctionKind::Inlinable:
+  case FragileFunctionKind::AlwaysEmitIntoClient:
+  case FragileFunctionKind::DefaultArgument:
+  case FragileFunctionKind::PropertyInitializer:
+    return ResilienceExpansion::Minimal;
+  case FragileFunctionKind::None:
+    return ResilienceExpansion::Maximal;
+  }
+
+  llvm_unreachable("Bad fragile function kind");
+}
+
+FragileFunctionKind DeclContext::getFragileFunctionKind() const {
   auto &context = getASTContext();
   return evaluateOrDefault(context.evaluator,
-                           ResilienceExpansionRequest { const_cast<DeclContext *>(this) },
-                           ResilienceExpansion::Minimal);
+                           FragileFunctionKindRequest { const_cast<DeclContext *>(this) },
+                           {FragileFunctionKind::None, false});
 }
 
-ResilienceExpansion
-swift::ResilienceExpansionRequest::evaluate(Evaluator &evaluator,
+FragileFunctionKind
+swift::FragileFunctionKindRequest::evaluate(Evaluator &evaluator,
                                             DeclContext *context) const {
   for (const auto *dc = context->getLocalContext(); dc && dc->isLocalContext();
        dc = dc->getParent()) {
@@ -336,14 +348,19 @@ swift::ResilienceExpansionRequest::evaluate(Evaluator &evaluator,
       auto *VD = cast<ValueDecl>(dc->getAsDecl());
       assert(VD->hasParameterList());
 
-      auto access =
+      auto effectiveAccess =
         VD->getFormalAccessScope(/*useDC=*/nullptr,
                                  /*treatUsableFromInlineAsPublic=*/true);
+      auto formalAccess =
+        VD->getFormalAccessScope(/*useDC=*/nullptr,
+                                 /*treatUsableFromInlineAsPublic=*/false);
+      if (effectiveAccess.isPublic()) {
+        return {FragileFunctionKind::DefaultArgument,
+                !formalAccess.isPublic()};
+      }
 
-      if (access.isPublic())
-        return ResilienceExpansion::Minimal;
-
-      return ResilienceExpansion::Maximal;
+      return {FragileFunctionKind::None,
+              /*allowUsableFromInline=*/false};
     }
 
     // Stored property initializer contexts use minimal resilience expansion
@@ -354,12 +371,14 @@ swift::ResilienceExpansionRequest::evaluate(Evaluator &evaluator,
           NTD->getFormalAccessScope(/*useDC=*/nullptr,
                                     /*treatUsableFromInlineAsPublic=*/true);
         if (!nominalAccess.isPublic())
-          return ResilienceExpansion::Maximal;
+          return {FragileFunctionKind::None,
+                  /*allowUsableFromInline=*/false};
 
         if (NTD->isFormallyResilient())
-          return ResilienceExpansion::Maximal;
+          return {FragileFunctionKind::None,
+                  /*allowUsableFromInline=*/false};
 
-        return ResilienceExpansion::Minimal;
+        return {FragileFunctionKind::PropertyInitializer, true};
       }
     }
 
@@ -375,32 +394,44 @@ swift::ResilienceExpansionRequest::evaluate(Evaluator &evaluator,
 
       // If the function is not externally visible, we will not be serializing
       // its body.
-      if (!funcAccess.isPublic())
-        break;
+      if (!funcAccess.isPublic()) {
+        return {FragileFunctionKind::None,
+                /*allowUsableFromInline=*/false};
+      }
 
       // If the function is public, @_transparent implies @inlinable.
-      if (AFD->isTransparent())
-        return ResilienceExpansion::Minimal;
+      if (AFD->isTransparent()) {
+        return {FragileFunctionKind::Transparent,
+                /*allowUsableFromInline=*/true};
+      }
 
-      if (AFD->getAttrs().hasAttribute<InlinableAttr>())
-        return ResilienceExpansion::Minimal;
+      if (AFD->getAttrs().hasAttribute<InlinableAttr>()) {
+        return {FragileFunctionKind::Inlinable,
+                /*allowUsableFromInline=*/true};
+      }
 
-      if (AFD->getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>())
-        return ResilienceExpansion::Minimal;
+      if (AFD->getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>()) {
+        return {FragileFunctionKind::AlwaysEmitIntoClient,
+                /*allowUsableFromInline=*/true};
+      }
 
       // If a property or subscript is @inlinable or @_alwaysEmitIntoClient,
       // the accessors are @inlinable or @_alwaysEmitIntoClient also.
       if (auto accessor = dyn_cast<AccessorDecl>(AFD)) {
         auto *storage = accessor->getStorage();
-        if (storage->getAttrs().getAttribute<InlinableAttr>())
-          return ResilienceExpansion::Minimal;
-        if (storage->getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>())
-          return ResilienceExpansion::Minimal;
+        if (storage->getAttrs().getAttribute<InlinableAttr>()) {
+          return {FragileFunctionKind::Inlinable,
+                  /*allowUsableFromInline=*/true};
+        }
+        if (storage->getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>()) {
+          return {FragileFunctionKind::AlwaysEmitIntoClient,
+                  /*allowUsableFromInline=*/true};
+        }
       }
     }
   }
 
-  return ResilienceExpansion::Maximal;
+  return {FragileFunctionKind::None, false};
 }
 
 /// Determine whether the innermost context is generic.

lib/AST/TypeCheckRequests.cpp

@@ -616,8 +616,42 @@ void swift::simple_display(llvm::raw_ostream &os, PropertyWrapperMutability m) {
 }
 
 void swift::simple_display(llvm::raw_ostream &out,
-                           const ResilienceExpansion &value) {
-  out << value;
+                           ResilienceExpansion value) {
+  switch (value) {
+  case ResilienceExpansion::Minimal:
+    out << "minimal";
+    break;
+  case ResilienceExpansion::Maximal:
+    out << "maximal";
+    break;
+  }
+}
+
+void swift::simple_display(llvm::raw_ostream &out,
+                           FragileFunctionKind value) {
+  switch (value.kind) {
+  case FragileFunctionKind::Transparent:
+    out << "transparent";
+    break;
+  case FragileFunctionKind::Inlinable:
+    out << "inlinable";
+    break;
+  case FragileFunctionKind::AlwaysEmitIntoClient:
+    out << "alwaysEmitIntoClient";
+    break;
+  case FragileFunctionKind::DefaultArgument:
+    out << "defaultArgument";
+    break;
+  case FragileFunctionKind::PropertyInitializer:
+    out << "propertyInitializer";
+    break;
+  case FragileFunctionKind::None:
+    out << "none";
+    break;
+  }
+
+  out << ", allowUsableFromInline: "
+      << (value.allowUsableFromInline ? "true" : "false");
 }
 
 //----------------------------------------------------------------------------//