[SE] Allow where clauses on non-generic declarations in generic contexts

include/swift/AST/Decl.h

@@ -1218,7 +1218,9 @@ class RequirementRepr {
   void print(raw_ostream &OS) const;
   void print(ASTPrinter &Printer) const;
 };
-
+
+using GenericParamSource = PointerUnion<GenericContext *, GenericParamList *>;
+
 /// GenericParamList - A list of generic parameters that is part of a generic
 /// function or type, along with extra requirements placed on those generic
 /// parameters and types derived from them.

include/swift/AST/DiagnosticsParse.def

@@ -1650,10 +1650,9 @@ ERROR(redundant_class_requirement,none,
       "redundant 'class' requirement", ())
 ERROR(late_class_requirement,none,
       "'class' must come first in the requirement list", ())
-ERROR(where_without_generic_params,none,
-      "'where' clause cannot be attached to "
-      "%select{a non-generic|a protocol|an associated type}0 "
-      "declaration", (unsigned))
+ERROR(where_toplevel_nongeneric,none,
+      "'where' clause cannot be attached to non-generic "
+      "top-level declaration", ())
 ERROR(where_inside_brackets,none,
         "'where' clause next to generic parameters is obsolete, "
         "must be written following the declaration's type", ())

include/swift/AST/DiagnosticsSema.def

@@ -2751,6 +2751,10 @@ ERROR(dynamic_self_stored_property_init,none,
 ERROR(dynamic_self_default_arg,none,
       "covariant 'Self' type cannot be referenced from a default argument expression", ())
 
+ERROR(where_nongeneric_ctx,none,
+      "'where' clause on non-generic member declaration requires a "
+      "generic context", ())
+
 //------------------------------------------------------------------------------
 // MARK: Type Check Attributes
 //------------------------------------------------------------------------------

include/swift/AST/TypeCheckRequests.h

@@ -1108,7 +1108,7 @@ class InferredGenericSignatureRequest :
     public SimpleRequest<InferredGenericSignatureRequest,
                          GenericSignature (ModuleDecl *,
                                             GenericSignatureImpl *,
-                                            GenericParamList *,
+                                            GenericParamSource,
                                             SmallVector<Requirement, 2>,
                                             SmallVector<TypeLoc, 2>,
                                             bool),
@@ -1124,7 +1124,7 @@ class InferredGenericSignatureRequest :
   evaluate(Evaluator &evaluator,
            ModuleDecl *module,
            GenericSignatureImpl *baseSignature,
-           GenericParamList *gpl,
+           GenericParamSource paramSource,
            SmallVector<Requirement, 2> addedRequirements,
            SmallVector<TypeLoc, 2> inferenceSources,
            bool allowConcreteGenericParams) const;

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -83,7 +83,7 @@ SWIFT_REQUEST(TypeChecker, HasDynamicMemberLookupAttributeRequest,
               bool(CanType), Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, InferredGenericSignatureRequest,
               GenericSignature (ModuleDecl *, GenericSignatureImpl *,
-                                 GenericParamList *,
+                                 GenericParamSource,
                                  SmallVector<Requirement, 2>,
                                  SmallVector<TypeLoc, 2>, bool),
               Cached, NoLocationInfo)

include/swift/Basic/SimpleDisplay.h

@@ -135,6 +135,15 @@ namespace swift {
     }
     out << "}";
   }
+
+  template<typename T, typename U>
+  void simple_display(llvm::raw_ostream &out,
+                      const llvm::PointerUnion<T, U> &ptrUnion) {
+    if (const auto t = ptrUnion.template dyn_cast<T>())
+      simple_display(out, t);
+    else
+      simple_display(out, ptrUnion.template get<U>());
+  }
 }
 
 #endif // SWIFT_BASIC_SIMPLE_DISPLAY_H

include/swift/Parse/Parser.h

@@ -1066,7 +1066,7 @@ class Parser {
                                 bool allowClassRequirement,
                                 bool allowAnyObject);
   ParserStatus parseDeclItem(bool &PreviousHadSemi,
-                             Parser::ParseDeclOptions Options,
+                             ParseDeclOptions Options,
                              llvm::function_ref<void(Decl*)> handler);
   std::pair<std::vector<Decl *>, Optional<std::string>>
   parseDeclList(SourceLoc LBLoc, SourceLoc &RBLoc, Diag<> ErrorDiag,
@@ -1634,14 +1634,10 @@ class Parser {
   void
   diagnoseWhereClauseInGenericParamList(const GenericParamList *GenericParams);
 
-  enum class WhereClauseKind : unsigned {
-    Declaration,
-    Protocol,
-    AssociatedType
-  };
   ParserStatus
-  parseFreestandingGenericWhereClause(GenericParamList *GPList,
-                             WhereClauseKind kind=WhereClauseKind::Declaration);
+  parseFreestandingGenericWhereClause(GenericContext *genCtx,
+                                      GenericParamList *&GPList,
+                                      ParseDeclOptions flags);
 
   ParserStatus parseGenericWhereClause(
       SourceLoc &WhereLoc, SmallVectorImpl<RequirementRepr> &Requirements,

lib/AST/ASTContext.cpp

@@ -4470,19 +4470,22 @@ ASTContext::getOverrideGenericSignature(const ValueDecl *base,
   assert(isa<AbstractFunctionDecl>(base) || isa<SubscriptDecl>(base));
   assert(isa<AbstractFunctionDecl>(derived) || isa<SubscriptDecl>(derived));
 
-  auto baseClass = base->getDeclContext()->getSelfClassDecl();
-  auto derivedClass = derived->getDeclContext()->getSelfClassDecl();
+  const auto baseClass = base->getDeclContext()->getSelfClassDecl();
+  const auto derivedClass = derived->getDeclContext()->getSelfClassDecl();
 
   assert(baseClass != nullptr);
   assert(derivedClass != nullptr);
 
-  auto baseGenericSig = base->getAsGenericContext()->getGenericSignature();
-  auto derivedGenericSig = derived->getAsGenericContext()->getGenericSignature();
+  const auto baseGenericSig =
+      base->getAsGenericContext()->getGenericSignature();
+  const auto derivedGenericSig =
+      derived->getAsGenericContext()->getGenericSignature();
 
   if (base == derived)
     return derivedGenericSig;
 
-  if (derivedClass->getSuperclass().isNull())
+  const auto derivedSuperclass = derivedClass->getSuperclass();
+  if (derivedSuperclass.isNull())
     return nullptr;
 
   if (derivedGenericSig.isNull())
@@ -4491,12 +4494,6 @@ ASTContext::getOverrideGenericSignature(const ValueDecl *base,
   if (baseGenericSig.isNull())
     return derivedGenericSig;
 
-  auto baseClassSig = baseClass->getGenericSignature();
-  auto subMap = derivedClass->getSuperclass()->getContextSubstitutionMap(
-      derivedClass->getModuleContext(), baseClass);
-
-  unsigned derivedDepth = 0;
-
   auto key = OverrideSignatureKey(baseGenericSig,
                                   derivedGenericSig,
                                   derivedClass);
@@ -4506,22 +4503,25 @@ ASTContext::getOverrideGenericSignature(const ValueDecl *base,
     return getImpl().overrideSigCache.lookup(key);
   }
 
-  if (auto derivedSig = derivedClass->getGenericSignature())
-    derivedDepth = derivedSig->getGenericParams().back()->getDepth() + 1;
+  const auto derivedClassSig = derivedClass->getGenericSignature();
+
+  unsigned derivedDepth = 0;
+  unsigned baseDepth = 0;
+  if (derivedClassSig)
+    derivedDepth = derivedClassSig->getGenericParams().back()->getDepth() + 1;
+  if (const auto baseClassSig = baseClass->getGenericSignature())
+    baseDepth = baseClassSig->getGenericParams().back()->getDepth() + 1;
 
   SmallVector<GenericTypeParamType *, 2> addedGenericParams;
-  if (auto *gpList = derived->getAsGenericContext()->getGenericParams()) {
+  if (const auto *gpList = derived->getAsGenericContext()->getGenericParams()) {
     for (auto gp : *gpList) {
       addedGenericParams.push_back(
           gp->getDeclaredInterfaceType()->castTo<GenericTypeParamType>());
     }
   }
 
-  unsigned baseDepth = 0;
-
-  if (baseClassSig) {
-    baseDepth = baseClassSig->getGenericParams().back()->getDepth() + 1;
-  }
+  const auto subMap = derivedSuperclass->getContextSubstitutionMap(
+      derivedClass->getModuleContext(), baseClass);
 
   auto substFn = [&](SubstitutableType *type) -> Type {
     auto *gp = cast<GenericTypeParamType>(type);
@@ -4553,7 +4553,7 @@ ASTContext::getOverrideGenericSignature(const ValueDecl *base,
   auto genericSig = evaluateOrDefault(
       evaluator,
       AbstractGenericSignatureRequest{
-        derivedClass->getGenericSignature().getPointer(),
+        derivedClassSig.getPointer(),
         std::move(addedGenericParams),
         std::move(addedRequirements)},
       GenericSignature());

lib/AST/ASTScopeLookup.cpp

@@ -194,8 +194,8 @@ bool ASTScopeImpl::doesContextMatchStartingContext(
 // For a SubscriptDecl with generic parameters, the call tries to do lookups
 // with startingContext equal to either the get or set subscript
 // AbstractFunctionDecls. Since the generic parameters are in the
-// SubScriptDeclScope, and not the AbstractFunctionDecl scopes (after all how
-// could one parameter be in two scopes?), GenericParamScoped intercepts the
+// SubscriptDeclScope, and not the AbstractFunctionDecl scopes (after all how
+// could one parameter be in two scopes?), GenericParamScope intercepts the
 // match query here and tests against the accessor DeclContexts.
 bool GenericParamScope::doesContextMatchStartingContext(
     const DeclContext *context) const {

lib/AST/ASTWalker.cpp

@@ -126,6 +126,31 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
   //                                 Decls
   //===--------------------------------------------------------------------===//
 
+  bool visitGenericParamListIfNeeded(GenericContext *GC) {
+    // Must check this first in case extensions have not been bound yet
+    if (Walker.shouldWalkIntoGenericParams()) {
+      if (auto *params = GC->getGenericParams()) {
+        visitGenericParamList(params);
+      }
+      return true;
+    }
+    return false;
+  }
+
+  bool visitTrailingRequirements(GenericContext *GC) {
+    if (const auto Where = GC->getTrailingWhereClause()) {
+      for (auto &Req: Where->getRequirements())
+        if (doIt(Req))
+          return true;
+    } else if (!isa<ExtensionDecl>(GC)) {
+      if (const auto GP = GC->getGenericParams())
+        for (auto Req: GP->getTrailingRequirements())
+          if (doIt(Req))
+            return true;
+    }
+    return false;
+  }
+
   bool visitImportDecl(ImportDecl *ID) {
     return false;
   }
@@ -138,12 +163,9 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
       if (doIt(Inherit))
         return true;
     }
-    if (auto *Where = ED->getTrailingWhereClause()) {
-      for(auto &Req: Where->getRequirements()) {
-        if (doIt(Req))
-          return true;
-      }
-    }
+    if (visitTrailingRequirements(ED))
+      return true;
+
     for (Decl *M : ED->getMembers()) {
       if (doIt(M))
         return true;
@@ -223,15 +245,13 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
   }
 
   bool visitTypeAliasDecl(TypeAliasDecl *TAD) {
-    if (Walker.shouldWalkIntoGenericParams() && TAD->getGenericParams()) {
-      if (visitGenericParamList(TAD->getGenericParams()))
-        return true;
-    }
+    bool WalkGenerics = visitGenericParamListIfNeeded(TAD);
 
     if (auto typerepr = TAD->getUnderlyingTypeRepr())
       if (doIt(typerepr))
         return true;
-    return false;
+
+    return WalkGenerics && visitTrailingRequirements(TAD);
   }
 
   bool visitOpaqueTypeDecl(OpaqueTypeDecl *OTD) {
@@ -269,20 +289,9 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     }
 
     // Visit requirements
-    if (WalkGenerics) {
-      ArrayRef<swift::RequirementRepr> Reqs = None;
-      if (auto *Protocol = dyn_cast<ProtocolDecl>(NTD)) {
-        if (auto *WhereClause = Protocol->getTrailingWhereClause())
-          Reqs = WhereClause->getRequirements();
-      } else {
-        Reqs = NTD->getGenericParams()->getTrailingRequirements();
-      }
-      for (auto Req: Reqs) {
-        if (doIt(Req))
-          return true;
-      }
-    }
-
+    if (WalkGenerics && visitTrailingRequirements(NTD))
+      return true;
+
     for (Decl *Member : NTD->getMembers()) {
       if (doIt(Member))
         return true;
@@ -325,13 +334,9 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     if (doIt(SD->getElementTypeLoc()))
       return true;
 
-    if (WalkGenerics) {
-      // Visit generic requirements
-      for (auto Req : SD->getGenericParams()->getTrailingRequirements()) {
-        if (doIt(Req))
-          return true;
-      }
-    }
+   // Visit trailing requirements
+    if (WalkGenerics && visitTrailingRequirements(SD))
+      return true;
 
     if (!Walker.shouldWalkAccessorsTheOldWay()) {
       for (auto *AD : SD->getAllAccessors())
@@ -364,13 +369,9 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
         if (doIt(FD->getBodyResultTypeLoc()))
           return true;
 
-    if (WalkGenerics) {
-      // Visit trailing requirments
-      for (auto Req : AFD->getGenericParams()->getTrailingRequirements()) {
-        if (doIt(Req))
-          return true;
-      }
-    }
+    // Visit trailing requirements
+    if (WalkGenerics && visitTrailingRequirements(AFD))
+      return true;
 
     if (AFD->getBody(/*canSynthesize=*/false)) {
       AbstractFunctionDecl::BodyKind PreservedKind = AFD->getBodyKind();
@@ -1323,17 +1324,6 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     }
     return false;
   }
-
-private:
-  bool visitGenericParamListIfNeeded(GenericContext *gc) {
-    if (Walker.shouldWalkIntoGenericParams()) {
-      if (auto *params = gc->getGenericParams()) {
-        visitGenericParamList(params);
-        return true;
-      }
-    }
-    return false;
-  }
 };
 
 } // end anonymous namespace

lib/AST/Decl.cpp

@@ -1077,9 +1077,12 @@ void GenericContext::setGenericSignature(GenericSignature genericSig) {
 }
 
 SourceRange GenericContext::getGenericTrailingWhereClauseSourceRange() const {
-  if (!isGeneric())
-    return SourceRange();
-  return getGenericParams()->getTrailingWhereClauseSourceRange();
+  if (isGeneric())
+    return getGenericParams()->getTrailingWhereClauseSourceRange();
+  else if (const auto *where = getTrailingWhereClause())
+    return where->getSourceRange();
+
+  return SourceRange();
 }
 
 ImportDecl *ImportDecl::create(ASTContext &Ctx, DeclContext *DC,