[Sema] Improve diagnoses of generic specializations

include/swift/AST/DiagnosticsSema.def

@@ -4605,10 +4605,10 @@ NOTE(duplicated_key_declared_here, none,
 // Generic specializations
 ERROR(cannot_explicitly_specialize_generic_function,none,
       "cannot explicitly specialize a generic function", ())
-ERROR(not_a_generic_definition,none,
-      "cannot specialize a non-generic definition", ())
 ERROR(not_a_generic_type,none,
       "cannot specialize non-generic type %0", (Type))
+ERROR(not_a_generic_macro,none,
+      "cannot specialize a non-generic external macro %0", (const ValueDecl *))
 ERROR(protocol_declares_unknown_primary_assoc_type,none,
       "an associated type named %0 must be declared in the protocol %1 or a protocol it inherits",
       (Identifier, Type))

include/swift/AST/Types.h

@@ -7327,7 +7327,7 @@ class PlaceholderType : public TypeBase {
   // recursive property logic in PlaceholderType::get.
   using Originator =
       llvm::PointerUnion<TypeVariableType *, DependentMemberType *, VarDecl *,
-                         ErrorExpr *, PlaceholderTypeRepr *>;
+                         ErrorExpr *, TypeRepr *>;
 
   Originator O;
 

include/swift/Sema/CSFix.h

@@ -462,9 +462,12 @@ enum class FixKind : uint8_t {
   /// because its name doesn't appear in 'initializes' or 'accesses' attributes.
   AllowInvalidMemberReferenceInInitAccessor,
 
-  /// Ignore an attempt to specialize non-generic type.
+  /// Ignore an attempt to specialize a non-generic type.
   AllowConcreteTypeSpecialization,
 
+  /// Ignore an attempt to specialize a generic function.
+  AllowGenericFunctionSpecialization,
+
   /// Ignore an out-of-place \c then statement.
   IgnoreOutOfPlaceThenStmt,
 
@@ -3718,11 +3721,14 @@ class AllowInvalidMemberReferenceInInitAccessor final : public ConstraintFix {
 
 class AllowConcreteTypeSpecialization final : public ConstraintFix {
   Type ConcreteType;
+  ValueDecl *Decl;
 
   AllowConcreteTypeSpecialization(ConstraintSystem &cs, Type concreteTy,
-                                  ConstraintLocator *locator)
-      : ConstraintFix(cs, FixKind::AllowConcreteTypeSpecialization, locator),
-        ConcreteType(concreteTy) {}
+                                  ValueDecl *decl, ConstraintLocator *locator,
+                                  FixBehavior fixBehavior)
+      : ConstraintFix(cs, FixKind::AllowConcreteTypeSpecialization, locator,
+                      fixBehavior),
+        ConcreteType(concreteTy), Decl(decl) {}
 
 public:
   std::string getName() const override {
@@ -3736,13 +3742,41 @@ class AllowConcreteTypeSpecialization final : public ConstraintFix {
   }
 
   static AllowConcreteTypeSpecialization *
-  create(ConstraintSystem &cs, Type concreteTy, ConstraintLocator *locator);
+  create(ConstraintSystem &cs, Type concreteTy, ValueDecl *decl,
+         ConstraintLocator *locator, FixBehavior fixBehavior);
 
   static bool classof(const ConstraintFix *fix) {
     return fix->getKind() == FixKind::AllowConcreteTypeSpecialization;
   }
 };
 
+class AllowGenericFunctionSpecialization final : public ConstraintFix {
+  ValueDecl *Decl;
+
+  AllowGenericFunctionSpecialization(ConstraintSystem &cs, ValueDecl *decl,
+                                     ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::AllowGenericFunctionSpecialization, locator),
+        Decl(decl) {}
+
+public:
+  std::string getName() const override {
+    return "allow generic function specialization";
+  }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
+  static AllowGenericFunctionSpecialization *
+  create(ConstraintSystem &cs, ValueDecl *decl, ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowGenericFunctionSpecialization;
+  }
+};
+
 class IgnoreOutOfPlaceThenStmt final : public ConstraintFix {
   IgnoreOutOfPlaceThenStmt(ConstraintSystem &cs, ConstraintLocator *locator)
       : ConstraintFix(cs, FixKind::IgnoreOutOfPlaceThenStmt, locator) {}

include/swift/Sema/ConstraintLocator.h

@@ -985,13 +985,13 @@ class LocatorPathElt::ConformanceRequirement final
 };
 
 class LocatorPathElt::PlaceholderType final
-    : public StoredPointerElement<PlaceholderTypeRepr> {
+    : public StoredPointerElement<TypeRepr> {
 public:
-  PlaceholderType(PlaceholderTypeRepr *placeholderRepr)
+  PlaceholderType(TypeRepr *placeholderRepr)
       : StoredPointerElement(PathElementKind::PlaceholderType,
                              placeholderRepr) {}
 
-  PlaceholderTypeRepr *getPlaceholderRepr() const { return getStoredPointer(); }
+  TypeRepr *getPlaceholderRepr() const { return getStoredPointer(); }
 
   static bool classof(const LocatorPathElt *elt) {
     return elt->getKind() == ConstraintLocator::PlaceholderType;

lib/AST/ASTDumper.cpp

@@ -3987,8 +3987,8 @@ namespace {
         printFlag("error_expr");
       } else if (auto *DMT = originator.dyn_cast<DependentMemberType *>()) {
         printRec(DMT, "dependent_member_type");
-      } else if (originator.is<PlaceholderTypeRepr *>()) {
-        printFlag("placeholder_type_repr");
+      } else if (originator.is<TypeRepr *>()) {
+        printFlag("type_repr");
       } else {
         assert(false && "unknown originator");
       }

lib/AST/ASTPrinter.cpp

@@ -5870,8 +5870,8 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
         Printer << "error_expr";
       } else if (auto *DMT = originator.dyn_cast<DependentMemberType *>()) {
         visit(DMT);
-      } else if (originator.is<PlaceholderTypeRepr *>()) {
-        Printer << "placeholder_type_repr";
+      } else if (originator.is<TypeRepr *>()) {
+        Printer << "type_repr";
       } else {
         assert(false && "unknown originator");
       }

lib/Parse/ParseType.cpp

@@ -1476,7 +1476,9 @@ static bool isGenericTypeDisambiguatingToken(Parser &P) {
   auto &tok = P.Tok;
   switch (tok.getKind()) {
   default:
-    return false;
+    // If this is the end of the expr (wouldn't match parseExprSequenceElement),
+    // prefer generic type list over an illegal unary postfix '>' operator.
+    return P.isStartOfSwiftDecl() || P.isStartOfStmt(/*prefer expr=*/true);
   case tok::r_paren:
   case tok::r_square:
   case tok::l_brace:

lib/Sema/CSDiagnostics.cpp

@@ -9360,7 +9360,16 @@ bool InvalidMemberReferenceWithinInitAccessor::diagnoseAsError() {
 }
 
 bool ConcreteTypeSpecialization::diagnoseAsError() {
-  emitDiagnostic(diag::not_a_generic_type, ConcreteType);
+  if (isa<MacroDecl>(Decl)) {
+    emitDiagnostic(diag::not_a_generic_macro, Decl);
+  } else {
+    emitDiagnostic(diag::not_a_generic_type, ConcreteType);
+  }
+  return true;
+}
+
+bool GenericFunctionSpecialization::diagnoseAsError() {
+  emitDiagnostic(diag::cannot_explicitly_specialize_generic_function);
   return true;
 }
 

lib/Sema/CSDiagnostics.h

@@ -3127,12 +3127,25 @@ class InvalidMemberReferenceWithinInitAccessor final
 /// \endcode
 class ConcreteTypeSpecialization final : public FailureDiagnostic {
   Type ConcreteType;
+  ValueDecl *Decl;
 
 public:
   ConcreteTypeSpecialization(const Solution &solution, Type concreteTy,
-                             ConstraintLocator *locator)
-      : FailureDiagnostic(solution, locator),
-        ConcreteType(resolveType(concreteTy)) {}
+                             ValueDecl *decl, ConstraintLocator *locator,
+                             FixBehavior fixBehavior)
+      : FailureDiagnostic(solution, locator, fixBehavior),
+        ConcreteType(resolveType(concreteTy)), Decl(decl) {}
+
+  bool diagnoseAsError() override;
+};
+
+class GenericFunctionSpecialization final : public FailureDiagnostic {
+  ValueDecl *Decl;
+
+public:
+  GenericFunctionSpecialization(const Solution &solution, ValueDecl *decl,
+                                ConstraintLocator *locator)
+      : FailureDiagnostic(solution, locator), Decl(decl) {}
 
   bool diagnoseAsError() override;
 };

lib/Sema/CSFix.cpp

@@ -2605,15 +2605,28 @@ AllowInvalidMemberReferenceInInitAccessor::create(ConstraintSystem &cs,
 
 bool AllowConcreteTypeSpecialization::diagnose(const Solution &solution,
                                                bool asNote) const {
-  ConcreteTypeSpecialization failure(solution, ConcreteType, getLocator());
+  ConcreteTypeSpecialization failure(solution, ConcreteType, Decl, getLocator(),
+                                     fixBehavior);
   return failure.diagnose(asNote);
 }
 
-AllowConcreteTypeSpecialization *
-AllowConcreteTypeSpecialization::create(ConstraintSystem &cs, Type concreteTy,
-                                        ConstraintLocator *locator) {
+AllowConcreteTypeSpecialization *AllowConcreteTypeSpecialization::create(
+    ConstraintSystem &cs, Type concreteTy, ValueDecl *decl,
+    ConstraintLocator *locator, FixBehavior fixBehavior) {
+  return new (cs.getAllocator()) AllowConcreteTypeSpecialization(
+      cs, concreteTy, decl, locator, fixBehavior);
+}
+
+bool AllowGenericFunctionSpecialization::diagnose(const Solution &solution,
+                                                  bool asNote) const {
+  GenericFunctionSpecialization failure(solution, Decl, getLocator());
+  return failure.diagnose(asNote);
+}
+
+AllowGenericFunctionSpecialization *AllowGenericFunctionSpecialization::create(
+    ConstraintSystem &cs, ValueDecl *decl, ConstraintLocator *locator) {
   return new (cs.getAllocator())
-      AllowConcreteTypeSpecialization(cs, concreteTy, locator);
+      AllowGenericFunctionSpecialization(cs, decl, locator);
 }
 
 bool IgnoreOutOfPlaceThenStmt::diagnose(const Solution &solution,

lib/Sema/CSGen.cpp

@@ -1903,9 +1903,9 @@ namespace {
     /// introduce them as an explicit generic arguments constraint.
     ///
     /// \returns true if resolving any of the specialization types failed.
-    bool addSpecializationConstraint(
-        ConstraintLocator *locator, Type boundType,
-        ArrayRef<TypeRepr *> specializationArgs) {
+    void addSpecializationConstraint(ConstraintLocator *locator, Type boundType,
+                                     SourceLoc lAngleLoc,
+                                     ArrayRef<TypeRepr *> specializationArgs) {
       // Resolve each type.
       SmallVector<Type, 2> specializationArgTypes;
       auto options =
@@ -1916,61 +1916,35 @@ namespace {
           options |= TypeResolutionFlags::AllowPackReferences;
           elementEnv = OuterExpansions.back();
         }
-        const auto result = TypeResolution::resolveContextualType(
+        auto result = TypeResolution::resolveContextualType(
             specializationArg, CurDC, options,
             // Introduce type variables for unbound generics.
             OpenUnboundGenericType(CS, locator),
             HandlePlaceholderType(CS, locator),
             OpenPackElementType(CS, locator, elementEnv));
-        if (result->hasError())
-          return true;
-
+        if (result->hasError()) {
+          auto &ctxt = CS.getASTContext();
+          result = PlaceholderType::get(ctxt, specializationArg);
+          ctxt.Diags.diagnose(lAngleLoc,
+                              diag::while_parsing_as_left_angle_bracket);
+        }
         specializationArgTypes.push_back(result);
       }
 
-      CS.addConstraint(
-          ConstraintKind::ExplicitGenericArguments, boundType,
-          PackType::get(CS.getASTContext(), specializationArgTypes),
-          locator);
-      return false;
+      auto constraint = Constraint::create(
+          CS, ConstraintKind::ExplicitGenericArguments, boundType,
+          PackType::get(CS.getASTContext(), specializationArgTypes), locator);
+      CS.addUnsolvedConstraint(constraint);
+      CS.activateConstraint(constraint);
     }
 
     Type visitUnresolvedSpecializeExpr(UnresolvedSpecializeExpr *expr) {
       auto baseTy = CS.getType(expr->getSubExpr());
-
-      if (baseTy->isTypeVariableOrMember()) {
-        return baseTy;
-      }
-
-      // We currently only support explicit specialization of generic types.
-      // FIXME: We could support explicit function specialization.
-      auto &de = CS.getASTContext().Diags;
-      if (baseTy->is<AnyFunctionType>()) {
-        de.diagnose(expr->getSubExpr()->getLoc(),
-                    diag::cannot_explicitly_specialize_generic_function);
-        de.diagnose(expr->getLAngleLoc(),
-                    diag::while_parsing_as_left_angle_bracket);
-        return Type();
-      }
-
-      if (AnyMetatypeType *meta = baseTy->getAs<AnyMetatypeType>()) {
-        auto *overloadLocator = CS.getConstraintLocator(expr->getSubExpr());
-        if (addSpecializationConstraint(overloadLocator,
-                                        meta->getInstanceType(),
-                                        expr->getUnresolvedParams())) {
-          return Type();
-        }
-
-        return baseTy;
-      }
-
-      // FIXME: If the base type is a type variable, constrain it to a metatype
-      // of a bound generic type.
-      de.diagnose(expr->getSubExpr()->getLoc(),
-                  diag::not_a_generic_definition);
-      de.diagnose(expr->getLAngleLoc(),
-                  diag::while_parsing_as_left_angle_bracket);
-      return Type();
+      auto *overloadLocator = CS.getConstraintLocator(expr->getSubExpr());
+      addSpecializationConstraint(
+          overloadLocator, baseTy->getMetatypeInstanceType(),
+          expr->getLAngleLoc(), expr->getUnresolvedParams());
+      return baseTy;
     }
 
     Type visitSequenceExpr(SequenceExpr *expr) {
@@ -4080,10 +4054,9 @@ namespace {
 
       // Add explicit generic arguments, if there were any.
       if (expr->getGenericArgsRange().isValid()) {
-        if (addSpecializationConstraint(
-              CS.getConstraintLocator(expr), macroRefType,
-              expr->getGenericArgs()))
-          return Type();
+        addSpecializationConstraint(CS.getConstraintLocator(expr), macroRefType,
+                                    expr->getGenericArgsRange().Start,
+                                    expr->getGenericArgs());
       }
 
       // Form the applicable-function constraint. The result type
@@ -4828,11 +4801,11 @@ bool ConstraintSystem::generateConstraints(
         // If we have a placeholder originating from a PlaceholderTypeRepr,
         // tack that on to the locator.
         if (auto *placeholderTy = ty->getAs<PlaceholderType>())
-          if (auto *placeholderRepr = placeholderTy->getOriginator()
-                                          .dyn_cast<PlaceholderTypeRepr *>())
+          if (auto *typeRepr = placeholderTy->getOriginator()
+                                          .dyn_cast<TypeRepr *>())
             return getConstraintLocator(
                 convertTypeLocator,
-                LocatorPathElt::PlaceholderType(placeholderRepr));
+                LocatorPathElt::PlaceholderType(typeRepr));
         return convertTypeLocator;
       };