Improve diagnoses of generic specializations

Always add constraints, find fixes during simplify.
New separate fix for allow generic function specialization.
Improve parse heuristic for isGenericTypeDisambiguatingToken.
Degrade concrete type specialization fix to warning for macros.

Author: Greg Titus

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,