(More) Declaration checker support for tuple conformances

include/swift/AST/Decl.h

@@ -5178,21 +5178,19 @@ class ProtocolDecl final : public NominalTypeDecl {
 /// and conformances for tuple types.
 ///
 /// - The declared interface type is the special TheTupleType singleton.
-/// - The generic parameter list has one pack generic parameter, <Elements...>
-/// - The generic signature has no requirements, <Elements...>
+/// - The generic parameter list has one pack generic parameter, <each Element>
+/// - The generic signature has no requirements, <each Element>
 /// - The self interface type is the tuple type containing a single pack
-///   expansion, (Elements...).
+///   expansion, (repeat each Element).
 class BuiltinTupleDecl final : public NominalTypeDecl {
-  TupleType *TupleSelfType = nullptr;
-
 public:
   BuiltinTupleDecl(Identifier Name, DeclContext *Parent);
 
   SourceRange getSourceRange() const {
     return SourceRange();
   }
 
-  TupleType *getTupleSelfType() const;
+  TupleType *getTupleSelfType(const ExtensionDecl *owner) const;
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) {

include/swift/AST/DiagnosticsSema.def

@@ -2353,6 +2353,18 @@ ERROR(extension_access_with_conformances,none,
 ERROR(experimental_tuple_extension,none,
       "tuple extensions are experimental",
       ())
+ERROR(tuple_extension_wrong_type,none,
+      "tuple extension must be written as extension of %0", (Type))
+ERROR(tuple_extension_one_conformance,none,
+      "tuple extension must declare conformance to exactly one protocol", ())
+ERROR(tuple_extension_extra_requirement,none,
+      "tuple extension cannot require that %0 "
+      "%select{conforms to|subclasses|is the same type as|%error|%error}1 %2",
+      (Type, unsigned, Type))
+ERROR(tuple_extension_missing_requirement,none,
+      "tuple extension must require that %0 conforms to %1", (Type, Type))
+ERROR(tuple_extension_nested_type,none,
+      "type %0 cannot be nested in tuple extension", (const NominalTypeDecl *))
 ERROR(extension_metatype,none,
       "cannot extend a metatype %0", (Type))
 ERROR(extension_placeholder,none,
@@ -2721,10 +2733,23 @@ NOTE(ambiguous_witnesses_wrong_name,none,
 NOTE(no_witnesses_type,none,
      "protocol requires nested type %0; add nested type %0 for conformance",
      (const AssociatedTypeDecl *))
-NOTE(default_associated_type_req_fail,none,
+NOTE(no_witnesses_type_tuple,none,
+     "protocol requires nested type %0; add type alias %0 with underlying type %1 "
+     "for conformance",
+     (const AssociatedTypeDecl *, Type))
+NOTE(default_associated_type_unsatisfied_conformance,none,
+     "default type %0 for associated type %1 (from protocol %2) "
+     "does not conform to %3",
+     (Type, const AssociatedTypeDecl *, Type, Type))
+NOTE(default_associated_type_unsatisfied_superclass,none,
+     "default type %0 for associated type %1 (from protocol %2) "
+     "does not inherit from %3",
+     (Type, const AssociatedTypeDecl *, Type, Type))
+NOTE(default_associated_type_tuple,none,
      "default type %0 for associated type %1 (from protocol %2) "
-     "does not %select{inherit from|conform to}4 %3",
-     (Type, const AssociatedTypeDecl *, Type, Type, bool))
+     "is unsuitable for tuple conformance; the associated type requirement "
+     "must be fulfilled by a type alias with underlying type %3",
+     (Type, const AssociatedTypeDecl *, Type, Type))
 ERROR(associated_type_access,none,
       "associated type in "
       "%select{a private|a fileprivate|an internal|a package|a public|%error}0 protocol "
@@ -2752,10 +2777,19 @@ WARNING(associated_type_not_usable_from_inline_warn,none,
 NOTE(bad_associated_type_deduction,none,
      "unable to infer associated type %0 for protocol %1",
      (const AssociatedTypeDecl *, const ProtocolDecl *))
-NOTE(associated_type_deduction_witness_failed,none,
+NOTE(associated_type_deduction_unsatisfied_conformance,none,
+     "candidate would match and infer %0 = %1 if %1 "
+     "conformed to %2",
+     (const AssociatedTypeDecl *, Type, Type))
+NOTE(associated_type_deduction_unsatisfied_superclass,none,
      "candidate would match and infer %0 = %1 if %1 "
-     "%select{inherited from|conformed to}3 %2",
-     (const AssociatedTypeDecl *, Type, Type, bool))
+     "inherited from %2",
+     (const AssociatedTypeDecl *, Type, Type))
+NOTE(associated_type_deduction_tuple,none,
+     "cannot infer %0 = %1 in tuple conformance because "
+     "the associated type requirement must be fulfilled by a type alias with "
+     "underlying type %2",
+     (const AssociatedTypeDecl *, Type, Type))
 NOTE(associated_type_witness_conform_impossible,none,
      "candidate can not infer %0 = %1 because %1 "
      "is not a nominal type and so can't conform to %2",
@@ -2846,9 +2880,17 @@ NOTE(protocol_witness_enum_case_payload, none,
 
 NOTE(protocol_witness_type,none,
      "possibly intended match", ())
-NOTE(protocol_witness_nonconform_type,none,
+NOTE(protocol_type_witness_unsatisfied_conformance,none,
      "possibly intended match %0 does not "
-     "%select{inherit from|conform to}2 %1", (Type, Type, bool))
+     "conform to %1", (Type, Type))
+NOTE(protocol_type_witness_unsatisfied_superclass,none,
+     "possibly intended match %0 does not "
+     "inherit from %1", (Type, Type))
+NOTE(protocol_type_witness_tuple,none,
+     "possibly intended match %0 is unsuitable for tuple conformance; "
+     "the associated type requirement must be fulfilled by a type alias "
+     "with underlying type %1",
+     (Type, Type))
 
 NOTE(protocol_witness_circularity,none,
      "candidate references itself", ())

lib/AST/Decl.cpp

@@ -7861,27 +7861,30 @@ Type DeclContext::getSelfTypeInContext() const {
   return mapTypeIntoContext(getSelfInterfaceType());
 }
 
-TupleType *BuiltinTupleDecl::getTupleSelfType() const {
-  if (TupleSelfType)
-    return TupleSelfType;
-
+TupleType *BuiltinTupleDecl::getTupleSelfType(const ExtensionDecl *owner) const {
   auto &ctx = getASTContext();
 
-  // Get the generic parameter type 'Elements'.
-  auto paramType = getGenericParams()->getParams()[0]
-      ->getDeclaredInterfaceType();
+  // Get the generic parameter type 'each T'.
+  GenericParamList *genericParams;
+  if (owner != nullptr) {
+    genericParams = owner->getGenericParams();
+  } else {
+    genericParams = getGenericParams();
+  }
 
-  // Build the pack expansion type 'Elements...'.
+  assert(genericParams != nullptr);
+  assert(genericParams->getParams().size() == 1);
+  assert(genericParams->getOuterParameters() == nullptr);
+  auto paramType = genericParams->getParams()[0]->getDeclaredInterfaceType();
+
+  // Build the pack expansion type 'repeat each T'.
   Type packExpansionType = PackExpansionType::get(paramType, paramType);
 
-  // Build the one-element tuple type '(Elements...)'.
+  // Build the one-element tuple type '(repeat each T)'.
   SmallVector<TupleTypeElt, 1> elts;
   elts.push_back(packExpansionType);
 
-  const_cast<BuiltinTupleDecl *>(this)->TupleSelfType =
-      TupleType::get(elts, ctx);
-
-  return TupleSelfType;
+  return TupleType::get(elts, ctx);
 }
 
 /// Retrieve the interface type of 'self' for the given context.
@@ -7890,7 +7893,7 @@ Type DeclContext::getSelfInterfaceType() const {
 
   if (auto *nominalDecl = getSelfNominalTypeDecl()) {
     if (auto *builtinTupleDecl = dyn_cast<BuiltinTupleDecl>(nominalDecl))
-      return builtinTupleDecl->getTupleSelfType();
+      return builtinTupleDecl->getTupleSelfType(dyn_cast<ExtensionDecl>(this));
 
     if (isa<ProtocolDecl>(nominalDecl)) {
       auto *genericParams = nominalDecl->getGenericParams();