Sema: Allow omitting generic parameters when accessing member type with a fully-constrained 'where' clause

Fixes rdar://problem/78960468.

Author: slavapestov

lib/Sema/TypeCheckNameLookup.cpp

@@ -358,8 +358,25 @@ LookupResult TypeChecker::lookupMember(DeclContext *dc,
   return result;
 }
 
+static bool doesTypeAliasFullyConstrainAllOuterGenericParams(
+    TypeAliasDecl *aliasDecl) {
+  auto parentSig = aliasDecl->getDeclContext()->getGenericSignatureOfContext();
+  auto genericSig = aliasDecl->getGenericSignature();
+
+  if (!parentSig || !genericSig)
+    return false;
+
+  for (auto *paramType : parentSig->getGenericParams()) {
+    if (!genericSig->isConcreteType(paramType))
+      return false;
+  }
+
+  return true;
+}
+
 TypeChecker::UnsupportedMemberTypeAccessKind
-TypeChecker::isUnsupportedMemberTypeAccess(Type type, TypeDecl *typeDecl) {
+TypeChecker::isUnsupportedMemberTypeAccess(Type type, TypeDecl *typeDecl,
+                                           bool hasUnboundOpener) {
   // We don't allow lookups of a non-generic typealias of an unbound
   // generic type, because we have no way to model such a type in the
   // AST.
@@ -376,13 +393,18 @@ TypeChecker::isUnsupportedMemberTypeAccess(Type type, TypeDecl *typeDecl) {
     // underlying type is not dependent.
     if (auto *aliasDecl = dyn_cast<TypeAliasDecl>(typeDecl)) {
       if (!aliasDecl->isGeneric() &&
-          aliasDecl->getUnderlyingType()->hasTypeParameter()) {
+          aliasDecl->getUnderlyingType()->hasTypeParameter() &&
+          !doesTypeAliasFullyConstrainAllOuterGenericParams(aliasDecl)) {
         return UnsupportedMemberTypeAccessKind::TypeAliasOfUnboundGeneric;
       }
     }
 
     if (isa<AssociatedTypeDecl>(typeDecl))
       return UnsupportedMemberTypeAccessKind::AssociatedTypeOfUnboundGeneric;
+
+    if (isa<NominalTypeDecl>(typeDecl))
+      if (!hasUnboundOpener)
+        return UnsupportedMemberTypeAccessKind::NominalTypeOfUnboundGeneric;
   }
 
   if (type->isExistentialType() &&
@@ -433,7 +455,7 @@ LookupTypeResult TypeChecker::lookupMemberType(DeclContext *dc,
       continue;
     }
 
-    if (isUnsupportedMemberTypeAccess(type, typeDecl)
+    if (isUnsupportedMemberTypeAccess(type, typeDecl, true)
           != TypeChecker::UnsupportedMemberTypeAccessKind::None) {
       auto memberType = typeDecl->getDeclaredInterfaceType();
 

lib/Sema/TypeCheckType.cpp

@@ -712,11 +712,7 @@ static Type applyGenericArguments(Type type, TypeResolution resolution,
           if (const auto boundTy = openerFn(unboundTy))
             return boundTy;
 
-        // Complain if we're allowed to and bail out with an error.
-        if (!options.contains(TypeResolutionFlags::SilenceErrors))
-          diagnoseUnboundGenericType(type, loc);
-
-        return ErrorType::get(resolution.getASTContext());
+        return type;
       }
     }
 
@@ -914,11 +910,19 @@ Type TypeResolution::applyUnboundGenericArguments(
         return BoundGenericType::get(nominalDecl, parentTy, genericArgs);
       }
 
-      assert(!resultType->hasTypeParameter());
-      return resultType;
+      if (!resultType->hasTypeParameter())
+        return resultType;
+
+      auto parentSig = decl->getDeclContext()->getGenericSignatureOfContext();
+      if (parentSig) {
+        for (auto gp : parentSig->getGenericParams())
+          subs[gp->getCanonicalType()->castTo<GenericTypeParamType>()] =
+              genericSig->getConcreteType(gp);
+      }
+    } else {
+      subs = parentTy->getContextSubstitutions(decl->getDeclContext());
     }
 
-    subs = parentTy->getContextSubstitutions(decl->getDeclContext());
     skipRequirementsCheck |= parentTy->hasTypeVariable();
   } else if (auto genericEnv =
                  decl->getDeclContext()->getGenericEnvironmentOfContext()) {
@@ -1501,16 +1505,21 @@ static Type resolveNestedIdentTypeComponent(TypeResolution resolution,
 
   auto maybeDiagnoseBadMemberType = [&](TypeDecl *member, Type memberType,
                                         AssociatedTypeDecl *inferredAssocType) {
+    bool hasUnboundOpener = !!resolution.getUnboundTypeOpener();
+
     if (options.contains(TypeResolutionFlags::SilenceErrors)) {
-      if (TypeChecker::isUnsupportedMemberTypeAccess(parentTy, member)
+      if (TypeChecker::isUnsupportedMemberTypeAccess(parentTy, member,
+                                                     hasUnboundOpener)
             != TypeChecker::UnsupportedMemberTypeAccessKind::None)
         return ErrorType::get(ctx);
     }
 
-    switch (TypeChecker::isUnsupportedMemberTypeAccess(parentTy, member)) {
+    switch (TypeChecker::isUnsupportedMemberTypeAccess(parentTy, member,
+                                                       hasUnboundOpener)) {
     case TypeChecker::UnsupportedMemberTypeAccessKind::None:
       break;
 
+    case TypeChecker::UnsupportedMemberTypeAccessKind::NominalTypeOfUnboundGeneric:
     case TypeChecker::UnsupportedMemberTypeAccessKind::TypeAliasOfUnboundGeneric:
     case TypeChecker::UnsupportedMemberTypeAccessKind::AssociatedTypeOfUnboundGeneric:
       diagnoseUnboundGenericType(parentTy, parentRange.End);
@@ -1650,6 +1659,23 @@ resolveIdentTypeComponent(TypeResolution resolution,
     parentRange.End = nestedComp->getEndLoc();
   }
 
+  // Diagnose an error if the last component's generic arguments are missing.
+  auto lastComp = components.back();
+  auto options = resolution.getOptions();
+
+  if (result->is<UnboundGenericType>() &&
+      !isa<GenericIdentTypeRepr>(lastComp) &&
+      !resolution.getUnboundTypeOpener() &&
+      !options.is(TypeResolverContext::TypeAliasDecl)) {
+
+    if (!options.contains(TypeResolutionFlags::SilenceErrors)) {
+      diagnoseUnboundGenericType(result,
+                                 lastComp->getNameLoc().getBaseNameLoc());
+    }
+
+    return ErrorType::get(result->getASTContext());
+  }
+
   return result;
 }
 

lib/Sema/TypeChecker.h

@@ -846,13 +846,15 @@ enum class UnsupportedMemberTypeAccessKind : uint8_t {
   TypeAliasOfUnboundGeneric,
   TypeAliasOfExistential,
   AssociatedTypeOfUnboundGeneric,
-  AssociatedTypeOfExistential
+  AssociatedTypeOfExistential,
+  NominalTypeOfUnboundGeneric
 };
 
 /// Check whether the given declaration can be written as a
 /// member of the given base type.
 UnsupportedMemberTypeAccessKind
-isUnsupportedMemberTypeAccess(Type type, TypeDecl *typeDecl);
+isUnsupportedMemberTypeAccess(Type type, TypeDecl *typeDecl,
+                              bool hasUnboundOpener);
 
 /// @}
 

test/Generics/unbound.swift

@@ -91,3 +91,16 @@ func makeInner() -> Outer<String, String>.Middle.Inner {
 var innerProperty: Outer.Middle.Inner = makeInner()
 // expected-error@-1 {{reference to generic type 'Outer' requires arguments in <...>}}
 
+// Some nested generic cases
+struct OuterStruct<T> { // expected-note 2{{generic type 'OuterStruct' declared here}}
+  struct InnerStruct<U> {} // expected-note {{generic type 'InnerStruct' declared here}}
+}
+
+func nested(_: OuterStruct.InnerStruct) {}
+// expected-error@-1 {{reference to generic type 'OuterStruct' requires arguments in <...>}}
+
+func nested(_: OuterStruct.InnerStruct<Int>) {}
+// expected-error@-1 {{reference to generic type 'OuterStruct' requires arguments in <...>}}
+
+func nested(_: OuterStruct<Int>.InnerStruct) {}
+// expected-error@-1 {{reference to generic type 'OuterStruct<Int>.InnerStruct' requires arguments in <...>}}

test/decl/typealias/fully_constrained.swift

@@ -0,0 +1,64 @@
+// RUN: %target-typecheck-verify-swift
+
+struct OtherGeneric<U> {}
+
+struct Generic<T> {
+  // FIXME: Should work with 'T' as well
+  typealias NonGeneric = Int where T == Int
+
+  typealias Unbound = OtherGeneric where T == Int
+  typealias Generic = OtherGeneric where T == Int
+}
+
+extension Generic where T == Int {
+  // FIXME: Should work with 'T' as well
+  typealias NonGenericInExtension = Int
+
+  typealias UnboundInExtension = OtherGeneric
+  typealias GenericInExtension = OtherGeneric
+}
+
+func use(_: Generic.NonGeneric,
+         _: Generic.Unbound<String>,
+         _: Generic.Generic<String>,
+         _: Generic.NonGenericInExtension,
+         _: Generic.UnboundInExtension<String>,
+         _: Generic.GenericInExtension<String>) {
+
+  // FIXME: Get these working too
+#if false
+  let _ = Generic.NonGeneric.self
+  let _ = Generic.Unbound<String>.self
+  let _ = Generic.Generic<String>.self
+
+  let _ = Generic.NonGenericInExtension.self
+  let _ = Generic.UnboundInExtension<String>.self
+  let _ = Generic.GenericInExtension<String>.self
+
+  let _: Generic.NonGeneric = 123
+  let _: Generic.NonGenericInExtension = 123
+#endif
+
+  let _: Generic.Unbound = OtherGeneric<String>()
+  let _: Generic.Generic = OtherGeneric<String>()
+
+  let _: Generic.UnboundInExtension = OtherGeneric<String>()
+  let _: Generic.GenericInExtension = OtherGeneric<String>()
+}
+
+struct Use {
+  let a1: Generic.NonGeneric
+  let b1: Generic.Unbound<String>
+  let c1: Generic.Generic<String>
+  let a2: Generic.NonGenericInExtension
+  let b2: Generic.UnboundInExtension<String>
+  let c2: Generic.GenericInExtension<String>
+}
+
+extension Generic.NonGeneric {}
+extension Generic.Unbound {}
+extension Generic.Generic {}
+
+extension Generic.NonGenericInExtension {}
+extension Generic.UnboundInExtension {}
+extension Generic.GenericInExtension {}