[Type checker] Ensure that synthesized accessors get generic parameter lists.

When we synthesize the declaration for getters and setters from (e.g.) an
addressor, ensure that we clone the generic parameter list when we have a
generic subscript. Fixes rdar://problem/45046969.

Author: DougGregor

lib/Sema/CodeSynthesis.cpp

@@ -164,6 +164,20 @@ buildIndexForwardingParamList(AbstractStorageDecl *storage,
   return ParameterList::create(context, elements);
 }
 
+/// Create the generic parameters needed for the given accessor, if any.
+static GenericParamList *createAccessorGenericParams(
+                                              AbstractStorageDecl *storage) {
+  // Accessors of generic subscripts get a copy of the subscript's
+  // generic parameter list, because they're not nested inside the
+  // subscript.
+  if (auto *subscript = dyn_cast<SubscriptDecl>(storage)) {
+    if (auto genericParams = subscript->getGenericParams())
+      return genericParams->clone(subscript->getDeclContext());
+  }
+
+  return nullptr;
+}
+
 static AccessorDecl *createGetterPrototype(TypeChecker &TC,
                                            AbstractStorageDecl *storage) {
   assert(!storage->getGetter());
@@ -193,6 +207,8 @@ static AccessorDecl *createGetterPrototype(TypeChecker &TC,
     }
   }
 
+  GenericParamList *genericParams = createAccessorGenericParams(storage);
+
   // Add an index-forwarding clause.
   auto *getterParams = buildIndexForwardingParamList(storage, {});
 
@@ -209,7 +225,7 @@ static AccessorDecl *createGetterPrototype(TypeChecker &TC,
       AccessorKind::Get, AddressorKind::NotAddressor, storage,
       staticLoc, StaticSpellingKind::None,
       /*Throws=*/false, /*ThrowsLoc=*/SourceLoc(),
-      /*GenericParams=*/nullptr,
+      genericParams,
       getterParams,
       TypeLoc::withoutLoc(storageInterfaceType),
       storage->getDeclContext());
@@ -255,7 +271,9 @@ static AccessorDecl *createSetterPrototype(TypeChecker &TC,
 
   bool isStatic = storage->isStatic();
   bool isMutating = storage->isSetterMutating();
-  
+
+  GenericParamList *genericParams = createAccessorGenericParams(storage);
+
   // Add a "(value : T, indices...)" argument list.
   auto storageInterfaceType = storage->getValueInterfaceType();
   auto valueDecl = buildArgument(storage->getLoc(), storage->getDeclContext(),
@@ -269,7 +287,7 @@ static AccessorDecl *createSetterPrototype(TypeChecker &TC,
       AccessorKind::Set, AddressorKind::NotAddressor, storage,
       /*StaticLoc=*/SourceLoc(), StaticSpellingKind::None,
       /*Throws=*/false, /*ThrowsLoc=*/SourceLoc(),
-      /*GenericParams=*/nullptr, params,
+      genericParams, params,
       TypeLoc::withoutLoc(setterRetTy),
       storage->getDeclContext());
   setter->setImplicit();
@@ -379,15 +397,7 @@ createCoroutineAccessorPrototype(TypeChecker &TC,
   // Coroutine accessors always return ().
   Type retTy = TupleType::getEmpty(ctx);
 
-  // Accessors of generic subscripts get a copy of the subscript's
-  // generic parameter list, because they're not nested inside the
-  // subscript.
-  GenericParamList *genericParams = nullptr;
-  if (auto *subscript = dyn_cast<SubscriptDecl>(storage)) {
-    genericParams = subscript->getGenericParams();
-    if (genericParams)
-      genericParams = genericParams->clone(dc);
-  }
+  GenericParamList *genericParams = createAccessorGenericParams(storage);
 
   auto *accessor = AccessorDecl::create(
       ctx, loc, /*AccessorKeywordLoc=*/SourceLoc(),

test/SILGen/addressors.swift

@@ -411,6 +411,29 @@ class Sub : Base {
   }
 }
 
+// rdar://problem/45046969
+struct Bar<T> { }
+
+protocol FooProtocol {
+  subscript<T>(index: Bar<T>) -> T { get set }
+}
+
+// Make sure we get the right generic signatures for the synthesized
+// getter/setter.
+
+// CHECK: sil hidden [transparent] @$s10addressors3FooVyqd__AA3BarVyqd__Gcluig : $@convention(method) <Base><T> (Bar<T>, Foo<Base>)
+// CHECK: sil hidden [transparent] @$s10addressors3FooVyqd__AA3BarVyqd__Gcluis : $@convention(method) <Base><T> (@in T, Bar<T>, @inout Foo<Base>) -> ()
+struct Foo<Base>: FooProtocol {
+  subscript<T>(index: Bar<T>) -> T {
+    unsafeAddress {
+      return UnsafePointer<T>(bitPattern: 0)!
+    }
+    unsafeMutableAddress {
+      return UnsafeMutablePointer<T>(bitPattern: 0)!
+    }
+  }
+}
+
 // Make sure addressors don't get vtable entries.
 // CHECK-LABEL: sil_vtable Base {
 // CHECK-NEXT: #Base.data!getter.1: (Base) -> () -> UnsafeMutablePointer<Int32> : @$s10addressors4BaseC4dataSpys5Int32VGvg