Merge pull request #10910 from slavapestov/generic-subscript-materialize-for-set-infer-requirements-4.0

Sema: Explicitly infer requirements from subscript element type for materializeForSet [4.0]

Author: slavapestov

lib/Sema/TypeCheckGeneric.cpp

@@ -555,6 +555,26 @@ static bool checkGenericFuncSignature(TypeChecker &tc,
                                    source);
       }
     }
+
+    // If this is a materializeForSet, infer requirements from the
+    // storage type instead, since it's not part of the accessor's
+    // type signature.
+    if (fn->getAccessorKind() == AccessorKind::IsMaterializeForSet) {
+      if (builder) {
+        auto *storage = fn->getAccessorStorageDecl();
+        if (auto *subscriptDecl = dyn_cast<SubscriptDecl>(storage)) {
+          auto source =
+            GenericSignatureBuilder::FloatingRequirementSource::forInferred(
+                subscriptDecl->getElementTypeLoc().getTypeRepr(),
+                /*quietly=*/true);
+
+          TypeLoc type(nullptr, subscriptDecl->getElementInterfaceType());
+          assert(type.getType());
+          builder->inferRequirements(*func->getParentModule(),
+                                     type, source);
+        }
+      }
+    }
   }
 
   return badType;

test/SILGen/materializeForSet.swift

@@ -466,6 +466,28 @@ extension GenericSubscriptProtocol {
 
 struct GenericSubscriptDefaultWitness : GenericSubscriptProtocol { }
 
+// Make sure we correctly infer the 'T : Magic' requirement on all the accessors
+// of the subscript.
+
+struct GenericTypeWithRequirement<T : Magic> {}
+
+protocol InferredRequirementOnSubscriptProtocol {
+  subscript<T>(i: Int) -> GenericTypeWithRequirement<T> { get set }
+}
+
+struct InferredRequirementOnSubscript : InferredRequirementOnSubscriptProtocol {
+  subscript<T>(i: Int) -> GenericTypeWithRequirement<T> {
+    get { }
+    set { }
+  }
+}
+
+// CHECK-LABEL: sil hidden @_T017materializeForSet30InferredRequirementOnSubscriptV9subscriptAA015GenericTypeWithE0VyxGSicAA5MagicRzlufg : $@convention(method) <T where T : Magic> (Int, InferredRequirementOnSubscript) -> GenericTypeWithRequirement<T>
+
+// CHECK-LABEL: sil hidden @_T017materializeForSet30InferredRequirementOnSubscriptV9subscriptAA015GenericTypeWithE0VyxGSicAA5MagicRzlufs : $@convention(method) <T where T : Magic> (GenericTypeWithRequirement<T>, Int, @inout InferredRequirementOnSubscript) -> ()
+
+// CHECK-LABEL: sil hidden [transparent] @_T017materializeForSet30InferredRequirementOnSubscriptV9subscriptAA015GenericTypeWithE0VyxGSicAA5MagicRzlufm : $@convention(method) <T where T : Magic> (Builtin.RawPointer, @inout Builtin.UnsafeValueBuffer, Int, @inout InferredRequirementOnSubscript) -> (Builtin.RawPointer, Optional<Builtin.RawPointer>)
+
 // Test for materializeForSet vs static properties of structs.
 
 protocol Beverage {