[Sema] InitAccessors: Verify that a property never appears both in initializes(...) and accesses(...)

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -7289,6 +7289,9 @@ ERROR(init_accessor_initializes_attribute_on_other_declaration,none,
 ERROR(init_accessor_accesses_attribute_on_other_declaration,none,
       "accesses(...) attribute could only be used with init accessors",
       ())
+ERROR(init_accessor_property_both_init_and_accessed,none,
+      "property %0 cannot be both initialized and accessed",
+      (DeclName))
 
 
 #define UNDEFINE_DIAGNOSTIC_MACROS

lib/Sema/TypeCheckAttr.cpp

@@ -3569,7 +3569,23 @@ void AttributeChecker::visitAccessesAttr(AccessesAttr *attr) {
     return;
   }
 
-  (void)attr->getPropertyDecls(accessor);
+  // Check whether there are any intersections between initializes(...) and
+  // accesses(...) attributes.
+
+  Optional<ArrayRef<VarDecl *>> initializedProperties;
+  if (auto *initAttr = D->getAttrs().getAttribute<InitializesAttr>()) {
+    initializedProperties.emplace(initAttr->getPropertyDecls(accessor));
+  }
+
+  if (initializedProperties) {
+    for (auto *property : attr->getPropertyDecls(accessor)) {
+      if (llvm::is_contained(*initializedProperties, property)) {
+        diagnose(attr->getLocation(),
+                 diag::init_accessor_property_both_init_and_accessed,
+                 property->getName());
+      }
+    }
+  }
 }
 
 void AttributeChecker::visitImplementsAttr(ImplementsAttr *attr) {

test/decl/var/init_accessors.swift

@@ -84,3 +84,33 @@ func test_assignment_to_let_properties() {
     }
   }
 }
+
+func test_duplicate_and_computed_lazy_properties() {
+  struct Test1 {
+    var _a: Int
+    var _b: Int
+
+    var a: Int {
+      init(initialValue) initializes(_b _a) accesses(_a) {
+        // expected-error@-1 {{property '_a' cannot be both initialized and accessed}}
+      }
+    }
+  }
+
+  struct Test2 {
+    var _a: Int
+
+    var a: Int {
+      init(initialValue) initializes(a c) accesses(_a b) {}
+      // expected-error@-1 {{init accessor cannot refer to property 'a'; init accessors can refer only to stored properties}}
+      // expected-error@-2 {{init accessor cannot refer to property 'b'; init accessors can refer only to stored properties}}
+      // expected-error@-3 {{init accessor cannot refer to property 'c'; init accessors can refer only to stored properties}}
+    }
+
+    var b: Int {
+      get { 42 }
+    }
+
+    lazy var c: Int = 42
+  }
+}