Prevent list/set member from targeting container

docs/source/spec/core.rst

@@ -415,7 +415,8 @@ list
 The :dfn:`list` type represents a homogeneous collection of values. A list is
 defined using a :token:`list_statement`. A list statement consists of the
 shape named followed by an object with a single key-value pair of "member"
-that defines the :ref:`member <member>` of the list.
+that defines the :ref:`member <member>` of the list. The member of a list
+cannot target the containing list shape.
 
 The following example defines a list with a string member from the
 :ref:`prelude <prelude>`:
@@ -513,7 +514,8 @@ set
 The :dfn:`set` type represents an unordered collection of unique homogeneous
 values. A set is defined using a :token:`set_statement` that consists of the
 shape named followed by an object with a single key-value pair of "member"
-that defines the :ref:`member <member>` of the set.
+that defines the :ref:`member <member>` of the set. The member of a set
+cannot target the containing set shape.
 
 The following example defines a set of strings:
 

smithy-model/src/main/java/software/amazon/smithy/model/validation/validators/TargetValidator.java

@@ -45,9 +45,9 @@
  */
 public class TargetValidator extends AbstractValidator {
 
-    /** Valid member shape targets. */
     private static final Set<ShapeType> INVALID_MEMBER_TARGETS = SetUtils.of(
             ShapeType.SERVICE, ShapeType.RESOURCE, ShapeType.OPERATION, ShapeType.MEMBER);
+    private static final Set<ShapeType> INVALID_RECURSIVE_MEMBER_TARGETS = SetUtils.of(ShapeType.LIST, ShapeType.SET);
 
     @Override
     public List<ValidationEvent> validate(Model model) {
@@ -85,6 +85,10 @@ private Optional<ValidationEvent> validateTarget(ShapeIndex index, Shape shape,
                 if (INVALID_MEMBER_TARGETS.contains(target.getType())) {
                     return Optional.of(error(shape, format(
                             "Members cannot target %s shapes, but found %s", target.getType(), target)));
+                } else if (target.getId().equals(shape.getId().withoutMember())
+                           && INVALID_RECURSIVE_MEMBER_TARGETS.contains(target.getType())) {
+                    return Optional.of(error(shape, format(
+                            "%s shape members cannot target their container", target.getType())));
                 }
             case MAP_KEY:
                 return target.asMemberShape().flatMap(m -> validateMapKey(shape, m.getTarget(), index));

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/target-validator.errors

@@ -8,6 +8,7 @@
 [ERROR] ns.foo#InvalidListMemberReference$member: member shape targets an unresolved shape `ns.foo#NotFound` | Target
 [ERROR] ns.foo#InvalidListMemberResource$member: Members cannot target resource shapes, but found (resource: `ns.foo#MyResource`) | Target
 [ERROR] ns.foo#InvalidListMemberService$member: Members cannot target service shapes, but found (service: `ns.foo#MyService`) | Target
+[ERROR] ns.foo#InvalidRecursiveList$member: list shape members cannot target their container | Target
 [ERROR] ns.foo#InvalidMapType: Map key member targets (structure: `ns.foo#ValidInput`), but is expected to target a string | Target
 [ERROR] ns.foo#InvalidOperationBadErrorTraits: Operation error targets an invalid structure, `ns.foo#ValidInput`, that is not marked with the `error` trait. | Target
 [ERROR] ns.foo#InvalidOperationBadErrorTraits: Operation input targets an invalid structure `ns.foo#ValidError` that is marked with the `error` trait. | Target

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/target-validator.json

@@ -32,6 +32,12 @@
                     "target": "MyService"
                 }
             },
+            "InvalidRecursiveList": {
+                "type": "list",
+                "member": {
+                    "target": "InvalidRecursiveList"
+                }
+            },
             "MyService": {
                 "type": "service",
                 "version": "2017-01-17",