Fix shapes_for for recursive shapes

gems/smithy/lib/smithy/vise/structure_parser.rb

@@ -32,22 +32,24 @@ def initialize(model)
         @shapes = model['shapes']
       end
 
-      def shapes_for(structure)
+      def shapes_for(structure, visited = {})
         shapes = {}
         _id, structure = structure.first
-        structure['members']&.each_value { |member| parse_member(member, shapes) }
+        structure['members']&.each_value { |member| parse_member(member, shapes, visited) }
         shapes
       end
 
       private
 
-      def parse_member(member_ref, shapes)
+      def parse_member(member_ref, shapes, visited)
         target = member_ref['target']
+        return if visited.include?(target)
         return if PRELUDE_SHAPES.include?(target)
 
         shape = @shapes[target]
         shapes[target] = shape
-        shape['members']&.each_value { |member| parse_member(member, shapes) }
+        visited[target] = true
+        shape['members']&.each_value { |member| parse_member(member, shapes, visited) }
       end
     end
   end

gems/smithy/spec/fixtures/recursive/model.json

@@ -0,0 +1,31 @@
+{
+    "smithy": "2.0",
+    "shapes": {
+        "smithy.ruby.tests#Operation": {
+            "type": "operation",
+            "input": {
+                "target": "smithy.ruby.tests#Structure"
+            },
+            "output": {
+                "target": "smithy.ruby.tests#Structure"
+            }
+        },
+        "smithy.ruby.tests#Recursive": {
+            "type": "service",
+            "version": "1.0.0",
+            "operations": [
+                {
+                    "target": "smithy.ruby.tests#Operation"
+                }
+            ]
+        },
+        "smithy.ruby.tests#Structure": {
+            "type": "structure",
+            "members": {
+                "structure": {
+                    "target": "smithy.ruby.tests#Structure"
+                }
+            }
+        }
+    }
+}

gems/smithy/spec/fixtures/recursive/model.smithy

@@ -0,0 +1,17 @@
+$version: "2"
+
+namespace smithy.ruby.tests
+
+service Recursive {
+    version: "1.0.0"
+    operations: [Operation]
+}
+
+operation Operation {
+    input: Structure
+    output: Structure
+}
+
+structure Structure {
+    structure: Structure
+}

gems/smithy/spec/smithy/vise/service_index_spec.rb

@@ -35,6 +35,19 @@ module Vise
           actual = subject.shapes_for(service)
           expect(actual.keys).to match_array(expected.keys)
         end
+
+        context 'recursive structures' do
+          let(:fixture) do
+            JSON.load_file(File.expand_path('../../fixtures/recursive/model.json', __dir__))
+          end
+
+          it 'handles recursive shapes' do
+            service =
+              fixture['shapes']
+              .select { |id, _| id == 'smithy.ruby.tests#Recursive' }
+            subject.shapes_for(service)
+          end
+        end
       end
     end
   end