Support possible types in no-unreachable-types rule (#361)

Author: kamilkisiela

.changeset/smooth-chairs-argue.md

@@ -0,0 +1,5 @@
+---
+'@graphql-eslint/eslint-plugin': patch
+---
+
+Support possible types in no-unreachable-types rule

packages/plugin/src/graphql-ast.ts

@@ -44,9 +44,13 @@ export function collectReachableTypes(schema: GraphQLSchema): Set<string> {
 
   function collectFrom(type?: GraphQLNamedType): void {
     if (type && shouldCollect(type.name)) {
-      if (isObjectType(type) || isInterfaceType(type)) {
+      if (isObjectType(type)) {
         collectFromFieldMap(type.getFields());
         collectFromInterfaces(type.getInterfaces());
+      } else if (isInterfaceType(type)) {
+        collectFromFieldMap(type.getFields());
+        collectFromInterfaces(type.getInterfaces());
+        collectFromImplementations(type);
       } else if (isUnionType(type)) {
         type.getTypes().forEach(collectFrom);
       } else if (isInputObjectType(type)) {
@@ -94,6 +98,10 @@ export function collectReachableTypes(schema: GraphQLSchema): Set<string> {
     collectFrom(schema.getType(resolveName(input)));
   }
 
+  function collectFromImplementations(type: GraphQLInterfaceType): void {
+    schema.getPossibleTypes(type).forEach(collectFrom);
+  }
+
   function resolveName(type: GraphQLOutputType | GraphQLInputType) {
     if (isListType(type) || isNonNullType(type)) {
       return resolveName(type.ofType);

packages/plugin/src/rules/no-unreachable-types.ts

@@ -48,10 +48,9 @@ const rule: GraphQLESLintRule = {
   create(context) {
     function ensureReachability(node) {
       const typeName = node.name.value;
-      const implemented = node.interfaces?.map(instance => instance.name.value) || [];
       const reachableTypes = requireReachableTypesFromContext('no-unreachable-types', context);
 
-      if (!reachableTypes.has(typeName) && implemented.filter(name => reachableTypes.has(name)).length === 0) {
+      if (!reachableTypes.has(typeName)) {
         context.report({
           node,
           messageId: UNREACHABLE_TYPE,

packages/plugin/tests/no-unreachable-types.spec.ts

@@ -76,6 +76,41 @@ ruleTester.runGraphQLTests('no-unreachable-types', rule, {
         address: String
       }
     `),
+    useSchema(/* GraphQL */ `
+      interface User {
+        id: String
+      }
+
+      type SuperUser implements User {
+        id: String
+        superDetail: SuperDetail
+      }
+
+      type SuperDetail {
+        detail: String
+      }
+
+      type Query {
+        user: User!
+      }
+    `),
+    useSchema(/* GraphQL */ `
+    interface User {
+      id: String
+    }
+
+    type SuperUser implements User {
+      id: String
+    }
+
+    extend type SuperUser {
+      detail: String
+    }
+
+    type Query {
+      user: User!
+    }
+  `),
   ],
   invalid: [
     {