Cache for parsing the schema (#137)

* simple cache for schema parsing

* add CHANGELOG entry for schema cache

Author: Kristján Oddsson

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Change log
 ### vNEXT
 - Retrieves `.graphqlconfig` relative to the file being linted, which re-enables support for `vscode-eslint` using `.graphqlconfig` in [#108](https://github.com/apollographql/eslint-plugin-graphql/pull/108) by [Jon Wong][https://github.com/jnwng/]
+- Cache schema reading/parsing results each time a rule is created in [#137](https://github.com/apollographql/eslint-plugin-graphql/pull/137) by [Kristján Oddsson](https://github.com/koddsson)
 
 ### v2.0.0
 - Add support for `graphql-js@^0.12.0` and `graphql-js@^0.13.0` in [Jon Wong](https://github.com/jnwng/)[#119] (https://github.com/apollographql/eslint-plugin-graphql/pull/93)

src/index.js

@@ -243,7 +243,13 @@ export const rules = {
   },
 };
 
+const schemaCache = {};
+
 function parseOptions(optionGroup, context) {
+  const cacheHit = schemaCache[JSON.stringify(optionGroup)];
+  if (cacheHit) {
+    return cacheHit;
+  }
   const {
     schemaJson, // Schema via JSON object
     schemaJsonFilepath, // Or Schema via absolute filepath
@@ -322,7 +328,9 @@ function parseOptions(optionGroup, context) {
       return require(`graphql/validation/rules/${name}`)[name];
     }
   });
-  return {schema, env, tagName, validators};
+  const results = {schema, env, tagName, validators};
+  schemaCache[JSON.stringify(optionGroup)] = results;
+  return results;
 }
 
 function initSchema(json) {