buildClientSchema fails when converting apollo introspection json

[tjtaill]

BUG/FIX

Hi I am using a vscode plugin to do graphql autocompletes https://marketplace.visualstudio.com/items?itemName=kumar-harsh.graphql-for-vscode

It requires a gql file so I use grahpql-tools https://www.npmjs.com/package/gql-tools?activeTab=readme.

I download the json scheme
gqlschema http://example.com/graphql -i

Then I convert it to the gql using this library
in a script I call gql-json-to-sdl.js
with the following

const { buildClientSchema, printSchema } = require("graphql");
const fs = require("fs");

const introspectionSchemaResult = JSON.parse(fs.readFileSync("graphql_schema.json"));
const graphqlSchemaObj = buildClientSchema(introspectionSchemaResult);
fs.writeFileSync('graphql_schema.gql', printSchema(graphqlSchemaObj));

I get the following stack trace

TypeError: Cannot read property 'types' of undefined
at buildClientSchema (.../node_modules/graphql/utilities/buildClientSchema.js:57:61)
at Object. (.../gql-json-to-sdl.js:5:26)
at Module._compile (internal/modules/cjs/loader.js:689:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
at Module.load (internal/modules/cjs/loader.js:599:32)
at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
at Function.Module._load (internal/modules/cjs/loader.js:530:3)
at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
at startup (internal/bootstrap/node.js:283:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:743:3)

If I change the following https://github.com/graphql/graphql-js/blob/master/src/utilities/buildClientSchema.js#L76

to

var schemaIntrospection = introspection.__schema || introspection.data.__schema;

it works wondering if that change is a valid fix for this repo or just a one
off solution for my own situation

[IvanGoncharov]

@tjtaill Every graphql response including introspection one have data and errors and buildClientSchema accepts data. So your code should look like:

if (introspectionSchemaResult.errors) {
  // do something with errors
}
const graphqlSchemaObj = buildClientSchema(introspectionSchemaResult.data);

[IvanGoncharov]

@tjtaill It's common issue so I added dev check (in #1974) to prevent such situations in future.