Access to query variables in validationRules

My feature request is partially related to #1627. Generally, I want to integrate with a graphql-query-complexity library that creates validationRules but it need access to the query variables values and they’re not present in ValidationContext in graphql-js. Here’s how it’s configured using plain express-graphql middleware:

import queryComplexity from 'graphql-query-complexity';
import express from 'express';
import graphqlHTTP from 'express-graphql';
import schema from './schema';

const app = express();
app.use('/api', graphqlHTTP(async (request, response, {variables}) => ({
  schema,
  validationRules: [ queryComplexity({
    maximumComplexity: 1000,
    variables,
    onComplete: (complexity: number) => {console.log('Query Complexity:', complexity);},
  }) ]
})));

In graphql-yoga there is a callback, like in apollo-server for context: https://github.com/prisma/graphql-yoga/blob/3362b13374190fd2390594495dc08064e5ee4815/src/types.ts#L64-L77

And I think that apollo-server should support this kind of configuration too 😉 Changing ValidationContext mechanism in graphql-js is much more complicated and the only way that the author has figured out is by making validationRules dynamic in Apollo Server: https://github.com/slicknode/graphql-query-complexity/issues/7#issuecomment-427435851

[MichalLytek]

Here is a working example of graphql-query-complexity integration with Apollo Server 💪 https://github.com/19majkel94/type-graphql/blob/4501867fffe3e6f5b3e71af0b71651efcd48d9c3/examples/query-complexity/index.ts#L16-L64

[martijnwalraven]

@19majkel94 Complexity calculation is a fine solution, but using the didResolveOperation hook from the request pipeline plugin API would be a better place for this because it gets called for every request and has access both to the specific operation that gets executed and the query variables.