Allow GraphQL schemas without Query type

[mbroecheler]

Right now, the compiler and servlet expect a query type and at least one field inside the type in order to run. This means users cannot define a schema that only accepts mutations.

deploy-servlet-1              | 16:48:07.819 [vert.x-eventloop-thread-0] ERROR io.vertx.core.impl.launcher.commands.VertxIsolatedDeployer - Failed in deploying verticle
deploy-servlet-1              | graphql.schema.validation.InvalidSchemaException: invalid schema:
deploy-servlet-1              | "Query" must define one or more fields.
deploy-servlet-1              |     at graphql.schema.GraphQLSchema$Builder.validateSchema(GraphQLSchema.java:935) ~[vertx-server.jar:?]
deploy-servlet-1              |     at graphql.schema.GraphQLSchema$Builder.buildImpl(GraphQLSchema.java:929) ~[vertx-server.jar:?]
deploy-servlet-1              |     at graphql.schema.GraphQLSchema$Builder.build(GraphQLSchema.java:894) ~[vertx-server.jar:?]
deploy-servlet-1              |     at graphql.schema.idl.SchemaGenerator.makeExecutableSchemaImpl(SchemaGenerator.java:117) ~[vertx-server.jar:?]
deploy-servlet-1              |     at graphql.schema.idl.SchemaGenerator.makeExecutableSchema(SchemaGenerator.java:87) ~[vertx-server.jar:?]
deploy-servlet-1              |     at graphql.schema.idl.SchemaGenerator.makeExecutableSchema(SchemaGenerator.java:58) ~[vertx-server.jar:?]
deploy-servlet-1              |     at com.datasqrl.graphql.server.BuildGraphQLEngine.visitRoot(BuildGraphQLEngine.java:83) ~[vertx-server.jar:?]
deploy-servlet-1              |     at com.datasqrl.graphql.server.BuildGraphQLEngine.visitRoot(BuildGraphQLEngine.java:47) ~[vertx-server.jar:?]
deploy-servlet-1              |     at com.datasqrl.graphql.server.Model$RootGraphqlModel.accept(Model.java:53) ~[vertx-server.jar:?]
deploy-servlet-1              |     at com.datasqrl.graphql.GraphQLServer.createGraphQL(GraphQLServer.java:154) ~[vertx-server.jar:?]
deploy-servlet-1              |     at com.datasqrl.graphql.GraphQLServer.start(GraphQLServer.java:102) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.vertx.core.impl.DeploymentManager.lambda$doDeploy$5(DeploymentManager.java:196) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:264) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:246) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.vertx.core.impl.EventLoopContext.lambda$runOnContext$0(EventLoopContext.java:43) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:174) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:167) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:470) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:569) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[vertx-server.jar:?]
deploy-servlet-1              |     at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[vertx-server.jar:?]
deploy-servlet-1              |     at java.lang.Thread.run(Thread.java:829) ~[?:?]

[henneberger]

Would love to except it is against the graphql spec. We'd have to put in a no-op function as a placeholder.

https://spec.graphql.org/June2018/#sec-Root-Operation-Types

The query root operation type must be provided and must be an Object type.

And later

An Object type must define one or more fields

[henneberger]

Fixed in #447

[henneberger]

Reopening. A refactor removed this feature and it needs to be reintroduced.