Reduce size impact of populateExchange (#122)

* Reuse more helpers and add mutations where necessary in populateExchange

Refactor some parts to avoid unnecessary immutability for micro-perf optimisations,
and reduce size where possible by reusing helpers and swapping out immutability for
mutability.

Total minzipped size:
8.24kB -> 8.19kB

* Remove usage of Array.from

This isn't supported in IE11 and hence breaks compatibility
if it isn't user polyfilled.

See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from

* Remove another internal immutable change in addTypenamesToQuery

* Extract unwrapType helper and enhance type-safety

* Remove userFragments/typeFragments reduce

Removes additional closures that aren't needed.
Addresses PR comments

* Remove additional map for for-loop

* Use Kind enum from graphql

* Refactor extractSelectionsFromQuery and addFragmentsToQuery

* Add IntrospectionQuery type from populate to cache

* Simplify GraphQLFlatType

* Moving map.ts to src/helpers/

docs/help.md

@@ -261,11 +261,14 @@ field somewhere, maybe due to a typo.
 
 ## (18) Invalid TypeInfo state <a id="18"></a>
 
-> Invalid TypeInfo state: Found an abstract type when none was expected.
+> Invalid TypeInfo state: Found no flat schema type when one was expected.
 
 When you're using the populate exchange with an introspected schema, it will
 start collecting used fragments and selection sets on all of your queries.
-This error may occur if it hits unexpected abstract types when doing so.
+This error may occur if it hits unexpected types or inexistent types when doing so.
+
+Check whether your schema is up-to-date or whether you're using an invalid
+field somewhere, maybe due to a typo.
 
 Please open an issue if it happens on a query that you expect to be supported
 by the `populateExchange`.

src/ast/node.ts

@@ -6,10 +6,13 @@ import {
   InlineFragmentNode,
   FieldNode,
   FragmentDefinitionNode,
+  GraphQLOutputType,
   Kind,
+  isListType,
+  isNonNullType,
 } from 'graphql';
 
-import { SelectionSet } from '../types';
+import { SelectionSet, GraphQLFlatType } from '../types';
 
 /** Returns the name of a given node */
 export const getName = (node: { name: NameNode }): string => node.name.value;
@@ -40,3 +43,11 @@ export const isFieldNode = (node: SelectionNode): node is FieldNode =>
 export const isInlineFragment = (
   node: SelectionNode
 ): node is InlineFragmentNode => node.kind === Kind.INLINE_FRAGMENT;
+
+export const unwrapType = (
+  type: null | undefined | GraphQLOutputType
+): GraphQLFlatType | null => {
+  return type && (isListType(type) || isNonNullType(type))
+    ? type.ofType
+    : type || null;
+};

src/cacheExchange.ts

@@ -7,6 +7,7 @@ import {
   CacheOutcome,
 } from 'urql';
 
+import { IntrospectionQuery } from 'graphql';
 import { filter, map, merge, pipe, share, tap } from 'wonka';
 import { query, write, writeOptimistic } from './operations';
 import { SchemaPredicates } from './ast/schemaPredicates';
@@ -85,7 +86,7 @@ export interface CacheExchangeOpts {
   resolvers?: ResolverConfig;
   optimistic?: OptimisticMutationConfig;
   keys?: KeyingConfig;
-  schema?: object;
+  schema?: IntrospectionQuery;
 }
 
 export const cacheExchange = (opts?: CacheExchangeOpts): Exchange => ({