chore(gatsby): migrate schema reducer to TypeScript

This commit implements the migration of the schema reducer to
TypeScript by adding the SET_SCHEMA action to the ActionsUnion and
by adding the basic types from the IGatsbyState.

packages/gatsby/src/redux/reducers/index.js

@@ -1,6 +1,7 @@
 const reduxNodes = require(`./nodes`)
 const lokiNodes = require(`../../db/loki/nodes`).reducer
 import { redirectsReducer } from "./redirects"
+import { schemaReducer } from "./schema"
 import { staticQueryComponentsReducer } from "./static-query-components"
 import { statusReducer } from "./status"
 import { webpackReducer } from "./webpack"
@@ -56,7 +57,7 @@ module.exports = {
   flattenedPlugins: require(`./flattened-plugins`),
   config: require(`./config`),
   pages: require(`./pages`),
-  schema: require(`./schema`),
+  schema: schemaReducer,
   status: statusReducer,
   componentDataDependencies: require(`./component-data-dependencies`),
   components: require(`./components`),

packages/gatsby/src/redux/reducers/schema.ts

@@ -0,0 +1,13 @@
+import { ActionsUnion, IGatsbyState } from "../types"
+
+export const schemaReducer = (
+  state: IGatsbyState["schema"] | {} = {},
+  action: ActionsUnion
+): IGatsbyState["schema"] | {} => {
+  switch (action.type) {
+    case `SET_SCHEMA`:
+      return action.payload
+    default:
+      return state
+  }
+}

packages/gatsby/src/redux/types.ts

@@ -226,6 +226,7 @@ export type ActionsUnion =
   | IReplaceWebpackConfigAction
   | ISetPluginStatusAction
   | ISetProgramStatusAction
+  | ISetSchemaAction
   | ISetWebpackCompilationHashAction
   | ISetWebpackConfigAction
   | IUpdatePluginsHashAction
@@ -411,3 +412,8 @@ export interface ISetWebpackConfigAction {
   type: `SET_WEBPACK_CONFIG`
   payload: Partial<IGatsbyState["webpack"]>
 }
+
+export interface ISetSchemaAction {
+  type: `SET_SCHEMA`
+  payload: IGatsbyState["schema"]
+}