Add grid support for old views with groupBy specified, and any other datasource that has a custom means of determining a datasource schema

packages/frontend-core/src/components/grid/stores/datasource.js

@@ -1,5 +1,5 @@
 import { derived, get } from "svelte/store"
-import { getDatasourceDefinition } from "../../../fetch"
+import { getDatasourceDefinition, getDatasourceSchema } from "../../../fetch"
 import { memo } from "../../../utils"
 
 export const createStores = () => {
@@ -11,10 +11,14 @@ export const createStores = () => {
 }
 
 export const deriveStores = context => {
-  const { definition, schemaOverrides, columnWhitelist, datasource } = context
+  const { API, definition, schemaOverrides, columnWhitelist, datasource } = context
 
   const schema = derived(definition, $definition => {
-    let schema = $definition?.schema
+    let schema = getDatasourceSchema({
+      API,
+      datasource: get(datasource),
+      definition: $definition
+    })
     if (!schema) {
       return null
     }

packages/frontend-core/src/fetch/index.js

@@ -32,12 +32,24 @@ export const fetchData = ({ API, datasource, options }) => {
   return new Fetch({ API, datasource, ...options })
 }
 
-// Fetches the definition of any type of datasource
+// Creates an empty fetch instance with no datasource configured, so no data
-export const getDatasourceDefinition = async ({ API, datasource }) => {
+// will initially be loaded
+const createEmptyFetchInstance = ({ API, datasource }) => {
   const handler = DataFetchMap[datasource?.type]
   if (!handler) {
     return null
   }
-  const instance = new handler({ API })
+  return new handler({ API })
-  return await instance.getDefinition(datasource)
+}
+
+// Fetches the definition of any type of datasource
+export const getDatasourceDefinition = async ({ API, datasource }) => {
+  const instance = createEmptyFetchInstance({ API, datasource })
+  return await instance?.getDefinition(datasource)
+}
+
+// Fetches the schema of any type of datasource
+export const getDatasourceSchema = ({ API, datasource, definition }) => {
+  const instance = createEmptyFetchInstance({ API, datasource })
+  return instance?.getSchema(datasource, definition)
 }