[#683] Convert merge.js to typescript (#687)

* chore: rename merge.js to merge.ts (#683)

* chore: add type to deepmerge(#683)

* chore: add FlowFixMe temporarily for files converted to TS (#683)

* chore: add underscore in arg for unused param

packages/cli/src/tools/config/index.js

@@ -20,6 +20,7 @@ import type {
   DependencyConfigT,
 } from 'types';
 import assign from '../assign';
+// $FlowFixMe - converted to TS
 import merge from '../merge';
 import resolveNodeModuleDir from './resolveNodeModuleDir';
 

packages/cli/src/tools/merge.ts

@@ -0,0 +1,15 @@
+import deepmerge from 'deepmerge';
+
+/**
+ * `deepmerge` concatenates arrays by default instead of overwriting them.
+ * We define custom merging function for arrays to change that behaviour
+ */
+export default function merge(
+  x: Array<{[key: string]: any}>,
+  y: Array<{[key: string]: any}>,
+) {
+  return deepmerge(x, y, {
+    arrayMerge: (_destinationArray: any[], sourceArray: any[]): any[] =>
+      sourceArray,
+  });
+}