feat: lone values will now be passed to mergeOthers rather than just …

…returned (#57)

Previously if a value had nothing to be merged with, it would just be used as the result. Now it is
instead passed to the `mergeOthers` function so that the result can be customized if wanted

package.json

@@ -99,6 +99,7 @@
     "@semantic-release/github": "^8.0.2",
     "@semantic-release/npm": "^9.0.0",
     "@semantic-release/release-notes-generator": "^10.0.3",
+    "@types/lodash": "^4.14.178",
     "@types/node": "^17.0.16",
     "@types/rollup-plugin-auto-external": "^2.0.2",
     "@typescript-eslint/eslint-plugin": "^5.11.0",
@@ -128,6 +129,7 @@
     "eslint-plugin-unicorn": "^40.1.0",
     "husky": "^7.0.4",
     "lint-staged": "^12.3.3",
+    "lodash": "^4.17.21",
     "markdownlint-cli": "^0.31.1",
     "marked": "^4.0.12",
     "nyc": "^15.1.0",

src/deepmerge.ts

@@ -123,13 +123,6 @@ export function deepmergeCustom<
    * The customized deepmerge function.
    */
   function customizedDeepmerge(...objects: ReadonlyArray<unknown>) {
-    if (objects.length === 0) {
-      return undefined;
-    }
-    if (objects.length === 1) {
-      return objects[0];
-    }
-
     return mergeUnknowns<
       ReadonlyArray<unknown>,
       typeof utils,
@@ -186,6 +179,17 @@ function mergeUnknowns<
   M,
   MM extends Readonly<Record<PropertyKey, unknown>>
 >(values: Ts, utils: U, meta: M | undefined): DeepMergeHKT<Ts, MF, M> {
+  if (values.length === 0) {
+    return undefined as DeepMergeHKT<Ts, MF, M>;
+  }
+  if (values.length === 1) {
+    return utils.mergeFunctions.mergeOthers(
+      values,
+      utils,
+      meta
+    ) as DeepMergeHKT<Ts, MF, M>;
+  }
+
   const type = getObjectType(values[0]);
 
   // eslint-disable-next-line functional/no-conditional-statement -- add an early escape for better performance.
@@ -274,14 +278,11 @@ function mergeRecords<
       parents: values,
     } as unknown as MM);
 
-    result[key] =
-      propValues.length === 1
-        ? propValues[0]
-        : mergeUnknowns<ReadonlyArray<unknown>, U, MF, M, MM>(
-            propValues,
-            utils,
-            updatedMeta
-          );
+    result[key] = mergeUnknowns<ReadonlyArray<unknown>, U, MF, M, MM>(
+      propValues,
+      utils,
+      updatedMeta
+    );
   }
 
   /* eslint-enable functional/no-loop-statement, functional/no-conditional-statement */

tests/deepmerge-custom.test.ts

@@ -1,6 +1,7 @@
 /* eslint-disable @typescript-eslint/consistent-type-definitions, @typescript-eslint/no-unused-vars */
 
 import test from "ava";
+import _ from "lodash";
 
 import { deepmergeCustom } from "@/deepmerge";
 import type {
@@ -563,3 +564,29 @@ test("custom merge with parents", (t) => {
 
   t.deepEqual(merged, expected);
 });
+
+test("custom merge that clones", (t) => {
+  const x = { foo: { bar: { baz: { qux: [1, 2, 3] } } } };
+  const y = { bar: new Date("2021-02-02"), baz: { qux: 1 } };
+
+  const expected = {
+    foo: _.cloneDeep(x.foo),
+    bar: _.cloneDeep(y.bar),
+    baz: _.cloneDeep(y.baz),
+  } as const;
+
+  const customizedDeepmerge = deepmergeCustom({
+    mergeOthers: (values, utils) =>
+      _.cloneDeep(utils.defaultMergeFunctions.mergeOthers(values)),
+  });
+
+  const merged = customizedDeepmerge(x, y);
+
+  t.deepEqual(merged, expected);
+  t.not(merged.foo, x.foo);
+  t.not(merged.foo.bar, x.foo.bar);
+  t.not(merged.foo.bar.baz, x.foo.bar.baz);
+  t.not(merged.foo.bar.baz.qux, x.foo.bar.baz.qux);
+  t.not(merged.bar, y.bar);
+  t.not(merged.baz, y.baz);
+});

yarn.lock

@@ -1280,6 +1280,11 @@
   resolved "https://registry.yarnpkg.com/@types/json5/-/json5-0.0.29.tgz#ee28707ae94e11d2b827bcbe5270bcea7f3e71ee"
   integrity sha1-7ihweulOEdK4J7y+UnC86n8+ce4=
 
+"@types/lodash@^4.14.178":
+  version "4.14.178"
+  resolved "https://registry.yarnpkg.com/@types/lodash/-/lodash-4.14.178.tgz#341f6d2247db528d4a13ddbb374bcdc80406f4f8"
+  integrity sha512-0d5Wd09ItQWH1qFbEyQ7oTQ3GZrMfth5JkbN3EvTKLXcHLRDSXeLnlvlOn0wvxVIwK5o2M8JzP/OWz7T3NRsbw==
+
 "@types/mdast@^3.0.0":
   version "3.0.9"
   resolved "https://registry.yarnpkg.com/@types/mdast/-/mdast-3.0.9.tgz#3f7fa18faf9e567da9aa49e44ecc76ad33c359ce"