fix(mergeDeep): handle undefined sources correctly (#7012)

* chore(release): update monorepo packages versions (#6826)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

* fix(mergeDeep): handle `undefined` sources correctly

* Fix

* Major

* ..

---------

Co-authored-by: TheGuildBot <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

.changeset/chilly-icons-guess.md

@@ -0,0 +1,11 @@
+---
+'@graphql-tools/utils': patch
+---
+
+Fix the bug in `mergeDeep`;
+
+The following inputs and outputs are corrected;
+
+- `mergeDeep([{a:2}, undefined])` - Any nullish values should be ignored so it should return `{a:2}`
+- `mergeDeep([])` - no sources should return `undefined`
+- `mergeDeep([undefined])` - no sources should return `undefined`

packages/utils/src/mergeDeep.ts

@@ -12,6 +12,12 @@ export function mergeDeep<S extends any[]>(
   respectArrays = false,
   respectArrayLength = false,
 ): UnboxIntersection<UnionToIntersection<BoxedTupleTypes<S>>> & any {
+  if (sources.length === 0) {
+    return;
+  }
+  if (sources.length === 1) {
+    return sources[0];
+  }
   let expectedLength: number | undefined;
   let allArrays = true;
   const areArraysInTheSameLength = sources.every(source => {
@@ -46,14 +52,17 @@ export function mergeDeep<S extends any[]>(
   let firstObjectSource: any;
   if (respectPrototype) {
     firstObjectSource = sources.find(source => isObject(source));
-    if (output == null) {
-      output = {};
-    }
     if (firstObjectSource) {
+      if (output == null) {
+        output = {};
+      }
       Object.setPrototypeOf(output, Object.create(Object.getPrototypeOf(firstObjectSource)));
     }
   }
   for (const source of sources) {
+    if (source == null) {
+      continue;
+    }
     if (isObject(source)) {
       if (firstObjectSource) {
         const outputPrototype = Object.getPrototypeOf(output);

packages/utils/tests/mergeDeep.test.ts

@@ -72,4 +72,16 @@ describe('mergeDeep', () => {
     const b = { options: ['$A', '$B'] };
     expect(mergeDeep([a, b], undefined, true, true)).toEqual({ options: ['$A', '$B'] });
   });
+
+  it('filters nullish values', () => {
+    expect(mergeDeep([{ a: 'dsa' }, { a: 'dd', b: 1 }, undefined])).toEqual({ a: 'dd', b: 1 });
+  });
+
+  it('respects empty objects', () => {
+    expect(mergeDeep([{}])).toEqual({});
+  });
+
+  it('returns undefined when an empty sources array passed', () => {
+    expect(mergeDeep([])).toEqual(undefined);
+  });
 });