From 20c0dfb82e4273b10e5a02ba0e74aada42b9bb7a Mon Sep 17 00:00:00 2001
From: Rebecca Stevens <rebecca.stevens@outlook.co.nz>
Date: Sun, 12 Jun 2022 19:29:47 +1200
Subject: [PATCH] feat: treat module imports as records

fix #133
---
 package.json |  3 ---
 src/utils.ts | 48 +++++++++++++++++++++++++++++++++++++++++++++---
 yarn.lock    |  1 -
 3 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/package.json b/package.json
index a6f579c0..bc114821 100644
--- a/package.json
+++ b/package.json
@@ -78,9 +78,6 @@
     "test:js": "c8 ava",
     "test:types": "dtslint --localTs node_modules/typescript/lib --expectOnly tests/types"
   },
-  "dependencies": {
-    "is-plain-object": "^5.0.0"
-  },
   "devDependencies": {
     "@commitlint/cli": "^17.0.2",
     "@commitlint/config-conventional": "^17.0.2",
diff --git a/src/utils.ts b/src/utils.ts
index 2aabdd93..8fe1bc5a 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -1,5 +1,3 @@
-import { isPlainObject } from "is-plain-object";
-
 /**
  * The different types of objects deepmerge-ts support.
  */
@@ -27,7 +25,7 @@ export function getObjectType(object: unknown): ObjectType {
     return ObjectType.ARRAY;
   }
 
-  if (isPlainObject(object)) {
+  if (isRecord(object)) {
     return ObjectType.RECORD;
   }
 
@@ -102,3 +100,47 @@ export function getIterableOfIterables<T>(
     },
   };
 }
+
+const validRecordToStringValues = new Set([
+  "[object Object]",
+  "[object Module]",
+]);
+
+/**
+ * Does the given object appear to be a record.
+ */
+function isRecord(value: object): value is Record<PropertyKey, unknown> {
+  // All records are objects.
+  if (!validRecordToStringValues.has(Object.prototype.toString.call(value))) {
+    return false;
+  }
+
+  const { constructor } = value;
+
+  // If has modified constructor.
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+  if (constructor === undefined) {
+    return true;
+  }
+
+  // eslint-disable-next-line prefer-destructuring
+  const prototype: unknown = constructor.prototype;
+
+  // If has modified prototype.
+  if (
+    prototype === null ||
+    typeof prototype !== "object" ||
+    !validRecordToStringValues.has(Object.prototype.toString.call(prototype))
+  ) {
+    return false;
+  }
+
+  // If constructor does not have an Object-specific method.
+  // eslint-disable-next-line sonarjs/prefer-single-boolean-return, no-prototype-builtins
+  if (!prototype.hasOwnProperty("isPrototypeOf")) {
+    return false;
+  }
+
+  // Most likely a record.
+  return true;
+}
diff --git a/yarn.lock b/yarn.lock
index f22902cc..b465e6f2 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3488,7 +3488,6 @@ __metadata:
     eslint-plugin-unicorn: ^42.0.0
     husky: ^8.0.1
     if-env-defined: ^1.0.0
-    is-plain-object: ^5.0.0
     lint-staged: ^13.0.1
     lodash: ^4.17.21
     markdownlint-cli: ^0.31.1