Properly type return value of clone() and cloneDeep() (#2572)

* Properly type `clone` and `cloneDeep` return types

* Format

Author: mattvague

types/index.d.ts

@@ -3115,7 +3115,7 @@ declare namespace math {
      * @returns A clone of object x
      */
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    clone(x: any): any
+    clone<TType>(x: TType): TType
 
     /**
      * Test whether a value is an numeric value. In case of a string,
@@ -3785,12 +3785,12 @@ declare namespace math {
      * Create a shallow clone of the node. The node itself is cloned, its
      * childs are not cloned.
      */
-    clone(): MathNode
+    clone(): this
     /**
      * Create a deep clone of the node. Both the node as well as all its
      * childs are cloned recursively.
      */
-    cloneDeep(): MathNode
+    cloneDeep(): this
     /**
      * Compile an expression into optimized JavaScript code. compile returns
      * an object with a function evaluate([scope]) to evaluate. Example:
@@ -6290,7 +6290,7 @@ declare namespace math {
      */
 
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    clone(this: MathJsChain<any>): MathJsChain<any>
+    clone<TValue>(this: MathJsChain<TValue>): MathJsChain<TValue>
 
     /**
      * Test whether a value is an integer number. The function supports

types/index.ts

@@ -23,6 +23,8 @@ import {
   SLUDecomposition,
   MathType,
   MathNumericType,
+  ConstantNode,
+  OperatorNode,
 } from 'mathjs'
 import * as assert from 'assert'
 import { expectTypeOf } from 'expect-type'
@@ -189,6 +191,11 @@ Chaining examples
     MathJsChain<MathCollection>
   >()
 
+  // chain
+  expectTypeOf(math.chain(12).bignumber().clone()).toMatchTypeOf<
+    MathJsChain<BigNumber>
+  >()
+
   // boolean
   expectTypeOf(math.chain(math.boolean(true))).toMatchTypeOf<
     MathJsChain<boolean>
@@ -1515,6 +1522,34 @@ Function round examples
   assert.throws(() => math.round([3.21, 3.82], [1, 2]), TypeError)
 }
 
+/*
+ Clone examples
+  */
+{
+  const math = create(all, {})
+  expectTypeOf(new math.ConstantNode(1).clone()).toMatchTypeOf<ConstantNode>()
+  expectTypeOf(
+    new math.OperatorNode('*', 'multiply', [
+      new math.ConstantNode(3),
+      new math.SymbolNode('x'),
+    ]).clone()
+  ).toMatchTypeOf<OperatorNode>()
+
+  expectTypeOf(
+    new math.ConstantNode(1).cloneDeep()
+  ).toMatchTypeOf<ConstantNode>()
+  expectTypeOf(
+    new math.OperatorNode('*', 'multiply', [
+      new math.ConstantNode(3),
+      new math.SymbolNode('x'),
+    ]).cloneDeep()
+  ).toMatchTypeOf<OperatorNode>()
+
+  expectTypeOf(
+    math.clone(new math.ConstantNode(1))
+  ).toMatchTypeOf<ConstantNode>()
+}
+
 /*
 JSON serialization/deserialization
 */