buffer: remove support for Symbol.toPrimitive

This is a special casing explicitly for `Buffer.from()` and we do
not have any other cases where we handle these. To remove ambiguity
from the input, remove support for it.

doc/api/buffer.md

@@ -869,15 +869,18 @@ appropriate for `Buffer.from()` variants.
 
 ### Class Method: Buffer.from(object[, offsetOrEncoding[, length]])
 <!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/27051
+    description: Dropped support for `Symbol.toPrimitive`.
 added: v8.2.0
 -->
 
-* `object` {Object} An object supporting `Symbol.toPrimitive` or `valueOf()`.
+* `object` {Object} An object supporting `valueOf()`.
 * `offsetOrEncoding` {integer|string} A byte-offset or encoding, depending on
-  the value returned either by `object.valueOf()` or
-  `object[Symbol.toPrimitive]()`.
-* `length` {integer} A length, depending on the value returned either by
-  `object.valueOf()` or `object[Symbol.toPrimitive]()`.
+  the value returned by `object.valueOf()`.
+* `length` {integer} A length, depending on the value returned by
+  `object.valueOf()`.
 
 For objects whose `valueOf()` function returns a value not strictly equal to
 `object`, returns `Buffer.from(object.valueOf(), offsetOrEncoding, length)`.
@@ -887,20 +890,6 @@ const buf = Buffer.from(new String('this is a test'));
 // Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
 ```
 
-For objects that support `Symbol.toPrimitive`, returns
-`Buffer.from(object[Symbol.toPrimitive](), offsetOrEncoding, length)`.
-
-```js
-class Foo {
-  [Symbol.toPrimitive]() {
-    return 'this is a test';
-  }
-}
-
-const buf = Buffer.from(new Foo(), 'utf8');
-// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
-```
-
 A `TypeError` will be thrown if `object` has not mentioned methods or is not of
 other type appropriate for `Buffer.from()` variants.
 

lib/buffer.js

@@ -208,12 +208,6 @@ Buffer.from = function from(value, encodingOrOffset, length) {
     const b = fromObject(value);
     if (b)
       return b;
-
-    if (typeof value[Symbol.toPrimitive] === 'function') {
-      return Buffer.from(value[Symbol.toPrimitive]('string'),
-                         encodingOrOffset,
-                         length);
-    }
   }
 
   throw new ERR_INVALID_ARG_TYPE(

test/parallel/test-buffer-from.js

@@ -28,7 +28,6 @@ class MyBadPrimitive {
 
 deepStrictEqual(Buffer.from(new String(checkString)), check);
 deepStrictEqual(Buffer.from(new MyString()), check);
-deepStrictEqual(Buffer.from(new MyPrimitive()), check);
 deepStrictEqual(
   Buffer.from(runInNewContext('new String(checkString)', { checkString })),
   check
@@ -42,7 +41,8 @@ deepStrictEqual(
   [{ valueOf: null }, 'object'],
   [Object.create(null), 'object'],
   [new Number(true), 'number'],
-  [new MyBadPrimitive(), 'number'],
+  [new MyBadPrimitive(), 'object'],
+  [new MyPrimitive(), 'object'],
   [Symbol(), 'symbol'],
   [5n, 'bigint'],
   [(one, two, three) => {}, 'function'],