repl: show proxies as Proxy objects

[bnoordhuis]

Fixes: #16483
CI: https://ci.nodejs.org/job/node-test-pull-request/10962/

Good idea, bad idea?

[fhinkel]

Good idea!

[jasnell]

I'm good with this but just noting that TC-39 has been consistent in their stance that the fact an object is a proxy should be transparent to users. This intentionally makes them non-transparent in the REPL... again, I'm perfectly fine with that and think it's a good thing to do.

[TimothyGu]

-1 from me, though I won't block.

In jsdom we are using Proxies for objects like element.attributes and document.querySelectorAll(). The [[ProxyTarget]] of those objects are in fact an empty object, and all the "properties" are made to look like they were actual properties on the object through a series of complex algorithms. If the original empty object was shown, it would convey 0 information to the users.

[bnoordhuis]

Since there is no real opposition I went ahead and landed this (commit 90a4390.)

I'll be conservative and tag it semver-major. If necessary we can flip the default to off. A similar line of reasoning applies to back-porting to the stable branches: could be done if needed, and default to off.

[BridgeAR]

I am to tired to look properly into this but it seems like this introduced a regression on the repl in some cases. On my terminal if I open the repl and write e.g. util.inspect("test") it will from now on always print the color codes. This patch seems like a partial fix but it does not solve the issue completely.

-    self.writer = (obj) => util.inspect(obj, self.writer.options);
-    self.writer.options = Object.assign(writer.options, { colors: true });
+    self.writer = (obj) =>
+      util.inspect(obj, Object.assign(writer.options, { colors: true }));

[bnoordhuis]

Ah, the bug is glaring in retrospect - the Object.assign() mutates util.inspect.defaultOptions if writer.options === util.inspect.defaultOptions. I'll fix it.