util.inspect with showHidden does not display exotic object name

[guybedford]

• Version: 15.2.1
• Platform: Windows
• Subsystem: Util

What steps will reproduce the bug?

test.mjs

import util from 'util';
import * as m from './test.mjs';
console.log(util.inspect(m, { showHidden: true }));

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior?

[Module] { [Symbol(Symbol.toStringTag)]: 'Module' }

What do you see instead?

[] { [Symbol(Symbol.toStringTag)]: 'Module' }

Where the leading [] seems like a display bug.

[BridgeAR]

It should probably be: [Module] {}. It's a custom inspect function that constructs a special object and it seems like the way it's constructed is not handled as it should be.

[BridgeAR]

I am quite confused about the value of the Symbol.toStringTag of m. It's actually a descriptor object even though it should be a string. @guybedford do you know where the symbol is assigned?

[guybedford]

@BridgeAR it's a module namespace exotic object, so it's a language symbol. The symbol logging seems like it makes sense when using showHidden, the issue is more that the tag name is being lost somehow.

[BridgeAR]

Ok, I found the issue. The array notation is hard coded, thus it's not working as expected. The output should be [Module: null prototype] { [Symbol(Symbol.toStringTag)]: 'Module' }. This is a fix:

index 4e1ed55c81..b02c4bd3e3 100644
--- a/lib/internal/util/inspect.js
+++ b/lib/internal/util/inspect.js
@@ -977,7 +977,7 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
 braces[0] = `${getPrefix(constructor, tag, 'WeakMap')}{`;
 formatter = ctx.showHidden ? formatWeakMap : formatWeakCollection;
 } else if (isModuleNamespaceObject(value)) {
- braces[0] = `[${tag}] {`;
+ braces[0] = `${getPrefix(constructor, tag, 'Module')}{`;
 // Special handle keys for namespace objects.
 formatter = formatNamespaceObject.bind(null, keys);
 } else if (isBoxedPrimitive(value)) {