feat: Add Messenger `parent` parameter #6142

Gudahtt · 2025-07-17T16:14:36Z

Explanation

Add the parent constructor parameter to the Messenger class for automatic delegation of all capabilities under that messenger's namespace. This significantly reduces boilerplate, making the messenger easier to use in a similar manner to how the old RestrictedMessenger class wored.

See this ADR PR for details: MetaMask/decisions#53

References

Depends upon #6132
Relates to #5626

Checklist

I've updated the test suite for new or updated code as appropriate
I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

packages/messenger/src/Messenger.ts

Gudahtt · 2025-08-13T16:30:59Z

Type tests can be found on this branch: https://github.com/MetaMask/core/tree/add-messenger-type-tests-parent

Gudahtt · 2025-08-13T17:06:49Z

packages/messenger/src/Messenger.ts

  Namespace extends string,
  Action extends ActionConstraint,
  Event extends EventConstraint,
+  Parent extends Messenger<


This is a new addition from what was described in the ADR. As you can see in the tests, it does make using this a bit more verbose, but it's not too bad IMO. This was the only way I could find to validate that the parent had all necessary actions/events (this was validated in the constructor params, but the method of validation relied on there being a generic type param to validate against).

Makes sense given how we've designed Messenger. I can't think of another way to do this. We can use the typeof trick you used in the tests, though, to make providing this type easier.

mcmire

LGTM!

mcmire · 2025-08-13T18:47:05Z

packages/messenger/src/Messenger.ts

+    string,
+    ActionConstraint,
+    EventConstraint,
+    // Use `any` to avoid preventing a parent from having a parent. `any` is harmless in a type


This does work, but wouldn't leaving this type parameter out also work? Then the default would be never which seems more accurate.

I was hesitant to do this because there is nothing really stopping someone from writing a messenger that is both a parent and has a parent. It might even be a reasonably good design. For example, if the TransactionController wanted to have internal messengers for each helper class it uses, they might delegate to the main transaction controller messenger so their actions/events can be used internally in the transaction controller.

Ah, I missed the double negative. "Avoid preventing". Got it :)

Yes I agree we should make it possible to essentially create a delegation chain.

mcmire · 2025-08-13T19:20:25Z

packages/messenger/src/Messenger.ts

    }
    this.#registerActionHandler(actionType, handler);
+    if (this.#parent) {
+      // @ts-expect-error The parent type isn't constructed in a way that proves it supports this


I feel like there ought to be a way to align the types so this isn't necessary, but I don't know how. I tried changing the type of #parent from DelegatedMessenger to Parent but then the if (messenger === this.#parent) { statement you added at the beginning of revoke failed because TypeScript thought there was no overlap between the two values. So it seems that we need @ts-expect-error somewhere...

I do agree this seems type-safe though given the check we have in the constructor.

mcmire · 2025-08-13T19:27:26Z

packages/messenger/src/Messenger.ts

  Namespace extends string,
  Action extends ActionConstraint,
  Event extends EventConstraint,
+  Parent extends Messenger<


Makes sense given how we've designed Messenger. I can't think of another way to do this. We can use the typeof trick you used in the tests, though, to make providing this type easier.

mcmire · 2025-08-13T19:28:50Z

packages/messenger/src/Messenger.ts

 */
 export class Messenger<
  Namespace extends string,
  Action extends ActionConstraint,


Side note, but should Action and Event default to never so that if you don't supply any type parameters to Messenger, allowing TypeScript to infer them, you don't end up with a messenger that recognizes all actions and events?

Good idea. I will try this separately

Done here: #6311

Add the `parent` constructor parameter to the `Messenger` class for automatic delegation of all capabilities under that messenger's namespace. This significantly reduces boilerplate, making the messenger easier to use in a similar manner to how the old `RestrictedMessenger` class wored. See this ADR PR for details: MetaMask/decisions#53

…native type check for parent

## Explanation The action and event type parameters for the new `@metamask/messenger` package's Messenger class now default to `never`. This should make it harder to accidentally create a messenger with overly broad inferred types, making it less type safe than the author might expect. The `Messenger` classes in `@metamask/base-controller` were not changed to avoid breaking changes. While this change itself wouldn't really be breaking by most definitions, it would require changes due to our use of the `@typescript-eslint/no-unnecessary-type-arguments` lint rule. ## References This was a suggestion from here: #6142 (comment) ## Checklist - [x] I've updated the test suite for new or updated code as appropriate - [x] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate - [x] I've communicated my changes to consumers by [updating changelogs for packages I've changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs), highlighting breaking changes as necessary - [x] I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

Gudahtt force-pushed the add-messenger-parent-param branch 3 times, most recently from 4ff719e to f3e18ba Compare July 17, 2025 16:31

Gudahtt changed the title ~~feat: Add Messenger parant parameter~~ feat: Add Messenger parent parameter Jul 17, 2025

Gudahtt force-pushed the add-messenger-delegation branch from 2dd241a to 6729773 Compare July 23, 2025 20:11

mcmire reviewed Jul 23, 2025

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packages/messenger/src/Messenger.ts Outdated Show resolved Hide resolved

Gudahtt force-pushed the add-messenger-delegation branch 2 times, most recently from 1e6b6ab to d6f1dc4 Compare August 7, 2025 12:40

Gudahtt force-pushed the add-messenger-parent-param branch from f3e18ba to 04b2069 Compare August 7, 2025 12:40

Gudahtt force-pushed the add-messenger-delegation branch 7 times, most recently from b9bef02 to f980adf Compare August 12, 2025 20:36

Gudahtt force-pushed the add-messenger-parent-param branch from 0a293cd to 11eece3 Compare August 12, 2025 21:03

Gudahtt force-pushed the add-messenger-delegation branch from f980adf to 61f5053 Compare August 13, 2025 15:21

Gudahtt force-pushed the add-messenger-parent-param branch from 11eece3 to f057a12 Compare August 13, 2025 15:22

Base automatically changed from add-messenger-delegation to main August 13, 2025 15:26

Gudahtt force-pushed the add-messenger-parent-param branch from eb8e095 to 764f8e9 Compare August 13, 2025 16:20

Gudahtt marked this pull request as ready for review August 13, 2025 16:31

Gudahtt requested a review from a team as a code owner August 13, 2025 16:31

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Gudahtt commented Aug 13, 2025

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mcmire approved these changes Aug 13, 2025

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Gudahtt force-pushed the add-messenger-parent-param branch from ad2eab7 to 29d3a01 Compare August 13, 2025 19:43

Gudahtt added 2 commits August 13, 2025 17:19

Use DelegatedMessenger as parent type

60681f4

Gudahtt added 2 commits August 13, 2025 17:19

Update DelegatedMessenger reference to remove generics, and use alter…

5fe0752

…native type check for parent

Update changelog with reference to new generic param

dfa154b

Gudahtt force-pushed the add-messenger-parent-param branch from 29d3a01 to dfa154b Compare August 13, 2025 19:49

Gudahtt enabled auto-merge (squash) August 13, 2025 19:49

Gudahtt merged commit c0a2946 into main Aug 13, 2025
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Gudahtt deleted the add-messenger-parent-param branch August 13, 2025 19:54

Gudahtt mentioned this pull request Aug 14, 2025

feat: Default action/event type params to never #6311

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feat: Add Messenger `parent` parameter #6142

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Gudahtt commented Jul 17, 2025

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feat: Add Messenger parent parameter #6142

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Gudahtt commented Jul 17, 2025

Explanation

References

Checklist

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feat: Add Messenger `parent` parameter #6142

feat: Add Messenger `parent` parameter #6142