I found another case for the Exposed attribute not working correctly.

It seems that using different runtime flags for the exposed contexts in the Exposed extended attribute does not prevent the other contexts from being exposed when one of the flags is activated. For example, if I do Exposed(DedicatedWorker Flag1, SharedWorker Flag2) with Flag1 being "experimental" status and Flag2 being "test" status, then the global interface listing tests in virtual/exposed for shared worker and service worker are affected.

I made a change to split the original WebUSBOnDedicatedAndSharedWorker flag into WebUSBOnDedicatedWorker and WebUSBOnSharedWorker. These two flags are used in the Exposed attribute for the WebUSB IDL files. Additionally, the WebUSBOnDedicatedWorker was set to "experimental" while WebUSBOnSharedWorker remained on "test". This caused the usb attribute in WorkerNavigator to be exposed to the virtual/stable/webexposed/global-interface-listing-shared-worker.html and the virtual/stable/http/tests/serviceworker/webexposed/global-interface-listing-service-worker.html tests. This shouldn't happen, since the WebUSBOnDedicatedWorker flag is attached to the DedicatedWorker context only.

This is the change where this bug occurs:
https://chromium-review.googlesource.com/c/chromium/src/+/1098031

Let me clarify and simplify these cases.

For the case in #0, an attribute "usb" is defined as following in IDL,

[Exposed=(DedicatedWorker, SharedWorker)]
partial interface WorkerNavigator {
  [RuntimeEnabled=WebUSBOnDedicatedOrSharedWorker] attribute USB usb;
};

but it is visible also in ServiceWorker, while it should not.


And the second case in #5 is, the IDL description is updated as

[Exposed(DedicatedWorker WebUSBOnDedicatedWorker, SharedWorker WebUSBOnSharedWorker)]
partial interface WorkerNavigator {
  attribute USB usb;
};

and then it becomes visible regardless runtime enabled flags.

The both cases in #6 happens with current IDL compiler.

First one is because we install "usb" in V8WorkerNavigator, without considering a global object.
The second one is because, adding to the first reason, we do not assume having multiple runtime_enabled_flags on an object.

We need to change the design of IDL compiler to work for these issues... :(

I see thank you. I also tried splitting into two WorkerNavigator partial interfaces for each context with the runtime flag in the Exposed attribute, and using the RuntimeEnabled on the attribute instead. I did these just to see what would happen, but it still does the same thing. WorkerNavigator.usb is exposed to Shared Workers in virtual/stable/webexposed and Service Workers in virtual/stable/http/tests/serviceworker/webexposed. So yes, it seems to be the case still. 

These are what I tried today:
---
[Exposed(DedicatedWorker WebUSBOnDedicatedWorker)]
partial interface WorkerNavigator {
  attribute USB usb;
};

[Exposed(SharedWorker WebUSBOnShareddWorker)]
partial interface WorkerNavigator {
  attribute USB usb;
};
---
[Exposed=DedicatedWorker]
partial interface WorkerNavigator {
  [RuntimeEnabled=WebUSBOnDedicatedWorker] attribute USB usb;
};

[Exposed=SharedWorker]
partial interface WorkerNavigator {
  [RuntimeEnabled=WebUSBOnSharedWorker] attribute USB usb;
};
---