This is being done so that we can embed DevTools within the new React (beta) docs.
The primary changes here are to `react-devtools-inline/backend`:
* Add a new `createBridge` API
* Add an option to the `activate` method to support passing in the custom bridge object.
The `react-devtools-inline` README has been updated to include these new methods.
To verify these changes, this commit also updates the test shell to add a new entry-point for multiple DevTools.
This commit also replaces two direct calls to `window.postMessage()` with `bridge.send()` (and adds the related Flow types).
Adds the concept of subtree modes to DevTools to bridge protocol as follows:
1. Add-root messages get two new attributes: one specifying whether the root is running in strict mode and another specifying whether the root (really the root's renderer) supports the concept of strict mode.
2. A new backend message type (TREE_OPERATION_SET_SUBTREE_MODE). This type specifies a subtree root (id) and a mode (bitmask). For now, the only mode this message deals with is strict mode.
The DevTools frontend has been updated as well to highlight non-StrictMode compliant components.
The changes to the bridge protocol require incrementing the bridge protocol version number, which will also require updating the version of react-devtools-core backend that is shipped with React Native.
## Summary
This commit is a proposal for handling duplicate installation of DevTools, in particular scoped to duplicates such as a dev build or the internal versions of DevTools installed alongside the Chrome Web Store extension.
Specifically, this commit makes it so when another instance of the DevTools extension is installed alongside the extension installed from the Chrome Web Store, we don't produce a stream of errors or crash Chrome, which is what would usually happen in this case.
### Detecting Duplicate Installations
- First, we check what type of installation the extension is: from the Chrome Web Store, the internal build of the extension, or a local development build.
- If the extension is from the **Chrome Web Store**:
- During initialization, we first check if the internal or local builds of the extension have already been installed and are enabled. To do this, we send a [cross-extension message](https://developer.chrome.com/docs/extensions/mv3/messaging/#external) to the internal and local builds of the extension using their extension IDs.
- We can do this because the extension ID for the internal build (and for the Chrome Web Store) is a stable ID.
- For the local build, at build time we hardcode a [`key` in the `manifest.json`](https://developer.chrome.com/docs/extensions/mv2/manifest/key/) which allows us to have a stable ID even for local builds.
- If we detect that the internal or local extensions are already installed, then we skip initializing the current extension altogether so as to not conflict with the other versions. This means we don't initialize the frontend or the backend at all.
- If the extension is the **Internal Build**:
- During initialization, we first check if the local builds of the extension has already been installed and is enabled. To do this, we send a [cross-extension message](https://developer.chrome.com/docs/extensions/mv3/messaging/#external) to the local build of the extension using its extension ID.
- We can do this for the local build because at build time we hardcode a [`key` in the `manifest.json`](https://developer.chrome.com/docs/extensions/mv2/manifest/key/) which allows us to have a stable ID even for local builds.
- If we detect that the local extension is already installed, then we skip initializing the current extension altogether so as to not conflict with the that version. This means we don't initialize the frontend or the backend at all.
- If the extension is a **Local Dev Build**:
- Since other extensions check for the existence of this extension and disable themselves if they detect it, we don't need any special handling during initialization and assume that there are no duplicate extensions. This means that we will generally prefer keeping this extension enabled.
This behavior means that the order of priority for keeping an extension enabled is the following:
1. Local build
2. Internal build
3. Public build
### Preventing duplicate backend initialization
Note that the backend is injected and initialized by the content script listening to a message posted to the inspected window (via `postMessage`). Since the content script will be injected twice, once each by each instance of the extension, even if we initialize the extension once, both content scripts would still receive the single message posted from the single frontend, and it would then still inject and initialize the backend twice.
In order to prevent this, we also add the extension ID to the message for injecting the backend. That way each content script can check if the message comes from its own extension, and if not it can ignore the message and avoid double injecting the backend.
### Other approaches
- I considered using the [`chrome.management`](https://developer.chrome.com/docs/extensions/reference/management/) API generally to detect other installations, but that requires adding additional permissions to our production extension, which didn't seem ideal.
- I also considered a few options of writing a special flag to the inspected window and checking for it before initializing the extension. However, it's hard to avoid race conditions in that case, and it seemed more reliable to check specifically for the WebStore extension, which is realistically where we would encounter the overlap.
### Rollout
- This commit needs to be published and rolled out to the Chrome Web Store first.
- After this commit is published to the Chrome Web Store, any duplicate instances of the extension that are built and installed after this commit will no longer conflict with the Chrome Web Store version.
### Next Steps
- In a subsequent PR, I will extend this code to show a warning when duplicate extensions have been detected.
Part of #22486
## How did you test this change?
### Basic Testing
- yarn flow
- yarn test
- yarn test-build-devtools
### Double installation testing
Testing double-installed extensions for this commit is tricky because we are relying on the extension ID of the internal and Chrome Web Store extensions, but we obviously can't actually test the Web Store version (since we can't modify the already published version).
In order to simulate duplicate extensions installed, I did the following process:
- Built separate extensions where I hardcoded a constant for whether the extension is internal or public (e.g. `EXTENSION_INSTALLATION_TYPE = 'internal'`). Then I installed these built extensions corresponding to the "internal" and "Web Store" builds.
- Build and run the regular development extension (with `yarn build:chrome:dev && yarn test:chrome`), using the extension IDs of the previously built extensions as the "internal" and "public" extension IDs.
With this set up in place, I tested the following on pages both with and without React:
- When only the local extension enabled, DevTools works normally.
- When only the "internal" extension enabled, DevTools works normally.
- When only the "public" extension enabled, DevTools works normally.
- When "internal" and "public" extensions are installed, "public" extension is disabled and "internal" extension works normally.
- When the local extension runs alongside the other extensions, other extensions disable themselves and local build works normally.
- When we can't recognize what type of build the extension corresponds to, we show an error.
- When all 3 extensions are installed and enabled in all different combinations, DevTools no longer produces errors or crashes Chrome, and works normally.
DevTools now 'untrack' Fibers (cleans up the ID-to-Fiber mapping) after a slight delay in order to support a Fast Refresh edge case:
1. Component type is updated and Fast Refresh schedules an update+remount.
2. flushPendingErrorsAndWarningsAfterDelay() runs, sees the old Fiber is no longer mounted (it's been disconnected by Fast Refresh), and calls untrackFiberID() to clear it from the Map.
3. React flushes pending passive effects before it runs the next render, which logs an error or warning, which causes a new ID to be generated for this Fiber.
4. DevTools now tries to unmount the old Component with the new ID.
The underlying problem here is the premature clearing of the Fiber ID, but DevTools has no way to detect that a given Fiber has been scheduled for Fast Refresh. (The '_debugNeedsRemount' flag won't necessarily be set.)
The best we can do is to delay untracking by a small amount, and give React time to process the Fast Refresh delay.
