Support editable useState hooks in DevTools #14906
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| } | ||
| if (currentHook !== null) { | ||
| let updatedState = copyWithSet(currentHook.memoizedState, path, value); | ||
| currentHook.queue.dispatch(updatedState); |
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This will work for useState but not useReducer, which I assume is intentional, correct?
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We really should support useReducer if we support useState since that’s the recommended one. Don’t want people choosing useState over useReducer based on DevTools.
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Interesting. I thought a little (not much) about useReducer support but didn't think it was necessary.
Edit for clarity: DevTools only supports edit functionality (currently) for useState but I could go back to the drawing board if we think it's important to support useReducer too!
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I see two possible semantics for editing state. One option is that we actually edit the application’s internal state. The other option is that we permanently shadow the value as it is returned to the render function until something forces it to release. Like we meant to do with props.
What are the tradeoffs for these approaches?
I don't think we necessarily meant to do this with props. It's something we've discussed but never committed to (at least not that I recall, although I'm forgetful). I think it could be nice in some cases, but I'm personally not convinced that it's useful often enough to justify the added complexity of building it to be honest. At least not at this stage of the rewrite. |
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I’d be happy to add the infra myself to help out adding this to props. I’d rather have an approach that is conceptually consistent than relies on subtle details of rerendering that breaks during refactors. We’re dealing with the exact problem for setNativeProps on Fabric now and it’s a pain. The difference with state is that conceptually you can update it to anything and it is persistent. So we don’t have to do it for state but I haven’t thought much about the tradeoffs yet. |
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I remain unconvinced that the added complexity of masking is worth it as a feature. Based on my recent Twitter poll (which isn't necessarily conclusive– but it did have 1,500 votes so I think it's at least worth consideration) only 19% of people use the feature regularly to begin with, and most of them only use it for toggling booleans to e.g. test visual state. Maybe you and I can talk about this today over a coffee or something and come to a consensus that unblocks me for now @sebmarkbage. |
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Okay. I've updated the implementation so that both I also added an explicit |
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I've pushed a version of the DevTools built with this React change to https://react-devtools-experimental.now.sh/ if you'd like to test out the editable |
| @@ -368,6 +369,27 @@ if (__DEV__) { | |||
| return copyWithSetImpl(obj, path, 0, value); | |||
| }; | |||
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| // Support DevTools editable values for useState and useReducer. | |||
| overrideHook = ( | |||
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Let's call this something specific to state since there are many other hooks. E.g. might want to override changed bits etc. for debugging context not updating. For Focal we might want to flip the booleans which are not state.
overrideHookState?
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I guess the isEditable just indicates that the "value" can be edited as is in whatever form it is. Maybe overrideHookDebugValue whatever the representation of debug tools' value is?
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Are you suggesting I rename the injected overrideHook method to overrideHookDebugValue? I think that sounds confusingly close to useDebugValue even though they aren't actually related. Maybe I'm misunderstanding you.
overrideHookState seems okay though. Probably more clearly indicates its purpose.
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I think I've complied with part of your request (renaming overrideHook to overrideHookState) but I'm still a little fuzzy on the other comment. Would you like me to also rename isEditable to something like isStateEditable?
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Chatted offline and the consensus was this:
- Replace
indexandisEditableproperties with a single property, e.g.overrideStatethat is either a function ornull. - DevTools will pass through the renderer-injected values to
react-debug-toolswhen inspecting a fiber. - For hooks that are editable,
react-debug-toolswill add anoverrideStatefunction that closes over the necessary info.
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Actually implementing the changes above is proving to be kind of complicated, and I'm having second thoughts about it being a good idea. It requires maintaining and coordinating several data structures, all of which are updated async.
Inspecting hooks
React itself has the hooks list stored in memoizedState. These hooks are what we actually need to update.
ReactDebugHooks has its own inspected hooks object, consisting of a pointer to the "native" hook, the name (e.g. "State"), value, array of sub-hooks (if it's a custom hook), and an overrideState function that closes over things needed to e.g. modify a state or reducer hook.
The frontend needs its own representation, but since this is sent across the Bridge– we need to replace the overrideState function with something that can be serialized. So we need an ID that lets us map back to the original closure function. This means a third structure– with an id, name, value, sub-hooks array, and an isStateEditable boolean indicating whether there's an overrideState function.
Overriding state
The frontend starts by sending an "overrideHookState" message with the hook id, path, override value, and the renderer ID (so the backend can find the right injected internals).
The agent uses the renderer ID to pass this info along to the appropriate renderer interface, which needs to be able to find the original inspected hook (from ReactDebugHooks, using our ID) so it can call the overrideState method.
Then the overrideState method needs a way to find the current fiber, and to call the renderer's injected overrideHookState method with that fiber along with the "native" hook, path, and value.
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@sebmarkbage Let's talk about this again. I'm not convinced that this change is a positive one after looking into how I would implement it. I think it adds a lot of complexity without adding enough value to offset it.
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Looks like the approach I was using of updating Edit - It looks like the approach had settled on for overriding both state and reducer hook values was broken by the change to bailout reducer bailout (PR #14569). This change makes supporting editable reducer hooks difficult, since I can't add an update to the queue (since there's no action for DevTools overrides). I can cheat around this by shallow-cloning This definitely highlights the need for unit tests covering this functionality to avoid future regressions. |
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For now I'm just pushing a fix to the bailout issue mentioned in my previous comment and a rename of the inspected hook |
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…e bool to hooks metadata
Expose a new
overrideHookStateto be injected into DevTools to enable state and reducer hooks to be editable in DevTools. Also updateReactDebugHookspackage to support this functionality.We should release the
react-debug-toolspackage soon.