From cb901708a0adf751f635baf758d94a42c797f1de Mon Sep 17 00:00:00 2001
From: Neo Nie <nihgwu@live.com>
Date: Sun, 7 Aug 2022 00:38:41 +0100
Subject: [PATCH] remove string based slot name

---
 text/0000-slots.md | 138 ++++++++++++++++++++-------------------------
 1 file changed, 60 insertions(+), 78 deletions(-)

diff --git a/text/0000-slots.md b/text/0000-slots.md
index d0e1111a..c4189cb3 100644
--- a/text/0000-slots.md
+++ b/text/0000-slots.md
@@ -4,39 +4,44 @@
 
 # Summary
 
-A way to support slots pattern in React, works similar to [Slots for Web Components](https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_templates_and_slots)
-but more powerful as we can interpolate slots.
+A way to support slots pattern in React, works similar to [Slots for Web Components](https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_templates_and_slots) but more powerful as we can interpolate slots.
 
 # Basic example
 
-In this example we introduced two method called `createHost` and `createSlot`.
+In this example we introduced two methods called `createHost` and `createSlot`.
 
-`createSlot` creates a component won't be rendered to real DOM but collect props.
+`createSlot` creates a component which won't be rendered to real DOM but only collect node info.
 
-`createHost` mounts the children included slotted components and read the
-collected slots props, and render the result to real DOM conditionally.
+`createHost` mounts the children which hosting slotted components and read the collected slots info, and render the result to real DOM conditionally.
 
 ```jsx
 import { createHost, createSlot } from "react-create-slots";
 
+const TextFieldLabel = createSlot();
+const TextFieldInput = createSlot();
+const TextFieldTag = createSlot();
+
 const Tag = (props) => <span {...props} />;
 
 const TextField = (props) => {
   const id = useId();
 
-  return createHost(props.children, (Slots) => {
-    const labelProps = Slots.get("label");
-    const inputProps = Slots.get("input");
-    const tagPropsList = Slots.getAll("tag");
+  return createHost(props.children, (slots) => {
+    // library author can create utlis to reduce the boilerplate
+    const labelSlot = slots.findLast((slot) => slot.type === TextFieldLabel);
+    const inputSlot = slots.findLast((slot) => slot.type === TextFieldInput);
+    const tagSlots = slots.filter((slot) => slot.type === TextFieldTag);
 
     return (
       <div>
-        {labelProps && <label htmlFor={inputProps.id ?? id} {...labelProps} />}
-        <input id={id} {...label} />
-        {tagPropsList.length > 0 && (
+        {labelSlot && (
+          <label htmlFor={inputSlot?.props.id ?? id} {...labelSlot.props} />
+        )}
+        <input id={id} {...inputSlot?.props} />
+        {tagSlots.length > 0 && (
           <div>
-            {tagPropsList.map((tagProps, index) => (
-              <Tag data-index={index} {...tagProps} />
+            {tagSlots.map((tagSlot, index) => (
+              <Tag key={index} data-index={index} {...tagSlot.props} />
             ))}
           </div>
         )}
@@ -45,10 +50,6 @@ const TextField = (props) => {
   });
 };
 
-const TextFieldLabel = createSlot("label");
-const TextFieldInput = createSlot("input");
-const TextFieldTag = createSlot("tag");
-
 export default function App() {
   return (
     <div>
@@ -67,96 +68,77 @@ export default function App() {
 
 ## Composite component in a configure manor
 
-When creating UI library, we have different approaches on the component
-API design. The most common way is the Configuration pattern used by
-most UI libraries, everything in one component and provides child props
-for composition, like `<TextField label helperText />`. It's easy to use,
-but when we need to to add some extra props to label like `data-testid`,
-then we have to introduce new props for that which will bloat the api
-very easily.
+When creating UI library, we have different approaches on the component API design. The most common way is the Configuration pattern used by most UI libraries, everything in one component and provides child props for composition, like `<TextField label helperText />`. It's easy to use, but when we need to to add some extra props to label like `data-testid`, then we have to introduce new props for that which will bloat the api very easily.
 
-Another way to solve this problem is Composition pattern, like
-`<TextField><TextFieldLabel /><TextFieldInput /></TextField>`,
-it provides the best flexibility, we are free to customise every
-part of our component, but it causes another problem: consistency,
-we have to organise your sub components exactly same order as expected,
-and the biggest problem is that it's harder to communicate between
-parent and children.
+Another way to solve this problem is Composition pattern, like `<TextField><TextFieldLabel /><TextFieldInput /></TextField>`, it provides the best flexibility, we are free to customise every part of our component, but it causes another problem: consistency, we have to organise your sub components exactly same order as expected, and the biggest problem is that it's harder to communicate between parent and children.
 
-For a dedicated Design System, we need consistent ui regardless how
-we compose it.
+For a dedicated Design System, we need consistent ui regardless how we compose it.
 
-Here the Slots pattern solve those problem perfectly, we can compose
-our component with both flexibility and consistency, and it's extreme
-easy to add A11y support thanks the ability of Inversion of Control.
+Here the Slots pattern solve those problem perfectly, we can compose our component with both flexibility and consistency, and it's extreme easy to add A11y support thanks the ability of Inversion of Control.
 
-## Accessible List
+## Accessible List and Virtualisation
 
-Quoted from [the comment](https://github.com/facebook/react/issues/24979#issuecomment-1193176328)
-by @devongovett
+Quoted from [the comment](https://github.com/facebook/react/issues/24979#issuecomment-1193176328) by @devongovett
 
 > A bunch of libraries have a problem where they need to know about certain types of descendants. For example, a list component with keyboard navigation needs to know what elements exist in the collection in order to implement things like typeahead, arrow keys, selection, etc. Reach UI has a good [overview](https://github.com/reach/reach-ui/tree/dev/packages/descendants) of a bunch of different approaches to this. The most commonly used of them involve rendering all of the items to the DOM, and using some kind of context-based registration system to tell the parent about themselves, and the DOM to sort them into the correct order.  
 > This has the downside that all of the items must be in the DOM at all times. In some cases, like virtualized scrolling, or a combobox/select where users can set the item without showing the list, some or all of the items shouldn't be rendered to the DOM. In React Aria, we walk the JSX tree to do this, which makes for a more natural API than giving up JSX completely (info). But this breaks composition, because only certain known element types are allowed.
 
-Even with the Reach UI's solution, it doesn't work well with SSR.
-With the Slots pattern, we don't render the children to real DOM but
-only collect information, so virtualisation is supported by nature.
+Even with the Reach UI's solution, it doesn't work well with SSR. With the Slots pattern, we don't render the children to real DOM but only collect information, so virtualisation is supported by nature.
 
 ## Why we want it built in core
 
-I've researched a lot different approaches, none of the current solutions
-work perfectly without any drawbacks, my [solution](https://github.com/nihgwu/create-slots)
-is the closest one. But as @devongovett pointed out [here](https://github.com/facebook/react/issues/24979#issuecomment-1205909188), `react-reconciler` is designed to do this job,
-It would be nice to see it in core, like `react-call-return`.
+I've researched a lot different approaches, none of the current solutions work perfectly without any drawbacks, my [solution](https://github.com/nihgwu/create-slots) is the closest one. But as @devongovett pointed out [here](https://github.com/facebook/react/issues/24979#issuecomment-1205909188), `react-reconciler` is designed to do this job, It would be nice to see it in core, like `react-call-return`.
 
-# Detailed design
+It seems `React.Children.forEach` can do the same job demoed in the example above, but there are a lot limitations which are well documented [here](https://github.com/reach/reach-ui/tree/dev/packages/descendants), with this proposal we are free to extend the slot and compose in any way, e.g.
+
+```jsx
+const StyledLabel = styled(TextField)``;
+
+const PartialTextField = ({ show }) => (
+  <>
+    {show && <StyledLabel>Dynamic styled label</StyledLabel>}
+    <>
+      <TextFieldInput />
+    </>
+  </>
+);
 
-The api is very similar to the [deleted](https://github.com/facebook/react/pull/12820)
-experimental package [`react-call-return`](https://github.com/facebook/react/pull/11364),
-but with a simpler mental model.
+export default function App() {
+  return (
+    <TextField>
+      <PartialTextField />
+    </TextField>
+  );
+}
+```
+
+# Detailed design
 
-`createSlot(slotName)` creates a slot component and won't be rendered to
-real DOM but only collect props, which will be used by `createHost`
+The api is very similar to the [deleted](https://github.com/facebook/react/pull/12820) experimental package [`react-call-return`](https://github.com/facebook/react/pull/11364), but with a simpler mental model.
 
-`createHost(children, callback)` mounts the children included slotted
-components and read the collected slots' props, and render the result to
-real DOM conditionally. The argument of `callback` provides the following
-methods:
+`createSlot<SlotProps>()` creates a slot component and won't be rendered to real DOM but only collect node info, which will be used by `createHost`, for TS/Flow users, `SlotProps` is the props we support in each slot, will be `LabelProps`, `InputProps`, `TagProps` for the example
 
-- `get(slotName: string)` returns the registered slot's props by name,
-  will return the last registered named slot if the host expect only one
-  but consumer provides more.
-- `getAll(slotName: string)` returns all the registered slots as array
-  this method is useful to create a list.
-- `getChildren()` returns the rest of children without slots, e.g.
-  `<Host>rest<Slot /></Host>` it will return `rest`.
+`createHost(children: JSX.Element, callback: (slots: React.Element) => JSX.Element | null)` mounts the children which hosting slotted components and read the collected slots elements, and render the result to real DOM conditionally. We can find the slots by filter the `slots`(shown in the example above), similar to Web Components, there could be nodes not wrapped in slots at all will be treated as unnamed slot(`<slot></slot>)`
 
 # Drawbacks
 
-Even we are going to support this feature in a separate package or entry,
-it will still increase the bundle size of React a bit as we need core support.
+Even we are going to support this feature in a separate package or entry, it will still increase the bundle size of React a bit as we need core support.
 
 # Alternatives
 
-- Bring back `react-call-return` which also could be used to implement this
-  feature, but the mental model is hard to understand.
-- Leave it to userspace to implement with current api, like [create-slots](https://github.com/nihgwu/create-slots), but not very efficient and have
-  some drawbacks, e.g. unable to catch children not wrapped in slots.
+- Bring back `react-call-return` which also could be used to implement this feature [demo](https://codesandbox.io/s/long-hill-os6msf?file=/src/App.js), but the mental model is hard to understand.
+- Leave it to userspace to implement with current api, like [create-slots](https://github.com/nihgwu/create-slots), but not very efficient and have some drawbacks, e.g. unable to catch children not wrapped in slots, for list slots we have to force update to get the correct index.
 
 # Adoption strategy
 
-There is no breaking changes, it's a new feature more for UI library authors
-instead of application developers.
+There is no breaking changes, it's a new feature more for UI library authors instead of application developers.
 
 # How we teach this
 
-Slots pattern is a native feature of Web Components, other popular frameworks
-like Vue and Svelte also provide similar concepts. So the concept itself is
-easy to understand, we only have to document the api.
+Slots pattern is a native feature of Web Components, other popular frameworks like Vue and Svelte also provide similar concepts. So the concept itself is easy to understand, we only have to document the api.
 
 # Unresolved questions
 
 - Finalise the namings
-- Do we need to provide internal key for list rendering, though I don't see it
-  in `react-call-return`
+- Do we need to provide internal key for list rendering?
 - Adding to a new package or to `React` directly