Merge branch 'main' into opaque-rune

Author: trueadm

.changeset/rare-cheetahs-laugh.md

@@ -23,8 +23,6 @@ Iterating over values can be done with an each block. The values in question can
 </ul>
 ```
 
-You can use each blocks to iterate over any array or array-like value — that is, any object with a `length` property.
-
 An each block can also specify an _index_, equivalent to the second argument in an `array.map(...)` callback:
 
 ```svelte

documentation/docs/03-template-syntax/03-each.md

@@ -12,10 +12,34 @@ The general syntax is `bind:property={expression}`, where `expression` is an _lv
 <input bind:value />
 ```
 
+
 Svelte creates an event listener that updates the bound value. If an element already has a listener for the same event, that listener will be fired before the bound value is updated.
 
 Most bindings are _two-way_, meaning that changes to the value will affect the element and vice versa. A few bindings are _readonly_, meaning that changing their value will have no effect on the element.
 
+## Function bindings
+
+You can also use `bind:property={get, set}`, where `get` and `set` are functions, allowing you to perform validation and transformation:
+
+```svelte
+<input bind:value={
+	() => value,
+	(v) => value = v.toLowerCase()}
+/>
+```
+
+In the case of readonly bindings like [dimension bindings](#Dimensions), the `get` value should be `null`:
+
+```svelte
+<div
+	bind:clientWidth={null, redraw}
+	bind:clientHeight={null, redraw}
+>...</div>
+```
+
+> [!NOTE]
+> Function bindings are available in Svelte 5.9.0 and newer.
+
 ## `<input bind:value>`
 
 A `bind:value` directive on an `<input>` element binds the input's `value` property:

documentation/docs/03-template-syntax/11-bind.md

@@ -66,6 +66,31 @@ The easiest way to log a value as it changes over time is to use the [`$inspect`
 The `%attribute%` attribute on `%html%` changed its value between server and client renders. The client value, `%value%`, will be ignored in favour of the server value
 ```
 
+Certain attributes like `src` on an `<img>` element will not be repaired during hydration, i.e. the server value will be kept. That's because updating these attributes can cause the image to be refetched (or in the case of an `<iframe>`, for the frame to be reloaded), even if they resolve to the same resource.
+
+To fix this, either silence the warning with a [`svelte-ignore`](basic-markup#Comments) comment, or ensure that the value stays the same between server and client. If you really need the value to change on hydration, you can force an update like this:
+
+```svelte
+<script>
+	let { src } = $props();
+
+	if (typeof window !== 'undefined') {
+		// stash the value...
+		const initial = src;
+
+		// unset it...
+		src = undefined;
+
+		$effect(() => {
+			// ...and reset after we've mounted
+			src = initial;
+		});
+	}
+</script>
+
+<img {src} />
+```
+
 ### hydration_html_changed
 
 ```
@@ -76,6 +101,31 @@ The value of an `{@html ...}` block changed between server and client renders. T
 The value of an `{@html ...}` block %location% changed between server and client renders. The client value will be ignored in favour of the server value
 ```
 
+If the `{@html ...}` value changes between the server and the client, it will not be repaired during hydration, i.e. the server value will be kept. That's because change detection during hydration is expensive and usually unnecessary.
+
+To fix this, either silence the warning with a [`svelte-ignore`](basic-markup#Comments) comment, or ensure that the value stays the same between server and client. If you really need the value to change on hydration, you can force an update like this:
+
+```svelte
+<script>
+	let { markup } = $props();
+
+	if (typeof window !== 'undefined') {
+		// stash the value...
+		const initial = markup;
+
+		// unset it...
+		markup = undefined;
+
+		$effect(() => {
+			// ...and reset after we've mounted
+			markup = initial;
+		});
+	}
+</script>
+
+{@html markup}
+```
+
 ### hydration_mismatch
 
 ```
@@ -86,6 +136,10 @@ Hydration failed because the initial UI does not match what was rendered on the
 Hydration failed because the initial UI does not match what was rendered on the server. The error occurred near %location%
 ```
 
+This warning is thrown when Svelte encounters an error while hydrating the HTML from the server. During hydration, Svelte walks the DOM, expecting a certain structure. If that structure is different (for example because the HTML was repaired by the DOM because of invalid HTML), then Svelte will run into issues, resulting in this warning.
+
+During development, this error is often preceeded by a `console.error` detailing the offending HTML, which needs fixing.
+
 ### invalid_raw_snippet_render
 
 ```
@@ -110,6 +164,10 @@ Tried to unmount a component that was not mounted
 %parent% passed a value to %child% with `bind:`, but the value is owned by %owner%. Consider creating a binding between %owner% and %parent%
 ```
 
+Consider three components `GrandParent`, `Parent` and `Child`. If you do `<GrandParent bind:value>`, inside `GrandParent` pass on the variable via `<Parent {value} />` (note the missing `bind:`) and then do `<Child bind:value>` inside `Parent`, this warning is thrown.
+
+To fix it, `bind:` to the value instead of just passing a property (i.e. in this example do `<Parent bind:value />`).
+
 ### ownership_invalid_mutation
 
 ```
@@ -120,6 +178,32 @@ Mutating a value outside the component that created it is strongly discouraged.
 %component% mutated a value owned by %owner%. This is strongly discouraged. Consider passing values to child components with `bind:`, or use a callback instead
 ```
 
+Consider the following code:
+
+```svelte
+<!--- file: App.svelte --->
+<script>
+	import Child from './Child.svelte';
+	let person = $state({ name: 'Florida', surname: 'Man' });
+</script>
+
+<Child {person} />
+```
+
+```svelte
+<!--- file: Child.svelte --->
+<script>
+	let { person } = $props();
+</script>
+
+<input bind:value={person.name}>
+<input bind:value={person.surname}>
+```
+
+`Child` is mutating `person` which is owned by `App` without being explicitly "allowed" to do so. This is strongly discouraged since it can create code that is hard to reason about at scale ("who mutated this value?"), hence the warning.
+
+To fix it, either create callback props to communicate changes, or mark `person` as [`$bindable`]($bindable).
+
 ### reactive_declaration_non_reactive_property
 
 ```

documentation/docs/98-reference/.generated/client-warnings.md

@@ -78,10 +78,16 @@ Sequence expressions are not allowed as attribute/directive values in runes mode
 Attribute values containing `{...}` must be enclosed in quote marks, unless the value only contains the expression
 ```
 
+### bind_group_invalid_expression
+
+```
+`bind:group` can only bind to an Identifier or MemberExpression
+```
+
 ### bind_invalid_expression
 
 ```
-Can only bind to an Identifier or MemberExpression
+Can only bind to an Identifier or MemberExpression or a `{get, set}` pair
 ```
 
 ### bind_invalid_name
@@ -94,6 +100,12 @@ Can only bind to an Identifier or MemberExpression
 `bind:%name%` is not a valid binding. %explanation%
 ```
 
+### bind_invalid_parens
+
+```
+`bind:%name%={get, set}` must not have surrounding parentheses
+```
+
 ### bind_invalid_target
 
 ```

documentation/docs/98-reference/.generated/compile-errors.md

@@ -610,6 +610,20 @@ Empty block
 Unused CSS selector "%name%"
 ```
 
+Svelte traverses both the template and the `<style>` tag to find out which of the CSS selectors are not used within the template, so it can remove them.
+
+In some situations a selector may target an element that is not 'visible' to the compiler, for example because it is part of an `{@html ...}` tag or you're overriding styles in a child component. In these cases, use [`:global`](/docs/svelte/global-styles) to preserve the selector as-is:
+
+```svelte
+<div class="post">{@html content}</div>
+
+<style>
+  .post :global {
+    p {...}
+  }
+</style>
+```
+
 ### element_invalid_self_closing_tag
 
 ```
@@ -622,6 +636,8 @@ Self-closing HTML tags for non-void elements are ambiguous — use `<%name% ...>
 Using `on:%name%` to listen to the %name% event is deprecated. Use the event attribute `on%name%` instead
 ```
 
+See [the migration guide](v5-migration-guide#Event-changes) for more info.
+
 ### export_let_unused
 
 ```
@@ -640,6 +656,8 @@ Component has unused export property '%name%'. If it is for external reference o
 Svelte 5 components are no longer classes. Instantiate them using `mount` or `hydrate` (imported from 'svelte') instead.
 ```
 
+See the [migration guide](v5-migration-guide#Components-are-no-longer-classes) for more info.
+
 ### node_invalid_placement_ssr
 
 ```
@@ -660,6 +678,30 @@ This code will work when the component is rendered on the client (which is why t
 `%name%` is updated, but is not declared with `$state(...)`. Changing its value will not correctly trigger updates
 ```
 
+This warning is thrown when the compiler detects the following:
+- a variable was declared without `$state` or `$state.raw`
+- the variable is reassigned
+- the variable is read in a reactive context
+
+In this case, changing the value will not correctly trigger updates. Example:
+
+```svelte
+<script>
+	let reactive = $state('reactive');
+	let stale = 'stale';
+</script>
+
+<p>This value updates: {reactive}</p>
+<p>This value does not update: {stale}</p>
+
+<button onclick={() => {
+	stale = 'updated';
+	reactive = 'updated';
+}}>update</button>
+```
+
+To fix this, wrap your variable declaration with `$state`.
+
 ### options_deprecated_accessors
 
 ```
@@ -732,6 +774,12 @@ Reassignments of module-level declarations will not cause reactive statements to
 `context="module"` is deprecated, use the `module` attribute instead
 ```
 
+```svelte
+<script ---context="module"--- +++context+++>
+	let foo = 'bar';
+</script>
+```
+
 ### script_unknown_attribute
 
 ```
@@ -744,12 +792,79 @@ Unrecognized attribute — should be one of `generics`, `lang` or `module`. If t
 Using `<slot>` to render parent content is deprecated. Use `{@render ...}` tags instead
 ```
 
+See [the migration guide](v5-migration-guide#Snippets-instead-of-slots) for more info.
+
 ### state_referenced_locally
 
 ```
 State referenced in its own scope will never update. Did you mean to reference it inside a closure?
 ```
 
+This warning is thrown when the compiler detects the following:
+- A reactive variable is declared
+- the variable is reassigned
+- the variable is referenced inside the same scope it is declared and it is a non-reactive context
+
+In this case, the state reassignment will not be noticed by whatever you passed it to. For example, if you pass the state to a function, that function will not notice the updates:
+
+```svelte
+<!--- file: Parent.svelte --->
+<script>
+	import { setContext } from 'svelte';
+
+	let count = $state(0);
+
+	// warning: state_referenced_locally
+	setContext('count', count);
+</script>
+
+<button onclick={() => count++}>
+	increment
+</button>
+```
+
+```svelte
+<!--- file: Child.svelte --->
+<script>
+	import { getContext } from 'svelte';
+
+	const count = getContext('count');
+</script>
+
+<!-- This will never update -->
+<p>The count is {count}</p>
+```
+
+To fix this, reference the variable such that it is lazily evaluated. For the above example, this can be achieved by wrapping `count` in a function:
+
+```svelte
+<!--- file: Parent.svelte --->
+<script>
+	import { setContext } from 'svelte';
+
+	let count = $state(0);
+	setContext('count', +++() => count+++);
+</script>
+
+<button onclick={() => count++}>
+	increment
+</button>
+```
+
+```svelte
+<!--- file: Child.svelte --->
+<script>
+	import { getContext } from 'svelte';
+
+	const count = getContext('count');
+</script>
+
+<!-- This will update -->
+<p>The count is {+++count()+++}</p>
+```
+
+For more info, see [Passing state into functions]($state#Passing-state-into-functions).
+
 ### store_rune_conflict
 
 ```
@@ -805,6 +920,8 @@ A derived value may be used in other contexts:
 `<svelte:self>` is deprecated — use self-imports (e.g. `import %name% from './%basename%'`) instead
 ```
 
+See [the note in the docs](legacy-svelte-self) for more info.
+
 ### unknown_code
 
 ```

documentation/docs/98-reference/.generated/compile-warnings.md

@@ -5,3 +5,5 @@
 ```
 `%name%(...)` is not available on the server
 ```
+
+Certain methods such as `mount` cannot be invoked while running in a server context. Avoid calling them eagerly, i.e. not during render.