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feat: add support for bind getter/setters (#14307)
* feat: add support for bind getters/setters * different direction * oops * oops * build * add changeset and tests * move validation * add comment * build * bind:group error * simpler to just keep it as a SequenceExpression * fix * lint * fix * move validation to visitor * fix * no longer needed * fix * parser changes are no longer needed * simplify * simplify * update messages * docs --------- Co-authored-by: Rich Harris <[email protected]> Co-authored-by: Simon Holthausen <[email protected]>
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‎.changeset/slimy-donkeys-hang.md‎

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---
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'svelte': patch
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---
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feat: add support for bind getters/setters

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

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@@ -12,10 +12,34 @@ The general syntax is `bind:property={expression}`, where `expression` is an _lv
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<input bind:value />
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```
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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.
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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.
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## Function bindings
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You can also use `bind:property={get, set}`, where `get` and `set` are functions, allowing you to perform validation and transformation:
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```svelte
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<input bind:value={
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() => value,
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(v) => value = v.toLowerCase()}
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/>
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```
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In the case of readonly bindings like [dimension bindings](#Dimensions), the `get` value should be `null`:
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```svelte
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<div
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bind:clientWidth={null, redraw}
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bind:clientHeight={null, redraw}
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>...</div>
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```
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> [!NOTE]
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> Function bindings are available in Svelte 5.9.0 and newer.
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## `<input bind:value>`
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A `bind:value` directive on an `<input>` element binds the input's `value` property:

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

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

‎packages/svelte/messages/compile-errors/template.md‎

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> Attribute values containing `{...}` must be enclosed in quote marks, unless the value only contains the expression
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## bind_group_invalid_expression
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> `bind:group` can only bind to an Identifier or MemberExpression
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## bind_invalid_expression
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> Can only bind to an Identifier or MemberExpression
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> Can only bind to an Identifier or MemberExpression or a `{get, set}` pair
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## bind_invalid_name
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> `bind:%name%` is not a valid binding
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> `bind:%name%` is not a valid binding. %explanation%
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## bind_invalid_parens
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> `bind:%name%={get, set}` must not have surrounding parentheses
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## bind_invalid_target
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> `bind:%name%` can only be used with %elements%

‎packages/svelte/src/compiler/errors.js‎

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}
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/**
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* Can only bind to an Identifier or MemberExpression
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* `bind:group` can only bind to an Identifier or MemberExpression
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* @param {null | number | NodeLike} node
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* @returns {never}
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*/
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export function bind_group_invalid_expression(node) {
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e(node, "bind_group_invalid_expression", "`bind:group` can only bind to an Identifier or MemberExpression");
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}
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/**
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* Can only bind to an Identifier or MemberExpression or a `{get, set}` pair
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* @param {null | number | NodeLike} node
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* @returns {never}
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*/
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export function bind_invalid_expression(node) {
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e(node, "bind_invalid_expression", "Can only bind to an Identifier or MemberExpression");
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e(node, "bind_invalid_expression", "Can only bind to an Identifier or MemberExpression or a `{get, set}` pair");
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}
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/**
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e(node, "bind_invalid_name", explanation ? `\`bind:${name}\` is not a valid binding. ${explanation}` : `\`bind:${name}\` is not a valid binding`);
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}
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/**
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* `bind:%name%={get, set}` must not have surrounding parentheses
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* @param {null | number | NodeLike} node
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* @param {string} name
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* @returns {never}
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*/
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export function bind_invalid_parens(node, name) {
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e(node, "bind_invalid_parens", `\`bind:${name}={get, set}\` must not have surrounding parentheses`);
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}
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/**
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* `bind:%name%` can only be used with %elements%
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* @param {null | number | NodeLike} node

‎packages/svelte/src/compiler/phases/2-analyze/visitors/BindDirective.js‎

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* @param {Context} context
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*/
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export function BindDirective(node, context) {
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validate_no_const_assignment(node, node.expression, context.state.scope, true);
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const assignee = node.expression;
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const left = object(assignee);
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if (left === null) {
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e.bind_invalid_expression(node);
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}
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const binding = context.state.scope.get(left.name);
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if (assignee.type === 'Identifier') {
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// reassignment
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if (
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node.name !== 'this' && // bind:this also works for regular variables
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(!binding ||
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(binding.kind !== 'state' &&
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binding.kind !== 'raw_state' &&
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binding.kind !== 'prop' &&
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binding.kind !== 'bindable_prop' &&
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binding.kind !== 'each' &&
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binding.kind !== 'store_sub' &&
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!binding.updated)) // TODO wut?
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) {
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e.bind_invalid_value(node.expression);
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}
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if (context.state.analysis.runes && binding?.kind === 'each') {
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e.each_item_invalid_assignment(node);
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}
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if (binding?.kind === 'snippet') {
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e.snippet_parameter_assignment(node);
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}
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}
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if (node.name === 'group') {
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if (!binding) {
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throw new Error('Cannot find declaration for bind:group');
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}
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// Traverse the path upwards and find all EachBlocks who are (indirectly) contributing to bind:group,
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// i.e. one of their declarations is referenced in the binding. This allows group bindings to work
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// correctly when referencing a variable declared in an EachBlock by using the index of the each block
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// entries as keys.
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const each_blocks = [];
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const [keypath, expression_ids] = extract_all_identifiers_from_expression(node.expression);
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let ids = expression_ids;
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let i = context.path.length;
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while (i--) {
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const parent = context.path[i];
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if (parent.type === 'EachBlock') {
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const references = ids.filter((id) => parent.metadata.declarations.has(id.name));
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if (references.length > 0) {
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parent.metadata.contains_group_binding = true;
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each_blocks.push(parent);
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ids = ids.filter((id) => !references.includes(id));
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ids.push(...extract_all_identifiers_from_expression(parent.expression)[1]);
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}
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}
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}
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// The identifiers that make up the binding expression form they key for the binding group.
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// If the same identifiers in the same order are used in another bind:group, they will be in the same group.
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// (there's an edge case where `bind:group={a[i]}` will be in a different group than `bind:group={a[j]}` even when i == j,
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// but this is a limitation of the current static analysis we do; it also never worked in Svelte 4)
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const bindings = expression_ids.map((id) => context.state.scope.get(id.name));
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let group_name;
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outer: for (const [[key, b], group] of context.state.analysis.binding_groups) {
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if (b.length !== bindings.length || key !== keypath) continue;
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for (let i = 0; i < bindings.length; i++) {
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if (bindings[i] !== b[i]) continue outer;
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}
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group_name = group;
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}
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if (!group_name) {
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group_name = context.state.scope.root.unique('binding_group');
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context.state.analysis.binding_groups.set([keypath, bindings], group_name);
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}
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node.metadata = {
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binding_group_name: group_name,
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parent_each_blocks: each_blocks
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};
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}
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if (binding?.kind === 'each' && binding.metadata?.inside_rest) {
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w.bind_invalid_each_rest(binding.node, binding.node.name);
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}
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const parent = context.path.at(-1);
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if (
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}
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}
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// When dealing with bind getters/setters skip the specific binding validation
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// Group bindings aren't supported for getter/setters so we don't need to handle
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// the metadata
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if (node.expression.type === 'SequenceExpression') {
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if (node.name === 'group') {
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e.bind_group_invalid_expression(node);
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}
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let i = /** @type {number} */ (node.expression.start);
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while (context.state.analysis.source[--i] !== '{') {
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if (context.state.analysis.source[i] === '(') {
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e.bind_invalid_parens(node, node.name);
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}
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}
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if (node.expression.expressions.length !== 2) {
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e.bind_invalid_expression(node);
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}
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return;
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}
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validate_no_const_assignment(node, node.expression, context.state.scope, true);
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const assignee = node.expression;
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const left = object(assignee);
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if (left === null) {
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e.bind_invalid_expression(node);
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}
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const binding = context.state.scope.get(left.name);
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if (assignee.type === 'Identifier') {
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// reassignment
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if (
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node.name !== 'this' && // bind:this also works for regular variables
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(!binding ||
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(binding.kind !== 'state' &&
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binding.kind !== 'raw_state' &&
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binding.kind !== 'prop' &&
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binding.kind !== 'bindable_prop' &&
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binding.kind !== 'each' &&
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binding.kind !== 'store_sub' &&
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!binding.updated)) // TODO wut?
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) {
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e.bind_invalid_value(node.expression);
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}
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if (context.state.analysis.runes && binding?.kind === 'each') {
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e.each_item_invalid_assignment(node);
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}
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if (binding?.kind === 'snippet') {
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e.snippet_parameter_assignment(node);
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}
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}
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if (node.name === 'group') {
184+
if (!binding) {
185+
throw new Error('Cannot find declaration for bind:group');
186+
}
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// Traverse the path upwards and find all EachBlocks who are (indirectly) contributing to bind:group,
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// i.e. one of their declarations is referenced in the binding. This allows group bindings to work
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// correctly when referencing a variable declared in an EachBlock by using the index of the each block
191+
// entries as keys.
192+
const each_blocks = [];
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const [keypath, expression_ids] = extract_all_identifiers_from_expression(node.expression);
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let ids = expression_ids;
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let i = context.path.length;
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while (i--) {
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const parent = context.path[i];
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if (parent.type === 'EachBlock') {
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const references = ids.filter((id) => parent.metadata.declarations.has(id.name));
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if (references.length > 0) {
204+
parent.metadata.contains_group_binding = true;
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each_blocks.push(parent);
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ids = ids.filter((id) => !references.includes(id));
208+
ids.push(...extract_all_identifiers_from_expression(parent.expression)[1]);
209+
}
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}
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}
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// The identifiers that make up the binding expression form they key for the binding group.
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// If the same identifiers in the same order are used in another bind:group, they will be in the same group.
215+
// (there's an edge case where `bind:group={a[i]}` will be in a different group than `bind:group={a[j]}` even when i == j,
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// but this is a limitation of the current static analysis we do; it also never worked in Svelte 4)
217+
const bindings = expression_ids.map((id) => context.state.scope.get(id.name));
218+
let group_name;
219+
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outer: for (const [[key, b], group] of context.state.analysis.binding_groups) {
221+
if (b.length !== bindings.length || key !== keypath) continue;
222+
for (let i = 0; i < bindings.length; i++) {
223+
if (bindings[i] !== b[i]) continue outer;
224+
}
225+
group_name = group;
226+
}
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228+
if (!group_name) {
229+
group_name = context.state.scope.root.unique('binding_group');
230+
context.state.analysis.binding_groups.set([keypath, bindings], group_name);
231+
}
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node.metadata = {
234+
binding_group_name: group_name,
235+
parent_each_blocks: each_blocks
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};
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}
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if (binding?.kind === 'each' && binding.metadata?.inside_rest) {
240+
w.bind_invalid_each_rest(binding.node, binding.node.name);
241+
}
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context.next();
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}

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