breaking: deprecate context="module" in favor of module (#12948)

* breaking: deprecate `context="module"` in favor of `module`

Also reserve a few attributes, which we may or may not use in the future

closes #12637

* fix tests

* one more

* add svelte package to the root so eslint and prettier can use it

* tweak messages

* warn on unknown attributes

* regenerate

---------

Co-authored-by: Rich Harris <[email protected]>

Author: dummdidumm

.changeset/quick-eagles-sit.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+breaking: deprecate `context="module"` in favor of `module`

documentation/docs/02-template-syntax/01-component-fundamentals.md

@@ -161,16 +161,16 @@ If you'd like to react to changes to a prop, use the `$derived` or `$effect` run
 
 For more information on reactivity, read the documentation around runes.
 
-## <script context="module">
+## <script module>
 
-A `<script>` tag with a `context="module"` attribute runs once when the module first evaluates, rather than for each component instance. Values declared in this block are accessible from a regular `<script>` (and the component markup) but not vice versa.
+A `<script>` tag with a `module` attribute runs once when the module first evaluates, rather than for each component instance. Values declared in this block are accessible from a regular `<script>` (and the component markup) but not vice versa.
 
 You can `export` bindings from this block, and they will become exports of the compiled module.
 
 You cannot `export default`, since the default export is the component itself.
 
 ```svelte
-<script context="module">
+<script module>
 	let totalComponents = 0;
 
 	// the export keyword allows this function to imported with e.g.

package.json

@@ -40,6 +40,7 @@
     "playwright": "^1.41.1",
     "prettier": "^3.2.4",
     "prettier-plugin-svelte": "^3.1.2",
+    "svelte": "workspace:^",
     "typescript": "^5.5.2",
     "typescript-eslint": "^8.0.0-alpha.34",
     "v8-natives": "^1.2.5",

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

@@ -16,7 +16,7 @@
 
 ## declaration_duplicate_module_import
 
-> Cannot declare same variable name which is imported inside `<script context="module">`
+> Cannot declare a variable with the same name as an import inside `<script module>`
 
 ## derived_invalid_export
 
@@ -152,7 +152,7 @@
 
 ## store_invalid_subscription
 
-> Cannot reference store value inside `<script context="module">`
+> Cannot reference store value inside `<script module>`
 
 ## store_invalid_subscription_module
 

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

@@ -216,12 +216,20 @@ HTML restricts where certain elements can appear. In case of a violation the bro
 
 ## script_duplicate
 
-> A component can have a single top-level `<script>` element and/or a single top-level `<script context="module">` element
+> A component can have a single top-level `<script>` element and/or a single top-level `<script module>` element
+
+## script_invalid_attribute_value
+
+> If the `%name%` attribute is supplied, it must be a boolean attribute
 
 ## script_invalid_context
 
 > If the context attribute is supplied, its value must be "module"
 
+## script_reserved_attribute
+
+> The `%name%` attribute is reserved and cannot be used
+
 ## slot_attribute_duplicate
 
 > Duplicate slot name '%name%' in <%component%>

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

@@ -50,6 +50,14 @@ HTML restricts where certain elements can appear. In case of a violation the bro
 
 This code will work when the component is rendered on the client (which is why this is a warning rather than an error), but if you use server rendering it will cause hydration to fail.
 
+## script_context_deprecated
+
+> `context="module"` is deprecated, use the `module` attribute instead
+
+## script_unknown_attribute
+
+> Unrecognized attribute — should be one of `generics`, `lang` or `module`. If this exists for a preprocessor, ensure that the preprocessor removes it
+
 ## slot_element_deprecated
 
 > Using `<slot>` to render parent content is deprecated. Use `{@render ...}` tags instead

packages/svelte/src/compiler/errors.js

@@ -99,12 +99,12 @@ export function declaration_duplicate(node, name) {
 }
 
 /**
- * Cannot declare same variable name which is imported inside `<script context="module">`
+ * Cannot declare a variable with the same name as an import inside `<script module>`
  * @param {null | number | NodeLike} node
  * @returns {never}
  */
 export function declaration_duplicate_module_import(node) {
-	e(node, "declaration_duplicate_module_import", "Cannot declare same variable name which is imported inside `<script context=\"module\">`");
+	e(node, "declaration_duplicate_module_import", "Cannot declare a variable with the same name as an import inside `<script module>`");
 }
 
 /**
@@ -417,12 +417,12 @@ export function store_invalid_scoped_subscription(node) {
 }
 
 /**
- * Cannot reference store value inside `<script context="module">`
+ * Cannot reference store value inside `<script module>`
  * @param {null | number | NodeLike} node
  * @returns {never}
  */
 export function store_invalid_subscription(node) {
-	e(node, "store_invalid_subscription", "Cannot reference store value inside `<script context=\"module\">`");
+	e(node, "store_invalid_subscription", "Cannot reference store value inside `<script module>`");
 }
 
 /**
@@ -1044,12 +1044,22 @@ export function render_tag_invalid_spread_argument(node) {
 }
 
 /**
- * A component can have a single top-level `<script>` element and/or a single top-level `<script context="module">` element
+ * A component can have a single top-level `<script>` element and/or a single top-level `<script module>` element
  * @param {null | number | NodeLike} node
  * @returns {never}
  */
 export function script_duplicate(node) {
-	e(node, "script_duplicate", "A component can have a single top-level `<script>` element and/or a single top-level `<script context=\"module\">` element");
+	e(node, "script_duplicate", "A component can have a single top-level `<script>` element and/or a single top-level `<script module>` element");
+}
+
+/**
+ * If the `%name%` attribute is supplied, it must be a boolean attribute
+ * @param {null | number | NodeLike} node
+ * @param {string} name
+ * @returns {never}
+ */
+export function script_invalid_attribute_value(node, name) {
+	e(node, "script_invalid_attribute_value", `If the \`${name}\` attribute is supplied, it must be a boolean attribute`);
 }
 
 /**
@@ -1061,6 +1071,16 @@ export function script_invalid_context(node) {
 	e(node, "script_invalid_context", "If the context attribute is supplied, its value must be \"module\"");
 }
 
+/**
+ * The `%name%` attribute is reserved and cannot be used
+ * @param {null | number | NodeLike} node
+ * @param {string} name
+ * @returns {never}
+ */
+export function script_reserved_attribute(node, name) {
+	e(node, "script_reserved_attribute", `The \`${name}\` attribute is reserved and cannot be used`);
+}
+
 /**
  * Duplicate slot name '%name%' in <%component%>
  * @param {null | number | NodeLike} node

packages/svelte/src/compiler/migrate/index.js

@@ -1,5 +1,4 @@
 /** @import { VariableDeclarator, Node, Identifier } from 'estree' */
-/** @import { SvelteNode } from '../types/template.js' */
 /** @import { Visitors } from 'zimmerframe' */
 /** @import { ComponentAnalysis } from '../phases/types.js' */
 /** @import { Scope } from '../phases/scope.js' */
@@ -58,6 +57,13 @@ export function migrate(source) {
 			needs_run: false
 		};
 
+		if (parsed.module) {
+			const context = parsed.module.attributes.find((attr) => attr.name === 'context');
+			if (context) {
+				state.str.update(context.start, context.end, 'module');
+			}
+		}
+
 		if (parsed.instance) {
 			walk(parsed.instance.content, state, instance_script);
 		}
@@ -223,7 +229,7 @@ export function migrate(source) {
  * }} State
  */
 
-/** @type {Visitors<SvelteNode, State>} */
+/** @type {Visitors<Compiler.SvelteNode, State>} */
 const instance_script = {
 	_(node, { state, next }) {
 		// @ts-expect-error
@@ -472,7 +478,7 @@ const instance_script = {
 	}
 };
 
-/** @type {Visitors<SvelteNode, State>} */
+/** @type {Visitors<Compiler.SvelteNode, State>} */
 const template = {
 	Identifier(node, { state, path }) {
 		handle_identifier(node, state, path);
@@ -590,7 +596,7 @@ const template = {
 /**
  * @param {VariableDeclarator} declarator
  * @param {MagicString} str
- * @param {Compiler.SvelteNode[]} path
+ * @param {Array<Compiler.SvelteNode>} path
  */
 function extract_type_and_comment(declarator, str, path) {
 	const parent = path.at(-1);

packages/svelte/src/compiler/phases/1-parse/read/script.js

@@ -4,32 +4,14 @@
 import * as acorn from '../acorn.js';
 import { regex_not_newline_characters } from '../../patterns.js';
 import * as e from '../../../errors.js';
+import * as w from '../../../warnings.js';
+import { is_text_attribute } from '../../../utils/ast.js';
 
 const regex_closing_script_tag = /<\/script\s*>/;
 const regex_starts_with_closing_script_tag = /^<\/script\s*>/;
 
-/**
- * @param {any[]} attributes
- * @returns {string}
- */
-function get_context(attributes) {
-	const context = attributes.find(
-		/** @param {any} attribute */ (attribute) => attribute.name === 'context'
-	);
-	if (!context) return 'default';
-
-	if (context.value.length !== 1 || context.value[0].type !== 'Text') {
-		e.script_invalid_context(context.start);
-	}
-
-	const value = context.value[0].data;
-
-	if (value !== 'module') {
-		e.script_invalid_context(context.start);
-	}
-
-	return value;
-}
+const RESERVED_ATTRIBUTES = ['server', 'client', 'worker', 'test', 'default'];
+const ALLOWED_ATTRIBUTES = ['context', 'generics', 'lang', 'module'];
 
 /**
  * @param {Parser} parser
@@ -60,14 +42,56 @@ export function read_script(parser, start, attributes) {
 	// TODO is this necessary?
 	ast.start = script_start;
 
+	/** @type {'default' | 'module'} */
+	let context = 'default';
+
+	for (const attribute of /** @type {Attribute[]} */ (attributes)) {
+		if (RESERVED_ATTRIBUTES.includes(attribute.name)) {
+			e.script_reserved_attribute(attribute, attribute.name);
+		}
+
+		if (!ALLOWED_ATTRIBUTES.includes(attribute.name)) {
+			w.script_unknown_attribute(attribute);
+		}
+
+		if (attribute.name === 'module') {
+			if (attribute.value !== true) {
+				// Deliberately a generic code to future-proof for potential other attributes
+				e.script_invalid_attribute_value(attribute, attribute.name);
+			}
+
+			context = 'module';
+		}
+
+		if (attribute.name === 'context') {
+			if (attribute.value === true || !is_text_attribute(attribute)) {
+				throw new Error('TODO');
+			}
+
+			if (attribute.value.length !== 1 || attribute.value[0].type !== 'Text') {
+				e.script_invalid_context(attribute);
+			}
+
+			const value = attribute.value[0].data;
+
+			if (value !== 'module') {
+				e.script_invalid_context(attribute);
+			}
+
+			w.script_context_deprecated(attribute);
+
+			context = 'module';
+		}
+	}
+
 	return {
 		type: 'Script',
 		start,
 		end: parser.index,
-		context: get_context(attributes),
+		context,
 		content: ast,
 		parent: null,
 		// @ts-ignore
-		attributes: attributes
+		attributes
 	};
 }

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -330,7 +330,7 @@ export function analyze_component(root, source, options) {
 
 			if (module.ast) {
 				for (const { node, path } of references) {
-					// if the reference is inside context="module", error. this is a bit hacky but it works
+					// if the reference is inside module, error. this is a bit hacky but it works
 					if (
 						/** @type {number} */ (node.start) > /** @type {number} */ (module.ast.start) &&
 						/** @type {number} */ (node.end) < /** @type {number} */ (module.ast.end) &&