add experimental.async option

Author: Rich-Harris

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

@@ -444,6 +444,12 @@ Expected token %token%
 Expected whitespace
 ```
 
+### experimental_async
+
+```
+Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless the `experimental.async` compiler option is `true`
+```
+
 ### export_undefined
 
 ```
@@ -501,7 +507,7 @@ The arguments keyword cannot be used within the template or at the top level of
 ### legacy_await_invalid
 
 ```
-Cannot use `await` at the top level of a component, or in the template, unless in runes mode
+Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless in runes mode
 ```
 
 ### legacy_export_invalid

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

@@ -70,6 +70,10 @@ This turned out to be buggy and unpredictable, particularly when working with de
 
 > `$effect()` can only be used as an expression statement
 
+## experimental_async
+
+> Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless the `experimental.async` compiler option is `true`
+
 ## export_undefined
 
 > `%name%` is not defined
@@ -100,7 +104,7 @@ This turned out to be buggy and unpredictable, particularly when working with de
 
 ## legacy_await_invalid
 
-> Cannot use `await` at the top level of a component, or in the template, unless in runes mode
+> Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless in runes mode
 
 ## legacy_export_invalid
 

packages/svelte/src/compiler/errors.js

@@ -168,6 +168,15 @@ export function effect_invalid_placement(node) {
 	e(node, 'effect_invalid_placement', `\`$effect()\` can only be used as an expression statement\nhttps://svelte.dev/e/effect_invalid_placement`);
 }
 
+/**
+ * Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless the `experimental.async` compiler option is `true`
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function experimental_async(node) {
+	e(node, 'experimental_async', `Cannot use \`await\` in deriveds and template expressions, or at the top level of a component, unless the \`experimental.async\` compiler option is \`true\`\nhttps://svelte.dev/e/experimental_async`);
+}
+
 /**
  * `%name%` is not defined
  * @param {null | number | NodeLike} node
@@ -234,12 +243,12 @@ export function invalid_arguments_usage(node) {
 }
 
 /**
- * Cannot use `await` at the top level of a component, or in the template, unless in runes mode
+ * Cannot use `await` in deriveds and template expressions, or at the top level of a component, unless in runes mode
  * @param {null | number | NodeLike} node
  * @returns {never}
  */
 export function legacy_await_invalid(node) {
-	e(node, 'legacy_await_invalid', `Cannot use \`await\` at the top level of a component, or in the template, unless in runes mode\nhttps://svelte.dev/e/legacy_await_invalid`);
+	e(node, 'legacy_await_invalid', `Cannot use \`await\` in deriveds and template expressions, or at the top level of a component, unless in runes mode\nhttps://svelte.dev/e/legacy_await_invalid`);
 }
 
 /**

packages/svelte/src/compiler/types/index.d.ts

@@ -212,6 +212,11 @@ export interface ModuleCompileOptions {
 	 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 	 */
 	warningFilter?: (warning: Warning) => boolean;
+	/** Experimental options */
+	experimental?: {
+		/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+		async?: boolean;
+	};
 }
 
 // The following two somewhat scary looking types ensure that certain types are required but can be undefined still

packages/svelte/src/compiler/validate-options.js

@@ -41,7 +41,11 @@ const common = {
 		return input;
 	}),
 
-	warningFilter: fun(() => true)
+	warningFilter: fun(() => true),
+
+	experimental: object({
+		async: boolean(false)
+	})
 };
 
 export const validate_module_options =

packages/svelte/types/index.d.ts

@@ -933,6 +933,11 @@ declare module 'svelte/compiler' {
 		 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 		 */
 		warningFilter?: (warning: Warning) => boolean;
+		/** Experimental options */
+		experimental?: {
+			/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+			async?: boolean;
+		};
 	}
 	/**
 	 * - `html`    — the default, for e.g. `<div>` or `<span>`
@@ -2635,6 +2640,11 @@ declare module 'svelte/types/compiler/interfaces' {
 		 * Use this to filter out warnings. Return `true` to keep the warning, `false` to discard it.
 		 */
 		warningFilter?: (warning: Warning_1) => boolean;
+		/** Experimental options */
+		experimental?: {
+			/** Allow `await` keyword in deriveds, template expressions, and the top level of components */
+			async?: boolean;
+		};
 	}
 	/**
 	 * - `html`    — the default, for e.g. `<div>` or `<span>`