disallow binding variables declared in await and catch

src/compiler/compile/nodes/Binding.ts

@@ -50,6 +50,13 @@ export default class Binding extends Node {
 				message: 'Cannot bind to a variable declared with the let: directive'
 			});
 		} else if (this.is_contextual) {
+			if (scope.is_await(name)) {
+				component.error(this, {
+					code: 'invalid-binding',
+					message: 'Cannot bind to a variable declared with {#await ... then} or {:catch} blocks'
+				});
+			}
+
 			scope.dependencies_for_name.get(name).forEach(name => {
 				const variable = component.var_lookup.get(name);
 				if (variable) {

src/compiler/compile/nodes/shared/TemplateScope.ts

@@ -42,4 +42,9 @@ export default class TemplateScope {
 		const owner = this.get_owner(name);
 		return owner && (owner.type === 'Element' || owner.type === 'InlineComponent');
 	}
+
+	is_await(name: string) {
+		const owner = this.get_owner(name);
+		return owner && (owner.type === 'ThenBlock' || owner.type === 'CatchBlock');
+	}
 }

test/validator/samples/binding-await-catch/errors.json

@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-binding",
+		"message": "Cannot bind to a variable declared with {#await ... then} or {:catch} blocks",
+		"pos": 79,
+		"start": { "line": 6, "column": 9, "character": 79 },
+		"end": { "line": 6, "column": 27, "character": 97 }
+	}
+]

test/validator/samples/binding-await-catch/input.svelte

@@ -0,0 +1,7 @@
+<script>
+  let promise = 0;
+</script>
+{#await promise}
+{:catch error}
+  <input bind:value={error} />
+{/await}

test/validator/samples/binding-await-then-2/errors.json

@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-binding",
+		"message": "Cannot bind to a variable declared with {#await ... then} or {:catch} blocks",
+		"pos": 78,
+		"start": { "line": 6, "column": 9, "character": 78 },
+		"end": { "line": 6, "column": 19, "character": 88 }
+	}
+]

test/validator/samples/binding-await-then-2/input.svelte

@@ -0,0 +1,7 @@
+<script>
+  let promise = 0;
+</script>
+{#await promise}
+{:then value}
+  <input bind:value />
+{/await}

test/validator/samples/binding-await-then/errors.json

@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-binding",
+		"message": "Cannot bind to a variable declared with {#await ... then} or {:catch} blocks",
+		"pos": 75,
+		"start": { "line": 5, "column": 9, "character": 75 },
+		"end": { "line": 5, "column": 19, "character": 85 }
+	}
+]

test/validator/samples/binding-await-then/input.svelte

@@ -0,0 +1,6 @@
+<script>
+  let promise = 0;
+</script>
+{#await promise then value}
+  <input bind:value />
+{/await}