fix: handle typescript $$Generic special type

src/postprocess.js

@@ -98,6 +98,7 @@ const is_valid_message = (block, message, translation) => {
 		case 'no-labels': return get_identifier(get_referenced_string(block, message)) !== '$';
 		case 'no-restricted-syntax': return message.nodeType !== 'LabeledStatement' || get_identifier(get_referenced_string(block, message)) !== '$';
 		case 'no-self-assign': return !state.var_names.has(get_identifier(get_referenced_string(block, message)));
+		case 'no-undef': return get_referenced_string(block, message) !== '$$Generic';
 		case 'no-unused-labels': return get_referenced_string(block, message) !== '$';
 		case '@typescript-eslint/quotes':
 		case 'quotes': return !translation.options.in_quoted_attribute;

test/samples/typescript-generics/.eslintrc.js

@@ -0,0 +1,11 @@
+module.exports = {
+	parser: '@typescript-eslint/parser',
+	extends: ['plugin:@typescript-eslint/recommended'],
+	plugins: ['@typescript-eslint'],
+	settings: {
+		'svelte3/typescript': require('typescript'),
+	},
+	rules: {
+		'no-undef': 'error',
+	},
+};

test/samples/typescript-generics/Input.svelte

@@ -0,0 +1,14 @@
+<script lang='ts'>
+	type T = $$Generic;
+	type U = $$Generic<string>;
+	export let items: T[];
+	export let message: U;
+</script>
+
+{#each items as item}
+	<slot {item} />
+{/each}
+
+{#if message}
+	{message}
+{/if}

test/samples/typescript-generics/expected.json

@@ -0,0 +1 @@
+[]