[fix] object destructuring bug using @const (#166)

Fixes #164

Author: si3nloong

Diff for: src/preprocess.js

@@ -173,7 +173,7 @@ export const preprocess = text => {
 					node.attributes.forEach(node => node.type === 'Let' && find_contextual_names(compiler, node.expression || node.name));
 				}
 				if (Array.isArray(node.children)) {
-					node.children.forEach(node => node.type === 'ConstTag' && find_contextual_names(compiler, node.expression.left.name));
+					node.children.forEach(node => node.type === 'ConstTag' && find_contextual_names(compiler, node.expression.left.name || node.expression.left));
 				}
 				if (contextual_names.length) {
 					nodes_with_contextual_scope.add(node);

Diff for: test/samples/const-tag/Input.svelte

@@ -1,6 +1,7 @@
 <script>
 	export let boxes;
 	let p;
+	let dimensions = [{ width: 100, height: 20 }];
 </script>
 
 {#each boxes as box}
@@ -10,6 +11,13 @@
 
 {area} <!-- undef -->
 
+{#each dimensions as dimension}
+	{@const { width, height } = dimension}
+	{width}
+	{height}
+	{unknown} <!-- undef -->
+{/each}
+
 {#await p}
 	wait
 {:then}

Diff for: test/samples/const-tag/expected.json

@@ -1,9 +1,16 @@
 [
 	{
 		"ruleId": "no-undef",
-		"line": 11,
+		"line": 12,
 		"column": 2,
-		"endLine": 11,
+		"endLine": 12,
 		"endColumn": 6
+	},
+	{
+		"ruleId": "no-undef",
+		"line": 18,
+		"column": 3,
+		"endLine": 18,
+		"endColumn": 10
 	}
 ]