Fix Comment Being Duplicated on Root Node Replacement (#29)

* Fix issue with comments being duplicated when replacing the root node

* Add test to verify comments aren't duplicated when replacing the root node

Author: BenBaryoPX

src/arborist.js

@@ -85,8 +85,8 @@ const Arborist = class {
 					const leadingComments =  rootNode.leadingComments || [];
 					const trailingComments = rootNode.trailingComments || [];
 					rootNode = rootNodeReplacement[1];
-					if (leadingComments.length) rootNode.leadingComments = (rootNode.leadingComments || []).concat(leadingComments);
-					if (trailingComments.length) rootNode.trailingComments = (rootNode.trailingComments || []).concat(trailingComments);
+					if (leadingComments.length && rootNode.leadingComments !== leadingComments) rootNode.leadingComments = (rootNode.leadingComments || []).concat(leadingComments);
+					if (trailingComments.length && rootNode.trailingComments !== trailingComments) rootNode.trailingComments = (rootNode.trailingComments || []).concat(trailingComments);
 				} else {
 					for (const targetNodeId of this.markedForDeletion) {
 						try {

tests/arborist.test.js

@@ -111,4 +111,25 @@ describe('Arborist tests', () => {
 		arborist.applyChanges();
 		assert.equal(arborist.script, code, 'Invalid changes were applied.');
 	});
+	it(`Verify comments aren't duplicated when replacing the root node`, () => {
+		const code = `//comment1\nconst a = 1, b = 2;`;
+		const expected = `//comment1\nconst a = 1;\nconst b = 2;`;
+		const arb = new Arborist(code);
+		const decls = [];
+		arb.ast.forEach(n => {
+			if (n.type === 'VariableDeclarator') {
+				decls.push({
+					type: 'VariableDeclaration',
+					kind: 'const',
+					declarations: [n],
+				});
+			}
+		});
+		arb.markNode(arb.ast[0], {
+			...arb.ast[0],
+			body: decls,
+		});
+		arb.applyChanges();
+		assert.equal(arb.script, expected);
+	});
 });