preserve ast to avoid re-parsing

src/Module.js

@@ -53,7 +53,8 @@ export default class Module {
 		}
 
 		this.comments = [];
-		this.statements = this.parse( ast );
+		this.ast = ast;
+		this.statements = this.parse();
 
 		this.declarations = blank();
 		this.analyse();
@@ -298,13 +299,13 @@ export default class Module {
 		return this.declarations['*'];
 	}
 
-	parse ( ast ) {
+	parse () {
 		// The ast can be supplied programmatically (but usually won't be)
-		if ( !ast ) {
+		if ( !this.ast ) {
 			// Try to extract a list of top-level statements/declarations. If
 			// the parse fails, attach file info and abort
 			try {
-				ast = parse( this.code, {
+				this.ast = parse( this.code, {
 					ecmaVersion: 6,
 					sourceType: 'module',
 					onComment: ( block, text, start, end ) => this.comments.push({ block, text, start, end }),
@@ -318,7 +319,7 @@ export default class Module {
 			}
 		}
 
-		walk( ast, {
+		walk( this.ast, {
 			enter: node => {
 				// eliminate dead branches early
 				if ( node.type === 'IfStatement' ) {
@@ -354,7 +355,7 @@ export default class Module {
 		let lastChar = 0;
 		let commentIndex = 0;
 
-		ast.body.forEach( node => {
+		this.ast.body.forEach( node => {
 			if ( node.type === 'EmptyStatement' ) return;
 
 			if (
@@ -637,6 +638,15 @@ export default class Module {
 		return marked;
 	}
 
+	toJSON () {
+		return {
+			id: this.id,
+			code: this.code,
+			originalCode: this.originalCode,
+			ast: this.ast
+		};
+	}
+
 	trace ( name ) {
 		if ( name in this.declarations ) return this.declarations[ name ];
 		if ( name in this.imports ) {

src/rollup.js

@@ -53,7 +53,7 @@ export function rollup ( options ) {
 		return {
 			imports: bundle.externalModules.map( module => module.id ),
 			exports: keys( bundle.entryModule.exports ),
-			modules: bundle.orderedModules.map( ( { id, code, originalCode } ) => ( { id, code, originalCode } ) ),
+			modules: bundle.orderedModules.map( module => module.toJSON() ),
 
 			generate: options => bundle.render( options ),
 			write: options => {