support minify() output as AST (#1878)

- `options.output.ast` (default `false`)
- `options.output.code` (default `true`)

bin/uglifyjs

@@ -212,7 +212,14 @@ function run() {
         fatal("ERROR: " + ex.message);
     }
     if (program.output == "spidermonkey") {
-        console.log(JSON.stringify(UglifyJS.parse(result.code).to_mozilla_ast(), null, 2));
+        console.log(JSON.stringify(UglifyJS.minify(result.code, {
+            compress: false,
+            mangle: false,
+            output: {
+                ast: true,
+                code: false
+            }
+        }).ast.to_mozilla_ast(), null, 2));
     } else if (program.output) {
         fs.writeFileSync(program.output, result.code);
         if (result.map) {
@@ -278,9 +285,17 @@ function parse_js(flag, constants) {
     return function(value, options) {
         options = options || {};
         try {
-            UglifyJS.parse(value, {
+            UglifyJS.minify(value, {
+                parse: {
                     expression: true
-            }).walk(new UglifyJS.TreeWalker(function(node) {
+                },
+                compress: false,
+                mangle: false,
+                output: {
+                    ast: true,
+                    code: false
+                }
+            }).ast.walk(new UglifyJS.TreeWalker(function(node) {
                 if (node instanceof UglifyJS.AST_Assign) {
                     var name = node.left.print_to_string();
                     var value = node.right;

lib/minify.js

@@ -108,6 +108,11 @@ function minify(files, options) {
                 toplevel = mangle_properties(toplevel, options.mangle.properties);
             }
         }
+        var result = {};
+        if (options.output.ast) {
+            result.ast = toplevel;
+        }
+        if (!HOP(options.output, "code") || options.output.code) {
             if (options.sourceMap) {
                 if (typeof options.sourceMap.content == "string") {
                     options.sourceMap.content = JSON.parse(options.sourceMap.content);
@@ -123,11 +128,11 @@ function minify(files, options) {
                     }
                 }
             }
+            delete options.output.ast;
+            delete options.output.code;
             var stream = OutputStream(options.output);
             toplevel.print(stream);
-        var result = {
-            code: stream.get()
-        };
+            result.code = stream.get();
             if (options.sourceMap) {
                 result.map = options.output.source_map.toString();
                 if (options.sourceMap.url == "inline") {
@@ -136,6 +141,7 @@ function minify(files, options) {
                     result.code += "\n//# sourceMappingURL=" + options.sourceMap.url;
                 }
             }
+        }
         if (warnings.length) {
             result.warnings = warnings;
         }