suggestions from @kzc

lib/compress.js

@@ -131,6 +131,10 @@ function Compressor(options, false_by_default) {
             return top_retain.indexOf(def.name) >= 0;
         };
     }
+    if (this.options["module"]) {
+        this.directives["use strict"] = true;
+        this.options["toplevel"] = true;
+    }
     var toplevel = this.options["toplevel"];
     this.toplevel = typeof toplevel == "string" ? {
         funcs: /funcs/.test(toplevel),
@@ -139,9 +143,6 @@ function Compressor(options, false_by_default) {
         funcs: toplevel,
         vars: toplevel
     };
-    if (this.options['module']) {
-        this.directives['use strict'] = true;
-    }
     var sequences = this.options["sequences"];
     this.sequences_limit = sequences == 1 ? 800 : sequences | 0;
     this.warnings_produced = {};

lib/minify.js

@@ -89,6 +89,7 @@ function minify(files, options) {
                 ie8: false,
                 keep_classnames: false,
                 keep_fnames: false,
+                module: false,
                 properties: false,
                 reserved: [],
                 safari10: false,

lib/scope.js

@@ -110,11 +110,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
 
     // pass 1: setup scope chaining and handle definitions
     var self = this;
-    var scope = null;
+    var scope = self.parent_scope = null;
-    if (options.module) {
-        scope = new AST_Scope(self);
-    }
-    self.parent_scope = scope;
     var labels = new Dictionary();
     var defun = null;
     var in_destructuring = null;
@@ -518,9 +514,13 @@ AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options) {
         ie8         : false,
         keep_classnames: false,
         keep_fnames : false,
+        module      : false,
         reserved    : [],
         toplevel    : false,
     });
+    if (options["module"]) {
+        options.toplevel = true;
+    }
     if (!Array.isArray(options.reserved)) options.reserved = [];
     // Never mangle arguments
     push_uniq(options.reserved, "arguments");

test/compress/harmony.js

@@ -1629,3 +1629,24 @@ module_mangle_scope: {
         let e = 10;
     }
 }
+
+module_enabled: {
+    options = {
+        module: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    mangle = {
+        module: true,
+    }
+    input: {
+        let apple = 10, b = 20;
+        console.log(apple++, b, apple++);
+        export { apple };
+    }
+    expect: {
+        let o = 10;
+        console.log(o++, 20, o++);
+        export { o as apple };
+    }
+}

test/mocha/cli.js

@@ -734,6 +734,15 @@ describe("bin/uglifyjs", function () {
             done();
         });
     });
+    it("Should mangle toplevel names with the --module option", function(done) {
+        var command = uglifyjscmd + " test/input/module/input.js --module -mc";
+        exec(command, function (err, stdout, stderr) {
+            if (err) throw err;
+
+            assert.strictEqual(stdout, "let e=1;export{e as foo};\n")
+            done();
+        });
+    });
     it("Should fail with --define a-b", function(done) {
         var command = uglifyjscmd + " test/input/issue-505/input.js --define a-b";
         exec(command, function (err, stdout, stderr) {