Module scope

[fabiosantoscode]

Taking a stab at #2964.

This creates a --module option, that's passed to compress and mangle both, where in compress, strict mode is turned on, and in mangle, it creates a new module-level scope for the file.

This means that top-level symbols, when you use --module, get mangled!

[kzc]

Could you please document the new module option in the minify section of the README?

https://github.com/mishoo/UglifyJS2/blob/harmony/README.md#minify-options
https://github.com/mishoo/UglifyJS2/blob/harmony/README.md#minify-options-structure
https://github.com/mishoo/UglifyJS2/blob/harmony/README.md#compress-options
https://github.com/mishoo/UglifyJS2/blob/harmony/README.md#mangle-options

[kzc]

double quotes please

[kzc]

If compress module is enabled, then compress toplevel can also be enabled.

[kzc]

Rather than creating a new scope all that needs to be done is to set mangle toplevel to true when mangle module is enabled. Then it will be handled automatically.

[kzc]

Once the toplevel changes have been made a new test could be added:

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 };
    }
}

Notice how b can be dropped due to compress toplevel being true.

[kzc]

I suggest using this approach for lib/compress.js and lib/scope.js:

diff --git a/lib/compress.js b/lib/compress.js
index 886a4b5..2654a07 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -73,6 +73,7 @@ function Compressor(options, false_by_default) {
         keep_fnames   : false,
         keep_infinity : false,
         loops         : !false_by_default,
+        module        : false,
         negate_iife   : !false_by_default,
         passes        : 1,
         properties    : !false_by_default,
@@ -130,6 +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),
diff --git a/lib/scope.js b/lib/scope.js
index 09687aa..c94fe89 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -514,9 +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");

[kzc]

The CLI option has an issue:

$ echo 'let foo = 1, bar = 2; export { foo };' | bin/uglifyjs --module -cm
Supported options:
  cache            null
  eval             false
  ie8              false
  keep_classnames  false
  keep_fnames      false
  properties       false
  reserved         []
  safari10         false
  toplevel         false
ERROR: `module` is not a supported option
    at DefaultsError.get

This patch ought to fix it:

--- a/lib/minify.js
+++ b/lib/minify.js
@@ -52,6 +52,7 @@ function minify(files, options) {
             keep_classnames: undefined,
             keep_fnames: false,
             mangle: {},
+            module: false,
             nameCache: null,
             output: {},
             parse: {},
@@ -76,6 +77,7 @@ function minify(files, options) {
         set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
         set_shorthand("keep_classnames", options, [ "compress", "mangle" ]);
         set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
+        set_shorthand("module", options, [ "compress", "mangle" ]);
         set_shorthand("safari10", options, [ "mangle", "output" ]);
         set_shorthand("toplevel", options, [ "compress", "mangle" ]);
         set_shorthand("warnings", options, [ "compress" ]);
@@ -87,6 +89,7 @@ function minify(files, options) {
                 ie8: false,
                 keep_classnames: false,
                 keep_fnames: false,
+                module: false,
                 properties: false,
                 reserved: [],
                 safari10: false,

$ echo 'let foo = 1, bar = 2; export { foo };' | bin/uglifyjs --module -cm
let e=1;export{e as foo};

Would be nice if there was a CLI test for --module in test/mocha/cli.js.

[fabiosantoscode]

Ok, I think this is all :)

[kzc]

+    --module                    Input is an ES6 module. If `compress` or `mangle` is
+                                enabled then the `toplevel` option will be enabled.

[kzc]

Please add:

If `compress` or `mangle` is enabled then the `toplevel` option will be enabled.

[fabiosantoscode]

Done too!

[kzc]

lgtm

[kzc]

We forgot about dealing with the implicit "use strict" for use with modules in lib/parse.js...

$ echo 'with (console) log("\101");' | node_modules/.bin/acorn --module
'with' in strict mode (1:0)

$ echo 'with (console) log("\101");' | bin/uglifyjs --module
with(console)log("A");

I think this should handle it:

diff --git a/lib/minify.js b/lib/minify.js
index ee1d478..e360da0 100644
--- a/lib/minify.js
+++ b/lib/minify.js
@@ -52,6 +52,7 @@ function minify(files, options) {
             keep_classnames: undefined,
             keep_fnames: false,
             mangle: {},
+            module: false,
             nameCache: null,
             output: {},
             parse: {},
@@ -76,6 +77,7 @@ function minify(files, options) {
         set_shorthand("ie8", options, [ "compress", "mangle", "output" ]);
         set_shorthand("keep_classnames", options, [ "compress", "mangle" ]);
         set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
+        set_shorthand("module", options, [ "parse", "compress", "mangle" ]);
         set_shorthand("safari10", options, [ "mangle", "output" ]);
         set_shorthand("toplevel", options, [ "compress", "mangle" ]);
         set_shorthand("warnings", options, [ "compress" ]);
@@ -87,6 +89,7 @@ function minify(files, options) {
                 ie8: false,
                 keep_classnames: false,
                 keep_fnames: false,
+                module: false,
                 properties: false,
                 reserved: [],
                 safari10: false,
diff --git a/lib/parse.js b/lib/parse.js
index d8cc9ac..bd2434a 100644
--- a/lib/parse.js
+++ b/lib/parse.js
@@ -859,6 +859,7 @@ function parse($TEXT, options) {
         expression     : false,
         filename       : null,
         html5_comments : true,
+        module         : false,
         shebang        : true,
         strict         : false,
         toplevel       : null,
@@ -2913,6 +2914,7 @@ function parse($TEXT, options) {
         var start = S.token;
         var body = [];
         S.input.push_directives_stack();
+        if (options.module) S.input.add_directive("use strict");
         while (!is("eof"))
             body.push(statement());
         S.input.pop_directives_stack();

$ echo 'with (console) log("\101");' | bin/uglifyjs
with(console)log("A");

$ echo 'with (console) log("\101");' | bin/uglifyjs --module
Parse error at 0:1,0
with (console) log("\101");
^
ERROR: Strict mode may not include a with statement

Would also need an entry in the README parse options section, and ideally a mocha test to prove it works.

[kzc]

This is obscure, but to get the parse option acorn to work with ES6 modules the following patch is required:

--- a/bin/uglifyjs
+++ b/bin/uglifyjs
@@ -44,6 +44,7 @@ program.option("--ecma <version>", "Specify ECMAScript release: 5, 6, 7 or 8.");
 program.option("--ie8", "Support non-standard Internet Explorer 8.");
 program.option("--keep-classnames", "Do not mangle/drop class names.");
 program.option("--keep-fnames", "Do not mangle/drop function names. Useful for code relying on Function.prototype.name.");
+program.option("--module", "Input is an ES6 module");
 program.option("--name-cache <file>", "File to hold mangled name mappings.");
 program.option("--rename", "Force symbol expansion.");
 program.option("--no-rename", "Disable symbol expansion.");
@@ -66,6 +67,7 @@ if (!program.output && program.sourceMap && program.sourceMap.url != "inline") {
     "compress",
     "ie8",
     "mangle",
+    "module",
     "safari10",
     "sourceMap",
     "toplevel",
@@ -195,7 +197,8 @@ function run() {
                     return require("acorn").parse(files[name], {
                         locations: true,
                         program: toplevel,
-                        sourceFile: name
+                        sourceFile: name,
+                        sourceType: options.module || program.parse.module ? "module" : "script",
                     });
                 });
             } else if (program.parse.spidermonkey) {

With patch:

$ echo 'with (console) log("\101");' | bin/uglifyjs -p acorn
with(console)log("A");

$ echo 'with (console) log("\101");' | bin/uglifyjs -p acorn --module
ERROR: 'with' in strict mode (1:0)

$ echo 'with (console) log("\101");' | bin/uglifyjs -p acorn,module
ERROR: 'with' in strict mode (1:0)

Note: The utility of this particular patch is limited because uglify-es only supports ES5 for the acorn parse option at this time. See #968.

[fabiosantoscode]

Well thought @kzc, done!

[guybedford]

Great to see this happening!

[fabiosantoscode]

Merged under my repo

[guybedford]

@fabiosantoscode have you tried asking @alexlamsl for publish rights to the uglify-es package, as it seems like you're effectively offering to maintain this?

[fabiosantoscode]

I think it has been refused, IIRC.

[guybedford]

@fabiosantoscode could you enable issues on your forked repo and we can discuss further there?

[fabiosantoscode]

@guybedford well spotted! Issues enabled