enable --module by default (#5738)

- fix corner case in `mangle`

Author: alexlamsl

.github/workflows/build.yml

@@ -12,8 +12,8 @@ jobs:
           - '-mb braces'
           - '--ie -c'
           - '-mc'
-          - '-p acorn --toplevel -mco spidermonkey'
-          - '--toplevel -mc passes=3,pure_getters,unsafe'
+          - '-p acorn -mco spidermonkey'
+          - '-mc passes=3,pure_getters,unsafe'
         script:
           - acorn.sh
           - bootstrap.sh

README.md

@@ -119,6 +119,8 @@ a double dash to prevent input files being used as option arguments:
     --keep-fnames               Do not mangle/drop function names.  Useful for
                                 code relying on Function.prototype.name.
     --module                    Process input as ES module (implies --toplevel)
+    --no-module                 Avoid optimizations which may alter runtime behavior
+                                under prior versions of JavaScript.
     --name-cache <file>         File to hold mangled name mappings.
     --self                      Build UglifyJS as a library (implies --wrap UglifyJS)
     --source-map [options]      Enable source map/specify source map options:
@@ -530,9 +532,9 @@ if (result.error) throw result.error;
   - `mangle.properties` (default: `false`) — a subcategory of the mangle option.
     Pass an object to specify custom [mangle property options](#mangle-properties-options).
 
-- `module` (default: `false`) — set to `true` if you wish to process input as
-  ES module, i.e. implicit `"use strict";` and support for top-level `await`,
-  alongside with `toplevel` enabled.
+- `module` (default: `true`) — process input as ES module, i.e. implicit
+  `"use strict";` and support for top-level `await`, alongside with `toplevel`
+  enabled.
 
 - `nameCache` (default: `null`) — pass an empty object `{}` or a previously
   used `nameCache` object if you wish to cache mangled variable and

bin/uglifyjs

@@ -108,7 +108,8 @@ function process_option(name, no_value) {
                 "  --ie                                     Support non-standard Internet Explorer.",
                 "  --keep-fargs                             Do not mangle/drop function arguments.",
                 "  --keep-fnames                            Do not mangle/drop function names. Useful for code relying on Function.prototype.name.",
-                "  --module                                 Process input as ES module (implies --toplevel)",
+                "  --module                                 Process input as ES module (implies --toplevel).",
+                "  --no-module                              Process input with improved JavaScript compatibility.",
                 "  --name-cache <file>                      File to hold mangled name mappings.",
                 "  --rename                                 Force symbol expansion.",
                 "  --no-rename                              Disable symbol expansion.",
@@ -155,7 +156,6 @@ function process_option(name, no_value) {
       case "expression":
       case "ie":
       case "ie8":
-      case "module":
       case "timings":
       case "toplevel":
       case "v8":
@@ -201,6 +201,12 @@ function process_option(name, no_value) {
         if (typeof options.mangle != "object") options.mangle = {};
         options.mangle.properties = parse_js(read_value(), options.mangle.properties);
         break;
+      case "module":
+        options.module = true;
+        break;
+      case "no-module":
+        options.module = false;
+        break;
       case "name-cache":
         nameCache = read_value(true);
         options.nameCache = JSON.parse(read_file(nameCache, "{}"));

lib/compress.js

@@ -10234,22 +10234,24 @@ Compressor.prototype.compress = function(node) {
     }
 
     function varify(self, compressor) {
-        return all(self.definitions, function(defn) {
+        if (all(self.definitions, function(defn) {
             return !defn.name.match_symbol(function(node) {
                 if (node instanceof AST_SymbolDeclaration) return !can_varify(compressor, node);
             }, true);
-        }) ? to_var(self, compressor.find_parent(AST_Scope)) : self;
+        })) return to_var(self, compressor.find_parent(AST_Scope));
     }
 
     OPT(AST_Const, function(self, compressor) {
         if (!compressor.option("varify")) return self;
+        var decl = varify(self, compressor);
+        if (decl) return decl;
         if (can_letify(self, compressor, 0)) return to_let(self);
-        return varify(self, compressor);
+        return self;
     });
 
     OPT(AST_Let, function(self, compressor) {
         if (!compressor.option("varify")) return self;
-        return varify(self, compressor);
+        return varify(self, compressor) || self;
     });
 
     function trim_optional_chain(node, compressor) {

lib/minify.js

@@ -82,14 +82,14 @@ function minify(files, options) {
             keep_fargs: false,
             keep_fnames: false,
             mangle: {},
-            module: false,
+            module: undefined,
             nameCache: null,
             output: {},
             parse: {},
             rename: undefined,
             sourceMap: false,
             timings: false,
-            toplevel: !!(options && !options["expression"] && options["module"]),
+            toplevel: undefined,
             v8: false,
             validate: false,
             warnings: false,
@@ -104,8 +104,10 @@ function minify(files, options) {
         if (options.ie) set_shorthand("ie", options, [ "compress", "mangle", "output", "rename" ]);
         if (options.keep_fargs) set_shorthand("keep_fargs", options, [ "compress", "mangle", "rename" ]);
         if (options.keep_fnames) set_shorthand("keep_fnames", options, [ "compress", "mangle", "rename" ]);
+        if (options.module === undefined && !options.ie) options.module = true;
         if (options.module) set_shorthand("module", options, [ "compress", "parse" ]);
-        if (options.toplevel) set_shorthand("toplevel", options, [ "compress", "mangle", "rename" ]);
+        if (options.toplevel === undefined && !options.expression && options.module) options.toplevel = true;
+        if (options.toplevel !== undefined) set_shorthand("toplevel", options, [ "compress", "mangle", "rename" ]);
         if (options.v8) set_shorthand("v8", options, [ "mangle", "output", "rename" ]);
         if (options.webkit) set_shorthand("webkit", options, [ "compress", "mangle", "output", "rename" ]);
         var quoted_props;

lib/scope.js

@@ -68,9 +68,7 @@ SymbolDef.prototype = {
         var cache = this.global && options.cache && options.cache.props;
         if (cache && cache.has(this.name)) {
             this.mangled_name = cache.get(this.name);
-        } else if (this.unmangleable(options)) {
-            names_in_use(this.scope, options).set(this.name, true);
-        } else {
+        } else if (!this.unmangleable(options)) {
             var def = this.redefined();
             if (def) {
                 this.mangled_name = def.mangled_name || def.name;
@@ -651,8 +649,12 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options) {
                 }, true);
             }
             var to_mangle = node.to_mangle = [];
-            node.variables.each(function(def) {
-                if (!defer_redef(def)) to_mangle.push(def);
+            node.variables.each(function(def, name) {
+                if (def.unmangleable(options)) {
+                    names_in_use(node, options).set(name, true);
+                } else if (!defer_redef(def)) {
+                    to_mangle.push(def);
+                }
             });
             descend();
             if (options.cache && node instanceof AST_Toplevel) {

test/compress/imports.js

@@ -167,6 +167,34 @@ rename_mangle: {
     }
 }
 
+mangle_export_import: {
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        export let o = A;
+        import { p as A } from "foo";
+    }
+    expect: {
+        export let o = p;
+        import { p } from "foo";
+    }
+}
+
+mangle_import_export: {
+    mangle = {
+        toplevel: true,
+    }
+    input: {
+        import { p as A } from "foo";
+        export let o = A;
+    }
+    expect: {
+        import { p } from "foo";
+        export let o = p;
+    }
+}
+
 keep_ref: {
     options = {
         reduce_vars: true,