enable unsafe for test/ufuzz.js (#2819)

- introduce `unsafe_undefined`
- safer `.toString()` compression

Miscellaneous
- rename `unsafe_Function`

README.md

@@ -737,7 +737,7 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   comparison are switching. Compression only works if both `comparisons` and
   `unsafe_comps` are both set to true.
 
-- `unsafe_Func` (default: `false`) -- compress and mangle `Function(args, code)`
+- `unsafe_Function` (default: `false`) -- compress and mangle `Function(args, code)`
   when both `args` and `code` are string literals.
 
 - `unsafe_math` (default: `false`) -- optimize numerical expressions like
@@ -749,6 +749,10 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 - `unsafe_regexp` (default: `false`) -- enable substitutions of variables with
   `RegExp` values the same way as if they are constants.
 
+- `unsafe_undefined` (default: `false`) -- substitute `void 0` if there is a
+  variable named `undefined` in scope (variable name will be mangled, typically
+  reduced to a single character)
+
 - `unused` (default: `true`) -- drop unreferenced functions and variables (simple
   direct variable assignments do not count as references unless set to `"keep_assign"`)
 
@@ -922,9 +926,6 @@ when this flag is on:
 - `new Object()` → `{}`
 - `String(exp)` or `exp.toString()` → `"" + exp`
 - `new Object/RegExp/Function/Error/Array (...)` → we discard the `new`
-- `void 0` → `undefined` (if there is a variable named "undefined" in
-  scope; we do it because the variable name will be mangled, typically
-  reduced to a single character)
 
 ### Conditional compilation
 

lib/compress.js

@@ -84,10 +84,11 @@ function Compressor(options, false_by_default) {
         typeofs       : !false_by_default,
         unsafe        : false,
         unsafe_comps  : false,
-        unsafe_Func   : false,
+        unsafe_Function: false,
         unsafe_math   : false,
         unsafe_proto  : false,
         unsafe_regexp : false,
+        unsafe_undefined: false,
         unused        : !false_by_default,
         warnings      : false,
     }, true);
@@ -4100,11 +4101,13 @@ merge(Compressor.prototype, {
                 break;
             } else if (exp instanceof AST_Dot) switch(exp.property) {
               case "toString":
-                if (self.args.length == 0) return make_node(AST_Binary, self, {
-                    left: make_node(AST_String, self, { value: "" }),
-                    operator: "+",
-                    right: exp.expression
-                }).optimize(compressor);
+                if (self.args.length == 0 && !exp.expression.may_throw_on_access(compressor)) {
+                    return make_node(AST_Binary, self, {
+                        left: make_node(AST_String, self, { value: "" }),
+                        operator: "+",
+                        right: exp.expression
+                    }).optimize(compressor);
+                }
                 break;
               case "join":
                 if (exp.expression instanceof AST_Array) EXIT: {
@@ -4212,7 +4215,7 @@ merge(Compressor.prototype, {
                 break;
             }
         }
-        if (compressor.option("unsafe_Func")
+        if (compressor.option("unsafe_Function")
             && is_undeclared_ref(exp)
             && exp.name == "Function") {
             // new Function() => function(){}
@@ -5220,7 +5223,7 @@ merge(Compressor.prototype, {
     }
 
     OPT(AST_Undefined, function(self, compressor){
-        if (compressor.option("unsafe")) {
+        if (compressor.option("unsafe_undefined")) {
             var undef = find_variable(compressor, "undefined");
             if (undef) {
                 var ref = make_node(AST_SymbolRef, self, {

test/compress/functions.js

@@ -218,7 +218,7 @@ issue_203: {
     options = {
         keep_fargs: false,
         side_effects: true,
-        unsafe_Func: true,
+        unsafe_Function: true,
         unused: true,
     }
     input: {

test/compress/issue-1443.js

@@ -4,7 +4,7 @@ unsafe_undefined: {
     options = {
         conditionals: true,
         if_return: true,
-        unsafe: true
+        unsafe_undefined: true,
     }
     mangle = {}
     input: {
@@ -30,7 +30,7 @@ keep_fnames: {
     options = {
         conditionals: true,
         if_return: true,
-        unsafe: true
+        unsafe_undefined: true,
     }
     mangle = {
         keep_fnames: true

test/compress/issue-1588.js

@@ -61,7 +61,7 @@ unsafe_undefined: {
     options = {
         conditionals: true,
         if_return: true,
-        unsafe: true,
+        unsafe_undefined: true,
     }
     mangle = {}
     input: {

test/compress/sequences.js

@@ -288,7 +288,7 @@ unsafe_undefined: {
         if_return: true,
         sequences: true,
         side_effects: true,
-        unsafe: true,
+        unsafe_undefined: true,
     }
     input: {
         function f(undefined) {

test/ufuzz.json

@@ -21,7 +21,13 @@
     {
         "compress": {
             "keep_fargs": false,
-            "passes": 100
+            "passes": 1e6,
+            "sequences": 1e6,
+            "unsafe": true,
+            "unsafe_Function": true,
+            "unsafe_math": true,
+            "unsafe_proto": true,
+            "unsafe_regexp": true
         }
     }
 ]