stay safe with constants in IE8- (#1547)

- `undefined` etc. can be redefined at top-level for IE8-, so disable related optimisations
- fixed `--support-ie8` catch mangle bug

README.md

@@ -75,8 +75,6 @@ The available options are:
   --support-ie8                 Use this flag to support Internet Explorer 6/7/8.
                                 Equivalent to setting `screw_ie8: false` in `minify()`
                                 for `compress`, `mangle` and `output` options.
-                                Note: `--support-ie8` may generate incorrect code
-                                for `try`/`catch` in ES5 compliant browsers.
   --expr                        Parse a single expression, rather than a
                                 program (for parsing JSON)
   -p, --prefix                  Skip prefix for original filenames that appear

bin/uglifyjs

@@ -26,7 +26,7 @@ mangling you need to use `-c` and `-m`.\
     .describe("source-map-include-sources", "Pass this flag if you want to include the content of source files in the source map as sourcesContent property.")
     .describe("in-source-map", "Input source map, useful if you're compressing JS that was generated from some other original code.")
     .describe("screw-ie8", "Do not support Internet Explorer 6/7/8. This flag is enabled by default.")
-    .describe("support-ie8", "Support non-standard Internet Explorer 6/7/8 javascript. Note: may generate incorrect code for try/catch in ES5 compliant browsers.")
+    .describe("support-ie8", "Support non-standard Internet Explorer 6/7/8 javascript.")
     .describe("expr", "Parse a single expression, rather than a program (for parsing JSON)")
     .describe("p", "Skip prefix for original filenames that appear in source maps. \
 For example -p 3 will drop 3 directories from file names and ensure they are relative paths. \

lib/compress.js

@@ -3348,7 +3348,9 @@ merge(Compressor.prototype, {
             return def;
         }
         // testing against !self.scope.uses_with first is an optimization
-        if (self.undeclared() && !isLHS(self, compressor.parent())
+        if (compressor.option("screw_ie8")
+            && self.undeclared()
+            && !isLHS(self, compressor.parent())
             && (!self.scope.uses_with || !compressor.find_parent(AST_With))) {
             switch (self.name) {
               case "undefined":

lib/scope.js

@@ -97,7 +97,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
     var labels = new Dictionary();
     var defun = null;
     var tw = new TreeWalker(function(node, descend){
-        if (options.screw_ie8 && node instanceof AST_Catch) {
+        if (node instanceof AST_Catch) {
             var save_scope = scope;
             scope = new AST_Scope(node);
             scope.init_scope_vars();
@@ -158,8 +158,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
             def.init = tw.parent().value;
         }
         else if (node instanceof AST_SymbolCatch) {
-            (options.screw_ie8 ? scope : defun)
-                .def_variable(node);
+            scope.def_variable(node);
         }
         else if (node instanceof AST_LabelRef) {
             var sym = labels.get(node.name);
@@ -209,6 +208,23 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
     });
     self.walk(tw);
 
+    // pass 3: fix up any scoping issue with IE8
+    if (!options.screw_ie8) {
+        self.walk(new TreeWalker(function(node, descend) {
+            if (node instanceof AST_SymbolCatch) {
+                var name = node.name;
+                var scope = node.thedef.scope.parent_scope;
+                var def = scope.find_variable(name) || self.globals.get(name) || scope.def_variable(node);
+                node.thedef.references.forEach(function(ref) {
+                    ref.thedef = def;
+                    ref.reference(options);
+                });
+                node.thedef = def;
+                return true;
+            }
+        }));
+    }
+
     if (options.cache) {
         this.cname = options.cache.cname;
     }

test/compress/screw-ie8.js

@@ -17,6 +17,26 @@ dont_screw: {
     expect_exact: 'f("\\x0B");';
 }
 
+do_screw_constants: {
+    options = {
+        screw_ie8: true,
+    }
+    input: {
+        f(undefined, Infinity);
+    }
+    expect_exact: "f(void 0,1/0);"
+}
+
+dont_screw_constants: {
+    options = {
+        screw_ie8: false,
+    }
+    input: {
+        f(undefined, Infinity);
+    }
+    expect_exact: "f(undefined,Infinity);"
+}
+
 do_screw_try_catch: {
     options = { screw_ie8: true };
     mangle = { screw_ie8: true };
@@ -46,8 +66,6 @@ do_screw_try_catch: {
 }
 
 dont_screw_try_catch: {
-    // This test is known to generate incorrect code for screw_ie8=false.
-    // Update expected result in the event this bug is ever fixed.
     options = { screw_ie8: false };
     mangle = { screw_ie8: false };
     beautify = { screw_ie8: false };
@@ -64,11 +82,11 @@ dont_screw_try_catch: {
     }
     expect: {
         bad = function(n){
-            return function(n){
+            return function(t){
                 try{
-                    t()
-                } catch(t) {
-                    n(t)
+                    n()
+                } catch(n) {
+                    t(n)
                 }
             }
         };
@@ -104,8 +122,6 @@ do_screw_try_catch_undefined: {
 }
 
 dont_screw_try_catch_undefined: {
-    // This test is known to generate incorrect code for screw_ie8=false.
-    // Update expected result in the event this bug is ever fixed.
     options = { screw_ie8: false };
     mangle = { screw_ie8: false };
     beautify = { screw_ie8: false };
@@ -121,14 +137,14 @@ dont_screw_try_catch_undefined: {
         };
     }
     expect: {
-        function a(o){
+        function a(n){
             try{
                 throw "Stuff"
-            } catch (n) {
-                console.log("caught: "+n)
+            } catch (undefined) {
+                console.log("caught: " + undefined)
             }
-            console.log("undefined is " + n);
-            return o === n
+            console.log("undefined is " + undefined);
+            return n === undefined
         }
     }
 }