fix corner cases in collapse_vars (#4978)

fixes #4977

lib/compress.js

@@ -652,6 +652,7 @@ merge(Compressor.prototype, {
                 d.escaped.push(parent);
                 if (depth > 1 && !(value && value.is_constant_expression(scope))) depth = 1;
                 if (!d.escaped.depth || d.escaped.depth > depth) d.escaped.depth = depth;
+                if (d.scope !== scope) d.escaped.cross_scope = true;
                 return;
             } else if (value_in_use(node, parent)) {
                 mark_escaped(tw, d, scope, parent, parent, level + 1, depth);
@@ -1973,6 +1974,7 @@ merge(Compressor.prototype, {
                     var read_toplevel = false;
                     var modify_toplevel = false;
                     // Locate symbols which may execute code outside of scanning range
+                    var well_defined = true;
                     var lvalues = get_lvalues(candidate);
                     var lhs_local = is_lhs_local(lhs);
                     var rvalue = get_rvalue(candidate);
@@ -2173,11 +2175,18 @@ merge(Compressor.prototype, {
                 }
                 if (node instanceof AST_ObjectIdentity) return symbol_in_lvalues(node, parent);
                 if (node instanceof AST_PropAccess) {
+                    if (side_effects) return true;
                     var exp = node.expression;
-                    return side_effects
-                        || exp instanceof AST_SymbolRef && is_arguments(exp.definition())
-                        || !value_def && (in_try || !lhs_local)
-                            && !node.optional && exp.may_throw_on_access(compressor);
+                    if (exp instanceof AST_SymbolRef && is_arguments(exp.definition())) return true;
+                    if (compressor.option("unsafe")) {
+                        if (is_undeclared_ref(exp) && global_names[exp.name]) return false;
+                        if (is_static_fn(exp)) return false;
+                    }
+                    if (!well_defined) return true;
+                    if (value_def) return false;
+                    if (!in_try && lhs_local) return false;
+                    if (node.optional) return false;
+                    return exp.may_throw_on_access(compressor);
                 }
                 if (node instanceof AST_Spread) return true;
                 if (node instanceof AST_SymbolRef) {
@@ -2537,8 +2546,7 @@ merge(Compressor.prototype, {
                 }
                 if (parent instanceof AST_PropAccess) {
                     var exp = parent.expression;
-                    if (exp === node) return find_stop_value(parent, level + 1);
-                    return find_stop_expr(exp, find_stop_value, node, parent, level);
+                    return exp === node ? find_stop_value(parent, level + 1) : node;
                 }
                 if (parent instanceof AST_Sequence) {
                     return (parent.tail_node() === node ? find_stop_value : find_stop_unused)(parent, level + 1);
@@ -2770,20 +2778,31 @@ merge(Compressor.prototype, {
 
             function get_lvalues(expr) {
                 var lvalues = new Dictionary();
-                if (expr instanceof AST_VarDef) lvalues.add(expr.name.name, lhs);
+                if (expr instanceof AST_VarDef) {
+                    if (!expr.name.definition().fixed) well_defined = false;
+                    lvalues.add(expr.name.name, lhs);
+                }
                 var find_arguments = scope.uses_arguments && !compressor.has_directive("use strict");
                 var scan_toplevel = scope instanceof AST_Toplevel;
                 var tw = new TreeWalker(function(node) {
                     var value;
                     if (node instanceof AST_SymbolRef) {
-                        value = node.fixed_value() || node;
+                        value = node.fixed_value();
+                        if (!value) {
+                            value = node;
+                            var def = node.definition();
+                            if (!def.undeclared && (def.assignments || !def.escaped || def.escaped.cross_scope)) {
+                                well_defined = false;
+                            }
+                        }
                     } else if (node instanceof AST_ObjectIdentity) {
                         value = node;
                     }
                     if (value) lvalues.add(node.name, is_modified(compressor, tw, node, value, 0));
                     if (find_arguments && node instanceof AST_Sub) {
                         scope.each_argname(function(argname) {
                             if (!compressor.option("reduce_vars") || argname.definition().assignments) {
+                                if (!argname.definition().fixed) well_defined = false;
                                 lvalues.add(argname.name, true);
                             }
                         });
@@ -4290,6 +4309,14 @@ merge(Compressor.prototype, {
         ],
     });
 
+    function is_static_fn(node) {
+        if (!(node instanceof AST_Dot)) return false;
+        var expr = node.expression;
+        if (!is_undeclared_ref(expr)) return false;
+        var static_fn = static_fns[expr.name];
+        return static_fn && (static_fn[node.property] || expr.name == "Math" && node.property == "random");
+    }
+
     // Accomodate when compress option evaluate=false
     // as well as the common constant expressions !0 and -1
     (function(def) {
@@ -4912,11 +4939,7 @@ merge(Compressor.prototype, {
                 if (global_pure_fns[expr.name]) return true;
                 if (this instanceof AST_New && global_pure_constructors[expr.name]) return true;
             }
-            if (expr instanceof AST_Dot && is_undeclared_ref(expr.expression)) {
-                var static_fn = static_fns[expr.expression.name];
-                return static_fn && (static_fn[expr.property]
-                    || expr.expression.name == "Math" && expr.property == "random");
-            }
+            if (is_static_fn(expr)) return true;
         }
         return compressor.option("annotations") && this.pure || !compressor.pure_funcs(this);
     });

test/compress/annotations.js

@@ -256,6 +256,7 @@ issue_3858: {
         collapse_vars: true,
         inline: true,
         keep_fargs: false,
+        unsafe: true,
         unused: true,
     }
     input: {

test/compress/arrows.js

@@ -421,6 +421,7 @@ collapse_value: {
         arrows: true,
         collapse_vars: true,
         keep_fargs: false,
+        unsafe: true,
         unused: true,
     }
     input: {

test/compress/classes.js

@@ -632,6 +632,7 @@ collapse_non_strict: {
 collapse_rhs: {
     options = {
         collapse_vars: true,
+        unsafe: true,
     }
     input: {
         "use strict";