fix `unsafe` on `evaluate` of `reduce_vars` (#1870)

Determine if variables with non-constant values can escape and be modified.

fixes #1865

1 files changed, 17 insertions, 11 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 63eaacad..919ee20f 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -283,6 +283,14 @@ merge(Compressor.prototype, {
                     if (d.fixed === undefined || !safe_to_read(d)
                         || is_modified(node, 0, is_immutable(node.fixed_value()))) {
                         d.fixed = false;
+                    } else {
+                        var parent = tw.parent();
+                        if (parent instanceof AST_Assign && parent.operator == "=" && node === parent.right
+                            || parent instanceof AST_Call && node !== parent.expression
+                            || parent instanceof AST_Return && node === parent.value && node.scope !== d.scope
+                            || parent instanceof AST_VarDef && node === parent.value) {
+                            d.escaped = true;
+                        }
                     }
                 }
                 if (node instanceof AST_SymbolCatch) {
@@ -482,6 +490,7 @@ merge(Compressor.prototype, {
         }
 
         function reset_def(def) {
+            def.escaped = false;
             if (!def.global || def.orig[0] instanceof AST_SymbolConst || compressor.toplevel(def)) {
                 def.fixed = undefined;
             } else {
@@ -1595,23 +1604,20 @@ merge(Compressor.prototype, {
                 : ev(this.alternative, compressor);
         });
         def(AST_SymbolRef, function(compressor){
-            if (this._evaluating) throw def;
+            if (!compressor.option("reduce_vars") || this._evaluating) throw def;
             this._evaluating = true;
             try {
                 var fixed = this.fixed_value();
-                if (compressor.option("reduce_vars") && fixed) {
-                    if (compressor.option("unsafe")) {
-                        if (!HOP(fixed, "_evaluated")) {
-                            fixed._evaluated = ev(fixed, compressor);
-                        }
-                        return fixed._evaluated;
-                    }
-                    return ev(fixed, compressor);
-                }
+                if (!fixed) throw def;
+                var value = ev(fixed, compressor);
+                if (!HOP(fixed, "_eval")) fixed._eval = function() {
+                    return value;
+                };
+                if (value && typeof value == "object" && this.definition().escaped) throw def;
+                return value;
             } finally {
                 this._evaluating = false;
             }
-            throw def;
         });
         def(AST_PropAccess, function(compressor){
             if (compressor.option("unsafe")) {