fix corner case in `assignments` (#3407)

fixes #3406

1 files changed, 14 insertions, 15 deletions

diff --git a/lib/compress.js b/lib/compress.js
index b63c0512..638fb7c0 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -5395,7 +5395,8 @@ merge(Compressor.prototype, {
 
     OPT(AST_UnaryPrefix, function(self, compressor) {
         var e = self.expression;
-        if (self.operator == "delete"
+        if (compressor.option("evaluate")
+            && self.operator == "delete"
             && !(e instanceof AST_SymbolRef
                 || e instanceof AST_PropAccess
                 || is_identifier_atom(e))) {
@@ -6254,6 +6255,7 @@ merge(Compressor.prototype, {
         if (compressor.option("dead_code")
             && self.left instanceof AST_SymbolRef
             && (def = self.left.definition()).scope === compressor.find_parent(AST_Lambda)) {
+            if (self.left.is_immutable()) return strip_assignment();
             var level = 0, node, parent = self;
             do {
                 node = parent;
@@ -6261,16 +6263,12 @@ merge(Compressor.prototype, {
                 if (parent instanceof AST_Exit) {
                     if (in_try(level, parent)) break;
                     if (is_reachable(def.scope, [ def ])) break;
-                    if (self.operator == "=") return self.right.optimize(compressor);
                     def.fixed = false;
-                    return make_node(AST_Binary, self, {
-                        operator: self.operator.slice(0, -1),
-                        left: self.left,
-                        right: self.right
-                    }).optimize(compressor);
+                    return strip_assignment();
                 }
             } while (parent instanceof AST_Binary && parent.right === node
-                || parent instanceof AST_Sequence && parent.tail_node() === node);
+                || parent instanceof AST_Sequence && parent.tail_node() === node
+                || parent instanceof AST_UnaryPrefix);
         }
         self = self.lift_sequences(compressor);
         if (!compressor.option("assignments")) return self;
@@ -6302,13 +6300,6 @@ merge(Compressor.prototype, {
                 expression: self.left
             });
         }
-        if (!compressor.option("ie8") && self.left instanceof AST_Symbol && self.left.is_immutable()) {
-            return (self.operator == "=" ? self.right : make_node(AST_Binary, self, {
-                operator: self.operator.slice(0, -1),
-                left: self.left,
-                right: self.right
-            })).optimize(compressor);
-        }
         return self;
 
         function in_try(level, node) {
@@ -6325,6 +6316,14 @@ merge(Compressor.prototype, {
                 }
             }
         }
+
+        function strip_assignment() {
+            return (self.operator != "=" ? make_node(AST_Binary, self, {
+                operator: self.operator.slice(0, -1),
+                left: self.left,
+                right: self.right
+            }) : maintain_this_binding(compressor, compressor.parent(), self, self.right)).optimize(compressor);
+        }
     });
 
     OPT(AST_Conditional, function(self, compressor) {