fix corner case in assignments (#3376)

fixes #3375

lib/ast.js

@@ -773,7 +773,7 @@ var AST_Label = DEFNODE("Label", "references", {
     }
 }, AST_Symbol);
 
-var AST_SymbolRef = DEFNODE("SymbolRef", null, {
+var AST_SymbolRef = DEFNODE("SymbolRef", "fixed", {
     $documentation: "Reference to some symbol (not definition/declaration)",
 }, AST_Symbol);
 

lib/compress.js

@@ -551,6 +551,7 @@ merge(Compressor.prototype, {
                 mark_assignment_to_arguments(sym);
                 return;
             }
+            if (sym.fixed) delete sym.fixed;
             var d = sym.definition();
             var safe = safe_to_assign(tw, d, sym.scope, node.right);
             d.assignments++;
@@ -560,7 +561,7 @@ merge(Compressor.prototype, {
             var value = eq ? node.right : node;
             if (is_modified(compressor, tw, node, value, 0)) return;
             if (!eq) d.chained = true;
-            d.fixed = eq ? function() {
+            sym.fixed = d.fixed = eq ? function() {
                 return node.right;
             } : function() {
                 return make_node(AST_Binary, node, {
@@ -574,7 +575,7 @@ merge(Compressor.prototype, {
             mark(tw, d, false);
             node.right.walk(tw);
             mark(tw, d, true);
-            mark_escaped(tw, d, sym.scope, node, value, 0, 1);
+            if (eq) mark_escaped(tw, d, sym.scope, node, value, 0, 1);
             return true;
         });
         def(AST_Binary, function(tw) {
@@ -730,6 +731,7 @@ merge(Compressor.prototype, {
             this.definition().fixed = false;
         });
         def(AST_SymbolRef, function(tw, descend, compressor) {
+            if (this.fixed) delete this.fixed;
             var d = this.definition();
             d.references.push(this);
             if (d.references.length == 1
@@ -797,13 +799,14 @@ merge(Compressor.prototype, {
                 mark_assignment_to_arguments(exp);
                 return;
             }
+            if (exp.fixed) delete exp.fixed;
             var d = exp.definition();
             var safe = safe_to_assign(tw, d, exp.scope, true);
             d.assignments++;
             var fixed = d.fixed;
             if (!fixed) return;
             d.chained = true;
-            d.fixed = function() {
+            exp.fixed = d.fixed = function() {
                 return make_node(AST_Binary, node, {
                     operator: node.operator.slice(0, -1),
                     left: make_node(AST_UnaryPrefix, node, {
@@ -874,10 +877,11 @@ merge(Compressor.prototype, {
         this.walk(tw);
     });
 
-    AST_Symbol.DEFMETHOD("fixed_value", function() {
+    AST_Symbol.DEFMETHOD("fixed_value", function(final) {
         var fixed = this.definition().fixed;
-        if (!fixed || fixed instanceof AST_Node) return fixed;
-        return fixed();
+        if (!fixed) return fixed;
+        if (!final && this.fixed) fixed = this.fixed;
+        return fixed instanceof AST_Node ? fixed : fixed();
     });
 
     AST_SymbolRef.DEFMETHOD("is_immutable", function() {
@@ -3514,7 +3518,7 @@ merge(Compressor.prototype, {
                         if (def.value.has_side_effects(compressor)) {
                             def.value.walk(tw);
                         }
-                        if (!node_def.chained && def.name.fixed_value() === def.value) {
+                        if (!node_def.chained && def.name.fixed_value(true) === def.value) {
                             fixed_ids[node_def.id] = def;
                         }
                     }
@@ -3785,7 +3789,7 @@ merge(Compressor.prototype, {
                 if (node instanceof AST_Assign) {
                     node.right.walk(tw);
                     if (node.left === sym) {
-                        if (!node_def.chained && sym.fixed_value() === node.right) {
+                        if (!node_def.chained && sym.fixed_value(true) === node.right) {
                             fixed_ids[node_def.id] = node;
                         }
                         if (!node.write_only) {

test/compress/assignment.js

@@ -289,3 +289,25 @@ increment_decrement_2: {
     }
     expect_stdout: "42"
 }
+
+issue_3375: {
+    options = {
+        assignments: true,
+        reduce_vars: true,
+    }
+    input: {
+        console.log(typeof function(b) {
+            var a = b += 1;
+            --b;
+            return a;
+        }("object"));
+    }
+    expect: {
+        console.log(typeof function(b) {
+            var a = b += 1;
+            --b;
+            return a;
+        }("object"));
+    }
+    expect_stdout: "string"
+}

test/compress/drop-unused.js

@@ -2005,3 +2005,24 @@ issue_3233: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3375: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var b = 1;
+        var a = c = [], c = --b + ("function" == typeof f && f());
+        var a = c && c[a];
+        console.log(a, b);
+    }
+    expect: {
+        var b = 1;
+        var a = [], c = --b + ("function" == typeof f && f());
+        a = c && c[a];
+        console.log(a, b);
+    }
+    expect_stdout: "0 0"
+}