fix corner case in collapse_vars (#5928)

fixes #5927

Author: alexlamsl

lib/compress.js

@@ -2734,7 +2734,7 @@ Compressor.prototype.compress = function(node) {
                 if (node instanceof AST_Function) {
                     return compressor.option("ie") && node.name && lvalues.has(node.name.name);
                 }
-                if (node instanceof AST_ObjectIdentity) return symbol_in_lvalues(node, parent);
+                if (node instanceof AST_ObjectIdentity) return symbol_in_lvalues(node);
                 if (node instanceof AST_PropAccess) {
                     var exp = node.expression;
                     if (compressor.option("unsafe")) {
@@ -2751,8 +2751,9 @@ Compressor.prototype.compress = function(node) {
                 }
                 if (node instanceof AST_Spread) return true;
                 if (node instanceof AST_SymbolRef) {
+                    var assign_direct = symbol_in_lvalues(node);
                     if (is_undeclared_ref(node) && node.is_declared(compressor)) return false;
-                    if (symbol_in_lvalues(node, parent)) return !is_direct_assignment(node, parent);
+                    if (assign_direct) return !is_direct_assignment(node, parent);
                     if (side_effects && may_modify(node)) return true;
                     var def = node.definition();
                     return (in_try || def.scope.resolve() !== scope) && !can_drop_symbol(node);
@@ -3618,7 +3619,7 @@ Compressor.prototype.compress = function(node) {
                 return true;
             }
 
-            function symbol_in_lvalues(sym, parent) {
+            function symbol_in_lvalues(sym) {
                 var lvalue = lvalues.get(sym.name);
                 if (!lvalue || all(lvalue, function(lhs) {
                     return !lhs;

test/compress/properties.js

@@ -1827,3 +1827,27 @@ issue_5682_sub_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5927: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        pure_getters: "strict",
+        reduce_vars: true,
+    }
+    input: {
+        A = {};
+        while (console.log("PASS"));
+        A.p;
+        A.q = 42;
+        A.q.r = 42;
+    }
+    expect: {
+        A = {};
+        while (console.log("PASS"));
+        A.p;
+        A.q = 42;
+        A.q.r = 42;
+    }
+    expect_stdout: "PASS"
+}