fix corner case in booleans (#5470)

fixes #5469

lib/compress.js

@@ -9174,11 +9174,12 @@ Compressor.prototype.compress = function(node) {
             child = parent;
             parent = compressor.parent(level++);
             if (parent instanceof AST_Binary) {
-                var op = parent.operator;
+                switch (child) {
-                if (!lazy_op[op]) return;
+                  case parent.left:
-                var left = parent.left;
+                    if (lazy_op[parent.operator]) continue;
-                if (left === child) continue;
+                    break;
-                if (match(left)) switch (op) {
+                  case parent.right:
+                    if (match(parent.left)) switch (parent.operator) {
                       case "&&":
                         node[negated ? "falsy" : "truthy"] = true;
                         break;
@@ -9187,6 +9188,8 @@ Compressor.prototype.compress = function(node) {
                         node[negated ? "truthy" : "falsy"] = true;
                         break;
                     }
+                    break;
+                }
             } else if (parent instanceof AST_Conditional) {
                 var cond = parent.condition;
                 if (cond === child) continue;

test/compress/booleans.js

@@ -762,3 +762,27 @@ issue_5228: {
     }
     expect_stdout: "true"
 }
+
+issue_5469: {
+    options = {
+        assignments: true,
+        booleans: true,
+        conditionals: true,
+        dead_code: true,
+        evaluate: true,
+        pure_getters: "strict",
+        side_effects: true,
+    }
+    input: {
+        console.log(function f(a) {
+            a && 42[a = A && null];
+        }());
+    }
+    expect: {
+        console.log(function f(a) {
+            a && A,
+            0;
+        }());
+    }
+    expect_stdout: "undefined"
+}