fix corner case in booleans (#5887)

fixes #5885

Author: alexlamsl

lib/compress.js

@@ -12119,7 +12119,11 @@ Compressor.prototype.compress = function(node) {
                 var exprs = [];
                 if (self.left.evaluate(compressor) instanceof AST_Node) exprs.push(self.left);
                 if (self.right.evaluate(compressor) instanceof AST_Node) exprs.push(self.right);
-                if (exprs.length < 2) {
+                switch (exprs.length) {
+                  case 0:
+                    return make_node(AST_True, self).optimize(compressor);
+                  case 1:
+                    exprs[0] = exprs[0].clone();
                     exprs.push(make_node(AST_True, self));
                     return make_sequence(self, exprs).optimize(compressor);
                 }

test/compress/functions.js

@@ -8968,3 +8968,32 @@ issue_5851_2: {
         "foo",
     ]
 }
+
+issue_5885: {
+    options = {
+        booleans: true,
+        evaluate: true,
+        inline: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a;
+        f();
+        function f() {
+            return ++a + "foo";
+        }
+        console.log(a = f());
+    }
+    expect: {
+        var a;
+        f();
+        function f() {
+            return ++a + "foo";
+        }
+        console.log(a = f());
+    }
+    expect_stdout: "NaNfoo"
+}