fix corner case in reduce_vars (#5056)

fixes #5055

lib/compress.js

@@ -526,26 +526,33 @@ merge(Compressor.prototype, {
             tw.fn_scanning = was_scanning;
         }
 
+        function revisit_fn_def(tw, fn) {
+            fn.enclosed.forEach(function(d) {
+                if (fn.variables.get(d.name) === d) return;
+                if (safe_to_read(tw, d)) return;
+                d.single_use = false;
+                var fixed = d.fixed;
+                if (typeof fixed == "function") fixed = fixed();
+                if (fixed instanceof AST_Lambda && HOP(fixed, "safe_ids")) return;
+                d.fixed = false;
+            });
+        }
+
         function mark_fn_def(tw, def, fn) {
             if (!HOP(fn, "safe_ids")) return;
             var marker = fn.safe_ids;
             if (marker === false) return;
-            if (fn.parent_scope.resolve().may_call_this === return_true) return;
+            if (fn.parent_scope.resolve().may_call_this === return_true) {
-            if (marker) {
+                if (member(fn, tw.fn_visited)) revisit_fn_def(tw, fn);
+            } else if (marker) {
                 var visited = member(fn, tw.fn_visited);
                 if (marker === tw.safe_ids) {
                     if (!visited) walk_fn_def(tw, fn);
-                } else if (!visited) {
+                } else if (visited) {
+                    revisit_fn_def(tw, fn);
+                } else {
                     fn.safe_ids = false;
-                } else fn.enclosed.forEach(function(d) {
+                }
-                    if (fn.variables.get(d.name) === d) return;
-                    if (safe_to_read(tw, d)) return;
-                    d.single_use = false;
-                    var fixed = d.fixed;
-                    if (typeof fixed == "function") fixed = fixed();
-                    if (fixed instanceof AST_Lambda && HOP(fixed, "safe_ids")) return;
-                    d.fixed = false;
-                });
             } else if (tw.fn_scanning && tw.fn_scanning !== def.scope.resolve()) {
                 fn.safe_ids = false;
             } else {

test/compress/reduce_vars.js

@@ -7725,3 +7725,49 @@ issue_5050: {
         "3",
     ]
 }
+
+issue_5055_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "PASS";
+        function f() {
+            console.log(a || "FAIL");
+        }
+        f(0 && (a = 0)(f(this)));
+    }
+    expect: {
+        var a = "PASS";
+        function f() {
+            console.log(a || "FAIL");
+        }
+        f(0);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5055_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        function f() {
+            console.log(a || "FAIL");
+        }
+        f(0 && (a = 0)(f(this)));
+    }
+    expect: {
+        var a = "PASS";
+        function f() {
+            console.log(a || "FAIL");
+        }
+        f(0 && (a = 0)(f()));
+    }
+    expect_stdout: "PASS"
+}