fix corner case in reduce_vars (#5731)

fixes #5730

lib/compress.js

@@ -1441,11 +1441,13 @@ Compressor.prototype.compress = function(node) {
                 break;
             }
             if (!ref.fixed) ref.fixed = d.fixed === 0 ? fixed : d.fixed;
-            var parent;
-            if (value instanceof AST_Lambda
-                && !((parent = tw.parent()) instanceof AST_Call && parent.expression === ref)) {
-                mark_fn_def(tw, d, value);
+            if (!value && fixed) value = fixed instanceof AST_Node ? fixed : fixed();
+            if (!(value instanceof AST_Lambda)) return;
+            if (d.fixed) {
+                var parent = tw.parent();
+                if (parent instanceof AST_Call && parent.expression === ref) return;
             }
+            mark_fn_def(tw, d, value);
         });
         def(AST_Template, function(tw, descend) {
             var node = this;

test/compress/reduce_vars.js

@@ -8062,3 +8062,89 @@ issue_5716_5: {
     }
     expect_stdout: "42"
 }
+
+issue_5730_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        L: {
+            var f = function() {
+                console.log(a);
+            };
+        }
+        f();
+        a++;
+    }
+    expect: {
+        var a = "PASS";
+        var f = function() {
+            console.log(a);
+        };
+        f();
+        a++;
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5730_2: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        try {
+            var f = function() {
+                console.log(a);
+            };
+        } finally {}
+        f();
+        a++;
+    }
+    expect: {
+        var a = "PASS";
+        try {
+            var f = function() {
+                console.log(a);
+            };
+        } finally {}
+        f();
+        a++;
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5730_3: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var f, a = "PASS";
+        L: {
+            f = function() {
+                console.log(a);
+            };
+        }
+        f();
+        a++;
+    }
+    expect: {
+        var f, a = "PASS";
+        f = function() {
+            console.log(a);
+        };
+        f();
+        a++;
+    }
+    expect_stdout: "PASS"
+}