fix corner case in join_vars (#5746)

fixes #5745

lib/compress.js

@@ -10255,8 +10255,18 @@ Compressor.prototype.compress = function(node) {
             return all(this.definitions, function(defn) {
                 return !defn.name.match_symbol(function(node) {
                     if (!(node instanceof AST_SymbolDeclaration)) return false;
-                    if (node.definition().first_decl !== node) return true;
-                    return !safe_from_tdz(compressor, node);
+                    var def = node.definition();
+                    if (def.first_decl !== node) return true;
+                    if (!safe_from_tdz(compressor, node)) return true;
+                    var defn_scope = node.scope;
+                    if (defn_scope instanceof AST_Scope) return false;
+                    return !all(def.references, function(ref) {
+                        var scope = ref.scope;
+                        do {
+                            if (scope === defn_scope) return true;
+                        } while (scope = scope.parent_scope);
+                        return false;
+                    });
                 }, true);
             });
         });

test/compress/let.js

@@ -2328,3 +2328,66 @@ issue_5741: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+issue_5745_1: {
+    options = {
+        join_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        "use strict";
+        {
+            let f = function() {
+                return f && "PASS";
+            };
+            var a = f();
+        }
+        a;
+        console.log(a);
+    }
+    expect: {
+        "use strict";
+        {
+            let f = function() {
+                return f && "PASS";
+            };
+            var a = f();
+        }
+        a;
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
+issue_5745_2: {
+    options = {
+        join_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        "use strict";
+        {
+            let f = function() {
+                return f && "PASS";
+            };
+            var a = f();
+            a;
+            console.log(a);
+        }
+    }
+    expect: {
+        "use strict";
+        {
+            let f = function() {
+                return f && "PASS";
+            }, a = f();
+            a;
+            console.log(a);
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}

tools/node.js

@@ -100,7 +100,7 @@ function infer_options(options) {
 exports.default_options = function() {
     var defs = infer_options({ 0: 0 });
     Object.keys(defs).forEach(function(component) {
-        var options = {};
+        var options = { module: false };
         options[component] = { 0: 0 };
         if (options = infer_options(options)) {
             defs[component] = options;