fix corner case in functions (#5035)

fixes #5034

lib/compress.js

@@ -6562,10 +6562,25 @@ merge(Compressor.prototype, {
                         if (def.orig.length > 1) return null;
                         if (def.assignments > 0) return false;
                         if (def.name == name) return def;
-                        if (name == "await" && is_async(fn)) return false;
-                        if (name == "yield" && is_generator(fn)) return false;
+                        var forbidden;
+                        switch (name) {
+                          case "await":
+                            forbidden = is_async;
+                            break;
+                          case "yield":
+                            forbidden = is_generator;
+                            break;
+                        }
                         return all(def.references, function(ref) {
-                            return ref.scope.find_variable(name) === sym;
+                            var scope = ref.scope;
+                            if (scope.find_variable(name) !== sym) return false;
+                            if (forbidden) {
+                                scope = scope.resolve();
+                                do {
+                                    if (forbidden(scope)) return false;
+                                } while ((scope = scope.parent_scope.resolve()) && scope !== fn);
+                            }
+                            return true;
                         }) && def;
                     }
 

test/compress/awaits.js

@@ -1989,3 +1989,37 @@ issue_5032_webkit: {
     ]
     node_version: ">=8"
 }
+
+issue_5034: {
+    options = {
+        functions: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            var await = function f() {
+                return async function() {
+                    return f;
+                };
+            };
+            await()().then(function(value) {
+                console.log(value === await ? "PASS" : "FAIL");
+            });
+        })();
+    }
+    expect: {
+        (function() {
+            var await = function f() {
+                return async function() {
+                    return f;
+                };
+            };
+            await()().then(function(value) {
+                console.log(value === await ? "PASS" : "FAIL");
+            });
+        })();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=8"
+}

test/compress/yields.js

@@ -1216,3 +1216,33 @@ issue_5032_webkit: {
     ]
     node_version: ">=4"
 }
+
+issue_5034: {
+    options = {
+        functions: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        console.log(function() {
+            var yield = function f() {
+                return function*() {
+                    return f;
+                };
+            };
+            return yield()().next().value === yield;
+        }() ? "PASS" : "FAIL");
+    }
+    expect: {
+        console.log(function() {
+            var yield = function f() {
+                return function*() {
+                    return f;
+                };
+            };
+            return yield()().next().value === yield;
+        }() ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}