[bardrop]

Fixes #1737

js_function_toString builds the native-code string from JS_GetProperty(this, "name"). When this is a callable proxy, that read goes through the proxy:

const r = Proxy.revocable(function () {}, {});
r.revoke();
Function.prototype.toString.call(r.proxy); // TypeError: revoked proxy

const p = new Proxy(function f() {}, { get(t, k) { console.log("get", k); return Reflect.get(t, k); } });
Function.prototype.toString.call(p);       // logs "get name"

A proxy that wraps a function keeps [[Call]] after it is revoked, so IsCallable is still true and Function.prototype.toString must return a NativeFunction string. The spec does not read name there, so the get trap should not run either.

The change uses an empty name for proxies (function () {\n [native code]\n}). V8, SpiderMonkey and JavaScriptCore also print a nameless native function for proxies. Non-proxy functions are unchanged.

Tests: added cases to test_function() in tests/test_builtin.js (revoked proxy, get trap not called, non-callable proxy still throws TypeError). They fail before the change. make test gives the same result as on master (only test_std.js test_poll_handler_order fails on my macOS machine, with or without this change). A local test262 run of built-ins/Function/prototype/toString (0/160 errors) and built-ins/Proxy (0/606 errors) passes.