nodejs/

module.rs

//! CommonJS module loader.
//!
//! Node's `require()` semantics, layered on the existing engine — no bespoke VM
//! primitive. A `.js` file is wrapped in the canonical Node module wrapper
//! `(function (exports, require, module, __dirname, __filename) { … })`, compiled
//! through the ordinary `compile` → `load_merged` path to obtain the wrapper
//! FUNCTION value, then `host::invoke`d with a fresh `module = { exports: {} }`.
//! Whatever the body assigns to `module.exports` (or hangs off `exports`) is the
//! module's value; it is cached by resolved absolute path so a second `require`
//! of the same file returns the identical object and circular requires observe
//! the partially-filled `exports`.
//!
//! Core modules (`fs`, `path`, `http`, …) short-circuit to their native
//! `JsObj::Builtin` namespace (see `stdlib::resolve`) and are never read from
//! disk. Everything else — relative paths, JSON files, and bare `node_modules`
//! packages with their `package.json` `"exports"`/`"main"` and `index.js`
//! fallbacks — resolves on the real filesystem and runs the genuine, unmodified
//! source.
//!
//! Per-module `require` is a real JS closure that bakes in the defining module's
//! directory, so a `require(...)` deferred inside a function called much later
//! still resolves against the module that defined it (a single global
//! "current dir" would resolve against the wrong module). The closure is minted
//! by a one-time compiled factory (`FACTORY`) invoked with the directory string;
//! it dispatches back into this loader through the `__cjs_require` /
//! `__cjs_resolve` global native builtins.

use std::cell::RefCell;
use std::collections::HashMap;
use std::path::{Path, PathBuf};

use crate::host::{self, with_host, JsObj};
use fusevm::Value;

thread_local! {
    /// Require cache: resolved absolute path → the `module` object (its `.exports`
    /// is re-read on every hit, matching Node — `module.exports = X` reassignment
    /// is observed by later requires).
    static CACHE: RefCell<HashMap<PathBuf, Value>> = RefCell::new(HashMap::new());
    /// Resolved `(specifier, from_dir)` to the CANONICAL absolute path it named,
    /// so a repeated `require` of an already-loaded module costs one hash lookup
    /// instead of walking `node_modules` and calling `canonicalize` again.
    ///
    /// Node keeps the same table (`Module._pathCache`) with the same
    /// consequence: a file that appears after a specifier has already resolved
    /// is not picked up by a later `require` of that specifier.
    static PATH_CACHE: RefCell<HashMap<(String, PathBuf), PathBuf>> =
        RefCell::new(HashMap::new());
    /// Base directory the ENTRY script's top-level `require` resolves against
    /// (the dir of `node app.js`, or cwd for `node -e`).
    static ENTRY_DIR: RefCell<PathBuf> = RefCell::new(std::env::current_dir().unwrap_or_default());
    /// The compiled per-module `require`-closure factory (see module docs),
    /// minted once per host and reused for every module.
    static FACTORY: RefCell<Option<Value>> = const { RefCell::new(None) };
    /// The compiled synthetic-CallSite-array factory (for `Error.captureStackTrace`
    /// under a custom `Error.prepareStackTrace`), minted once per host.
    static CALLSITE_FACTORY: RefCell<Option<Value>> = const { RefCell::new(None) };
}

/// Clear all per-host loader state. Called from `host::reset_host` so a fresh
/// eval (which rebuilds the heap) never reuses a stale heap handle.
pub fn reset() {
    CACHE.with(|c| c.borrow_mut().clear());
    PATH_CACHE.with(|c| c.borrow_mut().clear());
    FACTORY.with(|f| *f.borrow_mut() = None);
    CALLSITE_FACTORY.with(|f| *f.borrow_mut() = None);
    ENTRY_DIR.with(|d| *d.borrow_mut() = std::env::current_dir().unwrap_or_default());
}

/// The resolved filenames of every currently loaded module, in load order —
/// the keys `require.cache` exposes.
pub fn cache_keys() -> Vec<String> {
    CACHE.with(|c| {
        c.borrow()
            .keys()
            .map(|p| p.to_string_lossy().into_owned())
            .collect()
    })
}

/// The module object cached under the resolved filename `key`, if any.
pub fn cache_get(key: &str) -> Option<Value> {
    CACHE.with(|c| c.borrow().get(Path::new(key)).cloned())
}

/// Drop `key` from the module cache, so the next `require` of that file runs it
/// again. This is what `delete require.cache[id]` must do to mean anything.
pub fn cache_delete(key: &str) -> bool {
    CACHE.with(|c| c.borrow_mut().remove(Path::new(key)).is_some())
}

/// Set the base directory the ENTRY script's `require` resolves against.
pub fn set_entry_dir(dir: PathBuf) {
    ENTRY_DIR.with(|d| *d.borrow_mut() = dir);
}

/// The ENTRY script's base directory.
pub fn entry_dir() -> PathBuf {
    ENTRY_DIR.with(|d| d.borrow().clone())
}

/// Install the CJS wrapper variables the ENTRY script sees.
///
/// A `require`d module already receives `exports`/`require`/`module`/`__dirname`
/// /`__filename` as wrapper parameters (see `compile_wrapper`); the entry
/// script used to receive none of them, so `typeof module` was `"undefined"`
/// there and every UMD header took its browser branch. Node gives the entry
/// script the same five names, with values that DEPEND ON THE ENTRY POINT:
///
/// | | `node f.js` | `node -e` | `node -` / piped |
/// | --- | --- | --- | --- |
/// | `__filename` | resolved abs path | `[eval]` | `[stdin]` |
/// | `__dirname` | its directory | `.` | `.` |
/// | `module.id` | `.` | `[eval]` | `[stdin]` |
/// | `module.path` | its directory | `.` | `.` |
///
/// `module.filename` is `path.resolve(__filename)` in every case, so under `-e`
/// it is `<cwd>/[eval]` — a path that does not exist, which is Node's own
/// value. Measured on node v26.7.0.
///
/// `origin` is the `__filename` value: an absolute script path, or `[eval]` /
/// `[stdin]` for the two source-on-the-command-line entry points.
pub fn install_entry_globals(origin: &str) {
    let from_file = origin != "[eval]" && origin != "[stdin]";
    let (dirname, id) = if from_file {
        let dir = Path::new(origin)
            .parent()
            .map(|p| p.to_string_lossy().into_owned())
            .unwrap_or_else(|| ".".into());
        (dir, ".".to_string())
    } else {
        (".".to_string(), origin.to_string())
    };
    let filename = crate::stdlib::path::resolve_one(origin);
    let module = new_module(&id, &dirname, &filename);
    let exports = module_exports(&module);
    with_host(|h| {
        let origin_str = h.new_str(origin.to_string());
        let dirname = h.new_str(dirname);
        h.set_global("__filename", origin_str);
        h.set_global("__dirname", dirname);
        h.set_global("module", module.clone());
        // `require.main === module` in the entry script is the canonical
        // "am I the program" test, and it read `undefined === <module>`
        // because nothing ever set `main`. The ENTRY module is the value for
        // every `require` in the process, not just this one, so it is recorded
        // for the per-module closures too (`make_require` installs it).
        // …but only when the program IS a module. `node -e` and a script on
        // stdin run as a Script, not a CommonJS module, and node reports
        // `require.main` as `undefined` for both.
        if from_file {
            h.set_builtin_static("require", "main", module.clone());
        }
        h.set_global("exports", exports.clone());
        // Top-level `this`: the module's `exports` from a file (CommonJS
        // module), `globalThis` from `-e` and from stdin (a Script). See
        // `JsHost::set_top_this` for the measurements.
        let top = if from_file {
            exports
        } else {
            h.global_object()
        };
        h.set_top_this(top);
    });
}

// ── resolution ───────────────────────────────────────────────────────────────

/// Append `.ext` to a path (Node appends the extension, it does not replace an
/// existing one — `foo.min` → `foo.min.js`, not `foo.js`).
fn add_ext(p: &Path, ext: &str) -> PathBuf {
    let mut s = p.as_os_str().to_owned();
    s.push(".");
    s.push(ext);
    PathBuf::from(s)
}

/// `require`-as-a-file: `p`, then `p.js`, then `p.json`. `.node` native addons
/// are skipped (unsupported), matching the resolution order minus that step.
fn load_as_file(p: &Path) -> Option<PathBuf> {
    if p.is_file() {
        return Some(p.to_path_buf());
    }
    for ext in ["js", "json"] {
        let cand = add_ext(p, ext);
        if cand.is_file() {
            return Some(cand);
        }
    }
    None
}

/// `require`-as-a-directory: honor `package.json` `"exports"`/`"main"`, else
/// `index.js` / `index.json`.
fn load_as_dir(p: &Path) -> Option<PathBuf> {
    let pkg = p.join("package.json");
    if pkg.is_file() {
        if let Some(main) = pkg_entry(&pkg) {
            let mp = p.join(&main);
            if let Some(f) = load_as_file(&mp).or_else(|| load_index(&mp)) {
                return Some(f);
            }
        }
    }
    load_index(p)
}

/// `index.js` / `index.json` inside directory `p`.
fn load_index(p: &Path) -> Option<PathBuf> {
    for name in ["index.js", "index.json"] {
        let cand = p.join(name);
        if cand.is_file() {
            return Some(cand);
        }
    }
    None
}

/// The relative entry path a `package.json` declares: the `"."` (or main-string)
/// `"exports"` target if present, else `"main"`. Only the common `"exports"`
/// shapes are handled — a bare string, or an object whose `"."` maps to a string
/// or to `{ "require"/"default"/"node": "…" }`. Anything more exotic falls back
/// to `"main"`, then to the directory's `index.js`.
fn pkg_entry(pkg: &Path) -> Option<String> {
    let text = std::fs::read_to_string(pkg).ok()?;
    let json: serde_json::Value = serde_json::from_str(&text).ok()?;
    if let Some(e) = exports_main(json.get("exports")) {
        return Some(strip_dot_slash(&e));
    }
    json.get("main")
        .and_then(|m| m.as_str())
        .map(strip_dot_slash)
}

/// Resolve the `"exports"` field down to a single relative path for the `"."`
/// (package root) entry, across the shapes CommonJS packages commonly ship.
fn exports_main(exports: Option<&serde_json::Value>) -> Option<String> {
    let exports = exports?;
    // `"exports": "./index.js"` — a bare string is the `"."` target.
    if let Some(s) = exports.as_str() {
        return Some(s.to_string());
    }
    let obj = exports.as_object()?;
    // Either a subpath map keyed by `"."`, or a bare conditions map at the root.
    let target = obj.get(".").unwrap_or(exports);
    condition_target(target)
}

/// Reduce an `"exports"` target — a string, or a conditions object — to a path,
/// preferring the CommonJS-relevant conditions (`require`/`node`/`default`).
fn condition_target(target: &serde_json::Value) -> Option<String> {
    if let Some(s) = target.as_str() {
        return Some(s.to_string());
    }
    let obj = target.as_object()?;
    for cond in ["require", "node", "default"] {
        if let Some(v) = obj.get(cond) {
            if let Some(s) = condition_target(v) {
                return Some(s);
            }
        }
    }
    None
}

/// Drop a leading `./` from a package-relative path.
fn strip_dot_slash(s: &str) -> String {
    s.strip_prefix("./").unwrap_or(s).to_string()
}

/// Resolve `spec` (already known to be a bare specifier) by walking parent
/// directories from `from_dir`, checking `<dir>/node_modules/<spec>` at each
/// level with the file-then-directory rules.
fn resolve_bare(spec: &str, from_dir: &Path) -> Option<PathBuf> {
    let mut dir = Some(from_dir);
    while let Some(d) = dir {
        // Skip a `node_modules/node_modules` descent.
        if d.file_name().is_some_and(|n| n == "node_modules") {
            dir = d.parent();
            continue;
        }
        let candidate = d.join("node_modules").join(spec);
        if let Some(f) = load_as_file(&candidate).or_else(|| load_as_dir(&candidate)) {
            return Some(f);
        }
        dir = d.parent();
    }
    None
}

/// Resolve `spec` relative to `from_dir` to an absolute file path, or `None` if
/// no file matches (core modules are handled earlier, by the caller).
pub fn resolve(spec: &str, from_dir: &Path) -> Option<PathBuf> {
    let is_relative =
        spec.starts_with("./") || spec.starts_with("../") || spec == "." || spec == "..";
    let is_absolute = spec.starts_with('/');
    if is_relative || is_absolute {
        // NORMALIZED, not merely joined: `Path::join` keeps the `.` in
        // `<dir>/./d.js`, and that string is what `require.resolve` returns and
        // what keys the module cache — so `./d.js` and `d.js` from the same
        // directory would be two cache entries of one file.
        let joined = if is_absolute {
            spec.to_string()
        } else {
            from_dir.join(spec).to_string_lossy().into_owned()
        };
        let base = PathBuf::from(crate::stdlib::path::resolve_one(&joined));
        return load_as_file(&base).or_else(|| load_as_dir(&base));
    }
    resolve_bare(spec, from_dir)
}

// ── loading / execution ──────────────────────────────────────────────────────

/// `require(spec)` from `from_dir`: the single entry point shared by the
/// top-level `require` builtin and the per-module `__cjs_require`. Returns the
/// module's exports value.
pub fn require(spec: &str, from_dir: &Path) -> Result<Value, String> {
    // Core module: the native namespace value, never a file (mirrors the legacy
    // `require` path — `require('events')` yields the EventEmitter ctor, etc.).
    if let Some(v) = crate::stdlib::data_module(spec) {
        return Ok(v);
    }
    if let Some(ns) = crate::stdlib::resolve(spec) {
        return Ok(with_host(|h| h.alloc(JsObj::Builtin(ns.to_string()))));
    }
    // Resolution is filesystem work — a `node_modules` walk, a set of extension
    // probes, then `canonicalize` — and a program that requires the same
    // specifier in a loop paid all of it on every call even though the module
    // itself was already loaded and cached. The answer is memoized per
    // `(specifier, from_dir)`.
    let key = (spec.to_string(), from_dir.to_path_buf());
    if let Some(hit) = PATH_CACHE.with(|c| c.borrow().get(&key).cloned()) {
        return load_file(&hit);
    }
    let path = resolve(spec, from_dir).ok_or_else(|| {
        crate::host::plain_coded_error(
            "Error",
            "MODULE_NOT_FOUND",
            &format!("Cannot find module '{spec}'"),
        )
    })?;
    // A canonical absolute key so the same file required via different relative
    // specifiers shares one cache entry.
    let path = std::fs::canonicalize(&path).unwrap_or(path);
    PATH_CACHE.with(|c| c.borrow_mut().insert(key, path.clone()));
    load_file(&path)
}

/// Load the resolved absolute file `path` (`.json` parses to its value; `.js`
/// runs through the module wrapper) and return its exports, caching by path.
fn load_file(path: &Path) -> Result<Value, String> {
    if let Some(cached) = CACHE.with(|c| c.borrow().get(path).cloned()) {
        // Re-read `.exports` — a cached module may have reassigned it.
        return Ok(module_exports(&cached));
    }
    if path.extension().is_some_and(|e| e == "json") {
        let text = std::fs::read_to_string(path)
            .map_err(|e| format!("cannot read {}: {e}", path.display()))?;
        let src = with_host(|h| h.new_str(text));
        let val = crate::builtins::call_builtin_function("JSON.parse", vec![src])?;
        // A JSON module's value IS the parsed data; cache a synthetic wrapper so
        // repeated requires share it.
        let abs = path.to_string_lossy().into_owned();
        let dir = path.parent().unwrap_or(Path::new("")).to_string_lossy();
        let module = new_module(&abs, &dir, &abs);
        with_host(|h| {
            if let Some(JsObj::Object(p)) = h.get_mut(&module) {
                p.insert("exports".to_string(), val.clone());
                p.insert("loaded".to_string(), Value::Bool(true));
            }
        });
        CACHE.with(|c| c.borrow_mut().insert(path.to_path_buf(), module));
        return Ok(val);
    }

    let source = std::fs::read_to_string(path)
        .map_err(|e| format!("cannot read {}: {e}", path.display()))?;
    let dir = path.parent().map(Path::to_path_buf).unwrap_or_default();

    // Compile the Node module wrapper to obtain the wrapper FUNCTION value.
    // A compile error is annotated with the offending file (Node does likewise).
    let wrapper = compile_wrapper(&source)
        .map_err(|e| format!("{e}\n    while loading {}", path.display()))?;

    // The `module` object, plus the aliases the wrapper receives. A required
    // module's `id` IS its absolute filename (only the entry module's is `.`).
    let abs = path.to_string_lossy().into_owned();
    let module = new_module(&abs, &dir.to_string_lossy(), &abs);
    let exports = module_exports(&module);
    let require_fn = make_require(&dir)?;
    let (dirname, filename) = with_host(|h| {
        (
            h.new_str(dir.to_string_lossy().to_string()),
            h.new_str(path.to_string_lossy().to_string()),
        )
    });

    // Cache BEFORE running so a circular `require` back to this module observes
    // the partial `exports`.
    CACHE.with(|c| c.borrow_mut().insert(path.to_path_buf(), module.clone()));

    host::invoke(
        &wrapper,
        vec![exports, require_fn, module.clone(), dirname, filename],
        None,
    )?;
    mark_loaded(&module);

    Ok(module_exports(&module))
}

/// A fresh `module` object: `{ id, path, exports, filename, loaded, children,
/// paths }`, in that key order.
///
/// The order is observable (`Object.keys(module)`) and this is node's. Only
/// `exports` used to be present, so a module reading `module.id` or
/// `module.filename` — both of which a bundler-emitted or `__dirname`-avoiding
/// package does — got `undefined`.
///
/// `paths` is the `node_modules` chain from `dir` up to the root, the same walk
/// `require` performs to resolve a bare specifier. `loaded` starts `false`; it
/// is set once the body returns.
fn new_module(id: &str, dir: &str, filename: &str) -> Value {
    let mut node_modules: Vec<String> = Vec::new();
    let mut cur = Some(Path::new(dir));
    while let Some(d) = cur.filter(|d| !d.as_os_str().is_empty()) {
        node_modules.push(d.join("node_modules").to_string_lossy().into_owned());
        cur = d.parent();
    }
    with_host(|h| {
        let exports = h.new_object(indexmap::IndexMap::new());
        let mut props = indexmap::IndexMap::new();
        props.insert("id".to_string(), h.new_str(id.to_string()));
        props.insert("path".to_string(), h.new_str(dir.to_string()));
        props.insert("exports".to_string(), exports);
        props.insert("filename".to_string(), h.new_str(filename.to_string()));
        props.insert("loaded".to_string(), Value::Bool(false));
        // `module.parent` is long deprecated but PRESENT: node reports `null`
        // for a file the loader reached directly, and code still tests
        // `if (!module.parent)` to detect "run as the entry point". The key was
        // missing entirely, so `'parent' in module` was false.
        let null = h.null();
        props.insert("parent".to_string(), null);
        let children = h.new_array(Vec::new());
        props.insert("children".to_string(), children);
        let paths: Vec<Value> = node_modules.into_iter().map(|p| h.new_str(p)).collect();
        let paths = h.new_array(paths);
        props.insert("paths".to_string(), paths);
        let obj = h.new_object(props);
        // `parent` is present but NOT enumerable: `Object.keys(module)` does not
        // list it, while `'parent' in module` is true. Adding it as an ordinary
        // property changed the key order the es_parity module tests pin.
        h.hide_prop(&obj, "parent");
        obj
    })
}

/// The directories `require.resolve` would search for `spec`, in order.
///
/// A RELATIVE specifier resolves against one directory — the requiring one — so
/// node reports just that. A bare package name walks the `node_modules` chain
/// up to the root.
pub fn resolve_paths(spec: &str, from_dir: &std::path::Path) -> Vec<String> {
    if spec.starts_with('.') || spec.starts_with('/') {
        return vec![from_dir.to_string_lossy().into_owned()];
    }
    let mut out = Vec::new();
    let mut cur = Some(from_dir);
    while let Some(d) = cur {
        out.push(d.join("node_modules").to_string_lossy().into_owned());
        cur = d.parent();
    }
    out
}

/// Flip `module.loaded` once the body has run, as Node's loader does.
fn mark_loaded(module: &Value) {
    with_host(|h| {
        if let Some(JsObj::Object(p)) = h.get_mut(module) {
            p.insert("loaded".to_string(), Value::Bool(true));
        }
    });
}

/// Read `module.exports` (falls back to `undefined` for a malformed module).
fn module_exports(module: &Value) -> Value {
    with_host(|h| match h.get(module) {
        Some(JsObj::Object(p)) => p.get("exports").cloned().unwrap_or(Value::Undef),
        _ => Value::Undef,
    })
}

/// Compile `<source>` wrapped in the Node module wrapper and return the wrapper
/// FUNCTION value.
fn compile_wrapper(source: &str) -> Result<Value, String> {
    // A module may open with a hashbang line, which is only a comment at the
    // start of the TEXT; inside the wrapper it would not be, so it becomes a
    // `//` comment of the same length.
    let source = match source.strip_prefix("#!") {
        Some(rest) => format!("//{rest}"),
        None => source.to_string(),
    };
    // A trailing newline before `})` guards a source ending in a `//` comment.
    eval_binding(&format!(
        "(function (exports, require, module, __dirname, __filename) {{\n{source}\n}})"
    ))
}

/// Compile+run a single JS expression on the LIVE host — no reset, no
/// event-loop drain — and return its value.
///
/// This delegates to `crate::eval_in_global_scope`, the frontend's one
/// runtime-source evaluator, and two things changed with it. The wrapper used to
/// be compiled as `var __cjs_wN = (function …);` and read back out of the scope
/// with `read_name`, because a bare expression statement pops its value; a
/// completion-value compile returns the expression directly, so the capture
/// variable and its uniquifying counter are gone. And the run used to happen on
/// the CALLER's frame, which let a module body see the locals of whatever
/// function called `require`: measured against node v26.7.0,
/// `function outer(){ let secret = 1; return require('./m.js'); }` with `m.js` =
/// `module.exports = typeof secret` is `"undefined"` there and was `"number"`
/// here.
fn eval_binding(src: &str) -> Result<Value, String> {
    crate::eval_in_global_scope(src)
}

/// Build a per-module `require` closure bound to `dir` (see module docs).
fn make_require(dir: &Path) -> Result<Value, String> {
    let factory = factory()?;
    let dir_str = with_host(|h| h.new_str(dir.to_string_lossy().to_string()));
    let req = host::invoke(&factory, vec![dir_str], None)?;
    // Every `require` in the process reports the same `main` — the ENTRY
    // module — which is what `require.main === module` tests against.
    if let Some(main) = with_host(|h| h.builtin_static("require", "main")) {
        // `req` is a FUNCTION value, so its properties live in the fn-prop side
        // table, not in an object property map.
        with_host(|h| h.set_fn_prop(&req, "main", main));
    }
    Ok(req)
}

/// The one-time compiled `require`-closure factory. `require.resolve` /
/// `require.cache` are provided since some packages read them.
fn factory() -> Result<Value, String> {
    if let Some(f) = FACTORY.with(|f| f.borrow().clone()) {
        return Ok(f);
    }
    let src = "(function (__cjs_dir) {\n\
        var req = function (spec) { return __cjs_require(spec, __cjs_dir); };\n\
        req.resolve = function (spec) { return __cjs_resolve(spec, __cjs_dir); };\n\
        req.cache = __cjs_cache;\n\
        req.main = undefined;\n\
        req.extensions = {};\n\
        return req;\n\
    });";
    let f = eval_binding(src)?;
    FACTORY.with(|c| *c.borrow_mut() = Some(f.clone()));
    Ok(f)
}

/// An array of `depth` synthetic V8 CallSite objects for `Error.captureStackTrace`.
/// Stack-introspection packages (e.g. `depd`) set `Error.prepareStackTrace` to a
/// function that receives this array; the getters return neutral placeholders (no
/// real frame info is available), which is enough for those packages to build
/// their deprecation sites without throwing.
pub fn callsite_stack(depth: usize) -> Result<Value, String> {
    let factory = if let Some(f) = CALLSITE_FACTORY.with(|f| f.borrow().clone()) {
        f
    } else {
        let src = "(function (n) {\n\
            var a = [];\n\
            for (var i = 0; i < n; i++) {\n\
                a.push({\n\
                    getFileName: function () { return null; },\n\
                    getLineNumber: function () { return 0; },\n\
                    getColumnNumber: function () { return 0; },\n\
                    getFunctionName: function () { return null; },\n\
                    getMethodName: function () { return null; },\n\
                    getTypeName: function () { return null; },\n\
                    getThis: function () { return undefined; },\n\
                    isNative: function () { return false; },\n\
                    isEval: function () { return false; },\n\
                    toString: function () { return '<anonymous>'; }\n\
                });\n\
            }\n\
            return a;\n\
        });";
        let f = eval_binding(src)?;
        CALLSITE_FACTORY.with(|c| *c.borrow_mut() = Some(f.clone()));
        f
    };
    host::invoke(&factory, vec![Value::Float(depth as f64)], None)
}