boa/core/engine/src/module/loader.rs

use std::path::{Component, Path, PathBuf};

use rustc_hash::FxHashMap;

use boa_gc::GcRefCell;
use boa_parser::Source;

use crate::script::Script;
use crate::{
    js_string, object::JsObject, realm::Realm, vm::ActiveRunnable, Context, JsError, JsNativeError,
    JsResult, JsString,
};

use super::Module;

/// Resolves paths from the referrer and the specifier, normalize the paths and ensure the path
/// is within a base. If the base is empty, that last verification will be skipped.
///
/// The returned specifier is a resolved absolute path that is guaranteed to be
/// a descendant of `base`. All path component that are either empty or `.` and
/// `..` have been resolved.
///
/// # Errors
/// This predicate will return an error if the specifier is relative but the referrer
/// does not have a path, or if the resolved path is outside `base`.
///
/// # Examples
/// ```
/// #[cfg(target_family = "unix")]
/// # {
/// # use std::path::Path;
/// # use boa_engine::{Context, js_string};
/// # use boa_engine::module::resolve_module_specifier;
/// assert_eq!(
///     resolve_module_specifier(
///         Some(Path::new("/base")),
///         &js_string!("../a.js"),
///         Some(Path::new("/base/hello/ref.js")),
///         &mut Context::default()
///     ),
///     Ok("/base/a.js".into())
/// );
/// # }
/// ```
pub fn resolve_module_specifier(
    base: Option<&Path>,
    specifier: &JsString,
    referrer: Option<&Path>,
    _context: &mut Context,
) -> JsResult<PathBuf> {
    let base = base.map_or_else(|| PathBuf::from(""), PathBuf::from);
    let referrer_dir = referrer.and_then(|p| p.parent());

    let specifier = specifier.to_std_string_escaped();

    // On Windows, also replace `/` with `\`. JavaScript imports use `/` as path separator.
    #[cfg(target_family = "windows")]
    let specifier = specifier.replace("/", "\\");

    let short_path = Path::new(&specifier);

    // In ECMAScript, a path is considered relative if it starts with
    // `./` or `../`. In Rust it's any path that start with `/`.
    let is_relative = short_path.starts_with(".") || short_path.starts_with("..");

    let long_path = if is_relative {
        if let Some(r_path) = referrer_dir {
            base.join(r_path).join(short_path)
        } else {
            return Err(JsError::from_opaque(
                js_string!("relative path without referrer").into(),
            ));
        }
    } else {
        base.join(&specifier)
    };

    if long_path.is_relative() {
        return Err(JsError::from_opaque(
            js_string!("resolved path is relative").into(),
        ));
    }

    // Normalize the path. We cannot use `canonicalize` here because it will fail
    // if the path doesn't exist.
    let path = long_path
        .components()
        .filter(|c| c != &Component::CurDir || c == &Component::Normal("".as_ref()))
        .try_fold(PathBuf::new(), |mut acc, c| {
            if c == Component::ParentDir {
                if acc.as_os_str().is_empty() {
                    return Err(JsError::from_opaque(
                        js_string!("path is outside the module root").into(),
                    ));
                }
                acc.pop();
            } else {
                acc.push(c);
            }
            Ok(acc)
        })?;

    if path.starts_with(&base) {
        Ok(path)
    } else {
        Err(JsError::from_opaque(
            js_string!("path is outside the module root").into(),
        ))
    }
}

/// The referrer from which a load request of a module originates.
#[derive(Debug, Clone)]
pub enum Referrer {
    /// A [**Source Text Module Record**](https://tc39.es/ecma262/#sec-source-text-module-records).
    Module(Module),
    /// A [**Realm**](https://tc39.es/ecma262/#sec-code-realms).
    Realm(Realm),
    /// A [**Script Record**](https://tc39.es/ecma262/#sec-script-records)
    Script(Script),
}

impl Referrer {
    /// Gets the path of the referrer, if it has one.
    #[must_use]
    pub fn path(&self) -> Option<&Path> {
        match self {
            Self::Module(module) => module.path(),
            Self::Realm(_) => None,
            Self::Script(script) => script.path(),
        }
    }
}

impl From<ActiveRunnable> for Referrer {
    fn from(value: ActiveRunnable) -> Self {
        match value {
            ActiveRunnable::Script(script) => Self::Script(script),
            ActiveRunnable::Module(module) => Self::Module(module),
        }
    }
}

/// Module loading related host hooks.
///
/// This trait allows to customize the behaviour of the engine on module load requests and
/// `import.meta` requests.
pub trait ModuleLoader {
    /// Host hook [`HostLoadImportedModule ( referrer, specifier, hostDefined, payload )`][spec].
    ///
    /// This hook allows to customize the module loading functionality of the engine. Technically,
    /// this should call the [`FinishLoadingImportedModule`][finish] operation, but this simpler API just provides
    /// a closure that replaces `FinishLoadingImportedModule`.
    ///
    /// # Requirements
    ///
    /// - The host environment must perform `FinishLoadingImportedModule(referrer, specifier, payload, result)`,
    /// where result is either a normal completion containing the loaded Module Record or a throw
    /// completion, either synchronously or asynchronously. This is equivalent to calling the `finish_load`
    /// callback.
    /// - If this operation is called multiple times with the same `(referrer, specifier)` pair and
    /// it performs FinishLoadingImportedModule(referrer, specifier, payload, result) where result
    /// is a normal completion, then it must perform
    /// `FinishLoadingImportedModule(referrer, specifier, payload, result)` with the same result each
    /// time.
    /// - The operation must treat payload as an opaque value to be passed through to
    /// `FinishLoadingImportedModule`. (can be ignored)
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-HostLoadImportedModule
    /// [finish]: https://tc39.es/ecma262/#sec-FinishLoadingImportedModule
    #[allow(clippy::type_complexity)]
    fn load_imported_module(
        &self,
        referrer: Referrer,
        specifier: JsString,
        finish_load: Box<dyn FnOnce(JsResult<Module>, &mut Context)>,
        context: &mut Context,
    );

    /// Registers a new module into the module loader.
    ///
    /// This is a convenience method for module loaders caching already parsed modules, since it
    /// allows registering a new module through the `&dyn ModuleLoader` provided by
    /// [`Context::module_loader`].
    ///
    /// Does nothing by default.
    fn register_module(&self, _specifier: JsString, _module: Module) {}

    /// Gets the module associated with the provided specifier.
    ///
    /// This is a convenience method for module loaders caching already parsed modules, since it
    /// allows getting a cached module through the `&dyn ModuleLoader` provided by
    /// [`Context::module_loader`].
    ///
    /// Returns `None` by default.
    fn get_module(&self, _specifier: JsString) -> Option<Module> {
        None
    }

    /// Host hooks [`HostGetImportMetaProperties ( moduleRecord )`][meta] and
    /// [`HostFinalizeImportMeta ( importMeta, moduleRecord )`][final].
    ///
    /// This unifies both APIs into a single hook that can be overriden on both cases.
    /// The most common usage is to add properties to `import_meta` and return, but this also
    /// allows modifying the import meta object in more exotic ways before exposing it to ECMAScript
    /// code.
    ///
    /// The default implementation of `HostGetImportMetaProperties` is to return a new empty List.
    ///
    /// [meta]: https://tc39.es/ecma262/#sec-hostgetimportmetaproperties
    /// [final]: https://tc39.es/ecma262/#sec-hostfinalizeimportmeta
    fn init_import_meta(&self, _import_meta: &JsObject, _module: &Module, _context: &mut Context) {}
}

/// A module loader that throws when trying to load any modules.
///
/// Useful to disable the module system on platforms that don't have a filesystem, for example.
#[derive(Debug, Clone, Copy)]
pub struct IdleModuleLoader;

impl ModuleLoader for IdleModuleLoader {
    fn load_imported_module(
        &self,
        _referrer: Referrer,
        _specifier: JsString,
        finish_load: Box<dyn FnOnce(JsResult<Module>, &mut Context)>,
        context: &mut Context,
    ) {
        finish_load(
            Err(JsNativeError::typ()
                .with_message("module resolution is disabled for this context")
                .into()),
            context,
        );
    }
}

/// A simple module loader that loads modules relative to a root path.
///
/// # Note
///
/// This loader only works by using the type methods [`SimpleModuleLoader::insert`] and
/// [`SimpleModuleLoader::get`]. The utility methods on [`ModuleLoader`] don't work at the moment,
/// but we'll unify both APIs in the future.
#[derive(Debug)]
pub struct SimpleModuleLoader {
    root: PathBuf,
    module_map: GcRefCell<FxHashMap<PathBuf, Module>>,
}

impl SimpleModuleLoader {
    /// Creates a new `SimpleModuleLoader` from a root module path.
    pub fn new<P: AsRef<Path>>(root: P) -> JsResult<Self> {
        if cfg!(target_family = "wasm") {
            return Err(JsNativeError::typ()
                .with_message("cannot resolve a relative path in WASM targets")
                .into());
        }
        let root = root.as_ref();
        let absolute = root.canonicalize().map_err(|e| {
            JsNativeError::typ()
                .with_message(format!("could not set module root `{}`", root.display()))
                .with_cause(JsError::from_opaque(js_string!(e.to_string()).into()))
        })?;
        Ok(Self {
            root: absolute,
            module_map: GcRefCell::default(),
        })
    }

    /// Inserts a new module onto the module map.
    #[inline]
    pub fn insert(&self, path: PathBuf, module: Module) {
        self.module_map.borrow_mut().insert(path, module);
    }

    /// Gets a module from its original path.
    #[inline]
    pub fn get(&self, path: &Path) -> Option<Module> {
        self.module_map.borrow().get(path).cloned()
    }
}

impl ModuleLoader for SimpleModuleLoader {
    fn load_imported_module(
        &self,
        referrer: Referrer,
        specifier: JsString,
        finish_load: Box<dyn FnOnce(JsResult<Module>, &mut Context)>,
        context: &mut Context,
    ) {
        let result = (|| {
            let short_path = specifier.to_std_string_escaped();
            let path =
                resolve_module_specifier(Some(&self.root), &specifier, referrer.path(), context)?;
            if let Some(module) = self.get(&path) {
                return Ok(module);
            }

            let source = Source::from_filepath(&path).map_err(|err| {
                JsNativeError::typ()
                    .with_message(format!("could not open file `{short_path}`"))
                    .with_cause(JsError::from_opaque(js_string!(err.to_string()).into()))
            })?;
            let module = Module::parse(source, None, context).map_err(|err| {
                JsNativeError::syntax()
                    .with_message(format!("could not parse module `{short_path}`"))
                    .with_cause(err)
            })?;
            self.insert(path, module.clone());
            Ok(module)
        })();

        finish_load(result, context);
    }

    fn register_module(&self, specifier: JsString, module: Module) {
        let path = PathBuf::from(specifier.to_std_string_escaped());

        self.insert(path, module);
    }

    fn get_module(&self, specifier: JsString) -> Option<Module> {
        let path = specifier.to_std_string_escaped();

        self.get(Path::new(&path))
    }
}

#[cfg(test)]
mod tests {
    use std::path::PathBuf;

    use test_case::test_case;

    use super::*;

    // Tests on Windows and Linux are different because of the path separator and the definition
    // of absolute paths.
    #[rustfmt::skip]
    #[cfg(target_family = "unix")]
    #[test_case(Some("/hello/ref.js"),      "a.js",             Ok("/base/a.js"))]
    #[test_case(Some("/base/ref.js"),       "./b.js",           Ok("/base/b.js"))]
    #[test_case(Some("/base/other/ref.js"), "./c.js",           Ok("/base/other/c.js"))]
    #[test_case(Some("/base/other/ref.js"), "../d.js",          Ok("/base/d.js"))]
    #[test_case(Some("/base/ref.js"),        "e.js",            Ok("/base/e.js"))]
    #[test_case(Some("/base/ref.js"),        "./f.js",          Ok("/base/f.js"))]
    #[test_case(Some("./ref.js"),           "./g.js",           Ok("/base/g.js"))]
    #[test_case(Some("./other/ref.js"),     "./other/h.js",     Ok("/base/other/other/h.js"))]
    #[test_case(Some("./other/ref.js"),     "./other/../h1.js", Ok("/base/other/h1.js"))]
    #[test_case(Some("./other/ref.js"),     "./../h2.js",       Ok("/base/h2.js"))]
    #[test_case(None,                       "./i.js",           Err(()))]
    #[test_case(None,                       "j.js",             Ok("/base/j.js"))]
    #[test_case(None,                       "other/k.js",       Ok("/base/other/k.js"))]
    #[test_case(None,                       "other/../../l.js", Err(()))]
    #[test_case(Some("/base/ref.js"),       "other/../../m.js", Err(()))]
    #[test_case(None,                       "../n.js",          Err(()))]
    fn resolve_test(ref_path: Option<&str>, spec: &str, expected: Result<&str, ()>) {
        let base = PathBuf::from("/base");

        let mut context = Context::default();
        let spec = js_string!(spec);
        let ref_path = ref_path.map(PathBuf::from);

        let actual = resolve_module_specifier(
            Some(&base),
            &spec,
            ref_path.as_deref(),
            &mut context,
        );
        assert_eq!(actual.map_err(|_| ()), expected.map(PathBuf::from));
    }

    #[rustfmt::skip]
    #[cfg(target_family = "windows")]
    #[test_case(Some("a:\\hello\\ref.js"),       "a.js",                Ok("a:\\base\\a.js"))]
    #[test_case(Some("a:\\base\\ref.js"),        "./b.js",              Ok("a:\\base\\b.js"))]
    #[test_case(Some("a:\\base\\other\\ref.js"), "./c.js",              Ok("a:\\base\\other\\c.js"))]
    #[test_case(Some("a:\\base\\other\\ref.js"), "../d.js",             Ok("a:\\base\\d.js"))]
    #[test_case(Some("a:\\base\\ref.js"),        "e.js",                Ok("a:\\base\\e.js"))]
    #[test_case(Some("a:\\base\\ref.js"),        "./f.js",              Ok("a:\\base\\f.js"))]
    #[test_case(Some(".\\ref.js"),               "./g.js",              Ok("a:\\base\\g.js"))]
    #[test_case(Some(".\\other\\ref.js"),        "./other/h.js",        Ok("a:\\base\\other\\other\\h.js"))]
    #[test_case(Some(".\\other\\ref.js"),        "./other/../h1.js",    Ok("a:\\base\\other\\h1.js"))]
    #[test_case(Some(".\\other\\ref.js"),        "./../h2.js",          Ok("a:\\base\\h2.js"))]
    #[test_case(None,                            "./i.js",              Err(()))]
    #[test_case(None,                            "j.js",                Ok("a:\\base\\j.js"))]
    #[test_case(None,                            "other/k.js",          Ok("a:\\base\\other\\k.js"))]
    #[test_case(None,                            "other/../../l.js",    Err(()))]
    #[test_case(Some("\\base\\ref.js"),          "other/../../m.js",    Err(()))]
    #[test_case(None,                            "../n.js",             Err(()))]
    fn resolve_test(ref_path: Option<&str>, spec: &str, expected: Result<&str, ()>) {
        let base = PathBuf::from("a:\\base");

        let mut context = Context::default();
        let spec = js_string!(spec);
        let ref_path = ref_path.map(PathBuf::from);

        let actual = resolve_module_specifier(
            Some(&base),
            &spec,
            ref_path.as_deref(),
            &mut context,
        );
        assert_eq!(actual.map_err(|_| ()), expected.map(PathBuf::from));
    }
}