[gjs/esm/dynamic-imports: 2/5] Implement dynamic imports

[Philip Chimento <pchimento src gnome org>]

commit 5e67d83db4043fb210ab93f0df9d193233350adc
Author: Evan Welsh <contact evanwelsh com>
Date:   Sat Nov 14 14:36:27 2020 -0600

    Implement dynamic imports

 gjs/context.cpp            |   1 +
 gjs/module.cpp             | 124 +++++++++++++++++++++++++++++++++++++++++++++
 gjs/module.h               |   6 +++
 modules/internal/loader.js |  80 +++++++++++++++++++++++++++++
 4 files changed, 211 insertions(+)
---
diff --git a/gjs/context.cpp b/gjs/context.cpp
index 4d8e7144..64ef9605 100644
--- a/gjs/context.cpp
+++ b/gjs/context.cpp
@@ -553,6 +553,7 @@ GjsContextPrivate::GjsContextPrivate(JSContext* cx, GjsContext* public_context)
     }
 
     JS::SetModuleResolveHook(rt, gjs_module_resolve);
+    JS::SetModuleDynamicImportHook(rt, gjs_dynamic_module_resolve);
     JS::SetModuleMetadataHook(rt, gjs_populate_module_meta);
 
     if (!JS_DefineProperty(m_cx, internal_global, "moduleGlobalThis", global,
diff --git a/gjs/module.cpp b/gjs/module.cpp
index c810f7c9..264d83ce 100644
--- a/gjs/module.cpp
+++ b/gjs/module.cpp
@@ -21,6 +21,8 @@
 #include <js/Conversions.h>
 #include <js/GCVector.h>  // for RootedVector
 #include <js/Id.h>
+#include <js/Modules.h>
+#include <js/Promise.h>
 #include <js/PropertyDescriptor.h>
 #include <js/RootingAPI.h>
 #include <js/SourceText.h>
@@ -29,6 +31,7 @@
 #include <js/Value.h>
 #include <js/ValueArray.h>
 #include <jsapi.h>  // for JS_DefinePropertyById, ...
+#include <jsfriendapi.h>  // for SetFunctionNativeReserved
 
 #include "gjs/atoms.h"
 #include "gjs/context-private.h"
@@ -484,3 +487,124 @@ JSObject* gjs_module_resolve(JSContext* cx, JS::HandleValue importingModulePriv,
     g_assert(result.isObject() && "resolve hook failed to return an object!");
     return &result.toObject();
 }
+
+bool gjs_dynamic_module_get_meta(JSContext* cx, JS::HandleObject meta,
+                                 JS::MutableHandleValue importing_module_priv,
+                                 JS::MutableHandleString specifier,
+                                 JS::MutableHandleObject internal_promise) {
+    JS::RootedValue v_specifier(cx);
+    JS::RootedValue v_internal_promise(cx);
+    if (!JS_GetProperty(cx, meta, "priv", importing_module_priv) ||
+        !JS_GetProperty(cx, meta, "promise", &v_internal_promise) ||
+        !JS_GetProperty(cx, meta, "specifier", &v_specifier))
+        return false;
+
+    g_assert(v_specifier.isString());
+    g_assert(v_internal_promise.isObject());
+
+    specifier.set(v_specifier.toString());
+    internal_promise.set(&v_internal_promise.toObject());
+
+    return true;
+}
+
+bool gjs_dynamic_module_rejected(JSContext* cx, unsigned argc, JS::Value* vp) {
+    JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+
+    JS::Value priv_value = js::GetFunctionNativeReserved(&args.callee(), 0);
+    g_assert(!priv_value.isNull() && "Dynamic module rejection called twice");
+    JS::RootedObject meta(cx, &priv_value.toObject());
+    g_assert(meta && "Dynamic module rejection called twice");
+    js::SetFunctionNativeReserved(&args.callee(), 0, JS::NullValue());
+
+    JS::RootedValue importing_module_priv(cx);
+    JS::RootedString specifier(cx);
+    JS::RootedObject internal_promise(cx);
+    if (!gjs_dynamic_module_get_meta(cx, meta, &importing_module_priv,
+                                     &specifier, &internal_promise))
+        return false;
+
+    return JS::FinishDynamicModuleImport(cx, importing_module_priv, specifier,
+                                         internal_promise);
+}
+
+bool gjs_dynamic_module_resolved(JSContext* cx, unsigned argc, JS::Value* vp) {
+    JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+
+    JS::Value priv_value = js::GetFunctionNativeReserved(&args.callee(), 0);
+    g_assert(!priv_value.isNull() && "Dynamic module resolution called twice");
+    JS::RootedObject meta(cx, &priv_value.toObject());
+    g_assert(meta && "Dynamic module resolution called twice");
+    js::SetFunctionNativeReserved(&args.callee(), 0, JS::NullValue());
+
+    JS::RootedValue importing_module_priv(cx);
+    JS::RootedString specifier(cx);
+    JS::RootedObject internal_promise(cx);
+    if (!gjs_dynamic_module_get_meta(cx, meta, &importing_module_priv,
+                                     &specifier, &internal_promise))
+        return false;
+
+    JS::RootedObject global(cx, gjs_get_import_global(cx));
+    JSAutoRealm ar(cx, global);
+
+    g_assert(args[0].isObject());
+    JS::RootedObject module(cx, &args[0].toObject());
+
+    if (!JS::ModuleInstantiate(cx, module) || !JS::ModuleEvaluate(cx, module))
+        return JS::FinishDynamicModuleImport(cx, importing_module_priv,
+                                             specifier, internal_promise);
+
+    return JS::FinishDynamicModuleImport(cx, importing_module_priv, specifier,
+                                         internal_promise);
+}
+
+bool gjs_dynamic_module_resolve(JSContext* cx,
+                                JS::HandleValue importing_module_priv,
+                                JS::HandleString specifier,
+                                JS::HandleObject internal_promise) {
+    g_assert(gjs_global_is_type(cx, GjsGlobalType::DEFAULT) &&
+             "gjs_dynamic_module_resolve can only be called from the default "
+             "global.");
+
+    JS::RootedObject global(cx, JS::CurrentGlobalOrNull(cx));
+    JSAutoRealm ar(cx, global);
+
+    JS::RootedValue v_loader(
+        cx, gjs_get_global_slot(global, GjsGlobalSlot::MODULE_LOADER));
+    g_assert(v_loader.isObject());
+    JS::RootedObject loader(cx, &v_loader.toObject());
+
+    JS::RootedObject meta(cx, JS_NewPlainObject(cx));
+    if (!JS_DefineProperty(cx, meta, "specifier", specifier,
+                           JSPROP_PERMANENT) ||
+        !JS_DefineProperty(cx, meta, "promise", internal_promise,
+                           JSPROP_PERMANENT) ||
+        !JS_DefineProperty(cx, meta, "priv", importing_module_priv,
+                           JSPROP_PERMANENT))
+        return false;
+
+    JS::RootedValueArray<2> args(cx);
+    args[0].set(importing_module_priv);
+    args[1].setString(specifier);
+
+    JS::RootedValue result(cx);
+    if (!JS::Call(cx, loader, "moduleResolveAsyncHook", args, &result))
+        return JS::FinishDynamicModuleImport(cx, importing_module_priv,
+                                             specifier, internal_promise);
+
+    JS::RootedObject resolved(
+        cx, JS_GetFunctionObject(js::NewFunctionWithReserved(
+                cx, gjs_dynamic_module_resolved, 2, 0, "import resolved")));
+    JS::RootedObject rejected(
+        cx, JS_GetFunctionObject(js::NewFunctionWithReserved(
+                cx, gjs_dynamic_module_rejected, 2, 0, "import rejected")));
+    js::SetFunctionNativeReserved(resolved, 0, JS::ObjectValue(*meta));
+    js::SetFunctionNativeReserved(rejected, 0, JS::ObjectValue(*meta));
+
+    JS::RootedObject promise(cx, &result.toObject());
+
+    if (!JS::AddPromiseReactions(cx, promise, resolved, rejected))
+        return false;
+
+    return true;
+}
diff --git a/gjs/module.h b/gjs/module.h
index c754b114..dfe6f18c 100644
--- a/gjs/module.h
+++ b/gjs/module.h
@@ -39,4 +39,10 @@ GJS_JSAPI_RETURN_CONVENTION
 bool gjs_populate_module_meta(JSContext* cx, JS::HandleValue private_ref,
                               JS::HandleObject meta_object);
 
+GJS_JSAPI_RETURN_CONVENTION
+bool gjs_dynamic_module_resolve(JSContext* cx,
+                                JS::HandleValue importing_module_priv,
+                                JS::HandleString specifier,
+                                JS::HandleObject internal_promise);
+
 #endif  // GJS_MODULE_H_
diff --git a/modules/internal/loader.js b/modules/internal/loader.js
index fde96eb0..f28814c9 100644
--- a/modules/internal/loader.js
+++ b/modules/internal/loader.js
@@ -122,6 +122,79 @@ class ModuleLoader extends InternalModuleLoader {
 
         return this.resolveBareSpecifier(specifier);
     }
+
+    moduleResolveAsyncHook(importingModulePriv, specifier) {
+        // importingModulePriv may be falsy in the case of gjs_context_eval()
+        if (!importingModulePriv || !importingModulePriv.uri)
+            throw new ImportError('Cannot resolve relative imports from an unknown file.');
+
+        return this.resolveModuleAsync(specifier, importingModulePriv.uri);
+    }
+
+    /**
+     * Resolves a module import with optional handling for relative imports asynchronously.
+     *
+     * @param {string} specifier the specifier (e.g. relative path, root package) to resolve
+     * @param {string | null} importingModuleURI the URI of the module
+     *   triggering this resolve
+     * @returns {import("../types").Module}
+     */
+    async resolveModuleAsync(specifier, importingModuleURI) {
+        const registry = getRegistry(this.global);
+
+        // Check if the module has already been loaded
+        let module = registry.get(specifier);
+        if (module)
+            return module;
+
+        // 1) Resolve path and URI-based imports.
+        const uri = this.resolveSpecifier(specifier, importingModuleURI);
+        if (uri) {
+            module = registry.get(uri.uri);
+
+            // Check if module is already loaded (relative handling)
+            if (module)
+                return module;
+
+            const result = await this.loadURIAsync(uri);
+            if (!result)
+                return null;
+
+            const [text, internal = false] = result;
+
+            const priv = new ModulePrivate(uri.uri, uri.uri, internal);
+            const compiled = this.compileModule(priv, text);
+
+            registry.set(uri.uri, compiled);
+            return compiled;
+        }
+
+        // 2) Resolve internal imports.
+
+        return this.resolveBareSpecifier(specifier);
+    }
+
+    /**
+     * Loads a file or resource URI asynchronously
+     *
+     * @param {Uri} uri the file or resource URI to load
+     * @returns {Promise<[string] | [string, boolean] | null>}
+     */
+    async loadURIAsync(uri) {
+        if (uri.scheme) {
+            const loader = this.schemeHandlers.get(uri.scheme);
+
+            if (loader)
+                return loader.loadAsync(uri);
+        }
+
+        if (uri.scheme === 'file' || uri.scheme === 'resource') {
+            const result = await loadResourceOrFileAsync(uri.uri);
+            return [result];
+        }
+
+        return null;
+    }
 }
 
 const moduleLoader = new ModuleLoader(moduleGlobalThis);
@@ -167,4 +240,11 @@ moduleLoader.registerScheme('gi', {
 
         return [generateGIModule(namespace, version), true];
     },
+    /**
+     * @param {import("./internalLoader.js").Uri} uri the URI to load asynchronously
+     */
+    loadAsync(uri) {
+        // gi: only does string manipulation, so it is safe to use the same code for sync and async.
+        return this.load(uri);
+    },
 });