src: share common code paths for SEA and embedder script

Since SEA is very similar in principle to embedding functionality,
it makes sense to share code paths where possible. This commit does
so and addresses a `TODO` while doing so.

It also adds a utility to directly run CJS code to the embedder
startup callback, which comes in handy for this purpose.

Finally, this commit is breaking because it aligns the behavior
of `require()`ing internal modules; previously, embedders could
use the `require` function that they received to do so.
(If this is not considered breaking because accessing internals
is not covered by the API, then this would need ABI compatibility
patches for becoming fully non-breaking.)

PR-URL: #46825
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

Author: addaleax

lib/internal/main/embedding.js

@@ -0,0 +1,18 @@
+'use strict';
+const {
+  prepareMainThreadExecution,
+  markBootstrapComplete,
+} = require('internal/process/pre_execution');
+const { isSea } = internalBinding('sea');
+const { emitExperimentalWarning } = require('internal/util');
+const { embedderRequire, embedderRunCjs } = require('internal/util/embedding');
+const { getEmbedderEntryFunction } = internalBinding('mksnapshot');
+
+prepareMainThreadExecution(false, true);
+markBootstrapComplete();
+
+if (isSea()) {
+  emitExperimentalWarning('Single executable application');
+}
+
+return getEmbedderEntryFunction()(embedderRequire, embedderRunCjs);

lib/internal/main/environment.js

@@ -119,16 +119,25 @@ function main() {
   const {
     prepareMainThreadExecution
   } = require('internal/process/pre_execution');
+  const path = require('path');
 
   let serializeMainFunction = getEmbedderEntryFunction();
   const serializeMainArgs = [requireForUserSnapshot];
 
   if (serializeMainFunction) { // embedded case
     prepareMainThreadExecution(false, false);
+    // TODO(addaleax): Make this `embedderRunCjs` once require('module')
+    // is supported in snapshots.
+    const filename = process.execPath;
+    const dirname = path.dirname(filename);
+    function minimalRunCjs(source) {
+      const fn = compileSerializeMain(filename, source);
+      return fn(requireForUserSnapshot, filename, dirname);
+    }
+    serializeMainArgs.push(minimalRunCjs);
   } else {
     prepareMainThreadExecution(true, false);
     const file = process.argv[1];
-    const path = require('path');
     const filename = path.resolve(file);
     const dirname = path.dirname(filename);
     const source = readFileSync(file, 'utf-8');

lib/internal/main/mksnapshot.js

@@ -0,0 +1,47 @@
+'use strict';
+const { codes: { ERR_UNKNOWN_BUILTIN_MODULE } } = require('internal/errors');
+const { Module, wrapSafe } = require('internal/modules/cjs/loader');
+
+// This is roughly the same as:
+//
+// const mod = new Module(filename);
+// mod._compile(contents, filename);
+//
+// but the code has been duplicated because currently there is no way to set the
+// value of require.main to module.
+//
+// TODO(RaisinTen): Find a way to deduplicate this.
+
+function embedderRunCjs(contents) {
+  const filename = process.execPath;
+  const compiledWrapper = wrapSafe(filename, contents);
+
+  const customModule = new Module(filename, null);
+  customModule.filename = filename;
+  customModule.paths = Module._nodeModulePaths(customModule.path);
+
+  const customExports = customModule.exports;
+
+  embedderRequire.main = customModule;
+
+  const customFilename = customModule.filename;
+
+  const customDirname = customModule.path;
+
+  return compiledWrapper(
+    customExports,
+    embedderRequire,
+    customModule,
+    customFilename,
+    customDirname);
+}
+
+function embedderRequire(path) {
+  if (!Module.isBuiltin(path)) {
+    throw new ERR_UNKNOWN_BUILTIN_MODULE(path);
+  }
+
+  return require(path);
+}
+
+module.exports = { embedderRequire, embedderRunCjs };

lib/internal/main/single_executable_application.js

@@ -528,17 +528,15 @@ MaybeLocal<Value> LoadEnvironment(
   return StartExecution(env, cb);
 }
 
-MaybeLocal<Value> LoadEnvironment(
-    Environment* env,
-    const char* main_script_source_utf8) {
-  CHECK_NOT_NULL(main_script_source_utf8);
+MaybeLocal<Value> LoadEnvironment(Environment* env,
+                                  std::string_view main_script_source_utf8) {
+  CHECK_NOT_NULL(main_script_source_utf8.data());
   return LoadEnvironment(
       env, [&](const StartExecutionCallbackInfo& info) -> MaybeLocal<Value> {
-        std::string name = "embedder_main_" + std::to_string(env->thread_id());
-        env->builtin_loader()->Add(name.c_str(), main_script_source_utf8);
-        Realm* realm = env->principal_realm();
-
-        return realm->ExecuteBootstrapper(name.c_str());
+        Local<Value> main_script =
+            ToV8Value(env->context(), main_script_source_utf8).ToLocalChecked();
+        return info.run_cjs->Call(
+            env->context(), Null(env->isolate()), 1, &main_script);
       });
 }
 

lib/internal/util/embedding.js

@@ -406,14 +406,12 @@ inline builtins::BuiltinLoader* Environment::builtin_loader() {
   return &builtin_loader_;
 }
 
-inline const StartExecutionCallback&
-Environment::embedder_mksnapshot_entry_point() const {
-  return embedder_mksnapshot_entry_point_;
+inline const StartExecutionCallback& Environment::embedder_entry_point() const {
+  return embedder_entry_point_;
 }
 
-inline void Environment::set_embedder_mksnapshot_entry_point(
-    StartExecutionCallback&& fn) {
-  embedder_mksnapshot_entry_point_ = std::move(fn);
+inline void Environment::set_embedder_entry_point(StartExecutionCallback&& fn) {
+  embedder_entry_point_ = std::move(fn);
 }
 
 inline double Environment::new_async_id() {

src/api/environment.cc

@@ -948,8 +948,8 @@ class Environment : public MemoryRetainer {
 
 #endif  // HAVE_INSPECTOR
 
-  inline const StartExecutionCallback& embedder_mksnapshot_entry_point() const;
-  inline void set_embedder_mksnapshot_entry_point(StartExecutionCallback&& fn);
+  inline const StartExecutionCallback& embedder_entry_point() const;
+  inline void set_embedder_entry_point(StartExecutionCallback&& fn);
 
   inline void set_process_exit_handler(
       std::function<void(Environment*, ExitCode)>&& handler);
@@ -1133,7 +1133,7 @@ class Environment : public MemoryRetainer {
   std::unique_ptr<Realm> principal_realm_ = nullptr;
 
   builtins::BuiltinLoader builtin_loader_;
-  StartExecutionCallback embedder_mksnapshot_entry_point_;
+  StartExecutionCallback embedder_entry_point_;
 
   // Used by allocate_managed_buffer() and release_managed_buffer() to keep
   // track of the BackingStore for a given pointer.

src/env-inl.h

@@ -277,22 +277,17 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
 
   if (cb != nullptr) {
     EscapableHandleScope scope(env->isolate());
+    // TODO(addaleax): pass the callback to the main script more directly,
+    // e.g. by making StartExecution(env, builtin) parametrizable
+    env->set_embedder_entry_point(std::move(cb));
+    auto reset_entry_point =
+        OnScopeLeave([&]() { env->set_embedder_entry_point({}); });
 
-    if (env->isolate_data()->options()->build_snapshot) {
-      // TODO(addaleax): pass the callback to the main script more directly,
-      // e.g. by making StartExecution(env, builtin) parametrizable
-      env->set_embedder_mksnapshot_entry_point(std::move(cb));
-      auto reset_entry_point =
-          OnScopeLeave([&]() { env->set_embedder_mksnapshot_entry_point({}); });
+    const char* entry = env->isolate_data()->options()->build_snapshot
+                            ? "internal/main/mksnapshot"
+                            : "internal/main/embedding";
 
-      return StartExecution(env, "internal/main/mksnapshot");
-    }
-
-    if (StartExecution(env, "internal/main/environment").IsEmpty()) return {};
-    return scope.EscapeMaybe(cb({
-        env->process_object(),
-        env->builtin_module_require(),
-    }));
+    return scope.EscapeMaybe(StartExecution(env, entry));
   }
 
   // TODO(joyeecheung): move these conditions into JS land and let the
@@ -312,18 +307,6 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
     first_argv = env->argv()[1];
   }
 
-#ifndef DISABLE_SINGLE_EXECUTABLE_APPLICATION
-  if (sea::IsSingleExecutable()) {
-    // TODO(addaleax): Find a way to reuse:
-    //
-    // LoadEnvironment(Environment*, const char*)
-    //
-    // instead and not add yet another main entry point here because this
-    // already duplicates existing code.
-    return StartExecution(env, "internal/main/single_executable_application");
-  }
-#endif
-
   if (first_argv == "inspect") {
     return StartExecution(env, "internal/main/inspect");
   }

src/env.h

@@ -682,6 +682,7 @@ NODE_EXTERN std::unique_ptr<InspectorParentHandle> GetInspectorParentHandle(
 struct StartExecutionCallbackInfo {
   v8::Local<v8::Object> process_object;
   v8::Local<v8::Function> native_require;
+  v8::Local<v8::Function> run_cjs;
 };
 
 using StartExecutionCallback =
@@ -691,8 +692,7 @@ NODE_EXTERN v8::MaybeLocal<v8::Value> LoadEnvironment(
     Environment* env,
     StartExecutionCallback cb);
 NODE_EXTERN v8::MaybeLocal<v8::Value> LoadEnvironment(
-    Environment* env,
-    const char* main_script_source_utf8);
+    Environment* env, std::string_view main_script_source_utf8);
 NODE_EXTERN void FreeEnvironment(Environment* env);
 
 // Set a callback that is called when process.exit() is called from JS,