internal/node/node_loader.js - third_party/github/bazel-contrib/rules_nodejs - Git at Google

 /**
  * @license
  * Copyright 2017 The Bazel Authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  *
  * You may obtain a copy of the License at
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 /**
  * @fileoverview Patched NodeJS module loader for bazel. This template is
  * expanded to contain module name -> path mappings and then patches the
  * NodeJS require() function to substitute the appropriate paths.
  *
  * @see https://github.com/nodejs/node/blob/master/lib/module.js
  */
 'use strict';
 var path = require('path');
 var fs = require('fs');

 const DEBUG = false;

 /**
  * The module roots as pairs of a RegExp to match the require path, and a
  * module_root to substitute for the require path.
  * Ordered by regex length, longest to smallest.
  * @type {!Array<{module_name: RegExp, module_root: string}>}
  */
 var MODULE_ROOTS = [
   TEMPLATED_module_roots
 ].sort((a, b) => b.module_name.toString().length - a.module_name.toString().length);

 /**
  * Array of bootstrap modules that need to be loaded before the entry point.
  */
 var BOOTSTRAP = [TEMPLATED_bootstrap];

 const USER_WORKSPACE_NAME = 'TEMPLATED_user_workspace_name';
 const NODE_MODULES_ROOT = 'TEMPLATED_node_modules_root';
 const BIN_DIR = 'TEMPLATED_bin_dir';
 const GEN_DIR = 'TEMPLATED_gen_dir';

 if (DEBUG)
   console.error(`
 node_loader: running TEMPLATED_target with
   MODULE_ROOTS: ${JSON.stringify(MODULE_ROOTS, undefined, 2)}
   BOOTSTRAP: ${JSON.stringify(BOOTSTRAP, undefined, 2)}
   NODE_MODULES_ROOT: ${NODE_MODULES_ROOT}
   BIN_DIR: ${BIN_DIR}
   GEN_DIR: ${GEN_DIR}
 `);

 function resolveToModuleRoot(path) {
   if (!path) {
     throw new Error('resolveToModuleRoot missing path: ' + path);
   }

   // We want all possible matches.
   const orderedMatches = MODULE_ROOTS.filter(m => m.module_name.test(path));

   if (orderedMatches.length === 0) {
     return null;
   } else {
     // Longest regex wins when multiple match, and the list is already ordered by length.
     const m = orderedMatches[0];
     return path.replace(m.module_name, m.module_root);
   }
 }

 /**
  * The runfiles manifest maps from short_path
  * https://docs.bazel.build/versions/master/skylark/lib/File.html#short_path
  * to the actual location on disk where the file can be read.
  *
  * In a sandboxed execution, it does not exist. In that case, runfiles must be
  * resolved from a symlink tree under the runfiles dir.
  * See https://github.com/bazelbuild/bazel/issues/3726
  */
 function loadRunfilesManifest(manifestPath) {
   if (DEBUG) console.error(`node_loader: using manifest ${manifestPath}`);

   // Create the manifest and reverse manifest maps.
   const runfilesManifest = Object.create(null);
   const reverseRunfilesManifest = Object.create(null);
   const input = fs.readFileSync(manifestPath, {encoding: 'utf-8'});

   // Absolute path that refers to the local workspace path. We need to determine the absolute
   // path to the local workspace because it allows us to support absolute path resolving
   // for runfiles.
   let localWorkspacePath = null;

   for (const line of input.split('\n')) {
     if (!line) continue;
     const [runfilesPath, realPath] = line.split(' ');
     runfilesManifest[runfilesPath] = realPath;
     reverseRunfilesManifest[realPath] = runfilesPath;

     // We don't need to try determining the local workspace path for the current runfile
     // mapping in case we already determined the local workspace path, the current
     // runfile refers to a different workspace, or the current runfile resolves to a file
     // in the bazel-out directory (bin/genfiles directory).
     if (localWorkspacePath || !runfilesPath.startsWith(USER_WORKSPACE_NAME) ||
         realPath.includes(BIN_DIR) || realPath.includes(GEN_DIR)) {
       continue;
     }

     // Relative path for the runfile. We can compute that path by removing the leading
     // workspace name. e.g. `my_workspace/src/my-runfile.js` becomes `src/my-runfile.js`.
     const relativeWorkspacePath = runfilesPath.slice(USER_WORKSPACE_NAME.length + 1);

     // TODO(gregmagolan): should not be needed when --nolegacy_external_runfiles is default
     if (relativeWorkspacePath.startsWith('external/')) {
       continue;
     }

     localWorkspacePath = realPath.slice(0, -relativeWorkspacePath.length);
   }

   // Determine bin and gen root to convert absolute paths into runfile paths.
   const binRootIdx = manifestPath.indexOf(BIN_DIR);
   let binRoot, genRoot;
   if (binRootIdx !== -1) {
     const execRoot = manifestPath.slice(0, binRootIdx);
     binRoot = `${execRoot}${BIN_DIR}/`;
     genRoot = `${execRoot}${GEN_DIR}/`;
   }

   if (DEBUG) console.error(`node_loader: using binRoot ${binRoot}`);
   if (DEBUG) console.error(`node_loader: using genRoot ${genRoot}`);
   if (DEBUG) console.error(`node_loader: using localWorkspacePath ${localWorkspacePath}`);

   return { runfilesManifest, reverseRunfilesManifest, binRoot, genRoot, localWorkspacePath };
 }
 const { runfilesManifest, reverseRunfilesManifest, binRoot, genRoot, localWorkspacePath } =
     // On Windows, Bazel sets RUNFILES_MANIFEST_ONLY=1.
     // On every platform, Bazel also sets RUNFILES_MANIFEST_FILE, but on Linux
     // and macOS it's faster to use the symlinks in RUNFILES_DIR rather than resolve
     // through the indirection of the manifest file.
     // We also need to construct a reverse map to resolve relative files from existing
     // manifest entries.
     process.env.RUNFILES_MANIFEST_ONLY === '1' &&
     loadRunfilesManifest(process.env.RUNFILES_MANIFEST_FILE);

 function isFile(res) {
   try {
     return fs.statSync(res).isFile();
   } catch (e) {
     return false;
   }
 }

 function isDirectory(res) {
   try {
     return fs.statSync(res).isDirectory();
   } catch (e) {
     return false;
   }
 }

 function readDir(dir) {
   return fs.statSync(dir).isDirectory() ?
       Array.prototype.concat(...fs.readdirSync(dir).map(f => readDir(path.join(dir, f)))) :
       dir.replace(/\\/g, '/');
 }

 function loadAsFileSync(res) {
   if (isFile(res)) {
     return res;
   }
   if (isFile(res + '.js')) {
     return res;
   }
   return null;
 }

 function loadAsDirectorySync(res) {
   const pkgfile = path.join(res, 'package.json');
   if (isFile(pkgfile)) {
     try {
       const pkg = JSON.parse(fs.readFileSync(pkgfile, 'UTF-8'));
       const main = pkg['main'];
       if (main) {
         if (main === '.' || main === './') {
           main = 'index';
         }

         let maybe = loadAsFileSync(path.resolve(res, main));
         if (maybe) {
           return maybe;
         }

         maybe = loadAsDirectorySync(path.resolve(res, main));
         if (maybe) {
           return maybe;
         }
       }
     } catch (e) {
     }
   }
   return loadAsFileSync(path.resolve(res, 'index'));
 }

 function resolveManifestFile(res) {
   const maybe = runfilesManifest[res] || runfilesManifest[res + '.js'];
   if (maybe) {
     return maybe;
   }
   // Look for tree artifacts that match and update
   // the runfiles with files that are in the tree artifact.
   // Attempt to resolve again with the updated runfiles
   // if a tree artifact matched.
   let segments = res.split('/');
   segments.pop();
   while (segments.length) {
     const test = segments.join('/');
     const tree = runfilesManifest[test];
     if (tree && isDirectory(tree)) {
       // We have a tree artifact that matches
       const files = readDir(tree).map(f => path.relative(tree, f).replace(/\\/g, '/'));
       files.forEach(f => {
         runfilesManifest[path.posix.join(test, f)] = path.posix.join(tree, f);
       })
       return runfilesManifest[res] || runfilesManifest[res + '.js'];
     }
     segments.pop();
   }
 }

 function resolveManifestDirectory(res) {
   const pkgfile = runfilesManifest[path.posix.join(res, 'package.json')];
   if (pkgfile) {
     try {
       const pkg = JSON.parse(fs.readFileSync(pkgfile, 'UTF-8'));
       const main = pkg['main'];
       if (main) {
         if (main === '.' || main === './') {
           main = 'index';
         }

         let maybe = resolveManifestFile(path.posix.join(res, main));
         if (maybe) {
           return maybe;
         }

         maybe = resolveManifestDirectory(path.posix.join(res, main));
         if (maybe) {
           return maybe;
         }
       }
     } catch (e) {
     }
   }
   return resolveManifestFile(path.posix.join(res, 'index'));
 }

 function resolveRunfiles(parent, ...pathSegments) {
   // Remove any empty strings from pathSegments
   pathSegments = pathSegments.filter(segment => segment);

   const defaultPath = path.join(process.env.RUNFILES, ...pathSegments);

   if (runfilesManifest) {
     // Normalize to forward slash, because even on Windows the runfiles_manifest file
     // is written with forward slash.
     let runfilesEntry = pathSegments.join('/').replace(/\\/g, '/');

     if (parent && runfilesEntry.startsWith('.')) {
       // Resolve relative paths from manifest files.
       const normalizedParent = parent.replace(/\\/g, '/');
       const parentRunfile = reverseRunfilesManifest[normalizedParent];
       if (parentRunfile) {
         runfilesEntry = path.join(path.dirname(parentRunfile), runfilesEntry);
       }
     } else if (runfilesEntry.startsWith(binRoot) || runfilesEntry.startsWith(genRoot)
         || runfilesEntry.startsWith(localWorkspacePath)) {
       // For absolute paths, replace binRoot, genRoot or localWorkspacePath with
       // USER_WORKSPACE_NAME to enable lookups.
       // It's OK to do multiple replacements because all of these are absolute paths with drive
       // names (e.g. C:\), and on Windows you can't have drive names in the middle of paths.
       runfilesEntry = runfilesEntry
         .replace(binRoot, `${USER_WORKSPACE_NAME}/`)
         .replace(genRoot, `${USER_WORKSPACE_NAME}/`)
         .replace(localWorkspacePath, `${USER_WORKSPACE_NAME}/`);
     }

     // Normalize and replace path separators to conform to the ones in the manifest.
     runfilesEntry = path.normalize(runfilesEntry).replace(/\\/g, '/');

     if (DEBUG) console.error('node_loader: try to resolve in runfiles manifest', runfilesEntry);

     let maybe = resolveManifestFile(runfilesEntry);
     if (maybe) {
       if (DEBUG) console.error('node_loader: resolved manifest file', maybe);
       return maybe;
     }

     maybe = resolveManifestDirectory(runfilesEntry);
     if (maybe) {
       if (DEBUG) console.error('node_loader: resolved via manifest directory', maybe);
       return maybe;
     }
   } else {
     if (DEBUG) console.error('node_loader: try to resolve in runfiles', defaultPath);

     let maybe = loadAsFileSync(defaultPath);
     if (maybe) {
       if (DEBUG) console.error('node_loader: resolved file', maybe);
       return maybe;
     }

     maybe = loadAsDirectorySync(defaultPath);
     if (maybe) {
       if (DEBUG) console.error('node_loader: resolved via directory', maybe);
       return maybe;
     }
   }

   return defaultPath;
 }

 var originalResolveFilename = module.constructor._resolveFilename;
 module.constructor._resolveFilename = function(request, parent) {
   const parentFilename = (parent && parent.filename) ? parent.filename : undefined;
   if (DEBUG)
     console.error(`node_loader: resolve ${request} from ${parentFilename}`);

   const failedResolutions = [];

   // Attempt to resolve to module root.
   // This should be the first attempted resolution because:
   // - it's fairly cheap to check (regex over a small array);
   // - will throw if something is wrong and not cascade down;
   // - it is be very common when there are a lot of packages built from source;
   const moduleRoot = resolveToModuleRoot(request);
   if (moduleRoot) {
     const moduleRootInRunfiles = resolveRunfiles(undefined, moduleRoot);
     const filename = module.constructor._findPath(moduleRootInRunfiles, []);
     if (!filename) {
       throw new Error(`No file ${request} found in module root ${moduleRoot}`);
     }
     return filename;
   }

   // Built-in modules, relative, absolute imports and npm dependencies
   // can be resolved using request
   try {
     const resolved = originalResolveFilename(request, parent);
     if (resolved === request || request.startsWith('.') || request.startsWith('/') ||
         request.match(/^[A-Z]\:[\\\/]/i)) {
       if (DEBUG)
         console.error(
             `node_loader: resolved ${request} to built-in, relative or absolute import ` +
             `${resolved} from ${parentFilename}`
         );
       return resolved;
     } else {
       // Resolved is not a built-in module, relative or absolute import
       // but also allow imports within npm packages that are within the parent files
       // node_modules, meaning it is a dependency of the npm package making the import.
       const parentSegments = parentFilename ? parentFilename.replace(/\\/g, '/').split('/') : [];
       const parentNodeModulesSegment = parentSegments.indexOf('node_modules');
       if (parentNodeModulesSegment != -1) {
         const parentRoot = parentSegments.slice(0, parentNodeModulesSegment).join('/');
         const relative = path.relative(parentRoot, resolved);
         if (!relative.startsWith('..')) {
           // Resolved within parent node_modules
           if (DEBUG)
             console.error(
                 `node_loader: resolved ${request} within parent node_modules to ` +
                 `${resolved} from ${parentFilename}`
             );
           return resolved;
         } else {
           throw new Error(
               `Resolved to ${resolved} outside of parent node_modules ${parentFilename}`);
         }
       }
       throw new Error('Not a built-in module, relative or absolute import');
     }
   } catch (e) {
     failedResolutions.push(`built-in, relative, absolute, nested node_modules - ${e.toString()}`);
   }

   // If the import is not a built-in module, an absolute, relative import or a
   // dependency of an npm package, attempt to resolve against the runfiles location
   try {
     const resolved = originalResolveFilename(resolveRunfiles(parentFilename, request), parent);
     if (DEBUG)
       console.error(
           `node_loader: resolved ${request} within runfiles to ${resolved} from ${parentFilename}`
       );
     return resolved;
   } catch (e) {
     failedResolutions.push(`runfiles - ${e.toString()}`);
   }

   // If the parent file is from an external repository, attempt to resolve against
   // the external repositories node_modules (if they exist)
   let relativeParentFilename =
       parentFilename ? path.relative(process.env.RUNFILES, parent.filename) : undefined;
   if (relativeParentFilename && !relativeParentFilename.startsWith('..')) {
     // Remove leading USER_WORKSPACE_NAME/external so that external workspace name is
     // always the first segment
     // TODO(gregmagolan): should not be needed when --nolegacy_external_runfiles is default
     const externalPrefix = `${USER_WORKSPACE_NAME}/external/`;
     if (relativeParentFilename.startsWith(externalPrefix)) {
       relativeParentFilename = relativeParentFilename.substr(externalPrefix.length);
     }
     const parentSegments = relativeParentFilename.split('/');
     if (parentSegments[0] !== USER_WORKSPACE_NAME) {
       try {
         const resolved = originalResolveFilename(
             resolveRunfiles(undefined, parentSegments[0], 'node_modules', request), parent);
         if (DEBUG)
           console.error(
               `node_loader: resolved ${request} within node_modules ` +
               `(${parentSegments[0]}/node_modules) to ${resolved} from ${relativeParentFilename}`
           );
         return resolved;
       } catch (e) {
         failedResolutions.push(`${parentSegments[0]}/node_modules - ${e.toString()}`);
       }
     }
   }

   // If import was not resolved above then attempt to resolve
   // within the node_modules filegroup in use
   try {
     const resolved = originalResolveFilename(
         resolveRunfiles(undefined, NODE_MODULES_ROOT, request), parent);
     if (DEBUG)
       console.error(
           `node_loader: resolved ${request} within node_modules (${NODE_MODULES_ROOT}) to ` +
           `${resolved} from ${parentFilename}`
       );
     return resolved;
   } catch (e) {
     failedResolutions.push(`node_modules attribute (${NODE_MODULES_ROOT}) - ${e.toString()}`);
   }

   const error = new Error(
       `TEMPLATED_target cannot find module '${request}' required by '${parentFilename}'\n  looked in:\n` +
       failedResolutions.map(r => `    ${r}`).join('\n') + '\n');
   error.code = 'MODULE_NOT_FOUND';
   throw error;
 }

 // Before loading anything that might print a stack, install the
 // source-map-support.
 if (TEMPLATED_install_source_map_support) {
   try {
     const sourcemap_support_package = path.resolve(process.cwd(),
           '../build_bazel_rules_nodejs/third_party/github.com/source-map-support');
     require(sourcemap_support_package).install();
   } catch (_) {
     if (DEBUG) {
       console.error(`WARNING: source-map-support module not installed.
       Stack traces from languages like TypeScript will point to generated .js files.
       Set install_source_map_support = False in TEMPLATED_target to turn off this warning.
       `);
     }
   }
 }
 // Load all bootstrap modules before loading the entrypoint.
 for (var i = 0; i < BOOTSTRAP.length; i++) {
   try {
     module.constructor._load(BOOTSTRAP[i], this);
   } catch (e) {
     console.error('bootstrap failure ' + e.stack || e);
     process.exit(1);
   }
 }

 if (require.main === module) {
   // Set the actual entry point in the arguments list.
   // argv[0] == node, argv[1] == entry point.
   // NB: entry_point below is replaced during the build process.
   var mainScript = process.argv[1] = 'TEMPLATED_entry_point';
   try {
     module.constructor._load(mainScript, this, /*isMain=*/true);
   } catch (e) {
     console.error(e.stack || e);
     if (NODE_MODULES_ROOT === 'build_bazel_rules_nodejs/node_modules') {
       // This error is possibly due to a breaking change in 0.13.0 where
       // the default node_modules attribute of nodejs_binary was changed
       // from @//:node_modules to @build_bazel_rules_nodejs//:node_modules_none
       // (which is an empty filegroup).
       // See https://github.com/bazelbuild/rules_nodejs/wiki#migrating-to-rules_nodejs-013
       console.error(
           `\nWARNING: Due to a breaking change in rules_nodejs 0.13.0, target TEMPLATED_target\n` +
           `must now declare either an explicit node_modules attribute, or\n` +
           `list explicit deps[] or data[] fine grained dependencies on npm labels\n` +
           `if it has any node_modules dependencies.\n` +
           `See https://github.com/bazelbuild/rules_nodejs/wiki#migrating-to-rules_nodejs-013\n`);
     }
     process.exit(1);
   }
 }
	/**
	* @license
	* Copyright 2017 The Bazel Authors. All rights reserved.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	*
	* You may obtain a copy of the License at
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	/**
	* @fileoverview Patched NodeJS module loader for bazel. This template is
	* expanded to contain module name -> path mappings and then patches the
	* NodeJS require() function to substitute the appropriate paths.
	*
	* @see https://github.com/nodejs/node/blob/master/lib/module.js
	*/
	'use strict';
	var path = require('path');
	var fs = require('fs');

	const DEBUG = false;

	/**
	* The module roots as pairs of a RegExp to match the require path, and a
	* module_root to substitute for the require path.
	* Ordered by regex length, longest to smallest.
	* @type {!Array<{module_name: RegExp, module_root: string}>}
	*/
	var MODULE_ROOTS = [
	TEMPLATED_module_roots
	].sort((a, b) => b.module_name.toString().length - a.module_name.toString().length);

	/**
	* Array of bootstrap modules that need to be loaded before the entry point.
	*/
	var BOOTSTRAP = [TEMPLATED_bootstrap];

	const USER_WORKSPACE_NAME = 'TEMPLATED_user_workspace_name';
	const NODE_MODULES_ROOT = 'TEMPLATED_node_modules_root';
	const BIN_DIR = 'TEMPLATED_bin_dir';
	const GEN_DIR = 'TEMPLATED_gen_dir';

	if (DEBUG)
	console.error(`
	node_loader: running TEMPLATED_target with
	MODULE_ROOTS: ${JSON.stringify(MODULE_ROOTS, undefined, 2)}
	BOOTSTRAP: ${JSON.stringify(BOOTSTRAP, undefined, 2)}
	NODE_MODULES_ROOT: ${NODE_MODULES_ROOT}
	BIN_DIR: ${BIN_DIR}
	GEN_DIR: ${GEN_DIR}
	`);

	function resolveToModuleRoot(path) {
	if (!path) {
	throw new Error('resolveToModuleRoot missing path: ' + path);
	}

	// We want all possible matches.
	const orderedMatches = MODULE_ROOTS.filter(m => m.module_name.test(path));

	if (orderedMatches.length === 0) {
	return null;
	} else {
	// Longest regex wins when multiple match, and the list is already ordered by length.
	const m = orderedMatches[0];
	return path.replace(m.module_name, m.module_root);
	}
	}

	/**
	* The runfiles manifest maps from short_path
	* https://docs.bazel.build/versions/master/skylark/lib/File.html#short_path
	* to the actual location on disk where the file can be read.
	*
	* In a sandboxed execution, it does not exist. In that case, runfiles must be
	* resolved from a symlink tree under the runfiles dir.
	* See https://github.com/bazelbuild/bazel/issues/3726
	*/
	function loadRunfilesManifest(manifestPath) {
	if (DEBUG) console.error(`node_loader: using manifest ${manifestPath}`);

	// Create the manifest and reverse manifest maps.
	const runfilesManifest = Object.create(null);
	const reverseRunfilesManifest = Object.create(null);
	const input = fs.readFileSync(manifestPath, {encoding: 'utf-8'});

	// Absolute path that refers to the local workspace path. We need to determine the absolute
	// path to the local workspace because it allows us to support absolute path resolving
	// for runfiles.
	let localWorkspacePath = null;

	for (const line of input.split('\n')) {
	if (!line) continue;
	const [runfilesPath, realPath] = line.split(' ');
	runfilesManifest[runfilesPath] = realPath;
	reverseRunfilesManifest[realPath] = runfilesPath;

	// We don't need to try determining the local workspace path for the current runfile
	// mapping in case we already determined the local workspace path, the current
	// runfile refers to a different workspace, or the current runfile resolves to a file
	// in the bazel-out directory (bin/genfiles directory).
	if (localWorkspacePath \|\| !runfilesPath.startsWith(USER_WORKSPACE_NAME) \|\|
	realPath.includes(BIN_DIR) \|\| realPath.includes(GEN_DIR)) {
	continue;
	}

	// Relative path for the runfile. We can compute that path by removing the leading
	// workspace name. e.g. `my_workspace/src/my-runfile.js` becomes `src/my-runfile.js`.
	const relativeWorkspacePath = runfilesPath.slice(USER_WORKSPACE_NAME.length + 1);

	// TODO(gregmagolan): should not be needed when --nolegacy_external_runfiles is default
	if (relativeWorkspacePath.startsWith('external/')) {
	continue;
	}

	localWorkspacePath = realPath.slice(0, -relativeWorkspacePath.length);
	}

	// Determine bin and gen root to convert absolute paths into runfile paths.
	const binRootIdx = manifestPath.indexOf(BIN_DIR);
	let binRoot, genRoot;
	if (binRootIdx !== -1) {
	const execRoot = manifestPath.slice(0, binRootIdx);
	binRoot = `${execRoot}${BIN_DIR}/`;
	genRoot = `${execRoot}${GEN_DIR}/`;
	}

	if (DEBUG) console.error(`node_loader: using binRoot ${binRoot}`);
	if (DEBUG) console.error(`node_loader: using genRoot ${genRoot}`);
	if (DEBUG) console.error(`node_loader: using localWorkspacePath ${localWorkspacePath}`);

	return { runfilesManifest, reverseRunfilesManifest, binRoot, genRoot, localWorkspacePath };
	}
	const { runfilesManifest, reverseRunfilesManifest, binRoot, genRoot, localWorkspacePath } =
	// On Windows, Bazel sets RUNFILES_MANIFEST_ONLY=1.
	// On every platform, Bazel also sets RUNFILES_MANIFEST_FILE, but on Linux
	// and macOS it's faster to use the symlinks in RUNFILES_DIR rather than resolve
	// through the indirection of the manifest file.
	// We also need to construct a reverse map to resolve relative files from existing
	// manifest entries.
	process.env.RUNFILES_MANIFEST_ONLY === '1' &&
	loadRunfilesManifest(process.env.RUNFILES_MANIFEST_FILE);

	function isFile(res) {
	try {
	return fs.statSync(res).isFile();
	} catch (e) {
	return false;
	}
	}

	function isDirectory(res) {
	try {
	return fs.statSync(res).isDirectory();
	} catch (e) {
	return false;
	}
	}

	function readDir(dir) {
	return fs.statSync(dir).isDirectory() ?
	Array.prototype.concat(...fs.readdirSync(dir).map(f => readDir(path.join(dir, f)))) :
	dir.replace(/\\/g, '/');
	}

	function loadAsFileSync(res) {
	if (isFile(res)) {
	return res;
	}
	if (isFile(res + '.js')) {
	return res;
	}
	return null;
	}

	function loadAsDirectorySync(res) {
	const pkgfile = path.join(res, 'package.json');
	if (isFile(pkgfile)) {
	try {
	const pkg = JSON.parse(fs.readFileSync(pkgfile, 'UTF-8'));
	const main = pkg['main'];
	if (main) {
	if (main === '.' \|\| main === './') {
	main = 'index';
	}

	let maybe = loadAsFileSync(path.resolve(res, main));
	if (maybe) {
	return maybe;
	}

	maybe = loadAsDirectorySync(path.resolve(res, main));
	if (maybe) {
	return maybe;
	}
	}
	} catch (e) {
	}
	}
	return loadAsFileSync(path.resolve(res, 'index'));
	}

	function resolveManifestFile(res) {
	const maybe = runfilesManifest[res] \|\| runfilesManifest[res + '.js'];
	if (maybe) {
	return maybe;
	}
	// Look for tree artifacts that match and update
	// the runfiles with files that are in the tree artifact.
	// Attempt to resolve again with the updated runfiles
	// if a tree artifact matched.
	let segments = res.split('/');
	segments.pop();
	while (segments.length) {
	const test = segments.join('/');
	const tree = runfilesManifest[test];
	if (tree && isDirectory(tree)) {
	// We have a tree artifact that matches
	const files = readDir(tree).map(f => path.relative(tree, f).replace(/\\/g, '/'));
	files.forEach(f => {
	runfilesManifest[path.posix.join(test, f)] = path.posix.join(tree, f);
	})
	return runfilesManifest[res] \|\| runfilesManifest[res + '.js'];
	}
	segments.pop();
	}
	}

	function resolveManifestDirectory(res) {
	const pkgfile = runfilesManifest[path.posix.join(res, 'package.json')];
	if (pkgfile) {
	try {
	const pkg = JSON.parse(fs.readFileSync(pkgfile, 'UTF-8'));
	const main = pkg['main'];
	if (main) {
	if (main === '.' \|\| main === './') {
	main = 'index';
	}

	let maybe = resolveManifestFile(path.posix.join(res, main));
	if (maybe) {
	return maybe;
	}

	maybe = resolveManifestDirectory(path.posix.join(res, main));
	if (maybe) {
	return maybe;
	}
	}
	} catch (e) {
	}
	}
	return resolveManifestFile(path.posix.join(res, 'index'));
	}

	function resolveRunfiles(parent, ...pathSegments) {
	// Remove any empty strings from pathSegments
	pathSegments = pathSegments.filter(segment => segment);

	const defaultPath = path.join(process.env.RUNFILES, ...pathSegments);

	if (runfilesManifest) {
	// Normalize to forward slash, because even on Windows the runfiles_manifest file
	// is written with forward slash.
	let runfilesEntry = pathSegments.join('/').replace(/\\/g, '/');

	if (parent && runfilesEntry.startsWith('.')) {
	// Resolve relative paths from manifest files.
	const normalizedParent = parent.replace(/\\/g, '/');
	const parentRunfile = reverseRunfilesManifest[normalizedParent];
	if (parentRunfile) {
	runfilesEntry = path.join(path.dirname(parentRunfile), runfilesEntry);
	}
	} else if (runfilesEntry.startsWith(binRoot) \|\| runfilesEntry.startsWith(genRoot)
	\|\| runfilesEntry.startsWith(localWorkspacePath)) {
	// For absolute paths, replace binRoot, genRoot or localWorkspacePath with
	// USER_WORKSPACE_NAME to enable lookups.
	// It's OK to do multiple replacements because all of these are absolute paths with drive
	// names (e.g. C:\), and on Windows you can't have drive names in the middle of paths.
	runfilesEntry = runfilesEntry
	.replace(binRoot, `${USER_WORKSPACE_NAME}/`)
	.replace(genRoot, `${USER_WORKSPACE_NAME}/`)
	.replace(localWorkspacePath, `${USER_WORKSPACE_NAME}/`);
	}

	// Normalize and replace path separators to conform to the ones in the manifest.
	runfilesEntry = path.normalize(runfilesEntry).replace(/\\/g, '/');

	if (DEBUG) console.error('node_loader: try to resolve in runfiles manifest', runfilesEntry);

	let maybe = resolveManifestFile(runfilesEntry);
	if (maybe) {
	if (DEBUG) console.error('node_loader: resolved manifest file', maybe);
	return maybe;
	}

	maybe = resolveManifestDirectory(runfilesEntry);
	if (maybe) {
	if (DEBUG) console.error('node_loader: resolved via manifest directory', maybe);
	return maybe;
	}
	} else {
	if (DEBUG) console.error('node_loader: try to resolve in runfiles', defaultPath);

	let maybe = loadAsFileSync(defaultPath);
	if (maybe) {
	if (DEBUG) console.error('node_loader: resolved file', maybe);
	return maybe;
	}

	maybe = loadAsDirectorySync(defaultPath);
	if (maybe) {
	if (DEBUG) console.error('node_loader: resolved via directory', maybe);
	return maybe;
	}
	}

	return defaultPath;
	}

	var originalResolveFilename = module.constructor._resolveFilename;
	module.constructor._resolveFilename = function(request, parent) {
	const parentFilename = (parent && parent.filename) ? parent.filename : undefined;
	if (DEBUG)
	console.error(`node_loader: resolve ${request} from ${parentFilename}`);

	const failedResolutions = [];

	// Attempt to resolve to module root.
	// This should be the first attempted resolution because:
	// - it's fairly cheap to check (regex over a small array);
	// - will throw if something is wrong and not cascade down;
	// - it is be very common when there are a lot of packages built from source;
	const moduleRoot = resolveToModuleRoot(request);
	if (moduleRoot) {
	const moduleRootInRunfiles = resolveRunfiles(undefined, moduleRoot);
	const filename = module.constructor._findPath(moduleRootInRunfiles, []);
	if (!filename) {
	throw new Error(`No file ${request} found in module root ${moduleRoot}`);
	}
	return filename;
	}

	// Built-in modules, relative, absolute imports and npm dependencies
	// can be resolved using request
	try {
	const resolved = originalResolveFilename(request, parent);
	if (resolved === request \|\| request.startsWith('.') \|\| request.startsWith('/') \|\|
	request.match(/^[A-Z]\:[\\\/]/i)) {
	if (DEBUG)
	console.error(
	`node_loader: resolved ${request} to built-in, relative or absolute import ` +
	`${resolved} from ${parentFilename}`
	);
	return resolved;
	} else {
	// Resolved is not a built-in module, relative or absolute import
	// but also allow imports within npm packages that are within the parent files
	// node_modules, meaning it is a dependency of the npm package making the import.
	const parentSegments = parentFilename ? parentFilename.replace(/\\/g, '/').split('/') : [];
	const parentNodeModulesSegment = parentSegments.indexOf('node_modules');
	if (parentNodeModulesSegment != -1) {
	const parentRoot = parentSegments.slice(0, parentNodeModulesSegment).join('/');
	const relative = path.relative(parentRoot, resolved);
	if (!relative.startsWith('..')) {
	// Resolved within parent node_modules
	if (DEBUG)
	console.error(
	`node_loader: resolved ${request} within parent node_modules to ` +
	`${resolved} from ${parentFilename}`
	);
	return resolved;
	} else {
	throw new Error(
	`Resolved to ${resolved} outside of parent node_modules ${parentFilename}`);
	}
	}
	throw new Error('Not a built-in module, relative or absolute import');
	}
	} catch (e) {
	failedResolutions.push(`built-in, relative, absolute, nested node_modules - ${e.toString()}`);
	}

	// If the import is not a built-in module, an absolute, relative import or a
	// dependency of an npm package, attempt to resolve against the runfiles location
	try {
	const resolved = originalResolveFilename(resolveRunfiles(parentFilename, request), parent);
	if (DEBUG)
	console.error(
	`node_loader: resolved ${request} within runfiles to ${resolved} from ${parentFilename}`
	);
	return resolved;
	} catch (e) {
	failedResolutions.push(`runfiles - ${e.toString()}`);
	}

	// If the parent file is from an external repository, attempt to resolve against
	// the external repositories node_modules (if they exist)
	let relativeParentFilename =
	parentFilename ? path.relative(process.env.RUNFILES, parent.filename) : undefined;
	if (relativeParentFilename && !relativeParentFilename.startsWith('..')) {
	// Remove leading USER_WORKSPACE_NAME/external so that external workspace name is
	// always the first segment
	// TODO(gregmagolan): should not be needed when --nolegacy_external_runfiles is default
	const externalPrefix = `${USER_WORKSPACE_NAME}/external/`;
	if (relativeParentFilename.startsWith(externalPrefix)) {
	relativeParentFilename = relativeParentFilename.substr(externalPrefix.length);
	}
	const parentSegments = relativeParentFilename.split('/');
	if (parentSegments[0] !== USER_WORKSPACE_NAME) {
	try {
	const resolved = originalResolveFilename(
	resolveRunfiles(undefined, parentSegments[0], 'node_modules', request), parent);
	if (DEBUG)
	console.error(
	`node_loader: resolved ${request} within node_modules ` +
	`(${parentSegments[0]}/node_modules) to ${resolved} from ${relativeParentFilename}`
	);
	return resolved;
	} catch (e) {
	failedResolutions.push(`${parentSegments[0]}/node_modules - ${e.toString()}`);
	}
	}
	}

	// If import was not resolved above then attempt to resolve
	// within the node_modules filegroup in use
	try {
	const resolved = originalResolveFilename(
	resolveRunfiles(undefined, NODE_MODULES_ROOT, request), parent);
	if (DEBUG)
	console.error(
	`node_loader: resolved ${request} within node_modules (${NODE_MODULES_ROOT}) to ` +
	`${resolved} from ${parentFilename}`
	);
	return resolved;
	} catch (e) {
	failedResolutions.push(`node_modules attribute (${NODE_MODULES_ROOT}) - ${e.toString()}`);
	}

	const error = new Error(
	`TEMPLATED_target cannot find module '${request}' required by '${parentFilename}'\n looked in:\n` +
	failedResolutions.map(r => ` ${r}`).join('\n') + '\n');
	error.code = 'MODULE_NOT_FOUND';
	throw error;
	}

	// Before loading anything that might print a stack, install the
	// source-map-support.
	if (TEMPLATED_install_source_map_support) {
	try {
	const sourcemap_support_package = path.resolve(process.cwd(),
	'../build_bazel_rules_nodejs/third_party/github.com/source-map-support');
	require(sourcemap_support_package).install();
	} catch (_) {
	if (DEBUG) {
	console.error(`WARNING: source-map-support module not installed.
	Stack traces from languages like TypeScript will point to generated .js files.
	Set install_source_map_support = False in TEMPLATED_target to turn off this warning.
	`);
	}
	}
	}
	// Load all bootstrap modules before loading the entrypoint.
	for (var i = 0; i < BOOTSTRAP.length; i++) {
	try {
	module.constructor._load(BOOTSTRAP[i], this);
	} catch (e) {
	console.error('bootstrap failure ' + e.stack \|\| e);
	process.exit(1);
	}
	}

	if (require.main === module) {
	// Set the actual entry point in the arguments list.
	// argv[0] == node, argv[1] == entry point.
	// NB: entry_point below is replaced during the build process.
	var mainScript = process.argv[1] = 'TEMPLATED_entry_point';
	try {
	module.constructor._load(mainScript, this, /isMain=/true);
	} catch (e) {
	console.error(e.stack \|\| e);
	if (NODE_MODULES_ROOT === 'build_bazel_rules_nodejs/node_modules') {
	// This error is possibly due to a breaking change in 0.13.0 where
	// the default node_modules attribute of nodejs_binary was changed
	// from @//:node_modules to @build_bazel_rules_nodejs//:node_modules_none
	// (which is an empty filegroup).
	// See https://github.com/bazelbuild/rules_nodejs/wiki#migrating-to-rules_nodejs-013
	console.error(
	`\nWARNING: Due to a breaking change in rules_nodejs 0.13.0, target TEMPLATED_target\n` +
	`must now declare either an explicit node_modules attribute, or\n` +
	`list explicit deps[] or data[] fine grained dependencies on npm labels\n` +
	`if it has any node_modules dependencies.\n` +
	`See https://github.com/bazelbuild/rules_nodejs/wiki#migrating-to-rules_nodejs-013\n`);
	}
	process.exit(1);
	}
	}