module: resolve self-references

doc/api/cli.md

@@ -196,6 +196,14 @@ added: v11.8.0
 
 Enable experimental diagnostic report feature.
 
+### `--experimental-resolve-self`
+<!-- YAML
+added: REPLACEME
+-->
+
+Enable experimental support for a package using `require` or `import` to load
+itself.
+
 ### `--experimental-vm-modules`
 <!-- YAML
 added: v9.6.0
@@ -1010,6 +1018,7 @@ Node.js options that are allowed are:
 * `--experimental-policy`
 * `--experimental-repl-await`
 * `--experimental-report`
+* `--experimental-resolve-self`
 * `--experimental-vm-modules`
 * `--experimental-wasm-modules`
 * `--force-context-aware`

doc/api/esm.md

@@ -839,9 +839,6 @@ _isMain_ is **true** when resolving the Node.js application entry point.
 > 1. Let _packageSubpath_ be *undefined*.
 > 1. If _packageSpecifier_ is an empty string, then
 >    1. Throw an _Invalid Specifier_ error.
-> 1. If _packageSpecifier_ does not start with _"@"_, then
->    1. Set _packageName_ to the substring of _packageSpecifier_ until the
->       first _"/"_ separator or the end of the string.
 > 1. Otherwise,
 >    1. If _packageSpecifier_ does not contain a _"/"_ separator, then
 >       1. Throw an _Invalid Specifier_ error.
@@ -855,7 +852,7 @@ _isMain_ is **true** when resolving the Node.js application entry point.
 >    1. Set _packageSubpath_ to _"."_ concatenated with the substring of
 >       _packageSpecifier_ from the position at the length of _packageName_.
 > 1. If _packageSubpath_ contains any _"."_ or _".."_ segments or percent
->    encoded strings for _"/"_ or _"\\"_ then,
+>    encoded strings for _"/"_ or _"\\"_, then
 >    1. Throw an _Invalid Specifier_ error.
 > 1. If _packageSubpath_ is _undefined_ and _packageName_ is a Node.js builtin
 >    module, then
@@ -878,8 +875,31 @@ _isMain_ is **true** when resolving the Node.js application entry point.
 >             1. Return **PACKAGE_EXPORTS_RESOLVE**(_packageURL_,
 >                _packageSubpath_, _pjson.exports_).
 >       1. Return the URL resolution of _packageSubpath_ in _packageURL_.
+> 1. Set _selfUrl_ to the result of
+>    **SELF_REFERENCE_RESOLE**(_packageSpecifier_, _parentURL_).
+> 1. If _selfUrl_ isn't empty, return _selfUrl_.
 > 1. Throw a _Module Not Found_ error.
 
+**SELF_REFERENCE_RESOLVE**(_specifier_, _parentURL_)
+
+> 1. Let _packageURL_ be the result of **READ_PACKAGE_SCOPE**(_parentURL_).
+> 1. If _packageURL_ is **null**, then
+>    1. Return an empty result.
+> 1. Let _pjson_ be the result of **READ_PACKAGE_JSON**(_packageURL_).
+> 1. Set _name_ to _pjson.name_.
+> 1. If _name_ is empty, then return an empty result.
+> 1. If _name_ is equal to _specifier_, then
+>    1. Return the result of **PACKAGE_MAIN_RESOLVE**(_packageURL_, _pjson_).
+> 1. If _specifier_ starts with _name_ followed by "/", then
+>    1. Set _subpath_ to everything after the "/".
+>    1. If _pjson_ is not **null** and _pjson_ has an _"exports"_ key, then
+>       1. Let _exports_ be _pjson.exports_.
+>       1. If _exports_ is not **null** or **undefined**, then
+>          1. Return **PACKAGE_EXPORTS_RESOLVE**(_packageURL_, _subpath_,
+>             _pjson.exports_).
+>    1. Return the URL resolution of _subpath_ in _packageURL_.
+> 1. Otherwise return an empty result.
+
 **PACKAGE_MAIN_RESOLVE**(_packageURL_, _pjson_)
 
 > 1. If _pjson_ is **null**, then

doc/api/modules.md

@@ -159,8 +159,9 @@ require(X) from module at path Y
 3. If X begins with './' or '/' or '../'
    a. LOAD_AS_FILE(Y + X)
    b. LOAD_AS_DIRECTORY(Y + X)
-4. LOAD_NODE_MODULES(X, dirname(Y))
-5. THROW "not found"
+5. LOAD_NODE_MODULES(X, dirname(Y))
+4. LOAD_SELF_REFERENCE(X, dirname(Y))
+6. THROW "not found"
 
 LOAD_AS_FILE(X)
 1. If X is a file, load X as JavaScript text.  STOP
@@ -200,6 +201,13 @@ NODE_MODULES_PATHS(START)
    c. DIRS = DIRS + DIR
    d. let I = I - 1
 5. return DIRS
+
+LOAD_SELF_REFERENCE(X, START)
+1. Find the closest package scope to START.
+2. If no scope was found, throw "not found".
+3. If the name in `package.json` isn't a prefix of X, throw "not found".
+4. Otherwise, resolve the remainder of X relative to this package as if it
+   was loaded via `LOAD_NODE_MODULES` with a name in `package.json`.
 ```
 
 Node.js allows packages loaded via

lib/internal/modules/cjs/loader.js

@@ -58,6 +58,7 @@ const enableSourceMaps = getOptionValue('--enable-source-maps');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
 const experimentalModules = getOptionValue('--experimental-modules');
+const experimentalSelf = getOptionValue('--experimental-resolve-self');
 const manifest = getOptionValue('--experimental-policy') ?
   require('internal/process/policy').manifest :
   null;
@@ -241,6 +242,7 @@ function readPackage(requestPath) {
   try {
     const parsed = JSON.parse(json);
     const filtered = {
+      name: parsed.name,
       main: parsed.main,
       exports: parsed.exports,
       type: parsed.type
@@ -370,6 +372,125 @@ function findLongestRegisteredExtension(filename) {
   return '.js';
 }
 
+function resolveBasePath(basePath, exts, isMain, trailingSlash, request) {
+  let filename;
+
+  const rc = stat(basePath);
+  if (!trailingSlash) {
+    if (rc === 0) {  // File.
+      if (!isMain) {
+        if (preserveSymlinks) {
+          filename = path.resolve(basePath);
+        } else {
+          filename = toRealPath(basePath);
+        }
+      } else if (preserveSymlinksMain) {
+        // For the main module, we use the preserveSymlinksMain flag instead
+        // mainly for backward compatibility, as the preserveSymlinks flag
+        // historically has not applied to the main module.  Most likely this
+        // was intended to keep .bin/ binaries working, as following those
+        // symlinks is usually required for the imports in the corresponding
+        // files to resolve; that said, in some use cases following symlinks
+        // causes bigger problems which is why the preserveSymlinksMain option
+        // is needed.
+        filename = path.resolve(basePath);
+      } else {
+        filename = toRealPath(basePath);
+      }
+    }
+
+    if (!filename) {
+      // Try it with each of the extensions
+      if (exts === undefined)
+        exts = Object.keys(Module._extensions);
+      filename = tryExtensions(basePath, exts, isMain);
+    }
+  }
+
+  if (!filename && rc === 1) {  // Directory.
+    // try it with each of the extensions at "index"
+    if (exts === undefined)
+      exts = Object.keys(Module._extensions);
+    filename = tryPackage(basePath, exts, isMain, request);
+  }
+
+  return filename;
+}
+
+function trySelf(paths, exts, isMain, trailingSlash, request) {
+  if (!experimentalSelf) {
+    return false;
+  }
+
+  const { data: pkg, path: basePath } = readPackageScope(paths[0]);
+  if (!pkg) return false;
+  if (typeof pkg.name !== 'string') return false;
+
+  let expansion;
+  if (request === pkg.name) {
+    expansion = '';
+  } else if (StringPrototype.startsWith(request, `${pkg.name}/`)) {
+    expansion = StringPrototype.slice(request, pkg.name.length);
+  } else {
+    return false;
+  }
+
+  if (exts === undefined)
+    exts = Object.keys(Module._extensions);
+
+  if (expansion) {
+    // Use exports
+    const fromExports = applyExports(basePath, expansion);
+    if (!fromExports) return false;
+    return resolveBasePath(fromExports, exts, isMain, trailingSlash, request);
+  } else {
+    // Use main field
+    return tryPackage(basePath, exts, isMain, request);
+  }
+}
+
+function applyExports(basePath, expansion) {
+  const pkgExports = readPackageExports(basePath);
+  const mappingKey = `.${expansion}`;
+
+  if (typeof pkgExports === 'object' && pkgExports !== null) {
+    if (ObjectPrototype.hasOwnProperty(pkgExports, mappingKey)) {
+      const mapping = pkgExports[mappingKey];
+      return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping, '',
+                                  basePath, mappingKey);
+    }
+
+    let dirMatch = '';
+    for (const candidateKey of Object.keys(pkgExports)) {
+      if (candidateKey[candidateKey.length - 1] !== '/') continue;
+      if (candidateKey.length > dirMatch.length &&
+          StringPrototype.startsWith(mappingKey, candidateKey)) {
+        dirMatch = candidateKey;
+      }
+    }
+
+    if (dirMatch !== '') {
+      const mapping = pkgExports[dirMatch];
+      const subpath = StringPrototype.slice(mappingKey, dirMatch.length);
+      return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping,
+                                  subpath, basePath, mappingKey);
+    }
+  }
+  if (mappingKey === '.' && typeof pkgExports === 'string') {
+    return resolveExportsTarget(pathToFileURL(basePath + '/'), pkgExports,
+                                '', basePath, mappingKey);
+  }
+  if (pkgExports != null) {
+    // eslint-disable-next-line no-restricted-syntax
+    const e = new Error(`Package exports for '${basePath}' do not define ` +
+        `a '${mappingKey}' subpath`);
+    e.code = 'MODULE_NOT_FOUND';
+    throw e;
+  }
+
+  return path.resolve(basePath, mappingKey);
+}
+
 // This only applies to requests of a specific form:
 // 1. name/.*
 // 2. @scope/name/.*
@@ -384,43 +505,7 @@ function resolveExports(nmPath, request, absoluteRequest) {
     }
 
     const basePath = path.resolve(nmPath, name);
-    const pkgExports = readPackageExports(basePath);
-    const mappingKey = `.${expansion}`;
-
-    if (typeof pkgExports === 'object' && pkgExports !== null) {
-      if (ObjectPrototype.hasOwnProperty(pkgExports, mappingKey)) {
-        const mapping = pkgExports[mappingKey];
-        return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping, '',
-                                    basePath, mappingKey);
-      }
-
-      let dirMatch = '';
-      for (const candidateKey of Object.keys(pkgExports)) {
-        if (candidateKey[candidateKey.length - 1] !== '/') continue;
-        if (candidateKey.length > dirMatch.length &&
-            StringPrototype.startsWith(mappingKey, candidateKey)) {
-          dirMatch = candidateKey;
-        }
-      }
-
-      if (dirMatch !== '') {
-        const mapping = pkgExports[dirMatch];
-        const subpath = StringPrototype.slice(mappingKey, dirMatch.length);
-        return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping,
-                                    subpath, basePath, mappingKey);
-      }
-    }
-    if (mappingKey === '.' && typeof pkgExports === 'string') {
-      return resolveExportsTarget(pathToFileURL(basePath + '/'), pkgExports,
-                                  '', basePath, mappingKey);
-    }
-    if (pkgExports != null) {
-      // eslint-disable-next-line no-restricted-syntax
-      const e = new Error(`Package exports for '${basePath}' do not define ` +
-          `a '${mappingKey}' subpath`);
-      e.code = 'MODULE_NOT_FOUND';
-      throw e;
-    }
+    return applyExports(basePath, expansion);
   }
 
   return path.resolve(nmPath, request);
@@ -536,6 +621,13 @@ Module._findPath = function(request, paths, isMain) {
       return filename;
     }
   }
+
+  const selfFilename = trySelf(paths, exts, isMain, trailingSlash, request);
+  if (selfFilename) {
+    Module._pathCache[cacheKey] = selfFilename;
+    return selfFilename;
+  }
+
   return false;
 };
 

src/env.h

@@ -93,12 +93,15 @@ struct PackageConfig {
   enum class Exists { Yes, No };
   enum class IsValid { Yes, No };
   enum class HasMain { Yes, No };
+  enum class HasName { Yes, No };
   enum PackageType : uint32_t { None = 0, CommonJS, Module };
 
   const Exists exists;
   const IsValid is_valid;
   const HasMain has_main;
   const std::string main;
+  const HasName has_name;
+  const std::string name;
   const PackageType type;
 
   v8::Global<v8::Value> exports;