module: throw an error for invalid package.json main entries

We currently ignore invalid `main` entries in package.json files.
This does not seem to be very user friendly as it's certainly an
error if the `main` entry is not a valid file name. So instead of
trying to resolve the file otherwise, throw an error immediately to
improve the user experience.
To keep it backwards compatible `index.js` files in the same directory
as the `package.json` will continue to be resolved instead but that
behavior is now deprecated.

PR-URL: https://github.com/nodejs/node/pull/26823
Fixes: https://github.com/nodejs/node/issues/26588
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

1 files changed, 35 insertions, 11 deletions

diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index ea1faf9b7a..f205b47a4a 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -54,6 +54,7 @@ const {
   ERR_REQUIRE_ESM
 } = require('internal/errors').codes;
 const { validateString } = require('internal/validators');
+const pendingDeprecation = getOptionValue('--pending-deprecation');
 
 module.exports = Module;
 
@@ -224,15 +225,41 @@ function readPackage(requestPath) {
   }
 }
 
-function tryPackage(requestPath, exts, isMain) {
-  var pkg = readPackage(requestPath);
+function tryPackage(requestPath, exts, isMain, originalPath) {
+  const pkg = readPackage(requestPath);
 
-  if (!pkg) return false;
+  if (!pkg) {
+    return tryExtensions(path.resolve(requestPath, 'index'), exts, isMain);
+  }
 
-  var filename = path.resolve(requestPath, pkg);
-  return tryFile(filename, isMain) ||
-         tryExtensions(filename, exts, isMain) ||
-         tryExtensions(path.resolve(filename, 'index'), exts, isMain);
+  const filename = path.resolve(requestPath, pkg);
+  let actual = tryFile(filename, isMain) ||
+    tryExtensions(filename, exts, isMain) ||
+    tryExtensions(path.resolve(filename, 'index'), exts, isMain);
+  if (actual === false) {
+    actual = tryExtensions(path.resolve(requestPath, 'index'), exts, isMain);
+    if (!actual) {
+      // eslint-disable-next-line no-restricted-syntax
+      const err = new Error(
+        `Cannot find module '${filename}'. ` +
+        'Please verify that the package.json has a valid "main" entry'
+      );
+      err.code = 'MODULE_NOT_FOUND';
+      err.path = path.resolve(requestPath, 'package.json');
+      err.requestPath = originalPath;
+      // TODO(BridgeAR): Add the requireStack as well.
+      throw err;
+    } else if (pendingDeprecation) {
+      const jsonPath = path.resolve(requestPath, 'package.json');
+      process.emitWarning(
+        `Invalid 'main' field in '${jsonPath}' of '${pkg}'. ` +
+          'Please either fix that or report it to the module author',
+        'DeprecationWarning',
+        'DEP0128'
+      );
+    }
+  }
+  return actual;
 }
 
 // In order to minimize unnecessary lstat() calls,
@@ -351,10 +378,7 @@ Module._findPath = function(request, paths, isMain) {
       // try it with each of the extensions at "index"
       if (exts === undefined)
         exts = Object.keys(Module._extensions);
-      filename = tryPackage(basePath, exts, isMain);
-      if (!filename) {
-        filename = tryExtensions(path.resolve(basePath, 'index'), exts, isMain);
-      }
+      filename = tryPackage(basePath, exts, isMain, request);
     }
 
     if (filename) {