--preserve-symlinks-main not respected when using --require and --inspect-brk together

[matthewjh]

Version

16.11.0

Platform

Darwin NAMTJ0390J2KQ 21.6.0 Darwin Kernel Version 21.6.0: Mon Aug 22 20:19:52 PDT 2022; root:xnu-8020.140.49~2/RELEASE_ARM64_T6000 arm64

Subsystem

internal/modules/cjs

What steps will reproduce the bug?

No response

How often does it reproduce? Is there a required condition?

No response

What is the expected behavior?

That symlinks are preserved for main entrypoint file path resolution when --require, --preserve-symlinks-main, and --inspect-brk flags are all used.

What do you see instead?

When using a symlinked entry point, and calling node with all of --require, --preserve-symlinks-main, and --inspect-brk, the symlink for the entry point is not preserved, and the realpath of the entrypoint is used for module loading (and future module loads relative to that entry point).

Additional information

When using node --require preload.js --inspect-brk thing.js, Module.prototype._compile is entered for preload.js before the main entrypoint is loaded. Note the following code block:

https://github.com/nodejs/node/blob/main/lib/internal/modules/cjs/loader.js#L1126

 if (getOptionValue('--inspect-brk') && process._eval == null) {
    if (!resolvedArgv) {
      // We enter the repl if we're not given a filename argument.
      if (process.argv[1]) {
        try {
          resolvedArgv = Module._resolveFilename(process.argv[1], null, false);
        } catch {
          // We only expect this codepath to be reached in the case of a
          // preloaded module (it will fail earlier with the main entry)
          assert(ArrayIsArray(getOptionValue('--require')));
        }
      } else {
        resolvedArgv = 'repl';
      }
    }

Note especially that resolvedArgv = Module._resolveFilename(process.argv[1], null, false); will resolve the main entrypoint filename with the isMain arg set to false. This will cause --preserve-symlinks-main not to be applied for the filename resolution, and the realpath rather than the superficial (not following the links) path to be used.

Later, when the main entrypoint is loaded "for real", Module._resolveFilename is called with isMain = true (correctly). However, when this enters Module._findPath, the filename from the previous resolution, with isMain = false, is pulled from the cache on Module._pathCache, because the cache key does not incorporate the isMain arg value - only path info -, and this value is returned from Module._resolveFilename:

node/lib/internal/modules/cjs/loader.js

Line 549 in 2a4452a

const cacheKey = request + '\x00' + ArrayPrototypeJoin(paths, '\x00');

 const cacheKey = request + '\x00' + ArrayPrototypeJoin(paths, '\x00');
  const entry = Module._pathCache[cacheKey];
  if (entry)
    return entry;

So, even though a different file path would potentially emerge as a result of the logic below, the value from the cache is used:

node/lib/internal/modules/cjs/loader.js

Line 580 in 2a4452a

if (!isMain) {

 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);
        }

Potential actions:

1. Add isMain to the cache key used for Module._pathCache in Module._findPath. I think this is important, as other code in node that uses Module._findPath may create race conditions, because the cache key is insufficiently inclusive, making the function, in a sense, impure.
2. Pass isMain = true to the Module._resolveFilename call in the --inspect-brk logic in Module.prototype._compile. Isn't it guaranteed that we are dealing with the main module here, anyway?