fs: defer path resolution in realpath functions

[Xstoudi]

In fs.realpath and fs.realpathSync, path resolution is now performed after symlink traversal instead of before, ensuring correct behavior when dealing with parent directory references (..) in paths containing symlinks.

Fixes: #60779

I may be unaware of full implications of this change, feel free to let me know if it's not the right way to fix it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.53%. Comparing base (15bdf38) to head (e2b2166).
⚠️ Report is 24 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #61194   +/-   ##
=======================================
  Coverage   88.53%   88.53%           
=======================================
  Files         703      703           
  Lines      208598   208601    +3     
  Branches    40227    40226    -1     
=======================================
+ Hits       184674   184683    +9     
+ Misses      15951    15939   -12     
- Partials     7973     7979    +6     

Files with missing lines	Coverage Δ
lib/fs.js	98.19% <100.00%> (+<0.01%)	⬆️

... and 31 files with indirect coverage changes

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[aduh95]

All tests are passing, so that seems safe

/cc @nodejs/fs

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70640/

[aduh95]

Tests are consistently failing on Windows:

---
duration_ms: 393.004
exitcode: 1
severity: fail
stack: |-
  test_simple_error_callback
  test_simple_error_callback
  test_simple_error_cb_with_null_options
  test_simple_error_cb_with_null_options
  test_simple_relative_symlink
  fs.symlinkSync("../.tmp.397/cycles/root.js", "c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/symlink", "file")
  test_simple_relative_symlink
  fs.symlinkSync("../.tmp.397/cycles/root.js", "c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/symlink", "file")
  test_simple_absolute_symlink
  using type=dir
  test_simple_absolute_symlink
  using type=dir
  test_deep_relative_file_symlink
  test_deep_relative_file_symlink
  test_deep_relative_dir_symlink
  test_deep_relative_dir_symlink
  test_cyclic_link_protection
  test_cyclic_link_protection
  test_cyclic_link_overprotection
  test_cyclic_link_overprotection
  test_relative_input_cwd
  fs.symlinkSync("../cycles/realpath-3b", "test\\.tmp.397\\cycles\\realpath-3a", "dir")
  fs.symlinkSync("../cycles/realpath-3c", "c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/cycles/realpath-3b", "dir")
  fs.symlinkSync("root.js", "c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/cycles/realpath-3c", "file")
  start tests
  fs.symlinkSync("c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\fixtures\\nested-index\\one", "c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/symlink", "dir")
  fs.symlinkSync("c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\fixtures\\nested-index\\one", "c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/symlink", "dir")
  fn="test\\.tmp.397\\cycles\\realpath-3a"
  fn="c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/cycles/realpath-3b"
  fn="c:\\workspace\\node-test-binary-windows-js-suites\\node\\test\\.tmp.397/cycles/realpath-3c"
  node:internal/assert/utils:146
    throw error;
    ^

  AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:

  38 !== 17

      at process.<anonymous> (c:\workspace\node-test-binary-windows-js-suites\node\test\parallel\test-fs-realpath.js:653:10)
      at process.emit (node:events:520:22) {
    generatedMessage: true,
    code: 'ERR_ASSERTION',
    actual: 38,
    expected: 17,
    operator: 'strictEqual',
    diff: 'simple'
  }

  Node.js v26.0.0-pre
...

[Xstoudi]

Thanks for the warning, I'll setup a windows dual boot and try to fix it.

[Xstoudi]

Half the failing test are because my approach was too naive and won't work on Windows.
The other half comes from native realpath not resolving as intended on Windows and libuv is a bit out of my knowledge here.