fix(fs): walk does not apply exts filter to directories

[LeSingh1]

Fixes #6736.

walk and walkSync ran the exts filter against the directory name in include() when deciding whether to yield a directory entry. Directories generally don't have file extensions, so any exts option effectively dropped every directory from the output, even with includeDirs:true (the default).

Repro before the patch:

import { walkSync } from "jsr:@std/fs/walk";
for (const e of walkSync("./project", { includeDirs: true, exts: ["ts"] })) {
  console.log(e.path, e.isDirectory ? "(dir)" : "(file)");
}
// only "*.ts" files - every directory is missing

After:

./project (dir)
./project/sub (dir)
./project/sub/b.ts (file)
./project/a.ts (file)

The fix passes undefined for exts in the includeDirs branch of both walk and walkSync. The match and skip regex filters still apply to directories. The !followSymlinks symlink emission branch is unchanged because a symlink's name still has an extension just like the target.

Tests:

• Existing walk() / walkSync() accepts ext option as strings tests updated to include the root directory in the expected entries (the default includeDirs:true now actually yields it).
• Two new tests pin the includeDirs:false case so the intent stays explicit.

All ext-related tests pass. The four pre-existing * regExps failures in fs/walk_test.ts reproduce on origin/main (verified by stashing the patch and re-running) so they're unrelated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.57%. Comparing base (cdf74a8) to head (9fc18f1).
⚠️ Report is 18 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7167   +/-   ##
=======================================
  Coverage   94.57%   94.57%           
=======================================
  Files         636      636           
  Lines       52142    52142           
  Branches     9401     9401           
=======================================
  Hits        49315    49315           
  Misses       2249     2249           
  Partials      578      578           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[bartlomieju]

Nice, focused fix — I traced the recursion and confirmed it applies to nested directories too (each subdir becomes the root of a recursive walk() call), and the ext/regExp tests pass on the branch. Three points below; two are inline.

exts JSDoc is now slightly inaccurate (fs/walk.ts:71-77). The doc says "entries without the file extension specified by this option are excluded." That's no longer true for directories. Worth a one-line note like "Directory entries are not subject to this filter" so the docs match the new behavior.

[bartlomieju]

The same class of bug still exists for symlinks-to-directories in the !followSymlinks branch below (fs/walk.ts:488 and :920): include(path, exts, match, skip) still applies exts to the symlink entry. A symlink pointing at a directory has no extension, so includeSymlinks: true + exts will silently drop it — exactly the issue you're fixing here.

The PR description's justification ("a symlink's name still has an extension just like the target") isn't accurate for symlinks-to-directories. Either handle it consistently here, or — if you'd rather defer it — soften that line in the description so it doesn't read as verified-correct.

[bartlomieju]

Pre-existing copy-paste error (optional fix-along): this (excluding period prefix) test uses exts: [".rs", ".ts"] (with leading periods), which doesn't match its own name. Its async sibling above correctly uses ["rs", "ts"]. Since you're already editing this line, cheap to fix.