ln: follow a symlinked parent when replacing a link

[costajohnt]

replace_link in uucore falls back to opening the destination's parent with O_NOFOLLOW on EEXIST. When the parent's last component is a symlink to a directory (ln -sf target dst/ucc/modules with dst/ucc -> somedir), that open fails with ENOTDIR, a regression from #14623.

This drops NOFOLLOW on the parent open (earlier path components were already followed, so it only broke this case) and adds test_force_replace_in_symlinked_directory.

Closes #14795

[codspeed]

Merging this PR will degrade performance by 16.32%

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 387 untouched benchmarks
⏩ 54 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	three_39_bit_primes	467.5 ms	770.9 ms	-39.36%
⚡	Simulation	five_38_bit_primes	1.8 s	1.6 s	+15.48%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing costajohnt:ln-replace-link-symlink-parent (fb256eb) with main (a6d1eb3)}

Footnotes

1. 54 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[sylvestre]

could you please also cover the hard link case (-f without -s)? it goes through the same path

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)

[costajohnt]

Added the hard link case in fb256eb (test_force_replace_hard_link_in_symlinked_directory): ln -f new dirlink/link where dirlink points at real, then checks real/link and new share an inode.

The CodSpeed failure is on factor::three_39_bit_primes, which doesn't go through replace_link, and five_38_bit_primes moved the other way in the same run, so it looks like benchmark noise rather than something from this change.