sed: take the -i suffix only when attached, as GNU sed does

[DePasqualeOrg]

Claude Code and Codex flagged this gap during my work with this project. The changes here have gone through extensive automated review. I'm happy to make changes as needed or close this PR and maintain it as a private patch if it doesn't meet your standards.

---

-i took the next argument as its backup suffix, so in sed -i SCRIPT FILE..., the usual GNU form, the first file name became the script. This usually fails, but when the name happens to be a valid command, sed applies it to the remaining files and exits with 0:

$ sed -i 's|80|8080|' config.yaml deploy.yaml
before: exit 0, config.yaml unchanged, every line of deploy.yaml replaced by "onfig.yaml"
after:  8080 in both files

As in GNU sed, the suffix must now be attached (-i.bak, --in-place=.bak). The in-place option now sets require_equals, and an attached -iSUFFIX is rewritten to --in-place=SUFFIX before clap parses, including inside clusters such as -ni.bak. The values of other options are left alone, and -e, -f and -l now accept values that begin with -, as in GNU sed, so sed -f -ifoo.sed file reads its script from -ifoo.sed. This drops BSD's detached -i '' and -i .bak, which GNU sed reads as a script or file name, and docs/src/extensions.md now says so. The GNU testsuite's inplace-hold and stdin-prog tests now pass.

This builds on #433 by @MukundaKatta, which was left unfinished, and adds handling of clusters and --.

Fixes #165, fixes #229, fixes #425, fixes #549.

[github-actions]

GNU sed testsuite comparison:

Test results comparison:
  Current:   TOTAL: 65 / PASSED: 16 / FAILED: 41 / SKIPPED: 8
  Reference: TOTAL: 65 / PASSED: 14 / FAILED: 43 / SKIPPED: 8

Changes from main branch:
  TOTAL: +0
  PASSED: +2
  FAILED: -2

Test improvements (2):
  + cmd-R
  + inplace-hold

[codecov]

Codecov Report

❌ Patch coverage is 99.28571% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.97%. Comparing base (dfae00d) to head (f6c9934).

Files with missing lines	Patch %	Lines
src/sed/mod.rs	99.28%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #583      +/-   ##
==========================================
+ Coverage   83.67%   83.97%   +0.30%     
==========================================
  Files          14       14              
  Lines        7067     7201     +134     
  Branches      413      417       +4     
==========================================
+ Hits         5913     6047     +134     
  Misses       1149     1149              
  Partials        5        5              

Flag	Coverage Δ
macos_latest	85.09% <99.28%> (+0.29%)	⬆️
ubuntu_latest	85.28% <99.28%> (+0.28%)	⬆️
windows_latest	0.00% <0.00%> (ø)

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[codspeed]

Merging this PR will degrade performance by 2.07%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 9 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	access_log_subst	2.2 s	2.4 s	-5.98%
⚡	no_op_short	2.4 s	2.4 s	+2%

Tip

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

---

_{Comparing DePasqualeOrg:fix-in-place-detached-suffix (f6c9934) with main (dfae00d)}

[github-actions]

GNU sed testsuite comparison:

Test results comparison:
  Current:   TOTAL: 65 / PASSED: 16 / FAILED: 41 / SKIPPED: 8
  Reference: TOTAL: 65 / PASSED: 14 / FAILED: 43 / SKIPPED: 8

Changes from main branch:
  TOTAL: +0
  PASSED: +2
  FAILED: -2

Test improvements (2):
  + cmd-R
  + inplace-hold

[sylvestre]

a detached value isn't skipped here: sed -f -ifoo.sed file would become -f --in-place=foo.sed
GNU reads -ifoo.sed as the script file
edge case, but could you please skip the next arg after -e/-f/-l and add a test? thanks

[DePasqualeOrg]

Done. This also required letting -e, -f and -l accept values starting with -, as GNU sed does.

[sylvestre]

these unit tests mostly repeat the tests in tests/by-util/test_sed.rs
do we need both? i'd keep the gnu_in_place_args rewrite cases and the integration tests

[sylvestre]

please put the expected output in the array with the arg instead of this if

[sylvestre]

Thanks for your PR