[sylvestre]

An invalid back-reference such as s/\(a\)/\2/ is only detected after the flags are parsed, so the UUTILS_DIAG caret landed past the end of the command. It now points at the \2, including when the replacement spans several lines.

$ UUTILS_DIAG=always sed 's/\(a\)/\2/'
sed: <script argument 1>:1:9: error: invalid reference \2 on `s' command's RHS
   ╭─[ <script argument 1>:1:9 ]
   │
 1 │ s/\(a\)/\2/
   │         ─
───╯

[Copilot]

🟢 Approval recommended

The focused change preserves validation behavior and adds regression coverage, with no unresolved findings.

No open issues 🎉

What changed in this PR

Corrects sed’s invalid back-reference diagnostic so the caret points at the offending reference rather than past the command.

Changes:

• Records the first occurrence of the highest-numbered replacement reference.
• Uses that location for validation errors.
• Adds a regression test for caret placement.

File	Description
tests/​by-util/​test_sed.rs	Tests caret placement with repeated references.
src/​sed/​compiler.rs	Captures and uses the reference’s source location.
src/​sed/​command.rs	Stores an optional location in replacement templates.

_{Review effort: Balanced}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.10%. Comparing base (273dcfb) to head (9a6bd7d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #609   +/-   ##
=======================================
  Coverage   95.10%   95.10%           
=======================================
  Files          14       14           
  Lines        7490     7499    +9     
  Branches      443      444    +1     
=======================================
+ Hits         7123     7132    +9     
  Misses        366      366           
  Partials        1        1           

Flag	Coverage Δ
macos_latest	96.59% <100.00%> (+<0.01%)	⬆️
ubuntu_latest	96.53% <100.00%> (+<0.01%)	⬆️
windows_latest	0.00% <0.00%> (ø)

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[codspeed]

Merging this PR will improve performance by 3.52%

1 warning

⚠️ 4 benchmarks with a significant change ran on different hardware

Their base and head results were measured on machines with a different CPU, core count or memory, so the changes might not come from the code. Run base and head on the same runner type.

Learn more about Macro Runners

See affected benchmarks

⚡ 4 improved benchmarks
✅ 7 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	no_op_short	2.2 s	2.1 s	+4.77%
⚡	access_log_translit	991.9 ms	956.9 ms	+3.66%
⚡	access_log_no_op	1.6 s	1.5 s	+3.3%
⚡	access_log_append	1.1 s	1 s	+2.38%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing sylvestre:sed-backref-caret (9a6bd7d) with main (273dcfb)}

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