[not-matthias]

TLDR: Unsupported go test flags were dropped, but their separate value became a package: go test -p 1 ./... -bench . failed with package 1 is not in std after the benchmarks ran. The parser now knows each Go flag's arity and drops the value too.

• Go flags take 0 or 1 values, so cli.rs keeps the boolean (20) and value (47) flag lists from cmd/go (Go 1.24 to 1.27).
• Boolean flags (-v, -race) drop only themselves; test -v fmt keeps fmt.
• Value flags drop the next argument, even if it starts with - (-ldflags "-s -w").
• Flags unknown to go test (custom test flags) drop the next argument unless it starts with -, like Go.
• Unsupported flags still only warn (log::warn!); the run never fails before Go is invoked.

Review note: the flag lists need an update when Go adds go test or build flags.

Closes COD-4005

[codspeed]

Merging this PR will degrade performance by 15.49%

3 warnings

⚠️ Walltime results may be unreliable

Some benchmarks used the Walltime instrument outside CodSpeed Macro Runners, which can make the results inconsistent.

Learn more about Macro Runners

See affected benchmarks

⚠️ Unable to measure the execution of 1 benchmark

This benchmark measured no execution time, so its result is not comparable and counts as unchanged. This usually happens when the compiler removes the code under test.

Prevent compiler optimizations

See affected benchmarks

⚠️ 1 benchmark with a significant change ran on different hardware

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

Learn more about Macro Runners

See affected benchmarks

❌ 1 regressed benchmark
✅ 49 untouched benchmarks
⏩ 1 skipped benchmark¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	BenchmarkFibonacciDarwin	224.2 µs	265.3 µs	-15.49%

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 cod-4005-handle-unsupported-go-runner-flags-without-leaving-orphaned (a8f4f19) with main (84ece6e)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[greptile-apps]

Confidence Score: 4/5

[Medium impact] The change affects command-line parsing across Go runner benchmark runs.

Fix unsupported flag rejection and use tracing for the added warning before merging.

Findings

1.  Flags change package selection ▶
2.  Warning bypasses tracing ▶

Fix with agent prompt

### Issue 1
go-runner/src/cli.rs:133-139
With `test -v fmt`, the new code consumes `fmt` as a flag value and runs the default `./...` instead of the requested package. Conversely, `test -cpuprofile ./cpu.out ./...` keeps `./cpu.out` as a package, leaving the original failure unfixed.

Return `CliExit::UnknownFlag` before Go runs, as the PR description requires, rather than guessing which arguments belong to unsupported flags. Update the tests to expect rejection.

### Issue 2
go-runner/src/cli.rs:140
The new warning uses `eprintln!`, but the repository rule prohibits `println!` and `eprintln!` in Rust and requires tracing macros instead. Use `tracing::warn!` here to satisfy that requirement before merging.

```suggestion
                        tracing::warn!("ignoring value '{value}' of unsupported flag '{s}'");
```

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Summary

The PR adds a helper that guesses whether an argument is a package and skips presumed values of unsupported flags.

• The parser keeps many unsupported flag values out of the package list.

_{Reviews (1) · Last reviewed commit: "fix(cli): drop the value of unsupported ..." · Reviewed by Greptile}

[lvaroqui]

LGTM! 🎸