cksum: reject empty checksum filenames on WASI

[limadog9]

Handle empty checksum filenames correctly on WASI. Closes #15357.

[codspeed]

Merging this PR will regress 1 benchmark

⚠️ 121 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• du_all_wide_tree[(5000, 500)]
• cksum_multiple_files
• dd_copy_partial
• cksum_sysv
• cksum_raw_output
• factor_64bit_semiprime
• du_summarize_balanced_tree[(5, 4, 10)]
• dd_copy_with_skip
• factor_multiple_u64s[2]
• dd_copy_4k_blocks
• …and 111 more

ℹ️ 1 benchmark has no flame graph

The flamegraph could not be generated because too much time was spent in runtime internals, making the visualization not useful for performance analysis.

• sort_dictionary_order[500000]

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 399 untouched benchmarks
⏩ 70 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	factor_five_38_bit_primes	1.8 s	1.8 s	-4.37%
⚡	Simulation	factor_three_39_bit_primes	800.7 ms	560.7 ms	+42.8%

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 limadog9:fix/checksum-empty-filename-wasi (b8e8a2f) with main (2fb77e8)}

Footnotes

1. 70 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. ↩

[RenjiSann]

Suggested change

	for line in [format!("{digest} "), format!(" {digest}\t")] {
	new_ucmd!()
	.arg("--check")
	.pipe_in(format!("{line}\n"))
	for line in [format!("{digest} \n"), format!(" {digest}\t\n")] {
	new_ucmd!()
	.arg("--check")
	.pipe_in(line)

No need to wrap the digest in 2 formats

[limadog9]

@RenjiSann Applied your suggestion and removed the extra formatting step. Native and WASI regression checks pass. Thanks!