pr: report missing file as "pr: <file>: <message>"

[addielaruee]

Fixes #13013

What

When pr is given a path it can't open, it currently prints:

$ pr qwe
pr: No such file or directory (os error 2)

The file name is missing and Rust's raw (os error N) suffix leaks. GNU pr prints the file name and no errno:

$ pr qwe
pr: qwe: No such file or directory

Change

read_to_end mapped std::fs::read errors into PrError through the generic From<io::Error> impl, which only calls to_string() — so the path (still in scope at the call) was lost and the errno suffix kept.

This adds a dedicated PrError::ReadError { path, msg } variant and builds the message in read_to_end, reusing the existing uucore::error::strip_errno() helper (the same pattern already used in head and sort).

Only the read path is changed, so write errors (e.g. pr file >/dev/full) keep their current behavior and are not prefixed with the file name, matching the discussion on the issue.

After:

$ pr qwe
pr: qwe: No such file or directory

Test

Adds test_missing_file_error_message. The exact OS message differs by platform (for example, "The system cannot find the file specified." on Windows), so the test asserts the portable behavior — the file name is present and the (os error N) suffix is stripped — rather than a hardcoded string.

cargo test, cargo clippy --all-targets, and cargo fmt --check all pass locally.

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Note for triage: #13231 also targets this issue but has been stalled; its regression test hardcodes the Unix error string and fails on Windows CI. This PR is a minimal alternative that keeps a platform-independent test.

[codspeed-hq]

Merging this PR will improve performance by 3.53%

⚡ 1 improved benchmark
✅ 338 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	ls_recursive_balanced_tree[(6, 4, 15)]	51.2 ms	49.4 ms	+3.53%

Tip

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

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_{Comparing addielaruee:fix/13013-pr-error-message (d400d44) with main (70406bc)²}

Footnotes

1. 46 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. ↩

2. No successful run was found on main (bcb1d28) during the generation of this report, so 70406bc was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[cakebaker]

Thanks for your PR!