comm: fix comparison when reading from pipes

[martinkunkel2]

Use case is that two files are piped into comm, i.e. in bash

   comm <(cat file1) <(cat file2)

see also full example in #9537

Before the fix, comm reads from the pipes twice. Once in "fn comm" and
once in "fn are_files_identical". As such, part of the data is skipped
in comparison which leads to wrong output.

This is fixed by skipping the file comparison in case one of the files is not a regular file.

This fixes #9537

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[sylvestre]

could you please add a test to make sure we don't regress? thanks

[martinkunkel2]

Tried to add a test.

On my machine (Linux, WSL2, devcontainer) the test fails if the fix is not applied:

---- test_comm::test_anonymous_pipes stdout ----
bin: "/workspaces/coreutils/target/debug/coreutils"
run: /workspaces/coreutils/target/debug/coreutils comm -13 /proc/197084/fd/33 /proc/197084/fd/35

thread 'test_comm::test_anonymous_pipes' (197138) panicked at tests/by-util/test_comm.rs:696:10:
Command was expected to succeed. code: 1
stdout = 
 stderr = comm: file 1 is not in sorted order
comm: file 2 is not in sorted order
comm: input is not in sorted order

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    test_comm::test_anonymous_pipes

and passes with the applied fix in comm.rs.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[codspeed-hq]

Merging this PR will improve performance by 7.93%

⚡ 1 improved benchmark
✅ 281 untouched benchmarks
⏩ 38 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Memory	sort_ascii_utf8_locale	6.7 MB	6.2 MB	+7.93%

---

_{Comparing martinkunkel2:comm_fix_anonymous_pipes (4adb9f4) with main (0b58260)}

Footnotes

1. 38 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. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[martinkunkel2]

@sylvestre : test added. please re-review.

Failure in CI (windows-latest) is most likely independent of my changes. Could you please retrigger the job to be sure?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/follow-name. tests/tail/follow-name is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[martinkunkel2]

@sylvestre : resolved merged conflicts, ready to be reviewed.