reduce_errs seeds best_err with a synthetic Error::other("nil") placeholder
via unwrap_or. When the error slice is empty or every error is ignored,
err_counts is empty and nil_count is 0, so both nil tie-break conditions are
false and the else branch returned (0, Some(Error::other("nil"))). That
placeholder leaked to build_write_quorum_failure_summary, where dominant_error
became Some("nil"), skipping the nil_dominated early return and falling back to
the "other_error" metric label. Quorum decisions were unaffected (max_count 0
still fails any positive quorum), but write-quorum failure metric labels and
tracing fields were misclassified.
Add an explicit short-circuit: when best_count == 0 and nil_count == 0, return
the (0, None) sentinel so the placeholder never escapes. Add regression tests
for the all-ignored slice, empty slice, and the summary label path, which the
existing test_build_write_quorum_failure_summary (nil_count > 0) did not cover.
Fixes#957
Co-authored-by: heihutu <heihutu@gmail.com>
houseme
20d61c73bc