unexpand: reject too-large --tabs increment instead of overflowing#13383
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`--tabs=N,+M` adds an extra tab stop at `N + M`. When `N` is near
`usize::MAX` the sum overflowed: it aborts under overflow checks and, in
release builds, wraps to a bogus stop that then fails the ascending check
for the wrong reason. Use `checked_add` and reject the value as
`TabSizeTooLarge` ("tab stop value is too large"), matching GNU and the
existing handling of a single over-large tab number in `parse_tab_num`.
Fixes uutils#13378
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GNU testsuite comparison: |
sylvestre
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Jul 13, 2026
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| // A near-maximal last stop plus the increment can exceed `usize::MAX`. | ||
| // Reject it as too large (matching GNU) instead of overflowing, which | ||
| // aborts under overflow checks and wraps to a bogus stop otherwise. |
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a one line comment is probably enough
Address review feedback: a one-line comment is enough.
sylvestre
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Jul 13, 2026
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| // `--tabs=N,+M` adds one stop at `N + M`. When `N` is near `usize::MAX`, | ||
| // that sum must be rejected as too large rather than overflowing (which | ||
| // aborts under overflow checks and wraps to a bogus stop otherwise). |
Address review feedback: a one-line comment is enough.
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Summary
unexpand --tabs=N,+Madds one tab stop atN + M. WhenNis nearusize::MAX, that addition overflowed:under overflow checks (debug builds) it aborts:
in release builds it wraps to
0, which then fails the "tab sizes must be ascending" check for the wrong reason.Use
checked_addand reject the value asTabSizeTooLarge("tab stop value is too large"), matching GNU and the existing handling of a single over-large tab number inparse_tab_num.Fixes #13378.
Test
Added
test_extended_tabstop_increment_overflowasserting--tabs=<usize::MAX>,+1fails with "tab stop value is too large". All 37unexpandtests pass;cargo clippy --features unexpand --all-targets -- -D warningsandcargo fmtare clean.