https://bugs.kde.org/show_bug.cgi?id=527887
Bug ID: 527887
Summary: Natural sorting is not transitive for dotted numbers
since 0d10eff3; the order shown depends on listing
order
Classification: Applications
Product: dolphin
Version First git-master
Reported In:
Platform: Compiled Sources
OS: All
Status: REPORTED
Severity: normal
Priority: NOR
Component: view-engine: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
SUMMARY
Commit 0d10eff3 ("kfileitemmodel: sort dotted numeric names naturally",
BUG 411707) changed how `KFileItemModel::stringCompare()` treats dotted
numbers. It compares a two-part numeric chain such as `6.10` as a decimal
(6.10 < 6.9). Chains of different lengths are compared segment by segment,
like versions (6.9 < 6.9.1 < 6.10). Together the two rules make the
comparison non-transitive:
```
stringCompare("kernel-6.10.tar.xz", "kernel-6.9.tar.xz") < 0
stringCompare("kernel-6.9.tar.xz", "kernel-6.9.1.tar.xz") < 0
stringCompare("kernel-6.9.1.tar.xz", "kernel-6.10.tar.xz") < 0
```
Another example: `app-1.10.zip < app-1.5.zip < app-1.7.1.zip < app-1.10.zip`.
A sort with a non-transitive comparison has no single correct result. So the
order Dolphin shows for such files depends on the order they are listed in. I
sorted the three kernel names with a copy of the model's sort from c5849f9,
once for each of the 6 possible input orders. That gives 3 different results:
| input order starts with | shown order |
|---|---|
| kernel-6.9.tar.xz | kernel-6.9.1, kernel-6.10, kernel-6.9 |
| kernel-6.9.1.tar.xz | kernel-6.10, kernel-6.9, kernel-6.9.1 |
| kernel-6.10.tar.xz | kernel-6.9, kernel-6.9.1, kernel-6.10 |
STEPS TO REPRODUCE
In the unit test: add these rows to
`KFileItemModelTest::testStringCompare_data()`. All three pass, which means
a < b < c < a:
```cpp
QTest::newRow("cycle-1") << QStringLiteral("kernel-6.10.tar.xz") <<
QStringLiteral("kernel-6.9.tar.xz") << true << -1;
QTest::newRow("cycle-2") << QStringLiteral("kernel-6.9.tar.xz") <<
QStringLiteral("kernel-6.9.1.tar.xz") << true << -1;
QTest::newRow("cycle-3") << QStringLiteral("kernel-6.9.1.tar.xz") <<
QStringLiteral("kernel-6.10.tar.xz") << true << -1;
```
In Dolphin: create `kernel-6.9.tar.xz`, `kernel-6.9.1.tar.xz` and
`kernel-6.10.tar.xz` in a folder and sort by name with natural sorting (the
default). Whatever order is shown, one of the three pairs is out of order
according to the comparison. The order can change between folders and file
systems, because the listing order differs.
OBSERVED RESULT
The comparison is cyclic for names that mix two-part and three-part dotted
numbers. The displayed order depends on listing order.
EXPECTED RESULT
One consistent rule for dotted numbers, so that every listing order gives the
same result. Which rule is a design decision. For example, comparing every
chain segment by segment would make `0.1 < 0.09` and break the "decimal" test
row, so the decimal case needs a rule that still holds against three-part
chains.
SOFTWARE/OS VERSIONS
Dolphin git master c5849f9 (2026-10-24). The behaviour comes from 0d10eff3
(2026-04-02).
ADDITIONAL INFORMATION
Found while checking sort comparisons for consistency with a standalone copy
of the code. An AI coding assistant helped with the analysis; the results
above are from running the copied code.
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