Bug 811992

First, strictly speaking your examples are not valid -- rpmdev-vercmp takes (Epoch:)Version-Release strings as arguments, you're feeding it Name-Version-Release-Arch strings.  It doesn't seem to affect the outcome of the test cases though.

$ rpmdev-vercmp 1-1.fc17 1-1b.fc17
1-1.fc17 > 1-1b.fc17
$ rpmdev-vercmp 1-1.fc17 1-1p.fc17
1-1.fc17 < 1-1p.fc17

Anyway, this comes directly from rpm-python, reassigning to rpm:

$ python
>>> import rpm
>>> rpm.labelCompare((None, "1", "1.fc17"), (None, "1", "1b.fc17"))
1
>>> rpm.labelCompare((None, "1", "1.fc17"), (None, "1", "1p.fc17"))
-1

Just a hunch, if it's a-f characters that are behaving differently than others, maybe they're being interpreted as hex digits somewhere?

Heh, interesting corner-case. It's not interpreting as hex though, what's mixing things up is the dist tag. Here's what happens (some debug output added):

[pmatilai@localhost rpm]$ ./rpm --eval '%{lua:print(rpm.vercmp("1.fc17","1a.fc17"))}'
rpmvercmp: 1 - 1, isnum 1
rpmvercmp: fc - a, isnum 0
1
[pmatilai@localhost rpm]$ ./rpm --eval '%{lua:print(rpm.vercmp("1.fc17","1g.fc17"))}'
rpmvercmp: 1 - 1, isnum 1
rpmvercmp: fc - g, isnum 0
-1

rpmvercmp() works by looping through the version strings, seeking for all-numeric or all-alphabetic "segments" and comparing those. Any alphabet <-> digit character class change in a version string is a segment break. While a dot also is a segment break, it doesn't have any special "grouping" effect in the sense that one might expect here.

I guess I'll take this up on rpm-maint to see what others think, it does look "obviously wrong" but changing rpmvercmp() is fairly risky business, this behavior is more than a decade old AFAICS.

Yep, version compare is quite tricky, it's hard to get expected results for all cases, I remember all the issues when we were doing that for 'sort' and 'ls' utility version compare. At least 3 or 4 implementation (Debian has it's own, rpm it's own, gnulib has two (strverscmp(), filevercmp() ) - strverscmp() is close to the rpm one, filevercmp() is hopefully identical to the Debian one (and different from the output expected by reported btw.) )

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rpm-4.11.0-0.beta1.1.fc19.x86_64 has the same results for tests in comment 2.

This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle.
Changing version to '19'.

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cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.)

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has stopped maintaining and issuing updates for Fedora 19. It is 
Fedora's policy to close all bug reports from releases that are no 
longer maintained. Approximately 4 (four) weeks from now this bug will
be closed as EOL if it remains open with a Fedora 'version' of '19'.

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plan to fix it in a currently maintained version, simply change the 'version' 
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rpm-4.12.0.1-8.fc23.x86_64 still behaves as in comment 2.

This bug appears to have been reported against 'rawhide' during the Fedora 23 development cycle.
Changing version to '23'.

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OK, while this is confusing, we just can't change the way version compare is done. The way to solve this would be to introduce a new rpm tag as a new home of the dist tag. But this is another story for another time.