screening duplicate bugsBy Sean Richardson
If you have spent any time confirming UNCONFIRMED bugs or prescreening Browser-General bugs, or going through new bugs, you will have noticed that all too many bugs submitted by inexperienced reporters are DUPLICATE bugs. Even though probably less than half turn out to be duplicates, it is best to presume that each one is until you convince yourself otherwise.
This is a guide to help you identify as many of the duplicate incoming bug reports as you can, as efficiently as possible. It's assumed that you are already comfortable with the basics of searching Bugzilla for duplicates. If you haven't used the full range of matching types for text patterns in Bugzilla yet, including "all words"and "regular expression", you may find the Text Searching tutorial helpful.
This tutorial is written as if you are going to sit down and search for DUPLICATE bugs, one after the other, but most of it applies no matter how you come across a potentially-duplicate bug. If you do want to try identifying DUPs one after the other, bug lists that usually contain DUPs are shown at the end.
While you are checking bugs reports to see if they are DUPs, please confirm UNCONFIRMED bugs, add or simplify testcases, improve the steps to reproduce, improve the summary, report if you reproduced the bug on another platform, and/or do anything else that makes sense before moving on to the next if a bug does not appear to be a DUP.
To mark bugs as DUPLICATE, you need the "Can edit all aspects of any bug." permission. If you don't have that permission, email Gerv and ask about getting it added to your Bugzilla account. In the meantime, you can add a comment to any bug mentioning that it is or might be a duplicate.
The quick and obvious ones
- If you haven't already, please take some time to familiarize yourself with the
Mozilla QA Most Frequent Bugs List and the
Known Issues section of the
Firefox release notes
or the release notes of the latest
Mozilla suite version.
- If a report looks like an obvious recent regression, check out the
bugs recently reported
by the Smoketesting team, and the
newsgroup to see if the problem is already known.
- Also check over the list of
today's bugs for Firefox and Thunderbird
. See the smoketesting page if you want
to concentrate in this area.
- You'll have an easier time picking out the duplicates of bugs you already know
for certain have been reported. Rather than just going through a bug list in order,
scan it for bugs whose summaries look familiar first, so you can make as many
matches as possible without resorting to unguided searches. DUPs of bugs that you
have reported or have previously found duplicates of should be the easiest to find,
and the most productive to resolve, since you should be able to recognize and
evaluate the match quickly.
- Some ways to narrow down the query based on what you remember:
- If you can remember an e-mail address associated with the existing bug, enter it into one of the Email sections and set the appropriate role(s). Do the same if you think you added a comment to the existing bug.
- If you can remember roughly when the bug entered the system, choose "[Bug Creation]" in the Where the field(s) field, and set a date range in the dates and to fields.
- If you know you've seen some mail from email@example.com on the subject of an existing bug that's a candidate for a match lately, enter a number in the Changed in the last [ ] days field.
- If you get no matches, your recall may be fallible, so try the search again
without the restriction.
- If you were able to quickly find the correct bug report to mark a new bug a DUP of, but its summary contains none of the words the reporter of the new bug might have tried to search with, consider adding those words to the summary, or, if you can't do that, including them in a comment suggesting that they be added to the summary -- especially if the bug looks likely to get more duplicates.
- The first field, Status, is normally preset to find NEW,
ASSIGNED, and REOPENED bugs. Add UNCONFIRMED (use Ctrl-click in Windows,
Command-click in MacOS) to find duplicates among newly-entered bugs too.
- To cast a wider net, add RESOLVED and VERIFIED, or deselect everything in
the Status field. Do this if you wouldn't otherwise expect a
long bug list, or when trying again if you got a relatively short list with no
matches. It can be easier to find earlier DUPLICATE bugs (which will be RESOLVED)
and follow them to the "real" bug, especially if there are several DUPs
already. The existing bug you are hunting for may also have been fixed already.
- To exclude obviously extraneous bugs, narrow the search by making a choice
under Product. Usually it will be "Core" (for
Browser, HTML composition, and text-editing bugs) or "Firefox"
- If the proper component for previously reported bug is obvious (as could be
expected for, as an example, most "Bookmarks" bugs), choose that
component. You can select multiple components at once. Be prepared, though, to
retry you query without specifying a component if you don't find a match - not
all bugs end up where you'd expect.
- The same will apply to the
Not all bugs that should be labelled "fonts", for instance,
- Beside each of the Summary, Description entry,
and URL fields. There is a drop-down that lets you choose the type
of matching. Choose among "case-insensitive substring","case-sensitive
substring", "all words", "any words", or "regular
expression", as appropriate (hints on which work best for several common search
scenarios are available in the
tutorial). Although searching within the Description entry is much
slower than any other field, go ahead and use it if it makes sense or the search
terms available might not show up in the summary, but try to restrict the search
with other fields at the same time if you can.
- Boolean Charts are
an advanced feature that can let you do searches that are otherwise impossible.
You can use any kind of match with almost any field, and set up boolean
ands and ors. The first chart always ands with the
rest of the query form. As a trivial example, to search for bugs about the tab
key and exclude bugs about tables, add [Summary] [Does not contain
(case-insensitive) substring] ["table"] after putting "tab"
in the Summary field.
- If you don't find a match on the bug list generated by your first query, it is usually worth trying at least one or two more queries.
- When the bug list appears, scan it for anything that looks like a possible
match. It's useful to open bugs in a new window to preserve the list. At the
top of each column, clicking on its name will sort the bugs by that field.
You can add other fields to the bug list by clicking on
for some searches, the Components column can be very useful.
- If you find a clear and certain match, add a comment stating which bug
the duplicate bug is a DUPLICATE of (if the bug report that matches is itself
a DUP, follow the trail of "This bug has been marked as a duplicate of
00000" comments). If you
had to read deep into the existing bug or
puzzle out the connection, mention the date of the comment that explains the
match or describe the connection.
- If you are not certain of the match, but it looks probable or even possible,
add a comment, but also say how sure you are. Even if you are not completely
certain that a new bug is a DUP at all, if you think it probably is or even might
be, add a comment saying that.
- If the original report is deficient enough that you had to try to reproduce
the bug before you could understand what the report was saying, please add enough
detail so that the next person reading the bug won't have that problem, and will
have an easier time confirming or verifying the match. Even if you don't find a
match at all, please do this to make it easier for the next person, who might
make the connection immediately given your improved description.
- If the existing bug that the DUPLICATE matches to is in a different component,
change the Component field to match the existing bug.
- Finally, if you are sure that the bug is a DUPLICATE, go ahead and click on
the radio button beside Resolve bug, mark it as duplicate of bug #
[ ] and enter the bug number of the existing bug. Be sure
to check for a typo or transposition error before clicking on
- If, to the best of your knowledge, a new UNCONFIRMED bug is not a DUP, please follow the steps outlined in the Moving a Bug from Unconfirmed to New guidelines before moving on to the next.
Which is the Duplicate?
- Other things being equal, newer bugs should be made DUPLICATES of older bugs,
but, more importantly, whichever bug is further along in the process of getting
fixed should not be made a duplicate. Signs that progess has been made
- the bug is marked FIXED, a patch is attached or a fix is promised soon
- the bug is ASSIGNED to the right Component and developer
- the bug has been analyzed by developers
- the bug has been given a higher priority (e.g., [PDT+], beta2) or an imminent milestone
- the bug report has a explanation of how to reliably reproduce the bug and/or it has a simplified testcase
- UNCONFIRMED and "Browser-General" bugs should never have
another bug made a duplicate of them unless the other bug is also an UNCONFIRMED
or "Browser-General" bug. Even then, the bug reports that have less
detail and work should be made duplicate of the bug reports that are further
along, even if those are older. At that point the bug that receives the DUP
should normally be confirmed, if it is not already.
- If you are stumped, add a comment resembling the following:
This bug appears to be a duplicate of bug nnnnn, but I'm not sure which should be made DUPLICATE of which.
One Down, or, Keeping in the Groove
- Take another look at the bug list after making a match: there may well be
another DUPLICATE of the same bug lurking there. You might also see two bugs
on the list that look suspiciously similar even though neither matches the bug
you started with.
- After some time you will naturally become much more familiar with some
types of issues and some components than others. Go with that, focus on the
areas you can make sense of quickly. You might also have some existing expertise
or experience that makes it easier for you to evaluate some bugs. If you know
before identifying duplicates in any other area.
- Similarly, let your tools guide you, to some extent at least. If you know
how to use a Debugger, you can make more of a contribution to evaluating
Crashers than others can, so it makes sense to look at them. Similarly, some
bugs that are reported on Linux, Macs, or other platforms are specific to the
platform or platform/OS combination that they were reported on. Someone
unfamiliar with that platform won't be as efficient, so if you regularly use
something other than Microsoft Windows, please look at bugs reported on your
platform first, by selecting it on the query page. Use the
Edit this query
link at the bottom of a bug list to get back to the query form if you can't
use the [Back] button.
- By concentrating on the bug reports that you have the skills and experience to evaluate quickly and surely, you will be able to help more in the time you can contribute.
Specific Types of Duplicates
Some types of bug reports need or can benefit from special handling:
- Bug reports about a particular URL: Check first for a
substring (usually just the domain name is appropriate) of the URL in the URL
field, matching against bugs with any Status. Obvious exact DUPs should show
up easily that way, so long as the reporter filled in the URL field. In case
that was not done, check in the Description entry field if there is no match
in the URL field.
- Reports of Crashes: Crashes are identified by what
specific code crashed, not how they are reproduced, so some sort of debugging
output may be required before a determination can be made whether a crash
report is a DUP. If you reproduce a crash on a previously unreported platform
or OS, or using a current binary when the reporter was using a milestone
release, please add as much detail as you can. If a module name is reported
or you can generate a stack trace, use the
How to Pick a Component for
Crashing Bugs guide and look in that component for bugs with the
crash keyword. If you don't find a match, add "crash" to the keywords
field, so long as you were able to reproduce the crash.
- Multiply-DUPLICATE reports: Some bug reports describe
a number of often unrelated problems. If all of the problems mentioned are
clearly duplicates of existing bug reports, mark the new bug report as a
DUPLICATE based on the first issue. If it is clear that all but one
of the problems have already been reported, state that, citing the bug
numbers if possible, and adjust the Summary to refer to
the remaining problem.
- "Browser-General" bug reports: Be sure to
move the bug to the appropriate Component if you can identify it, and copy
over the QA contact, at the same time that you mark it as a DUP, so that
it can be verified by someone familiar with the existing bug report.
- Same Exact Bug, two bug numbers: Sometimes a bug report
ends up in the Bugzilla database twice in a row. If you see two bugs with
the same summary and adjacent bug numbers, mark one as a DUP of the other
immediately, before both get comments -- but look at both first, in case one
has comments already.
- An ASSIGNED bug may be a DUP: It does sometimes happen
that one assigned bug is a duplicate of another. If both are assigned to
the same engineer, add a comment to the one that is not as far along as the
other; if two different engineers are involved, add a comment to both,
pointing out the existence of the other and why it appears to be a DUP. Do
not resolve ASSIGNED bugs as DUPs yourself; the assignee should do that.
Lists Where Duplicates Lurk
- The greatest concentration of duplicate bugs is in those that enter the
database as UNCONFIRMED, although plenty of NEW bugs also turn out to be
DUPs. Bugs do occasionally get ASSIGNED before being found to be a DUP, but
that is what duplicate-screening is meant to prevent, so please concentrate
on UNCONFIRMED and NEW bugs.
- The bug lists below are displayed in rough descending order of prevalence
of duplicates. They will appear in new windows; you may want to open bugs
from the list in new windows too, to preserve the list. Happy matching; if you
find only one DUP, you'll have earned the thanks of a busy software enginner.
Today's & Yesterday's UNCONFIRMED and NEW Firefox and Thunderbird Bugs
(UNCONFIRMED-only | NEW-only)
- UNCONFIRMED Browser bugs unchanged for more than one week | Linux-only | Mac (Camino browser)-only | Customize
- UNCONFIRMED Thunderbird bugs unchanged for more than one week
- UNCONFIRMED Firefox bugs changed in the last week | Linux-only | Mac (Camino browser)-only | Customize
- UNCONFIRMED Thunderbird bugs changed in the last week
- Today's & Yesterday's UNCONFIRMED and NEW Firefox and Thunderbird Bugs | Customize
(Thanks to Jan Leger, Eli Goldberg, David Baron, John Morrison, Matthew Thomas, Gervase Markham and Terry Weissman for contributing to this document. Additional suggestions welcome.)