On 2014-11-28 6:17 AM, Nicolas B. Pierron wrote:
On 11/28/2014 11:06 AM, Jonathan Kew wrote:
On 28/11/14 08:46, L. David Baron wrote:
On Friday 2014-11-28 10:12 +0900, Mike Hommey wrote:
The downside from doing so, though, is that non-unified build *will*
be broken, and code "purity" (right includes in the right sources,
mostly) won't be ensured. Do you think this is important enough to keep
non-unified builds around?
Another disadvantage here is that it will make adding or removing
source files harder, because you'll have to clean up the accumulated
"nonunified" bustage that shows up when files are shifted around
between unified files. (This might be somewhat harder to fix a year
or two later than it is when causing it.)
IMO, it seems worth maintaining a non-unified build, to minimize this
obscure fragility that will otherwise tend to accumulate over time. We
could
reduce the infrastructure load by doing the non-unified build on a more
occasional basis; perhaps once a day would be enough?
We already have builds that (normally) happen once a day: nightlies. How
about switching to a pattern where in addition to the nightly build,
we also
kick off a non-unified build for each platform on the same changeset? If
that fails, we file a bug, and the normal expectation should be that such
bugs can and will be fixed within a day (more or less), so the
non-unified
builds aren't left perma-broken.
I agree, we should keep non-unified builds as it keeps our individual
files valid from the C++ point-of-view. If this is taking too many
resources, then I think it is acceptable to do it less frequently.
The question is: what do we gain from doing that, technical purity
aside? Note that as Mike mentioned, even with doing both unified and
non-unified builds, you may still get build failures when
adding/removing .cpp files, so keeping support for non-unified builds
will not fix that issue.
What is identified by non-unified build is a problem of responsibility.
Finding missing symbols is the responsibility of the person who is
adding references without including headers. This is not at the charge
of the person who is adding/removing files from a moz.build.
That is not the only failure mode though. You may for example get into
a situation where Unified_foo0.cpp includes windows.h and that header
#defines CreateEvent to something else, and you remove a file from the
unified compilation causing a file from Unified_foo1.cpp to fall into
Unified_foo0.cpp and break because of the CreateEvent macro that is now
in effect in that translation unit.
Also, as I have mentioned upthread, we have never been in a situation
where each source file includes all of the headers that it requires, and
unified builds only barely make that problem worse.
I know I made these mistake multiple times, and having B2G builds
reporting such issues was helpful at cleaning my patches at the earliest
time.
The point is, no amount of non-unified/unified build config combinations
can detect scenarios such as the above.
Cheers,
Ehsan
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