llvm dev - Nov 2018 - [cfe-dev] GN build roundtable summary; adding GN build files to the repo

If I read this correctly, there isn't much opposition to landing the gn
files as long as it's very clear that regular devs aren't supposed to
update them and that it's clear that they're experimental

The main concerns I've heard so far:

- Having two build systems is confusing. I can see this, but I think
putting the gn files below llvm/experimental/gn (instead of right into the
source, like I currently have) and updating GN.rst to explicitly say
"Reviewers should not ask patch authors to update gn files in addition to
the cmake files" will address this.

- Having a few people care about the GN build means these people won't
improve the cmake build. I think this has some merit (but I did clean up
parts of the cmake build a bit while reading all our cmake code to create
the gn build for example, and I have several ideas about improving the
cmake build I want to implement at some point; and it's also not a given
that the folks who may or may not end up working on the GN build would have
worked on the cmake build). However, this is true independently of where
the GN build files are stored.

- GN isn't a cmake replacement, for distro reasons and whatnot. I
wholeheartedly agree with this. Maybe GN will become better here, but cmake
is ubiquitous _today_, and it's backed by a company who's interested in
keeping it around, so it will be around for a long time. I think this is
cmake's biggest strength. That's why I'm not proposing on replacing
the
cmake build. If the GN build at some point is way better (compiler-rt,
lldb, etc added; out-of-tree build support; GN itself gets a real distro
story; ...) then this _may_ be different in a few years, at which point we
could reconsider. I think this is unlikely to happen.

(I still don't see that any of these problems are being solved by having
this in an overlay or a separate fork.)

And again, It's a real possibility that we check this in and it turns out
the people who are interested in don't feel it's all that useful, it
bitrots, and we delete it again. That's cool, no harm done. I think we
should have a very high standard for replacing the supported build system
(cmake), but I think it's cool to have a low bar for people experimenting
with unsupported build systems, as long as they get deleted if not used. If
someone wanted to a, say, llvm/experimental/meson to see how that would
feel, I think that'd be super cool too for example.

On Fri, Nov 2, 2018 at 2:06 AM Dean Michael Berris <dean.berris at
gmail.com>
wrote:
> I think this is how, after moving to a monorepo, it may be feasible to
> get this in a separate fork.
>
> Granted the Git Monorepo + GitHub happens, we can even make it so that
> the GN build is a branch on the official git repository, which can
> track the mainline development.
> On Fri, Nov 2, 2018 at 3:49 AM David Blaikie via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> >
> > Any easy way to do this as some kind of overlay, so they GN files
> wouldn't live in the LLVM repository, but in a separate one?
> >
> > (this might avoid some of the community discussion - though would
> perhaps still likely have the issue I see as most significant: With a
> sufficient number of developers using GN, the rate of build breaks due to
> those developers missing CMake file updates might rise to be a bit of a
> drag on the LLVM project - though I don't think that's likely to
ever be a
> huge deal, just an annoyance)
> >
> > On Wed, Oct 31, 2018 at 11:19 AM Nico Weber via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
> >>
> >> Hi,
> >>
> >> first things first: If you're happy with cmake, you can stop
reading
> now. Nobody is proposing that LLVM moves off cmake, and nobody is proposing
> anything that's causing people using cmake more work.
> >>
> >> At the LLVM conference, I gave a lightning talk [1] about using GN
[2]
> to build LLVM and clang. cmake is great for many use cases, but in my
> opinion local day-to-day development isn't one of them. So I wrote GN
build
> files for LLVM and clang, enough to make `ninja check-llvm check-clang
> check-lld` build everything needed for these three test suites and that all
> tests pass. This works on Linux, Mac, Win hosts targeting X86, ARM,
> AArch64. You can see them at [3].
> >>
> >> I had been worried that it would be a lot of work to keep the
build
> files up to date, but I've been using this for all my LLVM/clang/lld
> development the last 8 months, and it turned out to not be a big problem --
> LLVM's build files don't change very often, and GN build files are
a
> pleasure to work with in my opinion.
> >>
> >> I gave the lightning talk just to talk about my personal workflow,
but
> there was a lot of interest. We had a roundtable on the next day, and about
> 20 people said they'd be interested in using this for their development
> too. The main request was that the .gn files are checked in upstream, so
> that we can collaborate on keeping them working. Two to three orgs even
> said they'd be interested in moving their buildbots to GN.
> >>
> >> As mentioned at the top, the intention here is not to replace
cmake,
> only to offer an opt-in alternative for people who are interested in it.
> Keeping the GN build going would be the responsibility of people using it,
> not of the general LLVM community. If this fails to find use and bitrots,
> we can easily remove it again.
> >>
> >> Are there any concerns with checking in GN files? I've put
some initial
> docs for the GN build at https://reviews.llvm.org/D53944 ; it describes
> what the GN build is and is not, what its advantages are (speed and easier
> configurability), and some points about the philosophy behind the LLVM GN
> build.
> >>
> >> If folks are generally ok with GN files living in-tree, I'll
start
> sending patches for gradually adding gn files through the regular review
> process.
> >>
> >> If having a BUILD.gn file in every directory being confusing is a
> concern, GN has the concept of a "secondary tree" so that all GN
files
> could be below llvm/gn/tree/{llvm,clang,lld,...}.
> >>
> >> Cheers,
> >> Nico
> >>
> >> 1: https://llvm.org/devmtg/2018-10/talk-abstracts.html#lt2
> >> 2: https://gn.googlesource.com/gn , https://is.gd/gn_intro
> >> 3:
>
https://github.com/llvm-project/llvm-project-20170507/compare/master...nico:gn
> , click "Files Changed" to see the GN files.
> >> _______________________________________________
> >> cfe-dev mailing list
> >> cfe-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> --
> Dean
>
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If the files can exist in an isolated subdirectory, what's the benefit to
having them checked in with LLVM rather than in a separate project checked
out alongside or nested (the same way clang and other projects are checked
into subdirectories of the LLVM tree)?

If they're in a separate tree then it doesn't matter if they bitrot -
there's no cost to the LLVM project to that project/tree continuing to
exist.

(I guess one reason would be that these files may be version locked with
the LLVM source tree, and lining those up may be difficult unless it's in
the same repository? If that's the case, then, yeah, the difference between
a subdirectory of the llvm repo, or a separate repo in the llvm-project
repository... much of a muchness

Are you looking at this only for LLVM proper, or also Clang? Would each
project (LLVM, Clang, etc) then have their own "experimental/gn"
directories?)

(one of the things I'd be worried about is not maintenance/improvement of
the CMake stuff - but just the casual breakages that happen when files are
added/moved - if a substantial number of LLVM developers started using GN
as their main build system, the number of incidental breakages of the CMake
build seems likely to rise - though minor/short term breaks like that
aren't usually a huge drag - all the buildbots complain, fixes are usually
pretty quick/obvious for anyone to make, etc)

On Mon, Nov 5, 2018 at 1:16 PM Nico Weber <thakis at chromium.org> wrote:
> If I read this correctly, there isn't much opposition to landing the gn
> files as long as it's very clear that regular devs aren't supposed
to
> update them and that it's clear that they're experimental
>
> The main concerns I've heard so far:
>
> - Having two build systems is confusing. I can see this, but I think
> putting the gn files below llvm/experimental/gn (instead of right into the
> source, like I currently have) and updating GN.rst to explicitly say
> "Reviewers should not ask patch authors to update gn files in addition
to
> the cmake files" will address this.
>
> - Having a few people care about the GN build means these people won't
> improve the cmake build. I think this has some merit (but I did clean up
> parts of the cmake build a bit while reading all our cmake code to create
> the gn build for example, and I have several ideas about improving the
> cmake build I want to implement at some point; and it's also not a
given
> that the folks who may or may not end up working on the GN build would have
> worked on the cmake build). However, this is true independently of where
> the GN build files are stored.
>
> - GN isn't a cmake replacement, for distro reasons and whatnot. I
> wholeheartedly agree with this. Maybe GN will become better here, but cmake
> is ubiquitous _today_, and it's backed by a company who's
interested in
> keeping it around, so it will be around for a long time. I think this is
> cmake's biggest strength. That's why I'm not proposing on
replacing the
> cmake build. If the GN build at some point is way better (compiler-rt,
> lldb, etc added; out-of-tree build support; GN itself gets a real distro
> story; ...) then this _may_ be different in a few years, at which point we
> could reconsider. I think this is unlikely to happen.
>
> (I still don't see that any of these problems are being solved by
having
> this in an overlay or a separate fork.)
>
> And again, It's a real possibility that we check this in and it turns
out
> the people who are interested in don't feel it's all that useful,
it
> bitrots, and we delete it again. That's cool, no harm done. I think we
> should have a very high standard for replacing the supported build system
> (cmake), but I think it's cool to have a low bar for people
experimenting
> with unsupported build systems, as long as they get deleted if not used. If
> someone wanted to a, say, llvm/experimental/meson to see how that would
> feel, I think that'd be super cool too for example.
>
> On Fri, Nov 2, 2018 at 2:06 AM Dean Michael Berris <dean.berris at
gmail.com>
> wrote:
>
>> I think this is how, after moving to a monorepo, it may be feasible to
>> get this in a separate fork.
>>
>> Granted the Git Monorepo + GitHub happens, we can even make it so that
>> the GN build is a branch on the official git repository, which can
>> track the mainline development.
>> On Fri, Nov 2, 2018 at 3:49 AM David Blaikie via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> >
>> > Any easy way to do this as some kind of overlay, so they GN files
>> wouldn't live in the LLVM repository, but in a separate one?
>> >
>> > (this might avoid some of the community discussion - though would
>> perhaps still likely have the issue I see as most significant: With a
>> sufficient number of developers using GN, the rate of build breaks due
to
>> those developers missing CMake file updates might rise to be a bit of a
>> drag on the LLVM project - though I don't think that's likely
to ever be a
>> huge deal, just an annoyance)
>> >
>> > On Wed, Oct 31, 2018 at 11:19 AM Nico Weber via cfe-dev <
>> cfe-dev at lists.llvm.org> wrote:
>> >>
>> >> Hi,
>> >>
>> >> first things first: If you're happy with cmake, you can
stop reading
>> now. Nobody is proposing that LLVM moves off cmake, and nobody is
proposing
>> anything that's causing people using cmake more work.
>> >>
>> >> At the LLVM conference, I gave a lightning talk [1] about
using GN [2]
>> to build LLVM and clang. cmake is great for many use cases, but in my
>> opinion local day-to-day development isn't one of them. So I wrote
GN build
>> files for LLVM and clang, enough to make `ninja check-llvm check-clang
>> check-lld` build everything needed for these three test suites and that
all
>> tests pass. This works on Linux, Mac, Win hosts targeting X86, ARM,
>> AArch64. You can see them at [3].
>> >>
>> >> I had been worried that it would be a lot of work to keep the
build
>> files up to date, but I've been using this for all my
LLVM/clang/lld
>> development the last 8 months, and it turned out to not be a big
problem --
>> LLVM's build files don't change very often, and GN build files
are a
>> pleasure to work with in my opinion.
>> >>
>> >> I gave the lightning talk just to talk about my personal
workflow, but
>> there was a lot of interest. We had a roundtable on the next day, and
about
>> 20 people said they'd be interested in using this for their
development
>> too. The main request was that the .gn files are checked in upstream,
so
>> that we can collaborate on keeping them working. Two to three orgs even
>> said they'd be interested in moving their buildbots to GN.
>> >>
>> >> As mentioned at the top, the intention here is not to replace
cmake,
>> only to offer an opt-in alternative for people who are interested in
it.
>> Keeping the GN build going would be the responsibility of people using
it,
>> not of the general LLVM community. If this fails to find use and
bitrots,
>> we can easily remove it again.
>> >>
>> >> Are there any concerns with checking in GN files? I've put
some
>> initial docs for the GN build at https://reviews.llvm.org/D53944 ; it
>> describes what the GN build is and is not, what its advantages are
(speed
>> and easier configurability), and some points about the philosophy
behind
>> the LLVM GN build.
>> >>
>> >> If folks are generally ok with GN files living in-tree,
I'll start
>> sending patches for gradually adding gn files through the regular
review
>> process.
>> >>
>> >> If having a BUILD.gn file in every directory being confusing
is a
>> concern, GN has the concept of a "secondary tree" so that all
GN files
>> could be below llvm/gn/tree/{llvm,clang,lld,...}.
>> >>
>> >> Cheers,
>> >> Nico
>> >>
>> >> 1: https://llvm.org/devmtg/2018-10/talk-abstracts.html#lt2
>> >> 2: https://gn.googlesource.com/gn , https://is.gd/gn_intro
>> >> 3:
>>
https://github.com/llvm-project/llvm-project-20170507/compare/master...nico:gn
>> , click "Files Changed" to see the GN files.
>> >> _______________________________________________
>> >> cfe-dev mailing list
>> >> cfe-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>> --
>> Dean
>>
>
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Nico Weber via llvm-dev <llvm-dev at lists.llvm.org>
writes:
> If I read this correctly, there isn't much opposition to landing the gn
> files as long as it's very clear that regular devs aren't supposed
to
> update them and that it's clear that they're experimental
>
> The main concerns I've heard so far:
>
> - Having two build systems is confusing. I can see this, but I think
> putting the gn files below llvm/experimental/gn (instead of right into the
> source, like I currently have) and updating GN.rst to explicitly say
> "Reviewers should not ask patch authors to update gn files in addition
to
> the cmake files" will address this.
I haven't been following this discussion and I don't really know
anything about GN, but I'm not very convinced by this.

I'm opposed to adding a second build system in general. We all remember
having two build systems before and it's a pain keep track of as well as
a documentation nightmare in telling people yet more ways to do
things. Our docs are already confusing enough given that we currently
support two completely different layouts of source directories for
cmake.

I suppose putting it somewhere under utils/ as a kind of tool for people
who want to use it like we do with text editor support and such things
wouldn't be the end of the world, but the value of that is pretty
limited if you're explicitly opting them out of community maintenance.

If the build files can be maintained in their own directory, and will
only be updated by some set of people who are using them, why not track
them in a separate source repo? This way when a breaking change happens
your build system could still be made to work for the commits in between
the time that happens and the GN files are updated, since you'd be
maintaining a separate mapping of which versions work together.
> - Having a few people care about the GN build means these people won't
> improve the cmake build. I think this has some merit (but I did clean up
> parts of the cmake build a bit while reading all our cmake code to create
> the gn build for example, and I have several ideas about improving the
> cmake build I want to implement at some point; and it's also not a
given
> that the folks who may or may not end up working on the GN build would have
> worked on the cmake build). However, this is true independently of where
> the GN build files are stored.
>
> - GN isn't a cmake replacement, for distro reasons and whatnot. I
> wholeheartedly agree with this. Maybe GN will become better here, but cmake
> is ubiquitous _today_, and it's backed by a company who's
interested in
> keeping it around, so it will be around for a long time. I think this is
> cmake's biggest strength. That's why I'm not proposing on
replacing the
> cmake build. If the GN build at some point is way better (compiler-rt,
> lldb, etc added; out-of-tree build support; GN itself gets a real distro
> story; ...) then this _may_ be different in a few years, at which point we
> could reconsider. I think this is unlikely to happen.
>
> (I still don't see that any of these problems are being solved by
having
> this in an overlay or a separate fork.)
>
> And again, It's a real possibility that we check this in and it turns
out
> the people who are interested in don't feel it's all that useful,
it
> bitrots, and we delete it again. That's cool, no harm done. I think we
> should have a very high standard for replacing the supported build system
> (cmake), but I think it's cool to have a low bar for people
experimenting
> with unsupported build systems, as long as they get deleted if not used. If
> someone wanted to a, say, llvm/experimental/meson to see how that would
> feel, I think that'd be super cool too for example.
>
> On Fri, Nov 2, 2018 at 2:06 AM Dean Michael Berris <dean.berris at
gmail.com>
> wrote:
>
>> I think this is how, after moving to a monorepo, it may be feasible to
>> get this in a separate fork.
>>
>> Granted the Git Monorepo + GitHub happens, we can even make it so that
>> the GN build is a branch on the official git repository, which can
>> track the mainline development.
>> On Fri, Nov 2, 2018 at 3:49 AM David Blaikie via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> >
>> > Any easy way to do this as some kind of overlay, so they GN files
>> wouldn't live in the LLVM repository, but in a separate one?
>> >
>> > (this might avoid some of the community discussion - though would
>> perhaps still likely have the issue I see as most significant: With a
>> sufficient number of developers using GN, the rate of build breaks due
to
>> those developers missing CMake file updates might rise to be a bit of a
>> drag on the LLVM project - though I don't think that's likely
to ever be a
>> huge deal, just an annoyance)
>> >
>> > On Wed, Oct 31, 2018 at 11:19 AM Nico Weber via cfe-dev <
>> cfe-dev at lists.llvm.org> wrote:
>> >>
>> >> Hi,
>> >>
>> >> first things first: If you're happy with cmake, you can
stop reading
>> now. Nobody is proposing that LLVM moves off cmake, and nobody is
proposing
>> anything that's causing people using cmake more work.
>> >>
>> >> At the LLVM conference, I gave a lightning talk [1] about
using GN [2]
>> to build LLVM and clang. cmake is great for many use cases, but in my
>> opinion local day-to-day development isn't one of them. So I wrote
GN build
>> files for LLVM and clang, enough to make `ninja check-llvm check-clang
>> check-lld` build everything needed for these three test suites and that
all
>> tests pass. This works on Linux, Mac, Win hosts targeting X86, ARM,
>> AArch64. You can see them at [3].
>> >>
>> >> I had been worried that it would be a lot of work to keep the
build
>> files up to date, but I've been using this for all my
LLVM/clang/lld
>> development the last 8 months, and it turned out to not be a big
problem --
>> LLVM's build files don't change very often, and GN build files
are a
>> pleasure to work with in my opinion.
>> >>
>> >> I gave the lightning talk just to talk about my personal
workflow, but
>> there was a lot of interest. We had a roundtable on the next day, and
about
>> 20 people said they'd be interested in using this for their
development
>> too. The main request was that the .gn files are checked in upstream,
so
>> that we can collaborate on keeping them working. Two to three orgs even
>> said they'd be interested in moving their buildbots to GN.
>> >>
>> >> As mentioned at the top, the intention here is not to replace
cmake,
>> only to offer an opt-in alternative for people who are interested in
it.
>> Keeping the GN build going would be the responsibility of people using
it,
>> not of the general LLVM community. If this fails to find use and
bitrots,
>> we can easily remove it again.
>> >>
>> >> Are there any concerns with checking in GN files? I've put
some initial
>> docs for the GN build at https://reviews.llvm.org/D53944 ; it describes
>> what the GN build is and is not, what its advantages are (speed and
easier
>> configurability), and some points about the philosophy behind the LLVM
GN
>> build.
>> >>
>> >> If folks are generally ok with GN files living in-tree,
I'll start
>> sending patches for gradually adding gn files through the regular
review
>> process.
>> >>
>> >> If having a BUILD.gn file in every directory being confusing
is a
>> concern, GN has the concept of a "secondary tree" so that all
GN files
>> could be below llvm/gn/tree/{llvm,clang,lld,...}.
>> >>
>> >> Cheers,
>> >> Nico
>> >>
>> >> 1: https://llvm.org/devmtg/2018-10/talk-abstracts.html#lt2
>> >> 2: https://gn.googlesource.com/gn , https://is.gd/gn_intro
>> >> 3:
>>
https://github.com/llvm-project/llvm-project-20170507/compare/master...nico:gn
>> , click "Files Changed" to see the GN files.
>> >> _______________________________________________
>> >> cfe-dev mailing list
>> >> cfe-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>> --
>> Dean
>>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

The value in having them somewhere in-tree is that it's easier for people
collaborate on these files, and it's way lower setup overhead if someone
wants to try it out. If people prefer llvm/util over llvm/experimental,
that's fine with me.

There would only be a single directory that will contain build files for
all of llvm, clang, lld, etc. The build files would be in
llvm/whatever/gn/tree/{llvm,clang,lld,...}/... ("tree" can be any
name).
That's not the most natural way to use gn, but I agree that having BUILD.gn
files scattered all over the tree could make it look like gn is supported
at some level.

If adding the files in an isolated directory still ends up being confusing
in practice, we can move them out at that point. But I'd like to start with
the simpler way and see if that's good enough.

On Mon, Nov 5, 2018 at 8:22 PM Justin Bogner <mail at justinbogner.com>
wrote:
> Nico Weber via llvm-dev <llvm-dev at lists.llvm.org> writes:
> > If I read this correctly, there isn't much opposition to landing
the gn
> > files as long as it's very clear that regular devs aren't
supposed to
> > update them and that it's clear that they're experimental
> >
> > The main concerns I've heard so far:
> >
> > - Having two build systems is confusing. I can see this, but I think
> > putting the gn files below llvm/experimental/gn (instead of right into
> the
> > source, like I currently have) and updating GN.rst to explicitly say
> > "Reviewers should not ask patch authors to update gn files in
addition to
> > the cmake files" will address this.
>
> I haven't been following this discussion and I don't really know
> anything about GN, but I'm not very convinced by this.
>
> I'm opposed to adding a second build system in general. We all remember
> having two build systems before and it's a pain keep track of as well
as
> a documentation nightmare in telling people yet more ways to do
> things. Our docs are already confusing enough given that we currently
> support two completely different layouts of source directories for
> cmake.
>
> I suppose putting it somewhere under utils/ as a kind of tool for people
> who want to use it like we do with text editor support and such things
> wouldn't be the end of the world, but the value of that is pretty
> limited if you're explicitly opting them out of community maintenance.
>
> If the build files can be maintained in their own directory, and will
> only be updated by some set of people who are using them, why not track
> them in a separate source repo? This way when a breaking change happens
> your build system could still be made to work for the commits in between
> the time that happens and the GN files are updated, since you'd be
> maintaining a separate mapping of which versions work together.
>
> > - Having a few people care about the GN build means these people
won't
> > improve the cmake build. I think this has some merit (but I did clean
up
> > parts of the cmake build a bit while reading all our cmake code to
create
> > the gn build for example, and I have several ideas about improving the
> > cmake build I want to implement at some point; and it's also not a
given
> > that the folks who may or may not end up working on the GN build would
> have
> > worked on the cmake build). However, this is true independently of
where
> > the GN build files are stored.
> >
> > - GN isn't a cmake replacement, for distro reasons and whatnot. I
> > wholeheartedly agree with this. Maybe GN will become better here, but
> cmake
> > is ubiquitous _today_, and it's backed by a company who's
interested in
> > keeping it around, so it will be around for a long time. I think this
is
> > cmake's biggest strength. That's why I'm not proposing on
replacing the
> > cmake build. If the GN build at some point is way better (compiler-rt,
> > lldb, etc added; out-of-tree build support; GN itself gets a real
distro
> > story; ...) then this _may_ be different in a few years, at which
point
> we
> > could reconsider. I think this is unlikely to happen.
> >
> > (I still don't see that any of these problems are being solved by
having
> > this in an overlay or a separate fork.)
> >
> > And again, It's a real possibility that we check this in and it
turns out
> > the people who are interested in don't feel it's all that
useful, it
> > bitrots, and we delete it again. That's cool, no harm done. I
think we
> > should have a very high standard for replacing the supported build
system
> > (cmake), but I think it's cool to have a low bar for people
experimenting
> > with unsupported build systems, as long as they get deleted if not
used.
> If
> > someone wanted to a, say, llvm/experimental/meson to see how that
would
> > feel, I think that'd be super cool too for example.
> >
> > On Fri, Nov 2, 2018 at 2:06 AM Dean Michael Berris <
> dean.berris at gmail.com>
> > wrote:
> >
> >> I think this is how, after moving to a monorepo, it may be
feasible to
> >> get this in a separate fork.
> >>
> >> Granted the Git Monorepo + GitHub happens, we can even make it so
that
> >> the GN build is a branch on the official git repository, which can
> >> track the mainline development.
> >> On Fri, Nov 2, 2018 at 3:49 AM David Blaikie via llvm-dev
> >> <llvm-dev at lists.llvm.org> wrote:
> >> >
> >> > Any easy way to do this as some kind of overlay, so they GN
files
> >> wouldn't live in the LLVM repository, but in a separate one?
> >> >
> >> > (this might avoid some of the community discussion - though
would
> >> perhaps still likely have the issue I see as most significant:
With a
> >> sufficient number of developers using GN, the rate of build breaks
due
> to
> >> those developers missing CMake file updates might rise to be a bit
of a
> >> drag on the LLVM project - though I don't think that's
likely to ever
> be a
> >> huge deal, just an annoyance)
> >> >
> >> > On Wed, Oct 31, 2018 at 11:19 AM Nico Weber via cfe-dev <
> >> cfe-dev at lists.llvm.org> wrote:
> >> >>
> >> >> Hi,
> >> >>
> >> >> first things first: If you're happy with cmake, you
can stop reading
> >> now. Nobody is proposing that LLVM moves off cmake, and nobody is
> proposing
> >> anything that's causing people using cmake more work.
> >> >>
> >> >> At the LLVM conference, I gave a lightning talk [1] about
using GN
> [2]
> >> to build LLVM and clang. cmake is great for many use cases, but in
my
> >> opinion local day-to-day development isn't one of them. So I
wrote GN
> build
> >> files for LLVM and clang, enough to make `ninja check-llvm
check-clang
> >> check-lld` build everything needed for these three test suites and
that
> all
> >> tests pass. This works on Linux, Mac, Win hosts targeting X86,
ARM,
> >> AArch64. You can see them at [3].
> >> >>
> >> >> I had been worried that it would be a lot of work to keep
the build
> >> files up to date, but I've been using this for all my
LLVM/clang/lld
> >> development the last 8 months, and it turned out to not be a big
> problem --
> >> LLVM's build files don't change very often, and GN build
files are a
> >> pleasure to work with in my opinion.
> >> >>
> >> >> I gave the lightning talk just to talk about my personal
workflow,
> but
> >> there was a lot of interest. We had a roundtable on the next day,
and
> about
> >> 20 people said they'd be interested in using this for their
development
> >> too. The main request was that the .gn files are checked in
upstream, so
> >> that we can collaborate on keeping them working. Two to three orgs
even
> >> said they'd be interested in moving their buildbots to GN.
> >> >>
> >> >> As mentioned at the top, the intention here is not to
replace cmake,
> >> only to offer an opt-in alternative for people who are interested
in it.
> >> Keeping the GN build going would be the responsibility of people
using
> it,
> >> not of the general LLVM community. If this fails to find use and
> bitrots,
> >> we can easily remove it again.
> >> >>
> >> >> Are there any concerns with checking in GN files?
I've put some
> initial
> >> docs for the GN build at https://reviews.llvm.org/D53944 ; it
describes
> >> what the GN build is and is not, what its advantages are (speed
and
> easier
> >> configurability), and some points about the philosophy behind the
LLVM
> GN
> >> build.
> >> >>
> >> >> If folks are generally ok with GN files living in-tree,
I'll start
> >> sending patches for gradually adding gn files through the regular
review
> >> process.
> >> >>
> >> >> If having a BUILD.gn file in every directory being
confusing is a
> >> concern, GN has the concept of a "secondary tree" so
that all GN files
> >> could be below llvm/gn/tree/{llvm,clang,lld,...}.
> >> >>
> >> >> Cheers,
> >> >> Nico
> >> >>
> >> >> 1:
https://llvm.org/devmtg/2018-10/talk-abstracts.html#lt2
> >> >> 2: https://gn.googlesource.com/gn ,
https://is.gd/gn_intro
> >> >> 3:
> >>
>
https://github.com/llvm-project/llvm-project-20170507/compare/master...nico:gn
> >> , click "Files Changed" to see the GN files.
> >> >> _______________________________________________
> >> >> cfe-dev mailing list
> >> >> cfe-dev at lists.llvm.org
> >> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >> >
> >> > _______________________________________________
> >> > LLVM Developers mailing list
> >> > llvm-dev at lists.llvm.org
> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
> >>
> >>
> >> --
> >> Dean
> >>
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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