[llvm-dev] Upgrading LLVM's minimum required CMake version

[Eric Christopher via llvm-dev]

FWIW I do very much agree here.

Currently we specify a base set of compiler tools and cmake versions, but
at this point if we follow the proposals mentioned by Philip, Chris, and
Reid we need to actually give supported OS/Distro/Developer Tools versions
in order to let people know base requirements. I'm not against specifying
this, but I think we need consensus on how far back we're ok with "base
system" or "LTS release" we're willing to support and the technical debt
associated with such a support strategy :)

Thoughts?

-eric

On Thu, Apr 9, 2020 at 4:13 PM Philip Reames via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I would be opposed to this proposal.  I've worked with build systems that
> went this route before.  What happens is the script grows ever more
> complicated, the person who wrote the script eventually leaves, and no one
> knows how to build it outside of a particular frozen set of environments.
> I've literally seen code bases die (i.e. no one wants to work on them,
> eventual rewrite target) due to issues this can be traced solely back to
> this decision.
>
> The fact we use standard build tools is a feature not a bug.  Let's not
> "fix" our way into a much worse set of problems.
>
> Philip
>
> p.s. To be clear, I'm not stating an opinion on the original question of
> whether building cmake from source was a reasonable expectation.
> On 4/9/20 2:55 PM, Alexandre Ganea via llvm-dev wrote:
>
> Sorry if this was discussed,
>
>
>
> Why not have a *setup.sh*/*setup.bat*/*setup.exe* which could
> download/install/setup everything we want, at the version we want, on a
> vanilla system? Handle the cases described by Chris below? Why leave the
> burden to the end-user?
>
>
>
> Currently, it’s not exactly trivial to setup everything for building &
> running LLVM on Windows on a cloud VM if you want `ninja check-all` to pass
> on
> -DLLVM_ENABLE_PROJECTS=llvm;mlir;clang;lld;clang-tools-extra;compiler-rt;lldb.
> There are many manuals steps, and often things that you forget (GnuWin32
> FTW). On Ubuntu it is a bit easier, but still lots of trial and error.
>
>
>
> We use NuGet
> <https://docs.microsoft.com/en-us/nuget/install-nuget-client-tools>
> packages in our build system and for our developers, to ensure they always
> have the right setup. Our games always build and use the toolings from the
> .nugets, not the default installations on the machine. This guarantees
> universal determinism everywhere and makes the developer setup a
> *one-click-exe*. Setting up a similar thing for LLVM for different OSes
> could be a bit more tricky, but nothing insurmountable?
>
>
>
>
>
> *De :* llvm-dev <llvm-dev-bounces at lists.llvm.org>
> <llvm-dev-bounces at lists.llvm.org> *De la part de* Shoaib Meenai via
> llvm-dev
> *Envoyé :* April 9, 2020 4:26 PM
> *À :* Reid Kleckner <rnk at google.com> <rnk at google.com>; James Y Knight
> <jyknight at google.com> <jyknight at google.com>
> *Cc :* llvm-dev at lists.llvm.org
> *Objet :* Re: [llvm-dev] Upgrading LLVM's minimum required CMake version
>
>
>
> I agree that’s valuable, but then it’s also important to pin down exactly
> what a “modern OS” is, and which ones we should keep in mind when we’re
> considering e.g. which CMake versions are feasible. (The same applies even
> more so to toolchain requirements, of course.)
>
>
>
> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Reid
> Kleckner via llvm-dev <llvm-dev at lists.llvm.org>
> *Reply-To: *Reid Kleckner <rnk at google.com>
> *Date: *Thursday, April 9, 2020 at 1:20 PM
> *To: *James Y Knight <jyknight at google.com>
> *Cc: *"llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>
> *Subject: *Re: [llvm-dev] Upgrading LLVM's minimum required CMake version
>
>
>
> I would add my voice to Chris's: building out of the box on standard
> distros is a valuable feature. I don't have time to really participate in
> this discussion, but I'd discourage us from adding any more steps at all to
> the LLVM getting started document.
>
>
>
> When I started working on compilers, it was important that I could build
> LLVM on the system and hardware that I had. That was a meaningful
> differentiating advantage over GCC, which sent me off on a side quest to
> check out two unfamiliar arbitrary precision math libraries, and asked me
> if I wanted to do a two-stage bootstrap. Forget that. From a modern OS,
> building LLVM should be as simple as:
>
> - Install a standard C++ toolchain
>
> - Clone source
>
> - Paste a standard configuration command
>
> - make
>
>
>
> If we get too far away from that, we've lost something.
>
>
>
> On Wed, Apr 8, 2020 at 2:49 PM James Y Knight via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> I am strongly in favor of increasing the minimum CMake version.
>
>
>
> I think we should NOT be waiting for the next LLVM release to do so, but
> should do so as soon as practical (e.g. maybe a month from now). A warning
> message emitted in CMake spam is not likely to help users very much, IMO.
> An entry in the release notes saying "This version of LLVM now requires
> CMake X.Y.Z." along with a link to the completely-trivial instructions on
> how to get, build, and use a new version for building LLVM (WITHOUT having
> to install it!), should both suffice -- and is more likely to be useful.
>
>
>
> I do NOT think we should have a policy tying ourselves to versions
> supported by certain LTS releases. Users of such LTSes can download a newer
> cmake. We should, of course, strive to not be unnecessarily annoying --
> even though the amount of work to download a new version is small, it's not
> zero. We should _consider_ the versions that developers are likely to have
> pre-installed on their machines, and drop support for those versions only
> when the new features are judged compelling enough to offset the cost
> (small-pain-per-developer times number-of-deveopers-affected).
>
>
>
> I agree with others who say we should only upgrade when would be truly
> valuable -- not automatically just because a new version exists. We should
> avoid changing the minimum-requirement too often.
>
>
>
> FInally, I think we should put the decision of when such an upgrade is
> judged valuable into the hands of those who are spending the most time
> working on the build system. We do not need to redo this discussion every
> time.
>
>
>
>
>
> On Wed, Apr 8, 2020 at 4:36 PM Chris Tetreault via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> We should decide who we consider the major distros to be. In my mind this
> is Ubuntu, Debian, Fedora, and CentOS/RHEL. We should also consider Visual
> Studio releases and whatever OSX and the major BSD’s have. (I honestly have
> no idea so I’ll refrain from speculating)
>
>
>
> For all of these, we should try very hard to support the most recent LTS.
> For the previous LTS, it would be nice if we could support it, but we
> shouldn’t require it. Old LTSs tend to have really out of date packages,
> especially in times like now with Ubuntu where we’re really close to the
> current LTS becoming the old LTS.
>
>
>
> That said, if CMake version X has a killer feature that we need, we should
> consider upgrading even if it doesn’t fit this criteria. Similarly, we
> should not just upgrade because the minimum bound of CMake versions
> supported by this set of OSs increased. The point is to upgrade only when
> there’s a compelling reason, and this set of OSs is just a heuristic of
> “most people probably already have this CMake version.”
>
>
>
> *From:* Shoaib Meenai <smeenai at fb.com>
> *Sent:* Wednesday, April 8, 2020 12:58 PM
> *To:* Chris Tetreault <ctetreau at quicinc.com>; Eric Christopher <
> echristo at gmail.com>
> *Cc:* llvm-dev at lists.llvm.org
> *Subject:* [EXT] Re: [llvm-dev] Upgrading LLVM's minimum required CMake
> version
>
>
>
> Yeah, I don’t anticipate Windows posing problems. Also, it’s pretty common
> in Windows to just install software yourself, and CMake ships prebuilt
> binaries and an installer, so it’s pretty easy to get set up with it.
>
>
>
> Chris, I’m gonna reiterate a question of mine from an earlier email, since
> you may have thoughts on it:
>
>
>
> * If we want to limit ourselves to CMake versions supported by LTS
> releases of distros, which distros should we consider, and how far back
> should we go (i.e. is it just the latest LTS or the last two LTS versions)?
>
>
>
> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Chris
> Tetreault via llvm-dev <llvm-dev at lists.llvm.org>
> *Reply-To: *Chris Tetreault <ctetreau at quicinc.com>
> *Date: *Wednesday, April 8, 2020 at 12:51 PM
> *To: *Eric Christopher <echristo at gmail.com>
> *Cc: *"llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>
> *Subject: *Re: [llvm-dev] Upgrading LLVM's minimum required CMake version
>
>
>
> Visual studio 2019 ships with CMake 3.15.5, which is pretty darn new IMO.
> From what I can tell, CMake versions are tied to visual studio releases. So
> assuming we go with “what do recent LTS distros have” as our metric, I
> think it’s reasonable to say “what do recent visual studio versions have”.
> It probably makes sense to confirm with MS though before we assume that
> this is the case.
>
>
>
> *From:* Eric Christopher <echristo at gmail.com>
> *Sent:* Wednesday, April 8, 2020 12:41 PM
> *To:* Chris Tetreault <ctetreau at quicinc.com>
> *Cc:* Mehdi AMINI <joker.eph at gmail.com>; Louis Dionne <ldionne at apple.com>;
> llvm-dev at lists.llvm.org
> *Subject:* [EXT] Re: [llvm-dev] Upgrading LLVM's minimum required CMake
> version
>
>
>
> Hi All,
>
>
>
> Throwing a couple of comments in:
>
>
>
> Chris's position here has a lot of good points and we want to make sure
> we're not raising the barrier too high. I definitely want to be able to
> push ahead with our versions of tools; being able to update quickly is one
> of the hallmarks of the llvm project. That said, binary packages that can
> be updated are a minimal first step IMO. I'd really like to not build
> anything from source :) It seems like there are binaries available for
> cmake for all of our current platforms, but the windows use case that he
> brings is definitely a significant one. Can we perhaps reach out and find
> out the likelihood of a reasonably soonish update there? Linux distros are
> probably less of a problem - while we all can't use ppas we should be able
> to do something, similarly with osx.
>
>
>
> Thoughts?
>
>
>
> -eric
>
>
>
> On Wed, Apr 8, 2020 at 9:53 AM Chris Tetreault via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>
>
> A line has to be drawn in the sand somewhere. How many “easy” things are
> we going to require the user to do? Today it’s build a specific CMake from
> source. What’s next?
>
>
>
> Not having to manually track down a bunch of dependencies before building
> is a feature. Not having to have an internet connection at build time (if
> we were to script the getting of the custom CMake) is a feature. Being able
> to just call cmake instead of using some build_llvm.sh that (probably
> poorly) wraps cmake and downloads the correct version is a feature. Being
> able to use CMake that is distributed with visual studio so that invoking
> cmake from the developer powershell just works without fiddling with PATHs
> is a feature. Not having to install msys so that I can invoke
> download_cmake.sh is a feature. Not having to have the correct version of
> python (is it 2 or 3?) be on the path in order to invoke download_cmake.py
> is a feature. Not having to remember to do --recurse-submodules on the llvm
> repo if we include it as a git submodule is a feature. The list goes on.
> Yeah, these are all little things, but a bunch of little things adds up to
> a huge barrier.
>
>
>
> People use Linux distos because by and large they just have all the
> dependencies that they need. I know I personally hate installing some open
> source thing on my machines when they have some dependency that’s not in
> the repos. Sure, it may be easy to build CMake from source. But now I have
> two CMakes: one that is automatically updated when I do sudo apt-get
> upgrade, and one that is just randomly in some folder that’s probably not
> on the PATH. I personally would really appreciate it if we made an attempt
> to reduce this sort of friction.
>
>
>
> Thanks,
>
>    Christopher Tetreault
>
>
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Mehdi
> AMINI via llvm-dev
> *Sent:* Wednesday, April 8, 2020 9:06 AM
> *To:* Louis Dionne <ldionne at apple.com>
> *Cc:* llvm-dev at lists.llvm.org
> *Subject:* [EXT] Re: [llvm-dev] Upgrading LLVM's minimum required CMake
> version
>
>
>
>
>
>
>
> On Wed, Apr 8, 2020 at 9:02 AM Louis Dionne <ldionne at apple.com> wrote:
>
>
>
>
>
> On Apr 7, 2020, at 22:16, Mehdi AMINI via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>
>
>
>
>
>
> On Tue, Apr 7, 2020 at 11:27 AM David Blaikie <dblaikie at gmail.com> wrote:
>
> I think it does make a difference how many things we ask new developers to
> do to get up and running - because we've asked them to do one thing doesn't
> mean it's low-cost to ask them to do another thing.
>
>
>
> In this case I see it rather that if we ask them to do one quite big thing
> already, we should be OK with what seems like a trivial one.
>
>
>
> I strongly agree. I think Mehdi's point can be summarized as (Mehdi, feel
> free to correct me):
>
>
>
>     It's incredibly trivial to install CMake, so if a user is *already*
> required to install a non-default toolchain (which is not so trivial),
> requiring them to install a non-default CMake is not increasing the barrier
> by much.
>
>
>
> Thanks, this is my point indeed!
>
>
>
> I think it is even slightly stronger than what you wrote since you don't
> even need to *install* CMake as it can be built and used directly from the
> build directory: it is entirely non-intrusive on the system.
>
>
>
> --
>
> Mehdi
>
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