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From: | Philip McGrath |
Subject: | [bug#55248] [PATCH v3 8/9] gnu: chez-scheme-for-racket: Fix supported systems. |
Date: | Thu, 12 May 2022 01:26:36 -0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 |
Hi, On 5/9/22 05:36, Liliana Marie Prikler wrote:
Hi, Am Montag, dem 09.05.2022 um 03:55 -0400 schrieb Philip McGrath:Concretely, there are no other uses in Guix. I do not know a robust, correct way to use 'nix-system->chez-machine'---certainly not without it growing many additional features, like maybe computing endianness for pbarch backends when we are able to build them. For example, if we continued using it as we did in 'stex', you couldn't build a package graph for nonthreaded Chez simply by applying a package transformation to remove '--threads' from its '#:configure-flags', because that would change the machine type without updating the uses of 'nix-system-chez-machine'.True, you would have to change the machine type, but I think I already noted that we might want to use this machine type as a distinguishing factor in packages built on top of chez (and later chez-build-system perhaps). You could do this the other way round by deriving flags from the given machine-type, e.g. stex for threaded chez machine is given -- threads, otherwise it's not. Since we have named symbols for these features, we could have a "package-with-chez-features" or similar transformer. Being able to specify this machine is a strength, not a weakness.
I can imagine something like this might be useful eventually. My problem is that, right now, 'nix-system->chez-machine' is an attractive nuisance: it sounds useful, but I don't know any way of using it that wouldn't be subtly wrong. I don't even feel certain even about what cases 'nix-system->chez-machine' would need to cover to be correct and useful: a fair amount seems to depend on what turns out to be necessary for cross-compilation and the portable bytecode architectures (which I hope to work out by July).
The idea is that the "portable bytecode" backends should work, including thread support, on any system with a reasonably capable C compiler.The idea. In practice, what racket deems reasonably capable can change over time and might result in them dropping some architectures currently supported. What do you do then?
I mean, "over time", at the extreme, anything "might" happen, but I don't think that's worth worrying about. Racket has an extremely strong commitment to backwards compatibility. To pick one example, support libraries for racket/draw and racket/gui are still maintained for ppc-macosx, which the vendor hasn't released any software for in a decade or more (depending on how you prefer to count). The C code deliberately does not require C99 support.
>> The presence of an entry in '%chez-features-table' explicitly means >> that 'chez-scheme-for-racket' can generate native code. > That is not explicit at all. There might be an explicit comment > stating so somewhere, but in terms of actual code, it's super > implicit. >
There are no other "features" that vary among systems for 'chez-scheme-for-racket'. It doesn't rely on pre-built bootfiles for bootstrapping. Since the initial fork at the beginning of 2017, when support for new systems has been added, native threads have been supported immediately. Racket regularly merges all changes from upstream Chez (which has not added any supported systems during that time---not even the systems added already in Racket's variant).I'd still make "supported-by-racket" or however else you decide to name that feature an explicit part of that table rather than an implicit one, or use a separate "table" for platforms supported by racket.
I really don't understand how this would be helpful. I don't think it would make sense for a list returned by chez-upstream-features-for-system to include a symbol supported-by-racket, which has nothing to do with *upstream* features. Aside from that, we would be adding this symbol to every single entry in %chez-features-table. That would imply turning all of the #f entries into (supported-by-racket), and then we would need some other solution for identifying platforms with no support upstream.
Note that none of the racket-vm packages appear to currently carry supported-systems, which seems dubious.
The only constraint on the systems supported by 'racket-vm-cs' is from 'chez-scheme-for-racket'---i.e., the trouble with `configure` for systems without a native-code backend, which should be fixed by the next release, if not before. I expect the fact that the 'chez-scheme-for-racket' input is not supported to work as an alternative to duplicating the filtering in its supported-systems field (which I think would create a cyclic dependency issue).
AFAIK, 'racket-vm-cgc' and 'racket-vm-bc' should work everywhere (though possibly without the JIT, futures, and/or places) except that support for aarch64-macosx is prohibitively poor (IIUC due to W^X issues), which is fairly irrelevant for Guix.
-Philip
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