Re: [PATCH] build: Check for cargo when building rust language

[Iain Sandoe <idsandoe@googlemail.com>]

Hi Arthur,

> On 9 Apr 2024, at 13:01, Arthur Cohen <arthur.cohen@embecosm.com> wrote:
> 

> On 4/9/24 10:55, Iain Sandoe wrote:
>> Hi Arthur,
>>> On 9 Apr 2024, at 11:40, Arthur Cohen <arthur.cohen@embecosm.com> wrote:
>>> On 4/9/24 09:47, John Paul Adrian Glaubitz wrote:
>>>> Hello,
>>>> On Mon, 2024-04-08 at 18:33 +0200, pierre-emmanuel.patry@embecosm.com wrote:
>>>>> The rust frontend requires cargo to build some of it's components,
>>>>> it's presence was not checked during configuration.
>>>> Isn't this creating a hen-and-egg problem? How am I supposed to build a Rust
>>>> compiler for a target which is not supported by rustc (yet) when gccrs is
>>>> supposed to build-depend on cargo which requires rustc?
>>>> Adrian
>>> 
>>> Quick reminder in case you haven't seen our Request for Comments on the main ML that this is only a temporary solution. Once gccrs can compile its dependencies, we'll go through a more "classical" bootstrapping chain.
>> I don’t suppose there’s some way to make a “download prerequisites” action for this?
> 
> Do you mean downloading cargo/Rust as a prerequisite? I don't believe this is being done for GNAT/GDC, but I might be wrong.

No, you are quite correct, but the critical difference is that Ada and D both make use of earlier versions of GCC - so that (if one wished to be particular) it is possible to start with an earlier version of GCC and work forwards (in fact that’s what I’ve [I guess all of us] have done for D … and did a looong time ago for Ada).

The difference here is that we need to install an executable from somewhere else - and making that as simple and trustworthy as possible seems like a good move to encourage folks to build & test rust.

> If you mean the dependencies for our Rust components, those are currently being vendored so that we're able to build them offline. I'll push the commits soon.

OK.. I’m sorry to say this - but what’s actually needed is still a little fuzzy to me - but I am happy to wait to read the documentation patch and comment then.

thanks
Iain

> 
>> (I realise that the prerequisite might not be available for a given platform - but then the configure will then just fail to detect them and carry on).
>> At the least the build documentation requested should (ideally) try to lower the barrier to finding the deps and give reliable sources for them.
>>> rustc_codegen_gcc can probably already be used for building these dependencies however, if you'd like to have a look at that.
>> Detailing the verious options would also be a helpful part of the build doc.
>> thanks
>> Iain
> 
> Best,
> 
> Arthur