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

[Arthur Cohen <arthur.cohen@embecosm.com>]

On 4/9/24 12:09, Iain Sandoe wrote:
> 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.

Ah, that's fair. I guess it will require some modifications to the 
script though, as I would not want to impose Rust on anyone not looking 
to compile gccrs. I'll add this to the list of things to work on before 
14.1 :)

Thanks!

> 
>> 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
>