[Pkg-rust-maintainers] Bug#936029: apt fails to resolve multiple levels of provides

[Ximin Luo]

Control: reopen -1
Control: retitle -1 better error messages when failing to resolve multiple levels of provides

Julian Andres Klode:
> On Thu, Aug 29, 2019 at 02:27:45AM -0700, Ximin Luo wrote:
>> Package: apt
>> Version: 1.8.3
>> Severity: important
>>
>> Dear Maintainer,
>>
>> apt is having trouble resolving the (correct) dependencies of a certain rust package:
>>
>> $ sudo apt install librust-rand+default-dev
>> [..]
>> Some packages could not be installed. This may mean that you have
>> requested an impossible situation or if you are using the unstable
>> distribution that some required packages have not yet been created
>> or been moved out of Incoming.
>> The following information may help to resolve the situation:
>>
>> The following packages have unmet dependencies:
>>  librust-rand+default-dev : Depends: librust-rand-dev (= 0.6.4-2)
>>                             Depends: librust-rand+std-dev (= 0.6.4-2)
>> E: Unable to correct problems, you have held broken packages.
>> exit code 100
>>
> 
> There's a conflict between librust-rand-chacha-0.1-dev depending on
> librust-rand-core-0.3-dev and librust-rand-pcg-0.1-dev depending on
> librust-rand-core-0.4-dev (which conflicts with other versioned librust-rand-core)
> 
>   MarkInstall librust-rand+default-dev:amd64 < none -> 0.6.4-2 @un puN Ib > FU=1                                                                                                                                                                                                            
>     MarkInstall librust-rand-dev:amd64 < none -> 0.6.4-2 @un uN Ib > FU=0                                                                                                                                                                                                                   
>       MarkInstall librust-autocfg-dev:amd64 < none -> 0.1.4-1 @un uN > FU=0                                                                                                                                                                                                                 
>       MarkInstall librust-libc-dev:amd64 < none -> 0.2.62-1 @un uN > FU=0                                                                                                                                                                                                                   
>       MarkInstall librust-rand-chacha-0.1-dev:amd64 < none -> 0.1.1-2+b1 @un uN Ib > FU=0                                                                                                                                                                                                   
>         MarkInstall librust-rand-core-0.3-dev:amd64 < none -> 0.3.0-1+b1 @un uN > FU=0                                                                                                                                                                                                      
>       MarkInstall librust-rand-hc-0.1-dev:amd64 < none -> 0.1.0-1 @un uN > FU=0                                                                                                                                                                                                             
>       MarkInstall librust-rand-isaac-0.1-dev:amd64 < none -> 0.1.1-1 @un uN > FU=0                                                                                                                                                                                                          
>       MarkInstall librust-rand-pcg-0.1-dev:amd64 < none -> 0.1.2-1 @un uN Ib > FU=0                                                                                                                                                                                                         
>         MarkInstall librust-rand-core-0.4-dev:amd64 < none -> 0.4.0-2+b1 @un uN Ib > FU=0                                                                                                                                                                                                   
>           MarkDelete librust-rand-core-0.3-dev:amd64 < none -> 0.3.0-1+b1 @un uN > FU=0        
> 
> 
> This happens because librust-rand+default-dev depends on librust-rand-pcg-0.1+default-dev
> which is a virtual package provided by librust-rand-pcg-0.1-dev and
> librust-rand-pcg-dev.
> 
> Depending on virtual packages that have more than one provider without specifying
> a preferred provider (e.g. librust-rand-pcg-dev|librust-rand-pcg-0.1+default-dev)
> is not correct.
> 
> Please fix your packaging.
> 

Thanks for diagnosing. We forgot to upgrade rust-rand-pcg to version 0.2 when uploading rust-rand-pcg-0.1, and I have just done the former so the error should go away soon.

If apt had printed more details about the error (e.g. at the minimum, an advisory note on how to enable the debugging output you gave above) then we could have diagnosed this issue without filing a bug report about it. So I'll reopen this bug report and retitle it for improving the error message.

It's also the first time I'm hearing about the restriction "Depending on virtual packages that have more than one provider without specifying a preferred provider (e.g. librust-rand-pcg-dev|librust rand-pcg-0.1+default-dev) is not correct." -- where is that documented? This should also be part of the error message.

X

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