[Pkg-rust-maintainers] Bug#1124769: rustc: FTBFS rustc in Debian Bookworm because of conflict in build deps

[Sergei Semin]

Source: rustc
Version: 1.63.0+dfsg1-2
Severity: serious
Tags: ftbfs
Justification: fails to build from source (but built successfully in the past)
X-Debbugs-Cc: sergeysyomin at yandex.ru

Dear Maintainer,
it is impossible to build rustc on Debian Bookworm because of conflict in build deps.

How to reproduce.

Lets start new docker container with Debian Bookworm environment:
```
sudo docker run -it --rm debian:bookworm bash
```

Update apt cache:
```
apt update
```

Install some text editor:
```
apt install nano
```

Make backup of `/etc/apt/sources.list.d/debian.sources`:
```
cp /etc/apt/sources.list.d/debian.sources{,.bak}
```

Edit `/etc/apt/sources.list.d/debian.sources` and add deb-src:
```
nano /etc/apt/sources.list.d/debian.sources
```

Difference with original file:
```
root at 9925b7386ff9:/# diff /etc/apt/sources.list.d/debian.sources{.bak,}
1c1
< Types: deb
---
> Types: deb deb-src
8c8
< Types: deb
---
> Types: deb deb-src
root at 9925b7386ff9:/#
```

Update apt cache again:
```
apt update
```

Let's try to simulate installation of rustc build deps:
```
apt -s build-dep rustc
```

And this is a problem:
```
root at 9925b7386ff9:/# apt -s build-dep rustc
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
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:
 libstd-rust-web-dev : Conflicts: libstd-rust-dev
 rustc-web : Conflicts: rustc
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
root at 9925b7386ff9:/#
```

Problem reproduced on amd64 and arm64.

-- System Information:
Debian Release: 12.12
  APT prefers oldstable-updates
  APT policy: (500, 'oldstable-updates'), (500, 'oldstable-security'), (500, 'oldstable')
Architecture: arm64 (aarch64)

Kernel: Linux 5.15.0-1092-raspi (SMP w/4 CPU threads; PREEMPT)
Kernel taint flags: TAINT_CRAP, TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: unable to detect