Backport rustc 1.19 and cargo 0.20 to 14.04/16.04/17.04/17.10

[Rico Tzschichholz]

Firefox 56+ will require rust 1.17 and cargo 0.18 to build.

The beta-phase for Firefox 56.0 begins on 7th August and release candidates will be available from 18th September.

17.10/Artful still requires an update of cargo first while rustc is sufficient already.

https://wiki.mozilla.org/Rust_Update_Policy_for_Firefox

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Håkon A. Hjortland (post-hakn)]

I'm currently unable to compile the firefox package in Ubuntu 16.04 and 17.10 because the available versions of cargo and rustc are too old:

$ sudo apt build-dep firefox
Reading package lists... Done
Reading package lists... Done
Building dependency tree
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:
 builddeps:firefox : Depends: cargo (>= 0.20)
                     Depends: rustc (>= 1.19.0)
E: Unable to correct problems, you have held broken packages.

[Hans Joachim Desserud (hjd)]

Indeed, it looks like the newer versions of these packages are missing from older Ubuntu releases, making it impossible to rebuild Firefox from scratch.

[Karl-Philipp Richter (krichter722)]

Since I can reproduce this with Docker image `ubuntu:bionic` I assume that 18.04 is affected as well. This might change since it's not released yet, but it's worth mentioning it.

[Hans Joachim Desserud (hjd)]

Could you please post the complete error message for bionic? The cargo package version (https://launchpad.net/ubuntu/+source/cargo) should be sufficient there, but looks like there's a newer version of rustc which haven't migrated from the -proposed archive (https://launchpad.net/ubuntu/+source/rustc). Not sure why, but that might be the only problem for bionic. I believe packages are built with -proposed enabled, so I suppose that might be why it works.