Rust-src does not contain libsrc & libcore sources

[Dmitry Lapshin]

I have installed rust-src package to provide IDE support for Rust, yet it lacked libstd/libcore sources that were actually desired. Older version, 1.43, does contain those sources, and you can easily see that upgrading to 1.47 removes about 28 MiB of files.

I've tried looking up other packages to check if libstd sources are there using apt-file and haven't found any.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: rust-src 1.43.0+dfsg1+llvm-1~exp1ubuntu2
ProcVersionSignature: Ubuntu 5.8.0-48.54-generic 5.8.18
Uname: Linux 5.8.0-48-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu50.5
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 1 23:22:11 2021
Dependencies:

InstallationDate: Installed on 2017-03-05 (1488 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
ProcEnviron:
 TERM=tmux-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=ru_RU.UTF-8
 SHELL=/bin/bash
SourcePackage: rustc
UpgradeStatus: Upgraded to groovy on 2020-12-22 (100 days ago)