Broken libc++ installation in 20250528 release of Ubuntu libc++1-20 package

[ednolan]

Somewhere between release 1:20.1.6~++20250514063329+1e4d39e07757-1~exp1~20250514183345.117 and release 1:20.1.7~++20250528073536+7cf14539b644-1~exp1~20250528193553.123 of the Ubuntu libc++1-20 packages, the installed paths to the shared object files changed:

$ apt show libc++1-20
Package: libc++1-20
Version: 1:20.1.6~++20250514063329+1e4d39e07757-1~exp1~20250514183345.117
Status: install ok installed
Priority: optional
Section: libs
Source: llvm-toolchain-20
Maintainer: LLVM Packaging Team <pkg-llvm-team@lists.alioth.debian.org>
Installed-Size: 1,189 kB
Provides: libc++-x.y
Depends: libc++abi1-20 (>= 1:20.1.6~++20250514063329+1e4d39e07757), libc6 (>= 2.38), libunwind-20 (>= 1:20.1.6~++20250514063329+1e4d39e07757)
Suggests: clang
Conflicts: libc++-x.y
Replaces: libc++-x.y
Homepage: https://www.llvm.org/
Download-Size: unknown
APT-Manual-Installed: no
APT-Sources: /var/lib/dpkg/status
Description: LLVM C++ Standard library
 libc++ is another implementation of the C++ standard library.
 .
 Features and Goals
 .
   * Correctness as defined by the C++ standards.
   * Fast execution.
   * Minimal memory use.
   * Fast compile times.
   * ABI compatibility with gcc's libstdc++ for some low-level features such
     as exception objects, rtti and memory allocation.
   * Extensive unit tests.

Notice: There is 1 additional record. Please use the '-a' switch to see it
$ dpkg -L libc++1-20
/.
/usr
/usr/lib
/usr/lib/llvm-20
/usr/lib/llvm-20/lib
/usr/lib/llvm-20/lib/libc++.so.1.0
/usr/lib/x86_64-linux-gnu
/usr/share
/usr/share/doc
/usr/share/doc/libc++1-20
/usr/share/doc/libc++1-20/changelog.Debian.gz
/usr/share/doc/libc++1-20/copyright
/usr/share/lintian
/usr/share/lintian/overrides
/usr/share/lintian/overrides/libc++1-20
/usr/lib/llvm-20/lib/libc++.so.1
/usr/lib/x86_64-linux-gnu/libc++.so.1
/usr/lib/x86_64-linux-gnu/libc++.so.1.0

$ apt show libc++1-20
Package: libc++1-20
Version: 1:20.1.7~++20250528073536+7cf14539b644-1~exp1~20250528193553.123
Priority: optional
Section: libs
Source: llvm-toolchain-20
Maintainer: LLVM Packaging Team <pkg-llvm-team@lists.alioth.debian.org>
Installed-Size: 1187 kB
Depends: libc++abi1-20 (>= 1:20.1.7~++20250528073536+7cf14539b644), libc6 (>= 2.38), libunwind-20 (>= 1:20.1.7~++20250528073536+7cf14539b644)
Suggests: clang
Homepage: https://www.llvm.org/
Download-Size: 358 kB
APT-Manual-Installed: yes
APT-Sources: http://apt.llvm.org/oracular llvm-toolchain-oracular-20/main amd64 Packages
Description: LLVM C++ Standard library
 libc++ is another implementation of the C++ standard library.
 .
 Features and Goals
 .
   * Correctness as defined by the C++ standards.
   * Fast execution.
   * Minimal memory use.
   * Fast compile times.
   * ABI compatibility with gcc's libstdc++ for some low-level features such
     as exception objects, rtti and memory allocation.
   * Extensive unit tests.

Notice: There is 1 additional record. Please use the '-a' switch to see it
$ dpkg -L libc++1-20
/.
/usr
/usr/lib
/usr/lib/llvm-20
/usr/lib/llvm-20/lib
/usr/lib/llvm-20/lib/libc++.so.1.0.20
/usr/lib/x86_64-linux-gnu
/usr/share
/usr/share/doc
/usr/share/doc/libc++1-20
/usr/share/doc/libc++1-20/changelog.Debian.gz
/usr/share/doc/libc++1-20/copyright
/usr/share/lintian
/usr/share/lintian/overrides
/usr/share/lintian/overrides/libc++1-20
/usr/lib/x86_64-linux-gnu/libc++.so.1.0.20

With the old version, after having run apt-get install -y libc++1-20 libc++abi1-20 libunwind-20, the /usr/lib/llvm-20/lib directory would contain the following contents:

$ ls -l /usr/lib/llvm-20/lib/
total 702
lrwxrwxrwx 1 root root      13 Apr 30 01:49 libc++.so.1 -> libc++.so.1.0
-rw-r--r-- 1 root root 1120048 Apr 30 01:49 libc++.so.1.0
lrwxrwxrwx 1 root root      16 Apr 30 01:49 libc++abi.so.1 -> libc++abi.so.1.0
-rw-r--r-- 1 root root  253352 Apr 30 01:49 libc++abi.so.1.0
lrwxrwxrwx 1 root root      16 Apr 30 01:49 libunwind.so.1 -> libunwind.so.1.0
-rw-r--r-- 1 root root   51720 Apr 30 01:49 libunwind.so.1.0

Now, it just contains this:

$ ls -l /usr/lib/llvm-20/lib
total 699
-rw-r--r-- 1 root root 1120144 May 28 19:35 libc++.so.1.0.20
-rw-r--r-- 1 root root  253408 May 28 19:35 libc++abi.so.1.0.20
-rw-r--r-- 1 root root   51784 May 28 19:35 libunwind.so.1.0.20

[ldionne]

@sylvestre is responsible for these packages IIUC.

[firewave]

I wonder if this is related to #144501.

[ldionne]

Yes, I think it's a duplicate of that. Duping.