linux-64 package has undeclaired dependency on libiconv

The linux-64 libarchive packages have a direct dependency on libiconv that is not declared. This can cause problems if the package is installed with a version of libxml2 that does not require libiconv (such as the packages in defaults) as the library will not be available at run time.

This has the potential to break conda itself if installed in the base environment, conda/conda#8838.

Example:

[root@chi9 build_scripts]# conda create -n test_libarchive -c defaults -c conda-forge conda-forge::libarchive
Collecting package metadata (current_repodata.json): done
Solving environment: done

## Package Plan ##

  environment location: /opt/conda/envs/test_libarchive

  added / updated specs:
    - conda-forge::libarchive

The following NEW packages will be INSTALLED:

  bzip2              pkgs/main/linux-64::bzip2-1.0.6-h14c3975_5
  ca-certificates    pkgs/main/linux-64::ca-certificates-2019.5.15-0
  libarchive         conda-forge/linux-64::libarchive-3.3.3-hb44662c_1005
  libgcc-ng          pkgs/main/linux-64::libgcc-ng-9.1.0-hdf63c60_0
  libstdcxx-ng       pkgs/main/linux-64::libstdcxx-ng-9.1.0-hdf63c60_0
  libxml2            pkgs/main/linux-64::libxml2-2.9.9-hea5a465_1
  lz4-c              conda-forge/linux-64::lz4-c-1.8.3-he1b5a44_1001
  lzo                pkgs/main/linux-64::lzo-2.10-h49e0be7_2
  openssl            pkgs/main/linux-64::openssl-1.1.1c-h7b6447c_1
  xz                 pkgs/main/linux-64::xz-5.2.4-h14c3975_4
  zlib               pkgs/main/linux-64::zlib-1.2.11-h7b6447c_3
  zstd               conda-forge/linux-64::zstd-1.4.0-h3b9ef0a_0

Proceed ([y]/n)? y

Preparing transaction: done
Verifying transaction: done
Executing transaction: done
#
# To activate this environment, use
#
#     $ conda activate test_libarchive
#
# To deactivate an active environment, use
#
#     $ conda deactivate

[root@chi9 build_scripts]# conda activate test_libarchive
(test_libarchive) [root@chi9 build_scripts]# bsdcat --help
bsdcat: error while loading shared libraries: libiconv.so.2: cannot open shared object file: No such file or directory
(test_libarchive) [root@chi9 build_scripts]# readelf -d /opt/conda/envs/test_libarchive/lib/libarchive.so

Dynamic section at offset 0xb7a78 contains 34 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libiconv.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libcrypto.so.1.1]
 0x0000000000000001 (NEEDED)             Shared library: [liblzo2.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [liblzma.so.5]
 0x0000000000000001 (NEEDED)             Shared library: [libzstd.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [liblz4.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libbz2.so.1.0]
 0x0000000000000001 (NEEDED)             Shared library: [libz.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libxml2.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000e (SONAME)             Library soname: [libarchive.so.13]
 0x000000000000000f (RPATH)              Library rpath: [$ORIGIN/.]
 0x000000000000000c (INIT)               0x15000
...

The build logs did contain a warning about this missing dependency:

WARNING (libarchive,bin/bsdcat): Needed DSO lib/libiconv.so.2 found in ['libiconv']
WARNING (libarchive,bin/bsdcat): .. but ['libiconv'] not in reqs/run, (i.e. it is overlinking) (likely) or a missing dependency (less likely)

conda-forge / libarchive-feedstock

linux-64 package has undeclaired dependency on libiconv #35