Injected pip settings not working with multiple outputs

[jaimergp]

Actual Behavior

I was working on a multi-output recipe (with pep517 backend, which hardcodes --ignore-installed, but I don't know if that's relevant) and noticed pip was downloading all dependencies again for both build and run requirements. This shouldn't happen as it results in clobber warnings because PREFIX ends up with vendored dependencies.

Expected Behavior

Pip should not download dependencies, as it happens with toplevel, single-output recipes.

Intended behaviour can be regained if the environment variables set in this function are passed manually, as shown here.

Steps to Reproduce

See conda-forge/napari-feedstock#29.

Output of conda info

conda info

     active environment : base
    active env location : /opt/conda
            shell level : 1
       user config file : /home/conda/.condarc
 populated config files : /home/conda/.condarc
          conda version : 4.10.3
    conda-build version : 3.21.4
         python version : 3.8.12.final.0
       virtual packages : __linux=5.8.0=0
                          __glibc=2.12=0
                          __unix=0=0
                          __archspec=1=x86_64
       base environment : /opt/conda  (writable)
      conda av data dir : /opt/conda/etc/conda
  conda av metadata url : None
           channel URLs : https://conda.anaconda.org/conda-forge/linux-64
                          https://conda.anaconda.org/conda-forge/noarch
          package cache : /opt/conda/pkgs
                          /home/conda/.conda/pkgs
       envs directories : /opt/conda/envs
                          /home/conda/.conda/envs
               platform : linux-64
             user-agent : conda/4.10.3 requests/2.26.0 CPython/3.8.12 Linux/5.8.0-1042-azure centos/6.10 glibc/2.12
                UID:GID : 1001:1001
             netrc file : None
           offline mode : False

[jaimergp]

Duplicate of #3993