pip with ensure => latest can spuriously skip the install

The pip resource checks whether the latest version is installed using essentially pip search pkg_name | grep -i INSTALLED.*latest. This can give false positives if you have one or more other related packages already installed, because pip search matches package names and descriptions. It doesn't seem to have an option for matching the package name exactly.

I observed this in practice when installing multiple Google API packages, for example:

  $pip_packages = [
    'google-cloud-core',
    'google-cloud-dataflow',
    'google-cloud-storage',
    'google-api-python-client',
  ]

  python::pip { $pip_packages:
    ensure       => latest,
    virtualenv   => $virtual_env_dir,
    owner        => $::user,
  }

And google-api-python-client spuriously matched a bunch of installed packages:

Debug: Executing with ...: 'pip search  google-api-python-client | grep -i INSTALLED | grep -i latest'
Debug: /Stage[main]/Python::Pip[google-api-python-client]/Exec[pip_install_google-api-python-client]/unless:   INSTALLED: 0.0.2 (latest)
Debug: /Stage[main]/Python::Pip[google-api-python-client]/Exec[pip_install_google-api-python-client]/unless:   INSTALLED: 0.5.0 (latest)
Debug: /Stage[main]/Python::Pip[google-api-python-client]/Exec[pip_install_google-api-python-client]/unless:   INSTALLED: 0.7.5 (latest)
Debug: /Stage[main]/Python::Pip[google-api-python-client]/Exec[pip_install_google-api-python-client]/unless:   INSTALLED: 0.22.1 (latest)
Debug: /Stage[main]/Python::Pip[google-api-python-client]/Exec[pip_install_google-api-python-client]/unless:   INSTALLED: 2.6.0 (latest)
Debug: /Stage[main]/Python::Pip[google-api-python-client]/Exec[pip_install_google-api-python-client]/unless:   INSTALLED: 1.6.0 (latest)

The issue does not name a file or test; start by locating the pip resource's ensure => latest check and reproduce the shown pip search ... | grep ... command. Done means related package results no longer make an unrelated package appear installed, with a regression test for the Google package example.