`spack containerize` generates containers from envs (#14202)

This PR adds a new command to Spack:
```console
$ spack containerize -h
usage: spack containerize [-h] [--config CONFIG]

creates recipes to build images for different container runtimes

optional arguments:
  -h, --help       show this help message and exit
  --config CONFIG  configuration for the container recipe that will be generated
```
which takes an environment with an additional `container` section:
```yaml
spack:
  specs:
  - gromacs build_type=Release 
  - mpich
  - fftw precision=float
  packages:
    all:
      target: [broadwell]

  container:
    # Select the format of the recipe e.g. docker,
    # singularity or anything else that is currently supported
    format: docker
    
    # Select from a valid list of images
    base:
      image: "ubuntu:18.04"
      spack: prerelease

    # Additional system packages that are needed at runtime
    os_packages:
    - libgomp1
```
and turns it into a `Dockerfile` or a Singularity definition file, for instance:
```Dockerfile
# Build stage with Spack pre-installed and ready to be used
FROM spack/ubuntu-bionic:prerelease as builder

# What we want to install and how we want to install it
# is specified in a manifest file (spack.yaml)
RUN mkdir /opt/spack-environment \
&&  (echo "spack:" \
&&   echo "  specs:" \
&&   echo "  - gromacs build_type=Release" \
&&   echo "  - mpich" \
&&   echo "  - fftw precision=float" \
&&   echo "  packages:" \
&&   echo "    all:" \
&&   echo "      target:" \
&&   echo "      - broadwell" \
&&   echo "  config:" \
&&   echo "    install_tree: /opt/software" \
&&   echo "  concretization: together" \
&&   echo "  view: /opt/view") > /opt/spack-environment/spack.yaml

# Install the software, remove unecessary deps and strip executables
RUN cd /opt/spack-environment && spack install && spack autoremove -y
RUN find -L /opt/view/* -type f -exec readlink -f '{}' \; | \
    xargs file -i | \
    grep 'charset=binary' | \
    grep 'x-executable\|x-archive\|x-sharedlib' | \
    awk -F: '{print $1}' | xargs strip -s


# Modifications to the environment that are necessary to run
RUN cd /opt/spack-environment && \
    spack env activate --sh -d . >> /etc/profile.d/z10_spack_environment.sh

# Bare OS image to run the installed executables
FROM ubuntu:18.04

COPY --from=builder /opt/spack-environment /opt/spack-environment
COPY --from=builder /opt/software /opt/software
COPY --from=builder /opt/view /opt/view
COPY --from=builder /etc/profile.d/z10_spack_environment.sh /etc/profile.d/z10_spack_environment.sh

RUN apt-get -yqq update && apt-get -yqq upgrade                                   \
 && apt-get -yqq install libgomp1 \
 && rm -rf /var/lib/apt/lists/*

ENTRYPOINT ["/bin/bash", "--rcfile", "/etc/profile", "-l"]
```

1 files changed, 58 insertions, 0 deletions

diff --git a/lib/spack/spack/test/container/images.py b/lib/spack/spack/test/container/images.py
new file mode 100644
index 0000000000..808676c39a
--- /dev/null
+++ b/lib/spack/spack/test/container/images.py
@@ -0,0 +1,58 @@
+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import os.path
+
+import pytest
+
+import spack.container
+
+
+@pytest.mark.parametrize('image,spack_version,expected', [
+    ('ubuntu:18.04', 'develop', ('spack/ubuntu-bionic', 'latest')),
+    ('ubuntu:18.04', '0.14.0', ('spack/ubuntu-bionic', '0.14.0')),
+])
+def test_build_info(image, spack_version, expected):
+    output = spack.container.images.build_info(image, spack_version)
+    assert output == expected
+
+
+@pytest.mark.parametrize('image,spack_version', [
+    ('ubuntu:18.04', 'doesnotexist')
+])
+def test_build_info_error(image, spack_version):
+    with pytest.raises(ValueError, match=r"has no tag for"):
+        spack.container.images.build_info(image, spack_version)
+
+
+@pytest.mark.parametrize('image', [
+    'ubuntu:18.04'
+])
+def test_package_info(image):
+    update, install, clean = spack.container.images.package_info(image)
+    assert update
+    assert install
+    assert clean
+
+
+@pytest.mark.parametrize('extra_config,expected_msg', [
+    ({'modules': {'enable': ['tcl']}}, 'the subsection "modules" in'),
+    ({'concretization': 'separately'}, 'the "concretization" attribute'),
+    ({'config': {'install_tree': '/some/dir'}},
+     'the "config:install_tree" attribute has been set'),
+    ({'view': '/some/dir'}, 'the "view" attribute has been set')
+])
+def test_validate(
+        extra_config, expected_msg, minimal_configuration, config_dumper
+):
+    minimal_configuration['spack'].update(extra_config)
+    spack_yaml_dir = config_dumper(minimal_configuration)
+    spack_yaml = os.path.join(spack_yaml_dir, 'spack.yaml')
+
+    with pytest.warns(UserWarning) as w:
+        spack.container.validate(spack_yaml)
+
+    # Tests are designed to raise only one warning
+    assert len(w) == 1
+    assert expected_msg in str(w.pop().message)