cray: use the cle-release file to determine CNL version

- CNL OS previously used the *Cray PE* version to determine the OS
  version.  Cray does not synchronize PE and CLE releases; you can run
  CLE7 with PrgEnv 6 (and NERSC currently does).

- Fix Spack's OS detection by using the cle-release file to detect the OS
  version.  This file is updated with every CLE OS release.

- Add some tests for our parsing logic

lib/spack/spack/operating_systems/cnl.py

@@ -7,9 +7,42 @@
 
 import llnl.util.tty as tty
 
+import spack.version
 from spack.architecture import OperatingSystem
 from spack.util.module_cmd import module
 
+#: Location of the Cray CLE release file, which we look at to get the CNL
+#: OS version.
+_cle_release_file = '/etc/opt/cray/release/cle-release'
+
+
+def read_cle_release_file():
+    """Read the CLE release file and return a dict with its attributes.
+
+    The release file looks something like this::
+
+        RELEASE=6.0.UP07
+        BUILD=6.0.7424
+        ...
+
+    The dictionary we produce looks like this::
+
+        {
+          "RELEASE": "6.0.UP07",
+          "BUILD": "6.0.7424",
+          ...
+        }
+
+    """
+    with open(_cle_release_file) as release_file:
+        result = {}
+        for line in release_file:
+            # use partition instead of split() to ensure we only split on
+            # the first '=' in the line.
+            key, _, value = line.partition('=')
+            result[key] = value.strip()
+        return result
+
 
 class Cnl(OperatingSystem):
     """ Compute Node Linux (CNL) is the operating system used for the Cray XC
@@ -28,12 +61,11 @@ def __init__(self):
     def __str__(self):
         return self.name + str(self.version)
 
-    def _detect_crayos_version(self):
-        output = module("avail", "PrgEnv-cray")
-        matches = re.findall(r'PrgEnv-cray/(\d+).\d+.\d+', output)
-        major_versions = set(matches)
-        latest_version = max(major_versions)
-        return latest_version
+    @classmethod
+    def _detect_crayos_version(cls):
+        release_attrs = read_cle_release_file()
+        v = spack.version.Version(release_attrs['RELEASE'])
+        return v[0]
 
     def arguments_to_detect_version_fn(self, paths):
         import spack.compilers

lib/spack/spack/test/operating_system.py

@@ -0,0 +1,34 @@
+# Copyright 2013-2019 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 spack.operating_systems.cnl as cnl
+
+
+def test_read_cle_release_file(tmpdir, monkeypatch):
+    """test reading the Cray cle-release file"""
+    cle_release_path = tmpdir.join('cle-release')
+    with cle_release_path.open('w') as f:
+        f.write("""\
+RELEASE=6.0.UP07
+BUILD=6.0.7424
+DATE=20190611
+ARCH=noarch
+NETWORK=ari
+PATCHSET=35-201906112304
+DUMMY=foo=bar
+""")
+
+    monkeypatch.setattr(cnl, '_cle_release_file', str(cle_release_path))
+    attrs = cnl.read_cle_release_file()
+
+    assert attrs['RELEASE'] == '6.0.UP07'
+    assert attrs['BUILD'] == '6.0.7424'
+    assert attrs['DATE'] == '20190611'
+    assert attrs['ARCH'] == 'noarch'
+    assert attrs['NETWORK'] == 'ari'
+    assert attrs['PATCHSET'] == '35-201906112304'
+    assert attrs['DUMMY'] == 'foo=bar'
+
+    assert cnl.Cnl._detect_crayos_version() == 6