New package: date (#19515)

* Add new package: date

* date: resolve style conformance issues

* date: explicitly disable some cmake options

Explicitly disable CMake options corresponding to variant
'tzdb=download'

* date: make more cmake options explicit

* date: simplify defining cmake cli args

var/spack/repos/builtin/packages/date/package.py

@@ -0,0 +1,49 @@
+# 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)
+
+from spack import *
+
+
+class Date(CMakePackage):
+    """A date and time library based on the C++11/14/17 <chrono> header"""
+
+    homepage = "https://github.com/HowardHinnant/date"
+    url      = "https://github.com/HowardHinnant/date/archive/v3.0.0.zip"
+
+    version('3.0.0', sha256='ddbec664607bb6ec7dd4c7be1f9eefc3d8ce88293ffc9391486ce6ce887ec9b2')
+
+    variant('cxxstd',
+            default='17',
+            values=('11', '14', '17'),
+            description='Use the specified C++ standard when building')
+    variant('shared',
+            default=False,
+            description='Build shared instead of static libraries')
+    variant('tz', default=False, description='Build/install of TZ library')
+    variant('tzdb',
+            default='download',
+            values=('download', 'system', 'manual'),
+            description="Timezone database source (automatic download, use "
+                        "operating system's database, or manually specify)")
+
+    depends_on('cmake@3.7.0:', type='build')
+    depends_on('curl', when='+tz tzdb=download')
+
+    def cmake_args(self):
+        spec = self.spec
+        args = [
+            self.define('CMAKE_CXX_STANDARD', spec.variants['cxxstd'].value),
+            self.define('CMAKE_CXX_STANDARD_REQUIRED', True),
+            self.define('BUILD_SHARED_LIBS', '+shared' in spec),
+            self.define('BUILD_TZ_LIB', '+tz' in spec),
+        ]
+
+        tzdb = spec.variants['tzdb'].value
+        args.extend([
+            self.define('USE_SYSTEM_TZ_DB', tzdb == 'system'),
+            self.define('MANUAL_TZ_DB', tzdb == 'manual'),
+        ])
+
+        return args