gitconddb: new package at v0.1.1 (#15651)

Git-based conditions database for HEP and other experiments.

Use latest release version and current master to support Linux and
macOS. Add core known dependencies and conflicts related to C++17
support.

cxxstd variant added to help transitive dependencies, and for future
support for newer standards in future.

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

@@ -0,0 +1,43 @@
+# 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 Gitconddb(CMakePackage):
+    """Conditions Database library using a Git repository as the
+    storage backend"""
+
+    homepage = "https://gitlab.cern.ch/lhcb/GitCondDB"
+    url      = "https://gitlab.cern.ch/lhcb/GitCondDB/-/archive/0.1.1/GitCondDB-0.1.1.tar.gz"
+    git      = "https://gitlab.cern.ch/lhcb/GitCondDB.git"
+
+    maintainers = ['drbenmorgan']
+
+    version('master', branch='master')
+    version('0.1.1', sha256='024a6867722a3a622ed4327ea7d15641dd48e4e8411bdcc21915e406b3c479a2')
+
+    # Add the cxxstd variant for forward compatibility, though we require 17
+    _cxxstd_values = ('17',)
+    variant('cxxstd',
+            default='17',
+            values=_cxxstd_values,
+            multi=False,
+            description='Use the specified C++ standard when building.')
+
+    depends_on('cmake@3.10:', type='build')
+    depends_on('pkgconfig', type='build')
+    depends_on('nlohmann-json@3.2.0:', type='build')
+    depends_on('googletest@1.8.1:', type='build')
+
+    for s in _cxxstd_values:
+        depends_on('fmt@5.2.0: cxxstd=' + s, when='cxxstd=' + s)
+        # Maybe also a boost dependency for macOS older than catalina
+
+    depends_on('libgit2')
+
+    # Known conflicts on C++17 compatibility (aggressive for now)
+    conflicts('%gcc@:7.9.999', msg="GitCondDB requires GCC 8 or newer for C++17 support")
+    conflicts('%clang platform=darwin', when="@:0.1.99", msg="No Darwin support for clang in older versions")