clingo: modify recipe for bootstrapping (#22354)

* clingo: modify recipe for bootstrapping

Modifications:
- clingo builds with shared Python only if ^python+shared
- avoid building the clingo app for bootstrapping
- don't link to libpython when bootstrapping

* Remove option that breaks on linux

* Give more hints for the current Python

* Disable CLINGO_BUILD_PY_SHARED for bootstrapping

* bootstrapping: try to detect the current python from std library

This is much faster than calling external executables

* Fix compatibility with Python 2.6

* Give hints on which compiler and OS to use when bootstrapping

This change hints which compiler to use for bootstrapping clingo
(either GCC or Apple Clang on MacOS). On Cray platforms it also
hints to build for the frontend system, where software is meant
to be installed.

* Use spec_for_current_python to constrain module requirement

var/spack/repos/builtin/packages/clingo-bootstrap/package.py

@@ -9,6 +9,9 @@
 
 class ClingoBootstrap(Clingo):
     """Clingo with some options used for bootstrapping"""
+
+    maintainers = ['alalazo']
+
     variant('build_type', default='Release', values=('Release',),
             description='CMake build type')
 
@@ -41,6 +44,18 @@ class ClingoBootstrap(Clingo):
     # Clingo needs the Python module to be usable by Spack
     conflicts('~python', msg='Python support is required to bootstrap Spack')
 
+    @property
+    def cmake_py_shared(self):
+        return self.define('CLINGO_BUILD_PY_SHARED', 'OFF')
+
+    def cmake_args(self):
+        args = super(ClingoBootstrap, self).cmake_args()
+        args.extend([
+            # Avoid building the clingo executable
+            self.define('CLINGO_BUILD_APPS', 'OFF'),
+        ])
+        return args
+
     def setup_build_environment(self, env):
         if '%apple-clang platform=darwin' in self.spec:
             opts = '-mmacosx-version-min=10.13'

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

@@ -21,7 +21,7 @@ class Clingo(CMakePackage):
     url      = "https://github.com/potassco/clingo/archive/v5.2.2.tar.gz"
     git      = 'https://github.com/potassco/clingo.git'
 
-    maintainers = ["tgamblin"]
+    maintainers = ["tgamblin", "alalazo"]
 
     version('master', branch='master', submodules=True, preferred=True)
     version('spack', commit='2a025667090d71b2c9dce60fe924feb6bde8f667', submodules=True)
@@ -56,10 +56,17 @@ def cmake_python_hints(self):
         """Return standard CMake defines to ensure that the
         current spec is the one found by CMake find_package(Python, ...)
         """
+        python_spec = self.spec['python']
+        include_dir = python_spec.package.get_python_inc()
         return [
-            '-DPython_EXECUTABLE={0}'.format(str(self.spec['python'].command))
+            self.define('Python_EXECUTABLE', str(python_spec.command)),
+            self.define('Python_INCLUDE_DIR', include_dir)
         ]
 
+    @property
+    def cmake_py_shared(self):
+        return self.define('CLINGO_BUILD_PY_SHARED', 'ON')
+
     def cmake_args(self):
         try:
             self.compiler.cxx14_flag
@@ -69,10 +76,10 @@ def cmake_args(self):
         args = [
             '-DCLINGO_REQUIRE_PYTHON=ON',
             '-DCLINGO_BUILD_WITH_PYTHON=ON',
-            '-DCLINGO_BUILD_PY_SHARED=ON',
             '-DPYCLINGO_USER_INSTALL=OFF',
             '-DPYCLINGO_USE_INSTALL_PREFIX=ON',
-            '-DCLINGO_BUILD_WITH_LUA=OFF'
+            '-DCLINGO_BUILD_WITH_LUA=OFF',
+            self.cmake_py_shared
         ]
         if self.spec['cmake'].satisfies('@3.16.0:'):
             args += self.cmake_python_hints