Provide build_type variant for Metis. (#6808)

* Provide build_type variant for Metis.

+ Ideally, we would make Metis a CMakePackage, but `metis@:5` doesn't use CMake.
+ For now, provide a `build_type=` variant similar what is found in
  CMakePackage.
+ There is a potential for duplicate specification of `CMAKE_BUILD_TYPE` if both
  variants `+debug` and `build_type=` are specified. I am looking for advice on
  how this can be resolved.

* Update metis recipe in response to flake8 and user comments.

+ Wrap comment lines that used more than 80 columns.
+ Change `+debug` variant to avoid potential for multiple `-DCMAKE_BUID_TYPE=`
  arguments provided to cmake.  Specifying this variant no longer appends this
  configure option.  However, if `+debug` is specified, require
  `build_type=Debug` to maintain expected behavior.

* For metis, remove +debug variant; use build_type= instead.

+ Update recipe for metis@4 to extract `build_type=` values and set `OPTFLAGS`
  accordingly.
+ For metis@5:, the behavior from the previously supported variant `+debug` can
  be obtained with the options `+gdb build_type=Debug`

* Conflicts added for metis@4 when build_type != Release|Debug.

* Use spack function conflicts instead of 'raise InstallError'.

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

@@ -45,12 +45,25 @@ class Metis(Package):
     version('4.0.3', 'd3848b454532ef18dc83e4fb160d1e10')
 
     variant('shared', default=True, description='Enables the build of shared libraries.')
-    variant('debug', default=False, description='Builds the library in debug mode.')
+    variant('gdb', default=False, description='Enables gdb support (version 5+).')
-    variant('gdb', default=False, description='Enables gdb support.')
-
     variant('int64', default=False, description='Sets the bit width of METIS\'s index type to 64.')
     variant('real64', default=False, description='Sets the bit width of METIS\'s real type to 64.')
 
+    # For Metis version 5:, the build system is CMake, provide the
+    # `build_type` variant.
+    variant('build_type', default='Release',
+            description='The build type for the installation (only Debug or'
+            ' Release allowed for version 4).',
+            values=('Debug', 'Release', 'RelWithDebInfo', 'MinSizeRel'))
+
+    # Prior to version 5, the (non-cmake) build system only knows about
+    # 'build_type=Debug|Release'.
+    conflicts('@:4.999', when='build_type=RelWithDebInfo')
+    conflicts('@:4.999', when='build_type=MinSizeRel')
+    conflicts('@:4.999', when='+gdb')
+    conflicts('@:4.999', when='+int64')
+    conflicts('@:4.999', when='+real64')
+
     depends_on('cmake@2.8:', when='@5:', type='build')
 
     patch('install_gklib_defs_rename.patch', when='@5:')
@@ -87,12 +100,8 @@ def patch(self):
     @when('@:4')
     def install(self, spec, prefix):
         # Process library spec and options
-        if any('+{0}'.format(v) in spec for v in ['gdb', 'int64', 'real64']):
-            raise InstallError('METIS@:4 does not support the following '
-                               'variants: gdb, int64, real64.')
-
         options = ['COPTIONS={0}'.format(self.compiler.pic_flag)]
-        if '+debug' in spec:
+        if spec.variants['build_type'].value == 'Debug':
             options.append('OPTFLAGS=-g -O0')
         make(*options)
 
@@ -185,6 +194,11 @@ def install(self, spec, prefix):
         options.append('-DGKLIB_PATH:PATH=%s/GKlib' % source_directory)
         options.append('-DCMAKE_INSTALL_NAME_DIR:PATH=%s/lib' % prefix)
 
+        # Normally this is available via the 'CMakePackage' object, but metis
+        # IS-A 'Package' (not a 'CMakePackage') to support non-cmake metis@:5.
+        build_type = spec.variants['build_type'].value
+        options.extend(['-DCMAKE_BUILD_TYPE:STRING={0}'.format(build_type)])
+
         if '+shared' in spec:
             options.append('-DSHARED:BOOL=ON')
         else:
@@ -196,9 +210,6 @@ def install(self, spec, prefix):
                     rpath_options.append(o)
             for o in rpath_options:
                 options.remove(o)
-        if '+debug' in spec:
-            options.extend(['-DDEBUG:BOOL=ON',
-                            '-DCMAKE_BUILD_TYPE:STRING=Debug'])
         if '+gdb' in spec:
             options.append('-DGDB:BOOL=ON')