root: Rationalize and improve version, variant and ROOT option handling. (#14203)

* root: Rationalize and improve version, variant and ROOT option handling.

* Completely re-vamp CMake option handling for readability and maintainability:
  * Three categories of option: control, builtin and feature, alphabetically sorted.
  * Each option is described as a list: an option name followed by an optional value which is either Boolean or a string representing the name of a variant. If the value is omitted, it defaults to the option name.
  * New functions `_process_opts()` and `_process_opt()` (nested) to turn all supplied option/value specifications into CMake arguments.
  * Remove overly-terse per-option comments in favor of (much) more comprehensive notes in README.md.
* Variants and conflicts:
  * Remove `test` variant in favor of pegging ROOT `testing` option to the value of `self.run_tests` since the install is unaffected, per ROOT developer.
  * Remove commented-out and never-functional variants: `asimage`, `avahi`, `kerberos`, `ldap`, `libcxx`, `odbc`, `oracle`, `pythia8`, `xinetd`.
  * New variant `vmc` (default `OFF`) to control the Virtual Monte Carlo interface.
  * Conflict: `+opengl` is incompatible with `~x`.
  * Conflict: `http` is now an unconditional conflict due to dependency issues (see README.md).
* Remove commented-out and non-existent dependencies `avahi`, `kerberos`, `ldap`, `libcxx`, `odbc`, `oracle`, `pythia`, `veccore` (per #13949).
* New and changed options:
  * Option `pch` was inadvertently set to `OFF` due to its dependence on a nonexistent variant `pch`. As it happens its value is ignored in the ROOT configuration handling, so there was no deleterious effect. It has been fixed to `ON` to better reflect actual behavior pending enablement of tuntime C++ modules.
* Add new versions 6.18.0{0,2,4}:
  * Require CMake 3.9 for 6.18.00+.
  * Add conflicts for variants `qt4` and `table` representing ROOT build options for which support was discontinued. Remove redundant conflict on \@master.
  * C++ standard is now specified with `-DCMAKE_CXX_STANDARD=X` rather than `-Dcxx=X`.
* Remove old version 5.34.38 (wrong build system).

See README.md for more details of option-related changes.

* Flake8

* `rpath` option is a control option rather than a feature.

2 files changed, 357 insertions, 258 deletions

diff --git a/var/spack/repos/builtin/packages/root/README.md b/var/spack/repos/builtin/packages/root/README.md
new file mode 100644
index 0000000000..d808498b34
--- /dev/null
+++ b/var/spack/repos/builtin/packages/root/README.md
@@ -0,0 +1,170 @@
+# ROOT Recipe Notes
+
+ROOT has a significant number of build options. Not all of them are supported by this package recipe at this time. Relevant notes on support (or lack thereof) for various options is below.
+
+## Fixed and unsupported options
+
+### Missing dependencies
+
+The following configuration options are unsupported (set to `OFF`) due to missing dependencies:
+
+#### `alien`
+
+Requires `libgapiUI` from ALICE.
+
+#### `dcache`
+
+DCache support depends on `libdcap` from DESY.
+
+#### `gfal`
+
+#### `http`
+
+ROOT looks for and uses the FastCGI package on the system if found, creating a possible non-portable dependency. There is currently no `fastcgi` recipe, nor any way to unconditionally disable the search for the package.
+
+#### `monalisa`
+
+Monitoring with Monalisa depends on `libapmoncpp`.
+
+#### `odbc`
+
+#### `oracle`
+
+#### `pythia8`
+
+#### `tcmalloc`
+
+#### `veccore`
+
+#### `xinetd`
+
+### Discontinued options
+
+Support for several options was discontinued in ROOT without prior support in the recipe:
+
+#### `afdsmgrd`
+
+#### `afs`
+
+#### `bonjour`
+
+#### `castor`
+
+#### `chirp`
+
+#### `geocad`
+
+#### `glite`
+
+#### `globus`
+
+#### `hdfs`
+
+#### `ios`
+
+#### `krb5`
+
+#### `ldap`
+
+#### `rfio`
+
+#### `ruby`
+
+#### `sapdb`
+
+#### `srp`
+
+### Other fixed or unsupported options
+
+### `arrow=OFF`
+
+#### `asimage=ON`, `astiff=ON`, `builtin_afterimage=ON`
+
+Full control of `asimage` and `astiff` would require a package recipe for libAfterImage or Afterstep. In their absence, we use the provided and internally built version of libAfterImage.
+
+#### `ccache=OFF`
+
+Only useful for repeated builds.
+
+#### `cling=OFF`
+
+The use of Cling is assumed.
+
+#### `cxxmodules`
+
+This option should not be confused with `runtime_cxxmodules`. `cxxmodules` is an optimization that affects only the efficiency of building ROOT.
+
+#### `exceptions=ON`
+
+Support for C++ exceptions is assumed.
+
+#### `explicitlink=ON`
+
+Use of explicit linking when making shared libraries is assumed.
+
+#### `fail-on-missing=ON`
+
+Failure on missing dependencies is assumed (_vs_ automatically setting `builtin_XXX`).
+
+#### `gnuinstall=OFF`
+
+GNU-compliant install layout.
+
+#### `libcxx`
+
+This option controls use of the libC++ standard C++ library via compiler options. It is set automatically by ROOT's configuration on macOS >=10.7 when a Clang compiler is configured. Due to complexities related to compiler options and the way a compiler might have been configured, configurable support is disabled until (at least) Spack supports the standard library as a virtual dependency.
+
+#### `pch=ON`
+
+The use of pre-compiled headers when building is assumed.
+
+#### `roottest=OFF`
+
+`roottest` requires access to the network.
+
+#### `runtime_cxxmodules=OFF`
+
+This option tells ROOT to generate and use PCMs for its own libraries. This functionality is experimental for ROOT < 6.20, and is currently not supported by the recipe.
+
+#### `shared=ON`
+
+The use of shared libraries is assumed.
+
+#### `soversion=ON`
+
+The use of versioning for shared libraries is assumed.
+
+#### `testing`
+
+The building of ROOT's test suite and its availability for use by CTest is pegged to Spack's determination of whether testing is required for the current installation procedure.
+
+## Variants and version dependent support for options
+
+Some configuration options are version dependent---unavailable before or after a specific version. The current accounting for such options in the recipe is far from exhaustive, and a survey of the various options and the versions that support them would be useful. However, accounting for them is somewhat clumsy absent a `when` clause for variants, or similar.
+
+### Conflicting variants since 6.18
+
+#### `memstat`
+
+#### `qt4`
+
+Representing the obsolete `qt` and `qtgsi` ROOT build options.
+
+#### `table`
+
+### Temporarily conflicting variants
+
+The `http` variant is currently an unconditional conflict due to the non-portable dependency mentioned above.
+
+## Permanently removed variants
+
+The following variants have been removed from the recipe as they have always been ineffective:
+
+* `avahi`
+* `kerberos`
+* `ldap`
+* `libcxx`
+* `odbc`
+* `tiff`
+
+In addition, the `test` variant has been removed as its actions are irrelevant to the installed source---the corresponding `testing` ROOT option is enabled if and only if `self.run_tests` is set.
diff --git a/var/spack/repos/builtin/packages/root/package.py b/var/spack/repos/builtin/packages/root/package.py
index 975500655e..7270405ddc 100644
--- a/var/spack/repos/builtin/packages/root/package.py
+++ b/var/spack/repos/builtin/packages/root/package.py
@@ -6,6 +6,7 @@
 
 from spack import *
 import sys
+import types
 
 
 class Root(CMakePackage):
@@ -23,9 +24,13 @@ class Root(CMakePackage):
     # Development version (when more recent than production).
 
     # Production version
-    version('6.16.00', sha256='2a45055c6091adaa72b977c512f84da8ef92723c30837c7e2643eecc9c5ce4d8', preferred=True)
+    version('6.18.04', sha256='315a85fc8363f8eb1bffa0decbf126121258f79bd273513ed64795675485cfa4',
+            preferred=True)
 
     # Old versions
+    version('6.18.02', sha256='50ffffdbf2585a536c77a03f54aa631926138275ffeee02e5a16dde87e978c1d')
+    version('6.18.00', sha256='e6698d6cfe585f186490b667163db65e7d1b92a2447658d77fa831096383ea71')
+    version('6.16.00', sha256='2a45055c6091adaa72b977c512f84da8ef92723c30837c7e2643eecc9c5ce4d8')
     version('6.14.08', sha256='1b63b51cfb4dc20f1f5749faac6bbd1098eccab777f8b49911257d77186c73c4')
     version('6.14.06', sha256='0fb943b61396f282b289e35c455a9ab60126229be1bd3f04a8f00b37c13ab432')
     version('6.14.04', sha256='463ec20692332a422cfb5f38c78bedab1c40ab4d81be18e99b50cf9f53f596cf')
@@ -38,7 +43,6 @@ class Root(CMakePackage):
     version('6.06.06', sha256='0a7d702a130a260c72cb6ea754359eaee49a8c4531b31f23de0bfcafe3ce466b')
     version('6.06.04', sha256='ab86dcc80cbd8e704099af0789e23f49469932ac4936d2291602301a7aa8795b')
     version('6.06.02', sha256='18a4ce42ee19e1a810d5351f74ec9550e6e422b13b5c58e0c3db740cdbc569d1')
-    version('5.34.38', sha256='2c3bda69601d94836bdd88283a6585b4774eafc813deb6aa348df0af2922c4d2')
 
     # ###################### Patches ##########################
 
@@ -66,15 +70,11 @@ class Root(CMakePackage):
         patch('root6-60606-mathmore.patch', when='@6.06.06')
 
     # ###################### Variants ##########################
+    # See README.md for specific notes about what ROOT configuration
+    # options are or are not supported, and why.
 
-    variant('avahi', default=False,
-            description='Compile with avahi')
     variant('aqua', default=False,
             description='Enable Aqua interface')
-    # No need for a specific variant: libafterimage is not provided by spack
-    # By default always true, we get the builtin included in the source
-    # variant('asimage', default=True,
-    #         description='Enable image processing support')
     variant('davix', default=True,
             description='Compile with external Davix')
     variant('emacs', default=False,
@@ -100,12 +100,6 @@ class Root(CMakePackage):
             description='Enable HTTP server support')
     variant('jemalloc', default=False,
             description='Enable using the jemalloc allocator')
-    variant('kerberos', default=False,
-            description='Enable Kerberos support')
-    variant('ldap', default=False,
-            description='Enable LDAP support')
-    variant('libcxx', default=False,
-            description='Build using libc++')
     variant('math', default=True,
             description='Build the new libMathMore extended math library')
     variant('memstat', default=False,
@@ -115,17 +109,12 @@ class Root(CMakePackage):
     variant('minuit', default=True,
             description='Automatically search for support libraries')
     variant('mysql', default=False)
-    variant('odbc', default=False,
-            description='Enable ODBC support')
     variant('opengl', default=True,
             description='Enable OpenGL support')
-    # variant('oracle', default=False) - not supported by spack
     variant('postgres', default=False,
             description='Enable postgres support')
     variant('pythia6', default=False,
             description='Enable pythia6 support')
-    # variant('pythia8', default=False, - not suported by spack
-    #       description='Enable pythia8 support')
     variant('python', default=True,
             description='Enable Python ROOT bindings')
     variant('qt4', default=False,
@@ -148,12 +137,8 @@ class Root(CMakePackage):
             description='Build libTable contrib library')
     variant('tbb', default=True,
             description='TBB multi-threading support')
-    variant('test', default=False,
-            description='Enable test suit of ROOT with CTest')
     variant('threads', default=True,
             description='Enable using thread library')
-    variant('tiff', default=True,
-            description='Include Tiff support in image processing')
     variant('tmva', default=True,
             description='Build TMVA multi variate analysis library')
     variant('unuran', default=True,
@@ -162,10 +147,10 @@ class Root(CMakePackage):
             description='Enable Vc for adding new types for SIMD programming')
     variant('vdt', default=True,
             description='Enable set of fast and vectorisable math functions')
+    variant('vmc', default=False,
+            description='Enable the Virtual Monte Carlo interface')
     variant('x', default=True,
             description='Enable set of graphical options')
-    # variant('xinetd', default=False,  - not supported by spack
-    #       description='Enable a daemon process manager')
     variant('xml', default=True,
             description='Enable XML parser interface')
     variant('xrootd', default=False,
@@ -181,7 +166,8 @@ class Root(CMakePackage):
 
     # ###################### Dependencies ######################
 
-    depends_on('cmake@3.4.3:', type='build')
+    depends_on('cmake@3.4.3:', type='build', when='@:6.16.99')
+    depends_on('cmake@3.9:', type='build', when='@6.18.00:')
     depends_on('pkgconfig', type='build')
 
     depends_on('blas')
@@ -216,55 +202,30 @@ class Root(CMakePackage):
     # TMVA
     depends_on('py-numpy', when='+tmva')
 
-    # Asimage variant would need one of these two
-    # For the moment, we use the libafterimage provided by the root sources
-    # depends_on('libafterimage',    when='+asimage') - not supported
-    # depends_on('afterstep@2.2.11', when='+asimage') - not supported
-
     # Optional dependencies
-    depends_on('avahi',     when='+avahi')
     depends_on('davix',     when='+davix')
     depends_on('cfitsio',   when='+fits')
     depends_on('fftw',      when='+fftw')
     depends_on('graphviz',  when='+graphviz')
     depends_on('gsl',       when='+gsl')
     depends_on('jemalloc',  when='+jemalloc')
-    depends_on('kerberos',  when='+kerberos')
-    depends_on('ldap',      when='+ldap')
-    depends_on('libcxx',    when='+libcxx')
     depends_on('mysql-client',   when='+mysql')
-    depends_on('odbc',      when='+odbc')
-    # depends_on('oracle',   when='+oracle')
     depends_on('openssl',   when='+ssl')
-    depends_on('openssl', when='+davix')  # Also with davix
+    depends_on('openssl',   when='+davix')  # Also with davix
     depends_on('postgresql', when='+postgres')
-    depends_on('pythia6+root',  when='+pythia6')
-    # depends_on('pythia@8:8.999',  when='+pythia8') - not supported on Spack
-    depends_on('python@2.7:',     when='+python', type=('build', 'run'))
+    depends_on('pythia6+root', when='+pythia6')
+    depends_on('python@2.7:', when='+python', type=('build', 'run'))
     depends_on('r',         when='+r', type=('build', 'run'))
-    depends_on('r-rcpp',     when='+r', type=('build', 'run'))
-    depends_on('r-rinside',  when='+r', type=('build', 'run'))
+    depends_on('r-rcpp',    when='+r', type=('build', 'run'))
+    depends_on('r-rinside', when='+r', type=('build', 'run'))
     depends_on('shadow',    when='+shadow')
     depends_on('sqlite',    when='+sqlite')
     depends_on('tbb',       when='+tbb')
     depends_on('unuran',    when='+unuran')
     depends_on('vc',        when='+vc')
-    depends_on('veccore',   when='+veccore')
     depends_on('vdt',       when='+vdt')
     depends_on('libxml2',   when='+xml')
     depends_on('xrootd',    when='+xrootd')
-    # depends_on('hdfs') - supported (TODO)
-
-    # Not supported
-    # depends_on('monalisa')
-
-    # Grid packages - not supported yet by Spack
-    # depends_on('castor')
-    # depends_on('chirp')
-    # depends_on('dcap')
-    # depends_on('gfal')
-    # depends_on('ldap')
-    # depends_on('rfio')
 
     # ###################### Conflicts ######################
 
@@ -272,210 +233,154 @@ class Root(CMakePackage):
     # See https://sft.its.cern.ch/jira/browse/ROOT-7517
     conflicts('%intel')
 
+    # See README.md
+    conflicts('+http',
+              msg='HTTP server currently unsupported due to dependency issues')
+
     # Incompatible variants
-    conflicts('+tmva', when='~gsl', msg="TVMA requires GSL")
-    conflicts('cxxstd=11', when='+root7', msg="root7 requires at least C++14")
+    conflicts('+opengl', when='~x', msg='OpenGL requires X')
+    conflicts('+tmva', when='~gsl', msg='TVMA requires GSL')
+    conflicts('cxxstd=11', when='+root7', msg='root7 requires at least C++14')
 
-    # Feature removed:
-    conflicts('+memstat', when='@6.18.00:',
-              msg="Obsolete option +memstat selected.")
-    conflicts('+memstat', when='@master',
-              msg="Obsolete option +memstat selected.")
+    # Feature removed in 6.18:
+    [(conflicts('+{0}'.format(pkg), when='@6.18.00:',
+                msg='Obsolete option +{0} selected.'.format(pkg))) for pkg in
+     ('memstat', 'qt4', 'table')]
 
     def cmake_args(self):
         spec = self.spec
-        options = []
-
-        # #################### Base Settings #######################
-
-        # ROOT should not download its own dependencies
-        options = [
-            '-Dexplicitlink=ON',
-            '-Dexceptions=ON',
-            '-Dfail-on-missing=ON',
-            '-Dshared=ON',
-            '-Dsoversion=ON',
-            '-Dbuiltin_llvm=ON',
-            '-Dbuiltin_afterimage=ON',
-            '-Dasimage:BOOL=ON',  # if afterimage is taken from builtin
-            '-Dastiff:BOOL=ON',   # asimage and astiff must be ON too
-            '-Dbuiltin_cfitsio:BOOL=OFF',
-            '-Dbuiltin_davix:BOOL=OFF',
-            '-Dbuiltin_fftw3:BOOL=OFF',
-            '-Dbuiltin_freetype:BOOL=OFF',
-            '-Dbuiltin_ftgl:BOOL=OFF',
-            '-Dbuiltin_gl2ps:BOOL=OFF',
-            '-Dbuiltin_glew:BOOL=OFF',
-            '-Dbuiltin_gsl:BOOL=OFF',
-            '-Dbuiltin_lzma:BOOL=OFF',
-            '-Dbuiltin_openssl:BOOL=OFF',
-            '-Dbuiltin_pcre:BOOL=OFF',
-            '-Dbuiltin_tbb:BOOL=OFF',
-            '-Dbuiltin_unuran:BOOL=OFF',
-            '-Dbuiltin_vc:BOOL=OFF',
-            '-Dbuiltin_vdt:BOOL=OFF',
-            '-Dbuiltin_veccore:BOOL=OFF',
-            '-Dbuiltin_xrootd:BOOL=OFF',
-            '-Dbuiltin_zlib:BOOL=OFF'
-        ]
-
-        # LZ4 and xxhash do not work as external deps for older versions
-        options.extend([
-            '-Dbuiltin_lz4:BOOL=%s' % (
-                'ON' if self.spec.satisfies('@6.12.02:6.12.99') else 'OFF'),
-            '-Dbuiltin_xxhash:BOOL=%s' % (
-                'ON' if self.spec.satisfies('@6.12.02:6.12.99') else 'OFF'),
-        ])
-
-        # #################### ROOT options #######################
-
-        options.extend([
-            '-Dx11:BOOL=%s' % (
-                'ON' if '+x' in spec else 'OFF'),
-            '-Dxft:BOOL=%s' % (
-                'ON' if '+x' in spec else 'OFF'),
-            '-Dbonjour:BOOL=%s' % (
-                'ON' if '+avahi' in spec else 'OFF'),
-            '-Dcocoa:BOOL=%s' % (
-                'ON' if '+aqua' in spec else 'OFF'),
-            # -Dcxxmodules=OFF # use clang C++ modules
-            '-Ddavix:BOOL=%s' % (
-                'ON' if '+davix' in spec else 'OFF'),
-            '-Dfftw3:BOOL=%s' % (
-                'ON' if '+fftw' in spec else 'OFF'),
-            '-Dfitsio:BOOL=%s' % (
-                'ON' if '+fits' in spec else 'OFF'),
-            '-Dfortran:BOOL=%s' % (
-                'ON' if '+fortran' in spec else 'OFF'),
-            '-Dftgl:BOOL=%s' % (
-                'ON' if '+opengl' in spec else 'OFF'),
-            '-Dgdml:BOOL=%s' % (
-                'ON' if '+gdml' in spec else 'OFF'),
-            '-Dgl2ps:BOOL=%s' % (
-                'ON' if '+opengl' in spec else 'OFF'),
-            '-Dgenvector:BOOL=%s' % (
-                'ON' if '+math' in spec else 'OFF'),  # default ON
-            '-Dgminimal:BOOL=%s' % (  # Reduce unwanted surprises
-                'ON' if '+gminimal' in spec else 'OFF'),  # Default ON
-            '-Dgsl_shared:BOOL=%s' % (
-                'ON' if '+gsl' in spec else 'OFF'),
-            '-Dgviz:BOOL=%s' % (
-                'ON' if '+graphviz' in spec else 'OFF'),
-            '-Dhttp:BOOL=%s' % (
-                'ON' if '+http' in spec else 'OFF'),
-            '-Dimt:BOOL=%s' % (
-                'ON' if '+tbb' in spec else 'OFF'),
-            '-Djemalloc:BOOL=%s' % (
-                'ON' if '+jemalloc' in spec else 'OFF'),
-            '-Dkrb5:BOOL=%s' % (
-                'ON' if '+kerberos' in spec else 'OFF'),
-            '-Dldap:BOOL=%s' % (
-                'ON' if '+ldap' in spec else 'OFF'),
-            '-Dlibcxx:BOOL=%s' % (
-                'ON' if '+libcxx' in spec else 'OFF'),
-            '-Dmathmore:BOOL=%s' % (
-                'ON' if '+math' in spec else 'OFF'),
-            '-Dmemstat:BOOL=%s' % (
-                'ON' if '+memstat' in spec else 'OFF'),
-            '-Dminimal:BOOL=%s' % (
-                'ON' if '+minimal' in spec else 'OFF'),
-            '-Dminuit:BOOL=%s' % (
-                'ON' if '+minuit' in spec else 'OFF'),
-            '-Dminuit2:BOOL=%s' % (
-                'ON' if '+minuit' in spec else 'OFF'),
-            '-Dmysql:BOOL=%s' % (
-                'ON' if '+mysql' in spec else 'OFF'),
-            '-Dodbc:BOOL=%s' % (
-                'ON' if '+odbc' in spec else 'OFF'),
-            '-Dopengl:BOOL=%s' % (
-                'ON' if '+opengl' in spec else 'OFF'),
-            '-Doracle:BOOL=%s' % (
-                'ON' if '+oracle' in spec else 'OFF'),  # not supported
-            '-Dpch:BOOL=%s' % (
-                'ON' if '+pch' in spec else 'OFF'),  # needs cling
-            '-Dpgsql:BOOL=%s' % (
-                'ON' if '+postgres' in spec else 'OFF'),
-            '-Dpythia6:BOOL=%s' % (
-                'ON' if '+pythia6' in spec else 'OFF'),
-            # Force not to build pythia8 (not supported yet by spack), to avoid
-            # wrong defaults from ROOT at build time
-            '-Dpythia8:BOOL=%s' % (
-                'ON' if '+pythia8' in spec else 'OFF'),
-            '-Dpython:BOOL=%s' % (
-                'ON' if self.spec.satisfies('+python ^python@2.7:2.99.99')
-                else 'OFF'),
-            '-Dpython3:BOOL=%s' % (
-                'ON' if self.spec.satisfies('+python ^python@3.0:')
-                else 'OFF'),
-            '-Dqt:BOOL=%s' % (
-                'ON' if '+qt4' in spec else 'OFF'),
-            '-Dqtgsi:BOOL=%s' % (
-                'ON' if '+qt4' in spec else 'OFF'),
-            '-Dr:BOOL=%s' % (
-                'ON' if '+R' in spec else 'OFF'),
-            '-Droofit:BOOL=%s' % (
-                'ON' if '+roofit' in spec else 'OFF'),
-            '-Droot7:BOOL=%s' % (
-                'ON' if '+root7' in spec else 'OFF'),  # requires C++14
-            '-Dwebui:BOOL=%s' % (
-                'ON' if '+root7' in spec else 'OFF'),  # requires root7
-            '-Drpath:BOOL=%s' % (
-                'ON' if '+rpath' in spec else 'OFF'),
-            '-Dshadowpw:BOOL=%s' % (
-                'ON' if '+shadow' in spec else 'OFF'),
-            '-Dsqlite:BOOL=%s' % (
-                'ON' if '+sqlite' in spec else 'OFF'),
-            '-Dssl:BOOL=%s' % (
-                'ON' if '+ssl' in spec else 'OFF'),
-            '-Dtable:BOOL=%s' % (
-                'ON' if '+table' in spec else 'OFF'),
-            '-Dtbb:BOOL=%s' % (
-                'ON' if '+tbb' in spec else 'OFF'),
-            '-Dtesting:BOOL=%s' % (
-                'ON' if '+test' in spec else 'OFF'),
-            '-Dthread:BOOL=%s' % (
-                'ON' if '+threads' in spec else 'OFF'),
-            '-Dtmva:BOOL=%s' % (
-                'ON' if '+tmva' in spec else 'OFF'),
-            '-Dunuran:BOOL=%s' % (
-                'ON' if '+unuran' in spec else 'OFF'),
-            '-Dvc:BOOL=%s' % (
-                'ON' if '+vc' in spec else 'OFF'),
-            '-Dveccore:BOOL=%s' % (
-                'ON' if '+veccore' in spec else 'OFF'),  # not supported
-            '-Dvdt:BOOL=%s' % (
-                'ON' if '+vdt' in spec else 'OFF'),
-            '-Dxml:BOOL=%s' % (
-                'ON' if '+xml' in spec else 'OFF'),  # default ON
-            '-Dxrootd:BOOL=%s' % (
-                'ON' if '+xrootd' in spec else 'OFF'),  # default ON
-
-            # Fixed options
-            '-Dafdsmrgd:BOOL=OFF',  # not supported
-            '-Dafs:BOOL=OFF',       # not supported
-            '-Dalien:BOOL=OFF',
-            '-Dcastor:BOOL=OFF',    # not supported
-            '-Dccache:BOOL=OFF',    # not supported
-            '-Dchirp:BOOL=OFF',
-            '-Dcling:BOOL=ON',
-            '-Ddcache:BOOL=OFF',    # not supported
-            '-Dgeocad:BOOL=OFF',    # not supported
-            '-Dgfal:BOOL=OFF',      # not supported
-            '-Dglite:BOOL=OFF',     # not supported
-            '-Dglobus:BOOL=OFF',
-            '-Dgnuinstall:BOOL=OFF',
-            '-Dhdfs:BOOL=OFF',      # TODO pending to add
-            '-Dmonalisa:BOOL=OFF',  # not supported
-            '-Drfio:BOOL=OFF',      # not supported
-            '-Droottest:BOOL=OFF',  # requires network
-            '-Druby:BOOL=OFF',      # unmantained upstream
-            # Use clang C++ modules, experimental
-            '-Druntime_cxxmodules:BOOL=OFF',
-            '-Dsapdb:BOOL=OFF',     # option not implemented
-            '-Dsrp:BOOL=OFF',       # option not implemented
-            '-Dtcmalloc:BOOL=OFF'
-
-        ])
+
+        # ###################### Boolean Options ######################
+        # For option list format see _process_opts(), below.
+
+        # Options controlling gross build / config behavior.
+        control_opts\
+            = [
+                ['cxxmodules', False],
+                ['exceptions', True],
+                ['explicitlink', True],
+                ['fail-on-missing', True],
+                ['fortran'],
+                ['gminimal'],
+                ['gnuinstall', False],
+                ['libcxx', False],
+                ['pch', True],
+                ['roottest', False],
+                ['rpath'],
+                ['runtime_cxxmodules', False],
+                ['shared', True],
+                ['soversion', True],
+                ['testing', self.run_tests],
+                ['thread', 'threads']
+            ]
+
+        # Options related to ROOT's ability to download and build its own
+        # dependencies. Per Spack convention, this should generally be avoided.
+        builtin_opts\
+            = [
+                ['builtin_afterimage', True],
+                ['builtin_cfitsio', False],
+                ['builtin_davix', False],
+                ['builtin_fftw3', False],
+                ['builtin_freetype', False],
+                ['builtin_ftgl', False],
+                ['builtin_gl2ps', False],
+                ['builtin_glew', False],
+                ['builtin_gsl', False],
+                ['builtin_llvm', True],
+                ['builtin_lz4', self.spec.satisfies('@6.12.02:6.12.99')],
+                ['builtin_lzma', False],
+                ['builtin_openssl', False],
+                ['builtin_pcre', False],
+                ['builtin_tbb', False],
+                ['builtin_unuran', False],
+                ['builtin_vc', False],
+                ['builtin_vdt', False],
+                ['builtin_veccore', False],
+                ['builtin_xrootd', False],
+                ['builtin_xxhash', self.spec.satisfies('@6.12.02:6.12.99')],
+                ['builtin_zlib', False]
+            ]
+
+        # Features
+        feature_opts\
+            = [
+                ['afdsmrgd', False],
+                ['afs', False],
+                ['alien', False],
+                ['arrow', False],
+                ['asimage', True],
+                ['astiff', True],
+                ['bonjour', False],
+                ['castor', False],
+                ['ccache', False],
+                ['chirp', False],
+                ['cling', True],
+                ['cocoa', 'aqua'],
+                ['davix'],
+                ['dcache', False],
+                ['fftw3', 'fftw'],
+                ['fitsio', 'fits'],
+                ['ftgl', 'opengl'],
+                ['gdml'],
+                ['genvector', 'math'],
+                ['geocad', False],
+                ['gfal', False],
+                ['gl2ps', 'opengl'],
+                ['glite', False],
+                ['globus', False],
+                ['gsl_shared', 'gsl'],
+                ['gviz', 'graphviz'],
+                ['hdfs', False],
+                ['http'],  # See conflicts
+                ['imt', 'tbb'],
+                ['jemalloc'],
+                ['krb5', False],
+                ['ldap', False],
+                ['mathmore', 'math'],
+                ['memstat'],  # See conflicts
+                ['minimal'],
+                ['minuit'],
+                ['minuit2', 'minuit'],
+                ['monalisa', False],
+                ['mysql'],
+                ['odbc'],
+                ['opengl'],
+                ['oracle', False],
+                ['pgsql', 'postgres'],
+                ['pythia6'],
+                ['pythia8', False],
+                ['python', self.spec.satisfies('+python ^python@2.7:2.99.99')],
+                ['python3', self.spec.satisfies('+python ^python@3.0:')],
+                ['qt', 'qt4'],  # See conflicts
+                ['qtgsi', 'qt4'],  # See conflicts
+                ['r', 'R'],
+                ['rfio', False],
+                ['roofit'],
+                ['root7'],  # See conflicts
+                ['ruby', False],
+                ['sapdb', False],
+                ['shadowpw', 'shadow'],
+                ['sqlite'],
+                ['srp', False],
+                ['ssl'],
+                ['table'],
+                ['tbb'],
+                ['tcmalloc', False],
+                ['tmva'],
+                ['unuran'],
+                ['vc'],
+                ['vdt'],
+                ['veccore'],
+                ['vmc'],
+                ['webui', 'root7'],  # requires root7
+                ['x11', 'x'],
+                ['xft', 'x'],
+                ['xml'],
+                ['xrootd']
+            ]
+
+        options = self._process_opts(control_opts, builtin_opts, feature_opts)
 
         # #################### Compiler options ####################
 
@@ -486,9 +391,11 @@ class Root(CMakePackage):
                     '-DCMAKE_CXX_FLAGS=-D__builtin_unreachable=__builtin_trap',
                 ])
 
-        options.append(
-            '-Dcxx{0}=ON'.format(self.spec.variants['cxxstd'].value)
-        )
+        # Method for selecting C++ standard depends on ROOT version
+        options.append(('-DCMAKE_CXX_STANDARD={0}' if
+                        self.spec.satisfies('@6.18.00:') else
+                        '-Dcxx{0}:BOOL=ON').format
+                       (self.spec.variants['cxxstd'].value))
 
         if 'mysql-client' in self.spec:
             options.append('-DCMAKE_PROGRAM_PATH={0}'.format(
@@ -503,6 +410,7 @@ class Root(CMakePackage):
         if '+python' in self.spec:
             options.append('-DPYTHON_EXECUTABLE=%s' %
                            spec['python'].command.path)
+
         return options
 
     def setup_build_environment(self, env):
@@ -529,3 +437,24 @@ class Root(CMakePackage):
         env.set('ROOT_VERSION', 'v{0}'.format(self.version.up_to(1)))
         env.prepend_path('PYTHONPATH', self.prefix.lib)
         env.prepend_path('PATH', self.prefix.bin)
+
+    def _process_opts(self, *opt_lists):
+        """Process all provided boolean option lists into CMake arguments.
+
+        Args:
+            opt_list (list): list of elements, each of which is a list:
+                    <cmake-option>[, <bool-or-controlling-variant-name>]
+                The optional element in each sub-list defaults to
+                <cmake-option> if ommited.
+        """
+
+        def _process_opt(opt_name, cond_or_variant=None):
+            val = cond_or_variant if \
+                isinstance(cond_or_variant, types.BooleanType) else \
+                ('+{variant}'.format(variant=cond_or_variant or opt_name)
+                 in self.spec)
+            return '-D{opt}:BOOL={val}'.format(opt=opt_name, val='ON' if
+                                               val else 'OFF')
+
+        return [_process_opt(*opt_info) for opt_list in opt_lists for
+                opt_info in opt_list]