libvdwxc: unbreak concretization, request fftw-api (#18688)

* libvdwxc: unbreak concretization, request fftw-api

mixing both fftw and fftw-api in a dependency tree can trigger the
following:

```
$ spack spec cp2k@master +sirius
==> [2020-09-16-12:36:06.552981] sirius applying constraint gsl
==> [2020-09-16-12:36:06.554270] sirius applying constraint openblas@0.3.10%gcc@7.5.0~consistent_fpcsr~ilp64+pic+shared threads=none arch=linux-opensuse_leap15-sandybridge
Traceback (most recent call last):
  File "./bin/spack", line 64, in <module>
    sys.exit(spack.main.main())
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/main.py", line 762, in main
    return _invoke_command(command, parser, args, unknown)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/main.py", line 490, in _invoke_command
    return_val = command(parser, args)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/cmd/spec.py", line 103, in spec
    spec.concretize()
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2228, in concretize
    user_spec_deps=user_spec_deps),
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2716, in normalize
    visited, all_spec_deps, provider_index, tests)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2654, in _normalize_helper
    dep, visited, spec_deps, provider_index, tests)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2613, in _merge_dependency
    visited, spec_deps, provider_index, tests)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2654, in _normalize_helper
    dep, visited, spec_deps, provider_index, tests)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2554, in _merge_dependency
    provider = self._find_provider(dep, provider_index)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/spec.py", line 2489, in _find_provider
    providers = provider_index.providers_for(vdep)
  File "/data/tiziano/debug-spack/spack2/lib/spack/spack/provider_index.py", line 80, in providers_for
    return sorted(s.copy() for s in result)
  File "/data/tiziano/debug-spack/spack2/lib/spack/llnl/util/lang.py", line 249, in <lambda>
    lambda s, o: o is not None and s._cmp_key() < o._cmp_key())
TypeError: '<' not supported between instances of 'str' and 'NoneType'
```

while at the same point disallowing MKL as a fftw provider.
Solving both issues by depending on `fftw-api@3` instead and adding a
conflict on `^fftw~mpi` when using `+mpi` (thanks to alalazo).

* cp2k: use conflicts instead of runtime checks for fftw/openblas variants

2 files changed, 6 insertions, 26 deletions

diff --git a/var/spack/repos/builtin/packages/cp2k/package.py b/var/spack/repos/builtin/packages/cp2k/package.py
index ab17b7ca2a..486221957a 100644
--- a/var/spack/repos/builtin/packages/cp2k/package.py
+++ b/var/spack/repos/builtin/packages/cp2k/package.py
@@ -154,6 +154,10 @@ class Cp2k(MakefilePackage, CudaPackage):
     # cp2k with option smm=blas on aarch64
     conflicts('smm=libxsmm',  when='target=aarch64:', msg='libxsmm is not available on arm')
 
+    conflicts('^fftw~openmp', when='+openmp')
+    conflicts('^openblas threads=none', when='+openmp')
+    conflicts('^openblas threads=pthreads', when='+openmp')
+
     conflicts('~openmp', when='@8:', msg='Building without OpenMP is not supported in CP2K 8+')
 
     @property
@@ -178,31 +182,7 @@ class Cp2k(MakefilePackage, CudaPackage):
     def archive_files(self):
         return [os.path.join(self.stage.source_path, self.makefile)]
 
-    def consistency_check(self, spec):
-        """
-        Consistency checks.
-        Due to issue #1712 we can not put them into depends_on/conflicts.
-        """
-
-        if '+openmp' in spec:
-            if '^openblas' in spec and '^openblas threads=openmp' not in spec:
-                raise InstallError(
-                    '^openblas threads=openmp required for cp2k+openmp'
-                    ' with openblas')
-
-            if '^fftw' in spec and '^fftw +openmp' not in spec:
-                raise InstallError(
-                    '^fftw +openmp required for cp2k+openmp'
-                    ' with fftw')
-
-            # MKL doesn't need to be checked since they are
-            # OMP thread-safe when using mkl_sequential
-            # BUT: we should check the version of MKL IF it is used for FFTW
-            #      since there we need at least v14 of MKL to be safe!
-
     def edit(self, spec, prefix):
-        self.consistency_check(spec)
-
         pkgconf = which('pkg-config')
 
         if '^fftw' in spec:
diff --git a/var/spack/repos/builtin/packages/libvdwxc/package.py b/var/spack/repos/builtin/packages/libvdwxc/package.py
index 786561ce42..2e0934ab2f 100644
--- a/var/spack/repos/builtin/packages/libvdwxc/package.py
+++ b/var/spack/repos/builtin/packages/libvdwxc/package.py
@@ -19,13 +19,13 @@ class Libvdwxc(AutotoolsPackage):
     variant("mpi", default=True, description="Enable MPI support")
     variant("pfft", default=False, description="Enable support for PFFT")
 
-    depends_on("fftw@3:", when="~mpi")
+    depends_on("fftw-api@3")
     depends_on("mpi@2:", when="+mpi")
-    depends_on("fftw@3:+mpi", when="+mpi")
     depends_on("pfft", when="+pfft")
 
     # pfft needs MPI
     conflicts("~mpi", "+pfft")
+    conflicts("^fftw~mpi", "+mpi")
 
     def configure_args(self):
         spec = self.spec