$ spack spec libxext
Input spec
--------------------------------
libxext

Normalized
--------------------------------
libxext
    ^[email protected]:
        ^inputproto
            ^[email protected]:
            ^util-macros
        ^kbproto
        ^[email protected]:
            ^libpthread-stubs
            ^[email protected]:
                ^[email protected]:
            ^libxdmcp
            ^python@2:2.8
                ^bzip2
                ^ncurses
                ^openssl
                    ^zlib
                ^readline
                ^sqlite
            ^xcb-proto
        ^[email protected]:
        ^xtrans

Concretized
--------------------------------
Exception RuntimeError: 'maximum recursion depth exceeded while calling a Python object' in <type 'exceptions.TypeError'> ignored
Exception RuntimeError: 'maximum recursion depth exceeded while calling a Python object' in <type 'exceptions.TypeError'> ignored
Traceback (most recent call last):
  File "./spack", line 198, in <module>
    main()
  File "./spack", line 175, in main
    return_val = command(parser, args)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/cmd/spec.py", line 78, in spec
    spec.concretize()
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1507, in concretize
    changes = (self.normalize(force),
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1809, in normalize
    any_change = self._normalize_helper(visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1763, in _normalize_helper
    pkg_dep, deptypes, visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1734, in _merge_dependency
    visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1763, in _normalize_helper
    pkg_dep, deptypes, visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1734, in _merge_dependency
    visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1763, in _normalize_helper
    pkg_dep, deptypes, visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1734, in _merge_dependency
    visited, spec_deps, provider_index)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1758, in _normalize_helper
    pkg_dep = self._evaluate_dependency_conditions(dep_name)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 1629, in _evaluate_dependency_conditions
    sat = self.satisfies(when_spec, strict=True)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2058, in satisfies
    return self.satisfies_dependencies(other, strict=deps_strict)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2087, in satisfies_dependencies
    self_index = ProviderIndex(self.traverse(), restrict=True)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/provider_index.py", line 87, in __init__
    self.update(spec)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/provider_index.py", line 99, in update
    pkg = spec.package
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 945, in package
    return spack.repo.get(self)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/repository.py", line 75, in converter
    return function(self, spec_like, *args, **kwargs)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/repository.py", line 318, in get
    return self.repo_for_pkg(spec).get(spec)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/repository.py", line 75, in converter
    return function(self, spec_like, *args, **kwargs)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/repository.py", line 567, in get
    key = hash(spec)
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/llnl/util/lang.py", line 254, in <lambda>
    setter('__hash__', lambda self: hash(self._cmp_key()))
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2330, in _cmp_key
    for name, d in sorted(self._dependencies.items()))
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2330, in <genexpr>
    for name, d in sorted(self._dependencies.items()))
...
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2330, in _cmp_key
    for name, d in sorted(self._dependencies.items()))
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2330, in <genexpr>
    for name, d in sorted(self._dependencies.items()))
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/llnl/util/lang.py", line 254, in <lambda>
    setter('__hash__', lambda self: hash(self._cmp_key()))
  File "/blues/gpfs/home/ajstewart/spack/lib/spack/spack/spec.py", line 2330, in _cmp_key
    for name, d in sorted(self._dependencies.items()))
TypeError: object of type 'generator' has no len()