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Diffstat (limited to 'lib/spack/docs/packaging_guide.rst')
| -rw-r--r-- | lib/spack/docs/packaging_guide.rst | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/lib/spack/docs/packaging_guide.rst b/lib/spack/docs/packaging_guide.rst index 293e83a118..bdf557a346 100644 --- a/lib/spack/docs/packaging_guide.rst +++ b/lib/spack/docs/packaging_guide.rst @@ -2470,6 +2470,24 @@ Now, the ``py-numpy`` package can be used as an argument to ``spack activate``. When it is activated, all the files in its prefix will be symbolically linked into the prefix of the python package. +A package can only extend one other package at a time. To support packages +that may extend one of a list of other packages, Spack supports multiple +``extends`` directives as long as at most one of them is selected as +a dependency during concretization. For example, a lua package could extend +either lua or luajit, but not both: + +.. code-block:: python + + class LuaLpeg(Package): + ... + variant('use_lua', default=True) + extends('lua', when='+use_lua') + extends('lua-luajit', when='~use_lua') + ... + +Now, a user can install, and activate, the ``lua-lpeg`` package for either +lua or luajit. + ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Adding additional constraints ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |