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Diffstat (limited to 'lib/spack/docs/packaging_guide.rst')
| -rw-r--r-- | lib/spack/docs/packaging_guide.rst | 34 |
1 files changed, 27 insertions, 7 deletions
diff --git a/lib/spack/docs/packaging_guide.rst b/lib/spack/docs/packaging_guide.rst index 34be562c29..706144403d 100644 --- a/lib/spack/docs/packaging_guide.rst +++ b/lib/spack/docs/packaging_guide.rst @@ -1854,18 +1854,38 @@ from being linked in at activation time. ``depends_on('python')`` and ``extends(python)`` in the same package. ``extends`` implies ``depends_on``. +----- +Views +----- + +As covered in :ref:`filesystem-views`, the ``spack view`` command can be +used to symlink a number of packages into a merged prefix. The methods of +``PackageViewMixin`` can be overridden to customize how packages are added +to views. Generally this can be used to create copies of specific files rather +than symlinking them when symlinking does not work. For example, ``Python`` +overrides ``add_files_to_view`` in order to create a copy of the ``python`` +binary since the real path of the Python executable is used to detect +extensions; as a consequence python extension packages (those inheriting from +``PythonPackage``) likewise override ``add_files_to_view`` in order to rewrite +shebang lines which point to the Python interpreter. + ^^^^^^^^^^^^^^^^^^^^^^^^^ Activation & deactivation ^^^^^^^^^^^^^^^^^^^^^^^^^ +Adding an extension to a view is referred to as an activation. If the view is +maintained in the Spack installation prefix of the extendee this is called a +global activation. Activations may involve updating some centralized state +that is maintained by the extendee package, so there can be additional work +for adding extensions compared with non-extension packages. + Spack's ``Package`` class has default ``activate`` and ``deactivate`` implementations that handle symbolically linking extensions' prefixes -into the directory of the parent package. However, extendable -packages can override these methods to add custom activate/deactivate -logic of their own. For example, the ``activate`` and ``deactivate`` -methods in the Python class use the symbolic linking, but they also -handle details surrounding Python's ``.pth`` files, and other aspects -of Python packaging. +into a specified view. Extendable packages can override these methods +to add custom activate/deactivate logic of their own. For example, +the ``activate`` and ``deactivate`` methods in the Python class handle +symbolic linking of extensions, but they also handle details surrounding +Python's ``.pth`` files, and other aspects of Python packaging. Spack's extensions mechanism is designed to be extensible, so that other packages (like Ruby, R, Perl, etc.) can provide their own @@ -1880,7 +1900,7 @@ Let's look at Python's activate function: This function is called on the *extendee* (Python). It first calls ``activate`` in the superclass, which handles symlinking the -extension package's prefix into this package's prefix. It then does +extension package's prefix into the specified view. It then does some special handling of the ``easy-install.pth`` file, part of Python's setuptools. |