* Add options for sparse checkout in GitFetcher
Newer versions of git have a beta feature called sparse checkout
that allow users to check out a portion of a large repo.
This feature will be ideal for monolithic repo projects that want to
model their infrastructure via spack. This PR implements an addition
to the GitFetcher that allows users to add a `git_sparse_paths`
attribute to package classes or versions which will then use sparse
checkout on those directories/files for the package.
* Style
* Split git clone into multiple functions
* Add sparse-checkout impl
* Internalize src clone functions
* Docs
* Adding sparse clone test
* Add test for partial clone
* [@spackbot] updating style on behalf of psakievich
* Small fixes
* Restore default branch status
* Fix attributes for package
* Update lib/spack/docs/packaging_guide.rst
Co-authored-by: Matthew Mosby <44072882+mdmosby@users.noreply.github.com>
* Extend unit test to multiple git versions
* style
---------
Co-authored-by: psakievich <psakievich@users.noreply.github.com>
Co-authored-by: Matthew Mosby <44072882+mdmosby@users.noreply.github.com>
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