binary_distribution: content addressable url buildcache
Change how binary mirrors are laid out, adopting content addressing for every
piece of data spack stores in a binary mirror. Items (e.g. tarballs, specfiles, public
keys, indices, etc) are now discoverable via manifest files which give the size,
checksum, compression type, etc of the the stored item. The information in the
manifest, in turn, is used to find the actual data, which is stored by its content
address in the blobs directory. Additionally, signing is now applied to the manifest
files, rather than to the spec files themselves.
* Bump the package API of the `builtin` repo to `v2.0`
* Move `var/spack/repos/builtin` -> `var/spack/repos/spack_repo/builtin`
* Move test repos `var/spack/repos/{builtin.mock,tutorial,...}` -> `var/spack/test_repos/`
* Update package dir names to v2 format (`-` -> `_` etc)
* Change absolute imports `from spack.pkg.builtin.my_pkg ...` to relative imports `from ..my_pkg.package ...`
Users who have a repo on top of builtin should change imports from
```python
from spack.pkg.builtin.my_pkg import MyPkg
```
to
```python
from spack_repo.builtin.packages.my_pkg.package import MyPkg
```
and can configure their editors with
```
PYTHONPATH=$spack/lib/spack:$spack/var/spack/repos
```
[skip-verify-checksums]
This implements Package API v2.0, and is an opt-in feature for repos. It can be enabled with
```yaml
repo:
...
api: v2.0
```
It differs from the current default v1.0 as follows:
1. Package names can only contain `-` as a separator.
2. Package names can only be lowercase.
3. Package directory names are valid Python module names.
4. The repo namespace and its directory name are the same.
5. The `packages` subdir, which is configurable, should be a directory
name that is also a valid Python module name.
6. There is a one to one mapping between Spack package names and Python
module names.
7. Import statements `import spack.pkg.namespace.package_module` in
`package.py` files need to specify the canonical package module.
To go from Spack package name to Python module name:
- Replace `-` by `_`
- Add a leading `_` if the package name starts with a digit
To go from Python module name to Spack package name:
- Strip leading `_`
- Replace `_` by `-`.
