This isn't a rework of the concretizer but it speeds things up a LOT.
The main culprits were:
1. Variant code, `provider_index`, and `concretize.py` were calling
`spec.package` when they could use `spec.package_class`
- `spec.package` looks up a package instance by `Spec`, which requires a
(fast-ish but not that fast) DAG compare.
- `spec.package_class` just looks up the package's class by name, and you
should use this when all you need is metadata (most of the time).
- not really clear that the current way packages are looked up is
necessary -- we can consider refactoring that in the future.
2. `Repository.repo_for_pkg` parses a `str` argument into a `Spec` when
called with one, via `@_autospec`, but this is not needed.
- Add some faster code to handle strings directly and avoid parsing
This speeds up concretization 3-9x in my limited tests. Still not super
fast but much more bearable:
Before:
- `spack spec xsdk` took 33.6s
- `spack spec dealii` took 1m39s
After:
- `spack spec xsdk` takes 6.8s
- `spack spec dealii` takes 10.8s
65b38764ae