- Update to version 0.20.0 with the following features:
  * Exact versions: Spack did not previously have a way to distinguish a
    version if it was a prefix of some other version. For example, @3.2 would
    match 3.2, 3.2.1, 3.2.2, etc. You can now match exactly 3.2 with @=3.2.
    This is useful, for example, if you need to patch only the 3.2 version of a
    package
  * More stable concretization: Now, spack concretize will only concretize the
    new portions of the environment and will not change existing parts of an
    environment unless you specify --force.  This has always been true for
    unify:false, but not for unify:true and unify:when_possible environments.
  * The concretizer has a new --reuse-deps argument that only reuses dependencies.
    That is, it will always treat the roots of your environment as it would with
    --fresh. This allows you to upgrade just the roots of your environment while
    keeping everything else stable
  * Specs in buildcaches can be referenced by hash: Previously, you could run
    spack buildcache list and see the hashes in buildcaches, but referring to
    them by hash would fail.  You can now run commands like spack spec and
    spack install and refer to buildcache hashes directly, e.g. spack install
    /abc123
  * New package and buildcache index websites
    Our public websites for searching packages have been completely revamped
    and updated.  You can check them out here:
      Package Index: https://packages.spack.io
      Buildcache Index: https://cache.spack.io
    Both are searchable and more interactive than before. Currently major
    releases are shown; UI for browsing develop snapshots is coming soon.
  * Default CMake and Meson build types are now Release: Spack has historically
    defaulted to building with optimization and debugging, but packages like
    llvm can be enormous with debug turned on. Our default build type for all
    Spack packages is now Release. This has a number of benefits:

• Files Changed
• Browse Source