Bugfix: reinstalling updated develop specs (#25579)

PackageInstaller and Package.installed disagree over what it means
for a package to be installed: PackageInstaller believes it should be
enough for a database entry to exist, whereas Package.installed
requires a database entry & a prefix directory.

This leads to the following niche issue:

* a develop spec in an environment is successfully installed
* then somehow its install prefix is removed (e.g. through a bug fixed
  in #25583)
* you modify the sources and reinstall the environment
  1. spack checks pkg.installed and realizes the develop spec is NOT
     installed, therefore it doesn't need to have 'overwrite: true'
  2. the installer gets the build task and checks the database and
      realizes the spec IS installed, hence it doesn't have to install it.
  3. the develop spec is not rebuilt.

The solution is to make PackageInstaller and pkg.installed agree over
what it means to be installed, and this PR does that by dropping the
prefix directory check from pkg.installed, so that it only checks the
database.

As a result, spack will create a build task with overwrite: true for
the develop spec, and the installer in fact handles overwrite requests
fine even if the install prefix doesn't exist (it just does a normal
install).

0 files changed, 0 insertions, 0 deletions