ASP-based solver: discard unknown packages from reuse

This is an add-on to spack#28259 that cover for the case of
a single package.py being removed from a repository,
rather than an entire custom repository being removed.

lib/spack/spack/solver/asp.py

@@ -1661,8 +1661,8 @@ def _facts_from_concrete_spec(self, spec, possible):
         if spec.name in possible and h not in self.seen_hashes:
             try:
                 # Only consider installed packages for repo we know
-                spack.repo.path.repo_for_pkg(spec)
-            except spack.repo.UnknownNamespaceError:
+                spack.repo.path.get(spec)
+            except (spack.repo.UnknownNamespaceError, spack.repo.UnknownPackageError):
                 return
 
             # this indicates that there is a spec like this installed
@@ -2053,6 +2053,8 @@ def build_specs(self, function_tuples):
         # namespace assignment is done after the fact, as it is not
         # currently part of the solve
         for spec in self._specs.values():
+            if spec.namespace:
+                continue
             repo = spack.repo.path.repo_for_pkg(spec)
             spec.namespace = repo.namespace
 
@@ -2062,7 +2064,7 @@ def build_specs(self, function_tuples):
         # inject patches -- note that we' can't use set() to unique the
         # roots here, because the specs aren't complete, and the hash
         # function will loop forever.
-        roots = [spec.root for spec in self._specs.values()]
+        roots = [spec.root for spec in self._specs.values() if not spec.root.installed]
         roots = dict((id(r), r) for r in roots)
         for root in roots.values():
             spack.spec.Spec.inject_patches_variant(root)